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Building the Tom Henry RS
Part Six: Service, Seating, Tuning, an SS Hood and Nitrous Oxide End the Project
by Hib Halverson

Image: CHpg Staff.

We begin this final part of the Tom Henry RS project with how we solved a brake problem and how we found out later it was self-inflicted. For most of this project, the Camaro's brakes have been stock calipers with upgraded brake rotors from Baer Brake Systems.

The THRS front brakes uses drilled and slotted Baer two-piece rotors and stock calipers. Image: CHpg Staff.

In the run up to this part of the THRS series, we started feeling brake shudder during braking from highway speeds and the problem became progressively worse. Thinking this was a thickness variation or runout problem, we measured both. Turns out, we were wrong. Our Baer rotors were within factory limits for thickness variation and runout.

Further road testing demonstrated that, at slow speeds, just before the car came to a stop, the shudder's frequency became low enough that we could feel a back-and-forth sort of "rocking motion". We pulled the rotors and inspected them carefully. We saw sections of gray mixed with sections of normal surface appearance. Deciding this was a problem with transfer of brake pad material to sections of the rotor and thinking we could remove it with abrasives, we abraded them using an air grinder fitted with coarse, non-woven, metal finishing discs from Standard Abrasives. That didn't have much of an effect and the brakes still shuddered.

We had several conversations with Rick Pojman, the Customer Service rep at Baer Brake Systems. He said that uneven transfer of pad material to the rotor surface can be caused either by brake pads which were not properly bedded or by pads which have been overheated. If the problem was overheating, we had made the wrong choice in pads and a more aggressive pad might be necessary.

A benchmark of the service trade for IR thermometers is this Raytek ST-25. The one in our toolbox is ten years old and has been indispensable when we need to measure temperatures of various parts on a car. Image: Raytek Corporation.

We needed to take some brake temperature information before we could decide whether or not we were going to change to a different brake pad. We drove up into some nearby mountains then came back down the same curvy road. Several different times we stopped in a safe spot and shot one of the front rotors with our Raytek ST-2 Autopro infrared thermometer. The highest temperature we recorded was 519°F. Given that we never exceeded 80-mph and, because most of the braking areas were at the end of straights, the brakes were cooling between applications; we figured our peak brake temp was higher. We also noted that the brake shudder problem had become much worse. After our brake temp testing session, back at the shop, we pulled all the brake rotors again.

Looking at the fronts, it was obvious that the problem with pad material transferring to the rotors was more serious than before. That along with our temperature readings had us believing our problem was that we were exceeding the design envelope of the brake pads.

We contacted Baer's customer service agin, this time asking advice on what to do with our rotors. The always-helpful, Rick Pojamn said that a temporarily switch to a racing pad will wipe the transfer away. He added that the only surefire ways to fix the problem are either to machine the rotors or replace them.

Machining works well provided the rotors has minimal wear, the brake lathe operator knows how to apply the proper final finish and the amount of machining required is .005-in. or less. If the rotors are close to or below minimum thickness, rotor replacement is your only choice.

Since the Baer rotors had only minimal decrease in thickness, we decided to fix the pad transfer problem by having the rotors machined just enough to remove the coating of pad material. Image: CHpg Staff.

Our solution was two-fold. First, we took the rotors to Bob Woolever's Tire Shoppe and had Bob machine the rotors just enough to remove the pad material. This amounted to about a .005-in. thickness reduction and left us well over their minimum thickness specifications.

Next, we dialed up Porterfield Enterprises, a specialist in high-performance street and racing brake pads. The company was started in the mid-'80s by the late Andy Porterfield, a semi-professional road racer who spent most of his career driving Camaros and Corvettes in the SCCA Trans-Am, GT-1 and various "outlaw" road racing series on the West Coast. In 1986 he became the U.S. distributor for Ferrodo racing brake pads and, in the near 30 years since then, Porterfield Enterprises has become the go-to source for racing brake pads in the U.S. Porterfield is the only vendor which sells Raybestos racing brake pads to consumers.

The difference between street pads (left) and racing pads can be seen in the texture of the pad material. Also, the Raybestos pads (right) for the rear are only available in a C5 Corvette pad which fits the '98-'02 Camaro rear caliper but requires the pad abutment shims be deleted. That can cause some occasional rattling. Image: CHpg Staff.

After talking with Porterfield's, Tim Gray, we decided to try a set of pads made with Raybestos ST-43 compound. Raybestos terms this a full race pad compound but it can be used on a road car if one is willing to accept a bit higher pedal effort when the brakes are cold, some brake noise and quite a bit more brake dust than is emitted by stock pads or even some "performance street" pads. Additionally, these pads are harder on rotors. If you don't like brakes squeaking and dusting or you want rotor life the same as stock; don't use this brake pad, however, if you want brakes that really work well and are willing to replace rotors more often, the ST-43 is the way to go.

There are also a couple of "alternative fit" issues with these pads. First, they don't have the stock GM wear indicators which "screech" when the pads are near gone so use of them requires occasional brake pad checks. Secondly, the rear pads, while they fit Camaro rear calipers, are actually a C5 Corvette pad. Corvette rear pads have three locating tabs on their backing plates. If you install the calipers and caliper mounting brackets as a unit, there is no installation issues, however, if you change pads by simply removing the caliper from the caliper mounting bracket, you have to put the pads into the grooves in the mounting bracket then carefully work the caliper over the locating tabs. Doing that is a bit awkward but patience and care will get you through the process.

We cleaned up the parts with a little Simple Green Motorsports Degreaser then installed the Raybestos pads. Image: CHpg Staff.

So far the ST-43s are working well with no signs of brake shudder and–holy crap–do they stop! When we hit the brakes, the Porterfield/Raybestos pads really bite hard, stop quick and don't fade.

Braking performance was markedly improved. We've run the Raybestos pads we got from Porterfield Brakes for several months and, so far, no signs of brake shudder.

Oil Change and Oil Leaks

Because we're going to put the car back on the chassis dyno later in this article, and it's been quite a while since we changed the oil in the THRS's engine, we got the car up in the air, drained the crankcase then pulled the filter off. In went five quarts of fresh Red Line 10W30 Engine Oil. Next, we prefilled a new ACDelco UPF52 Ultragard Gold oil filter and screwed it in place. If you've followed this project from the start, you know we've used nothing but Red Line 10W30 in our mod'ed three-eight.

ACDelco's Ultragard Gold is GM's premium aftermarket oil filter. We use the UPF52 which not only is an upgrade over regular ACD "Duragard" design but also is a longer filter than the PF47 which is stock on a 3.8. Normally, '52s are used on trucks. We've been using Red Line 10W30 engine oil in the Tom Henry RS engine since the car was new. Image: CHpg Staff.

There are two main reasons for that. First, we prefer Red Line's robust base stock combination of esters and polyalphaolefins (PAO) and the better performance and protection at high oil temperatures they provide. The Tom Henry RS doesn't have an engine oil cooler and we're making 50% more power than stock which means, when we're running the engine hard for sustained periods–say we take a sporting run over one of our favorite twisty roads–we see as much as 260°F oil temperature. We use an AutoMeter Sport-Comp II electric temperature gauge (PN 3656) and its sensor is in the oil filter housing, perhaps the coolest place in the oiling system. If we have 260° at the oil filter, the oil may be 280° in bearings. Under that kind of abuse, the margin of safety offered by Red Line's thermal stability is desirable.

Second, we can run Red Line 10W30 to extended drain intervals as a way of recovering some of the oil's higher cost . Since the 1000 mile mark, the V6 in our Camaro has used Red Line and oil changes have been done every 18,000-20,000 miles with a filter change every 4000-5000 miles. We have over a dozen years of spectrographic oil analysis data to back up our advocacy of Red Line and extended drain intervals.

The car's Tremec T-5 five-speed manual transmission has been in service just under 120,000 miles and lately, we noted it has been weeping lubricant out of its rear seal. When we grabbed the driveshaft and pushed it up and pulled down, we could see the lip of the rear seal was deforming too much, indicating that the extension housing bushing was probably worn out. Considering how hard we've beat on the trans in this car, even Red Line MTL's superior lubrication couldn't make that bushing last more than 120K.

Tom Henry Racing's Parts Manager, Stan Lorence, told us GM does not service the bushing. You have to buy the whole housing to get it. The cost? Take a deep breath–630 bucks. We about had kittens when we heard the number.

We started looking on the aftermarket for the bushing. A session with Bing found one at Manualtransmissionparts.com in Alabama so we ordered the bushing (PN 44066) along with a rear seal from Tom Henry Racing.

We didn't expect the extension housing bushing we bought to be "hone-to-fit" but it was. Initially, we could not install the driveshaft into the transmission, so we had to get the housing off a second time and hone the bushing with a Brush Research "Flex-Hone". Image: CHpg Staff.

With the car up on stands, we removed the gearbox, unbolted its extension housing then, took it to a nearby automotive machine shop which had a hydraulic press and had them change the bushing. Back at our shop, we honed the bushing's inside diameter with a 1.375-in. 240-grit Flex-Hone (PN BC13824) to fit the output yoke on our Inland Empire Driveline Service aluminum drive shaft, wiped some Red Line Assembly lube in the I.D. of the bushing and reassembled the trans.

Since we had the trans out and its clutch release bearing assembly was ten years old, we replaced it with a new unit (PN 24264182) from Tom Henry Racing. We put the trans back in, reinstalled all the brackets and mounts. We wiped some more Red Line Assembly Lube on the O.D. of the yoke, then reinstalled our EDS aluminum shaft.

Worm's eye view of the back of the transmission. When the extension housing bushing is worn, the driveshaft front yoke can "wobble" on the output shaft splines. Once the end of the yoke moves a distance greater than the seal's lip can expand, it starts to leak. Image: CHpg Staff.

We filled our T-5 with "MTL" which stands for "manual transmission lubricant", Red Line Oil's low-viscosity, GL-4 gear lubricant. MTL is a performance upgrade over the ATF which most people use in T-5s and a better choice for severe duty, such as transmissions behind modified engines in street high-performance or racing applications. It's GL-4 rating means it's formulated specifically for lubricating spur gear or helical gear transmissions. It's, also, blended to have just the right friction coefficient for optimal performance of cone-type synchronizers. While it's rated 75W80 on the gear lubricant viscosity scale and 5W30 on the engine oil scale, both of which are somewhat higher viscosity than ATF; MTL still is a low-vis trans lube like GM's "Synchromesh" or "Manual Transaxle" lubricants. Red Line MTL has good low-temperature shift feel, high-temperature stability and overall lower shift effort.

Worm’s eye view of the power steering pump. It looks hard to change but, as long as you have pulley removal and installation tools, changing it is pretty easy. The key task in the pump change is vacuum bleeding the system once the pump is installed. Image: CHpg Staff


The five-speed was not the only thing leaking. During our work under the car to R&R the transmission, we noted the power steering pump was weeping fluid, too. Like the cost of the tail housing, the cost of a new steering pump was over-the-top, so we ordered an A-1 Cardone remanufactured pump from Rockauto.com (PN 20905). We like Cardone’s reman parts and, when we get them from Rockauto.com the price is competitive and the service is quick.  

The pump replacement was straight forward. We used a Bosch Automotive power steering pump pulley removal tool (PN J-25034-C) to get the pulley off, disconnected the hoses then unbolted the pump. Putting the Rockauto.com reman in place was, the reverse of removal. With the new pump in place, we used another  tool (PN J-25033-C) to reinstall the pulley. Finally, we filled the pump reservoir with Red Line Synthetic Power Steering Fluid. Again, we choose Red Line because it's a better for high performance use than the ordinary petroleum-based fluids. We bled the air out of the steering system per the Service Manual's instructions using a tool we made from a bathtub stopper.

Our Bosch Automotive power steering tools. At right is the pulley removal tool. At left is the installer. Image: CHpg Staff.

Lastly, we had a leaking rear axle shaft seal on the right side so, we dropped the rear axle cover, removed the axles and replaced the axle seals on both sides with parts we ordered from the Tom Henry Racing parts department.

The Fikse Profil 5 in 17x9-inch size. These wheels have been on the car for eight years. They look almost as good now as they did when they were installed in 2006. Image: CHpg Staff.

Round and Black

Several years ago, we put Fikse Profil 5S wheels on the Tom Henry RS. Because, Fikses are so light for a street wheel, we were able to go from a 16x8 to a 17x9.5 yet not increase unsprung weight. We expected this, considering their racing pedigree. Cars on Fikses have won both the World's preeminent endurance races, the 24 Hours of Daytona (4 times!) and the 24 Hours of LeMans.

The Fikse Profil 5S is a modular design with a rotary-forged, CNC-machined, clear powder-coated, aluminum center. The rims are forged, heat-treated aluminum. "TechniPolish" is Fikse‘s standard finish and features a robust, liquid-cured, clearcoat on the diamond-turned center section. The mirror-polished rims are left uncoated to allow for touch-ups as needed in case of minor scrapes.

Shown here during the tire's press introduction in the summer of 2000, the Goodyear F1 Supercar was designed for the C5 Corvette Z06.
Image: CHpg Staff.

The wheel change allowed us a significant tire improvement: the 265/40ZR17 Goodyear F1 Supercar. The Supercar was engineered specifically for the C5 Corvette Z06 of the early-'00s, but Goodyear's design has held up well and is still a good choice in ultra-performance summer tires of that size. It is one of a few tires which bridges the gap between all-round, performance tires, such as the Goodyear F1 GS-D3, which we used when we had 16s on the car, and DOT-approved, radial road race tires which are not acceptable for general street use because of short tread life and almost nonexistent, wet traction. While the F1 Supercar is more sticky than some other tires that size, it's not the drag race tire that a "drag radial" from Goodrich, Nitto or Goodyear might be. Nevertheless, the Supercar makes a great "compromise" tire which performs well in a variety of street performance situations other than heavy rain or freezing weather.

The outside of the F1 SC has large, stiff tread blocks and reduce tread depth. The stiffer the tread and the more shallow the grooves, the less the tire's contact patch "squirms" and the better the tire handles. The smaller blocks and wider grooves in the inside of the tread give the Supercar acceptable performance if we get caught on a wet road. Image: Goodyear Tire and Rubber Co.


This drawing illustrates what's under the tread of a F1 Supercar. The wedge, spiral-wound overlay and the steel belts contribute to the tire's performance. Image: Goodyear Tire and Rubber Co.

The main advantages to the Tom Henry RS with the F1 Supercars are improved at-limit handling due to more traction coming from a wider tread, more aggressive rubber compound, slightly reduced tread depth and a tread block design skewed towards handling. Additionally, the F1 Supercar casing design improves steering feel and yaw response.

One characteristic of the F1 Supercar has surprised us and that's tread life. We ran them on the car for seven years, putting them on in the early Spring, Summer and Fall and taking them off during the Winter. When that first set of Supercars was down to the wear indicating bars, there was no question as to our replacement choice. We had Tom Henry Racing's Stan Lorence order another set of Goodyear F1 Supercars.

Though the F1 Supercar's design is a bit dated, in the 17-inch size we use on the Tom Henry RS, it provides very good lateral grip as shown there in testing during the suspension work we did for Part 5. Image: CHpg Staff.

Inside Improvements

Now, for some interior upgrades. First thing was to fix the car's nasty-looking steering wheel. Most V6 Camaros have the base wheel, a simple, rubber-covered unit. On the upper (where you put your hands) and lower (where your knees slide under it) parts of the wheel, the smooth black surface of the rubber had worn away exposing a ugly-looking and rough-feeling, dark gray, sponge-like material.

We contacted two companies which advertise late model steering wheel repair and restoration: Mike's Custom Steering in Kentucky and Dallas Custom Steering Wheel in Texas. Both were unwilling to refurbish the THRS's stock steering wheel at any price.

After 13 years of use, the car's steering wheel–mainly the top 1/3–had worn severely.
Image: CHpg Staff.

Our next idea was to look for a new or used steering wheel. As for new–no way. Tom Henry Racing's Parts Manager, Stan Lorence, told us they're long since discontinued and no dealer in the country has any "new old stock". As for used units?Turns out, wheels for fourth-gen base cars in good condition are difficult to find. We saw several on eBay, but all were wearing the same way as ours.

We decided to install a leather rim cover, manufactured by Wheelskins, on the existing ugly wheel. Wheelskins are made of top-quality cowhide produced in the U.S. and can be had in a number of colors. The lacing is made from a nylon material similar to that used in "parachute cord" and is waxed to make the lacing process easier.

Our solution was a Wheelskin kit. It comes with everything needed to recover the wheel.
Image: CHpg Staff.

A Wheelskin is installed by stretching it around the rim of the wheel then taking the lacing tool–a large, dull-tipped needle included with the product–and the nylon cord and lacing the cover's sides together. The holes for the cord are already punched in the leather.

While the big needle used to thread the Wheelskin's lacing is not really sharp, it's easier on the fingers if you have a mechanic's glove on the hand that holds the needle. Image: CHpg Staff.

Installing the Wheelskin is easy work but tedious. The instructions suggest installation takes an hour but, for someone who's never done a Wheekskin before–that's us–it's more like three hours, working slowly and following the instructions to the letter.

Once the Wheelskin was in place, the THRS Camaro's steering wheel looked and felt much better. Image: CHpg Staff.

When we were done, the steering wheel in the THRS looked great and felt much better in our hands than did the original rubber covering, even when it was new. Another feature of the Wheelskin treatment we liked is that it increased the diameter of the wheel rim by about a 1/16 of an inch which doesn't seem like much but it contributed to the steering wheel feeling more substantial. Two thumbs up for the Wheelskin because, literally–as when one's hands are positioned correctly on the wheel, both thumbs point up–and figuratively as we really like this product.

The next step was to do something about the car's seats. The stock seats' lack of side support was our main problem. We tried two solutions. The first, our "quick-and-cheap" solution was to remove the driver seat and have a local upholstery shop increase the amount of padding on the edges of the back and the cushion and recover the seat. It had the effect of letting the driver settle deeper into the cushion and back, thus increasing side support. Considering the low cost, this was a great modification.

"Stage Two" of our seating program was to replace the stock seats with a pair of Scat Enterprises Procar "Rave" seats (PN 80-1600-64L and 80-1600-64R). which are an affordable, "weekend warrior" grade of racing seat with the added convenience of a reclining back.

The Procar seat installation begins with the adapter bolting to the stock seat mounting holes. Image: CHpg Staff.

Procar Raves are installed using a set of Scat's adapter brackets (PN 811068, left, and PN 811069, right) which are specific to the 4th gen cars. You're supposed to remove the stock seats, bolt the brackets to the stock seat mounting holes then install the seats onto the brackets.

This shows the one problem we had with the installation: the mounting system needing to be modified because of clearance problems. The mod was cutting the lower two holes of the front of each seat track.
Image: CHpg Staff.

Unfortunately, it wasn't that easy. In theory, Procar's method of fitting a single seat design to a wide variety of cars is pretty slick. In practice, it didn't work well on our Camaro. The mounting tabs on the seats have three holes, intended to give the installer a choice of height or rake depending on which holes are used to bolt the seat to the adapter bracket. During our test fit, we couldn't get the seat low enough because the front mounting tabs bottomed on the floor of the car before their uppermost holes, which provide the lowest mounting height, lined-up with the holes in the bracket. The seat was tilted back too far and the front was too high. The solution? A cutting wheel on our air grinder with which we removed most of the front mounting tabs. Once we did that, the Rave bolted in and the seat rake was better.

These seats were priced right, looked great and had the side support typical of a racing seat, but in our tests, they didn't work well for people with small butts and short legs. Image: CHpg Staff.

We road tested the Raves for several weeks. The increase in lateral support over our modified stock seats was significant. Lumbar support was better, too. A downside was the cavity in the seat cushion was too long for someone with shorter legs. With my butt against the seat back, I had to move the seat forward to reach the pedals. If I sat with front of the seat supporting my calves, there was a big gap between my butt and the seat back. Folks with longer legs probably would enjoy the Raves more that we did.

          In other interior news, right in the middle of getting this article together, the driver side window on the Tom Henry RS quit working. After diagnosing the problem, it's obvious to us that, If your Camaro is high mileage–like the Tom Henry RS is at 120,000 miles–it's not "if" but "when" the side window mechanism will fail.

          This is because there is a durability problem with the window sash channel which to which the side glass is attached. At either end of this channel are brackets to which the glass is attached with blind or "pop" rivets. The rear bracket also holds the axle for the roller which runs in the vertical window lift channel. When the widow is moving down and this roller gets to the bottom of the vertical channel it hits a stop. The force of the roller pushing against the stop causes the axle to be forced sideways and that causes the sash channel rear bracket to flex. Over a period of time, that flexing eventually cracks the bracket and the crack grows until either the axle falls out or the section of the rear bracket holding the axle breaks off. Once that happens the window lift fails.

          The pop rivets holding the glass to the sash channel are not the typical aluminum type with which most DIYs are familiar. They are made of steel and require a long-handled, commercial grade rivet "gun". In fact, at the assembly plant, the window glass was riveted to the channel brackets with an industrial-type, power-operated rivet gun. Most DIYs are not going to have access to a factory-type rivet gun and even the manually-operated, long-handled commercial guns are not going to be a tool to which most DIYs have access.

          I ran into this riveting problem with the THRS when the driver side window mechanism quit working. I disassembled the door, noted that the rear sash channel bracket had broken. I found the axle at the bottom of the door. To repair or replace the sash channel, you have to remove the glass, first and to do that, you must drill out the rivets. Once you do that, you can replace the sash channel. Once the new sash channel in in place, the Factory Service Manual says to replace the rivets with new units from GM. Problem was, no way did I own a pop rivet gun which could install steel rivets. 

This glass sash channel stud was used on all 2nd gen cars. GM could have kept using it on the 3rd and 4th gen cars, but, in the interest of quicker assembly, switched to rivets. Obviously, they decided not to allow easy service which is kinda stupid considering side glass replacement is not an unusual need. Image: Year One, Inc.

          My solution? Oldskool. The '67-'81 Camaros and Firebirds used bolts and large "washer/nuts" rather than rivets to hold the glass to the sash channel. It was very simple to order three door glass sash mount stud assemblies (PN598) from Year One, discard the large washer nuts and replace them with smaller, conventional 1/4-in. flat washers and 1/4-in. self-locking nuts  then use that set-up to attach the glass to the sash. That was much easier than trying to find a tool to install new blind rivets.

This is how the installation looks once the stud is in place. You have to supply your own 1/4-in. flat washer and self-locking nut both of which are easily to find at any hardware store. For comparison, the washer/nut which comes with the stud is shown. That part you discard. Image: Author.

Once I had the parts order from Year One, I had my driver side door back together in about an hour. The window mechanism works great. The sash mount studs can be found at https://www.yearone.com/Product/1967-81-camaro/sm598

Getting with the Program

The VCM Suite configuration we picked was the GM base and the uplevel MVPI Pro. Among other features, the MPVI Pro differs from the base model in that it has the hardware you need to bring a wide-band oxygen sensor signal into VCM Scanner so you can have wideband data. Image: HPTuners

Reprogramming the calibration of our V6's ECM was required because of the extent of its modifications–Comp cam, Mark DeGroff ported/polished/cc'ed heads with bigger valves, Katech valve springs and titanium retainers, Yella Terra 1.8:1 rockers, Extrude Honed intake manifold, Whisper Lid, headers, MSD coils, Denso IT-20 plugs and a Flowmaster exhaust.

We started reworking the THRS calibration in Part 5 and we finished it for this final installment of the series. We work with HPTuners' “VCM Suite” software, which we ordered from Summit Racing Equipment because the price was competitive and Summit turns around orders quickly. VCM Suite includes “VCM Editor,” an application for calibrating 1997 or later GM vehicles, and "VCM Scanner", a data logging app. We like HPTuners because it supports a wide range of GM engine controls platforms and it's popular tuning software amongst DIYs and professional calibrators, alike. HPTuners runs on PCs using Windows XP, 7 or 8. At Tom Henry Racing, we run it on an old Acer 5670 laptop loaded with Win 7.

In Part 5, we didn't have a wideband oxygen sensor on the car, yet, so we confined our tuning to some part throttle work which can be done with the OE narrow band sensors. We began our cal work for this article with a look at what the engine was doing at wide-open throttle. The car has never felt quite right at high-rpm. Not that it ran poorly–it just didn't feel right, especially, when running above 5700 rpm on a cool day at sea level.


To install an O2S bung, the exhaust is drilled just downstream of the 2-into-1 collector and just ahead of the catalytic converter. The hole is deburred, then the sensor bung is welded in place. Image: CHpg Staff.


Packaging constraints dictated that we have the sensor bung pointing to the center of the car. Image: CHpg Staff.

 A wide-band oxygen sensor is required for calibrating wide-open throttle, so the first thing to do was install one. We took the car to Big John's Performance Center and had their ace fabricator, Steve Munson, install an MSD oxygen sensor bung in the exhaust just ahead of the catalytic convertor. Then, we ordered Bosch Aftermarket (PN 17014) and Denso (PN-234-5117) wide-band sensors from RockAuto.com.

Initially, we tried the recommended Bosch sensor with the LC-1. Image: CHpg Staff.

We also ordered an Innovate Motorsports LC-1 controller (PN 3744) from Summit. Innovate markets a variety of wideband systems and was suggested to us by the Tuning School which is discussed in our sidebar about learning calibration.

We installed the Bosch wideband sensor then looped the cable up and over the exhaust. Image: CHpg Staff.


 In a perfectly-sized spot between the floor and the exhaust shield, we mounted the LC-1. Since this was a temporary installation, after we shot this image, we clamped the unit in place.
 Image: CHpg Staff.

We connected the LC-1, HPTuners' "MVPI" (short for "multi-vehicle protocol interface") which comes with the VCM Suite, an LED indicator, a push-button and a wiring harness we fabricated according to Innovate's and HPTuners' instructions. All that links to our laptop with a USB cable. While Innovate Motorsports supplies its own data logging software, so we could log wideband and engine controls data together; since we chose the uplevel "MVPI Pro" which as the capability of logging data from up to four 0-5-volt, external sources, we could configure VCM Scanner, to record the LC-1.

HPTuner's standard MVPI, the Pro model looks the same except for the MPVP Pro has a, green, push-in connector on the side. Provided they have analog outputs of from 0 to 5-volts, up to four external devices which you wish to log can be wired to that connector. Image: CHpg Staff.

We screwed a Bosch sensor into the Camaro's exhaust, set up HPTuners VCM Scanner to display the wideband data then headed for Westech Performance Group and its Superflow chassis dyno.

We made three runs. Afterwards, studying wideband data from VCM Scanner, I could see we still had problems with power enrichment (PE). At the low end it was at 0.86-lambda, which is about right, but then, it would get rich until around 5500 rpm after which, the mixture would begin to lean out. It would get back to .86λ then continue going lean.

With the LC-1 connected to the MVPI Pro though the wiring harness we fabricated, we can look at wideband data in synch with other engine controls data using VCM Scanner.
Image: CHpg Staff.

While we had done some work to the "PE Fuel Adder RPM vs. Time" table for Part 5, we were still having problems with rich mixture once PE was enabled, so we just zeroed that table for WOT periods shorter than 19-seconds then ran a few more dyno passes. Starting at 4750 rpm, VCM Scanner showed high injector duty cycles–understandable considering, at the time, we were making around 270-hp with injectors sized for 200. In fact, as we approached the rev limiter, the system was commanding over 100% duty cycle, which, of course, is impossible to achieve, because, at 100%, the injectors are held open.

Our choice was a set of RC Engineering SL2-0240, 240-cc/min. injectors. Image: CHpg Staff.

We asked RC Engineering, a leading supplier of aftermarket injectors for help. RC's John Park told us not only did we likely need injectors capable of flowing more fuel but that fuel mixture can get erratic above 80-85% duty cycle for extended periods because injectors overheat and may become difficult to control. RC Engineering recommended upgrading to a 240-cc/min. injector (PN SL2-0240) which is a noticeable jump in fuel flow over the stock 206-cc/min, Delphi injector. RC injectors use the disc fuel metering system, have corrosion-free, stainless steel internal parts and are known for their tight tolerance of flow spread (±1.5% or less) over a set of six injectors. All sets of RC injectors are tested before shipping and ours our went out the door with an even better, 0.3% spread.

Every set of injectors is tested by RC Engineering's John Park. Injectors, in groups of up to four at a time are tested for flow and spray pattern. Image: CHpg Staff.

What are the chief advantages of RC injectors over the more common and, admittedly, less expensive Bosch pintle injectors? First, the disc injectors are less prone to fouling. The pintle is a long shaft with a needle-like tip which sticks through a hole in the bottom of the injector. When the injector is energized, this pintle lifts and fuel flows between its tip and the edges of the hole.

When the engine is shut off, some intake valves are left open. Heat from inside cylinders with open valves rise to the injector. If there is fuel residue on the pintle tip protruding from the end of the injector, the fuel residue begins to bake onto the pintle. Also, carbon byproducts of combustion can collect on pintle tip. Over time, baked-on fuel residue and combustion byproducts may build-up, causing poor spray pattern, lean mixtures, drivability quirks and high emissions.

A cutaway Bosch-type, pintle injector.
Image: RC Engineering.


A cutaway of an RC Engineering, rotating disc injector. Image: RC Engineering.

When a disc injector is energized, a tiny disc is raised off a seat and fuel flows between the two. When the disc is off the seat it may rotate. This type of injector is more resistant to fouling because the disk and its seating surface are recessed in the body of the injector and that has them less exposed to heat.

The second advantage comes from a difference in the mass of the injector's moving parts. The disc's mass is about an eighth of that of a pintle, thus disc injectors can respond more accurately to short open times typical of idle and part throttle operation. That gives disc injectors a wider dynamic range.

While the Delphi and RC injectors have different overall lengths, the distance between the injectors' O-rings is similar and the RCs will fit with no problems. Image: CHpg Staff.


The RC injectors push into the same mountings in the fuel rail as did the stock Delphi units. Image: CHpg Staff.


Once you remove the alternator, getting the fuel rail and injector assembly on and off is easy. With its RCs in place, we reinstalled the fuel rail. Image: CHpg Staff.

Installing RCEngineering injectors is no more difficult than replacing stock fuel injectors. Both types fit the stock fuel rail and the injector mounts in the lower intake manifold. Once you get the alternator and the ignition system out of the way, use shop air or a shop vacuum to remove any dirt and debris which might have accumulated around the injector bases. Then, remove the fuel rail and injectors. Remove the injector retaining clips, pull out the old injectors. Then clean out the rail, install the RCs, put the clips back on and reinstall the fuel rail to the engine.

There is one feature which is quite different on an RC injector and that's its electrical connection. Initially, we thought we'd have to splice and solder the right connectors in to the THRS' wiring harness which would preclude us ever switching back, however, we discovered that our fuel pump supplier, Racetronix, sold "plug-and-play" adapters which connected between the stock wiring harness and the RC injectors so we ordered a set of six adapters. Image: CHpg Staff.

The only feature of these injectors that's different from stock are the electrical connectors.The RC disc injectors use a "minitimer" connector, whereas stock 3800 Series II injectors use the "Multec II" connector. To make the installation "plug-and-play," we ordered six Racetronix adapter harnesses (IA-M2M) and connected them between the OE injector connectors and the RC Engineering injectors.

Calibrating for the new injectors required a session on the RC Engineering web site at www.rceng.com using its fuel flow and pressure calculator. We converted our RC Injectors' 240-cc/min@43-psi flow rating to what flow would be at the V6's observed, 50-psi fuel pressure–259-cc/min. Next, we converted that into pounds-per-hour and using HPTuners VCM Editor, entered 24.6-lb/hr. into the calibration as the flow rate at zero manifold vacuum–wide open throttle.

A 3800 Series V6 calibration has injector flow numbers which vary according to the effect manifold pressure has on the injectors and on the fuel pressure regulator. To populate this table with 100% accuracy, you'd have to either flow test the injectors at a variety of MAP levels and fuel pressures which, of course, is impossible–unless you are GM Powertrain. We did the next best thing: we figured the differences in flow on a percentage basis for the stock injector flow data, then, using those percentages, figured new data for the RC injectors to put in the "Injector Flow Rate vs Kpa vacuum" table. Finally, I programmed the pulse width voltage offset data RC Engineering's John Park supplied.

This time, testing showed that, at WOT, the air:fuel ratio was now more consistent so, the next step was to reconfigure the calibration's main VE table at high throttle openings to better suit the changes in airflow caused by the aftermarket camshaft profile, larger valve sizes, head porting and intake manifold Extrude Honing.

This is how HP Tuners displays the main VE table. Changes can be made directly in each cell. Any engine which has had mods, such as a camshaft change, which affect its volumetric efficiency, will likely need tweaks to the main VE table.
Image: CHpg Staff.

Some DIYs marginalize the value of getting the main VE table right. Those who do are either too lazy to do the work or don't understand the need. If the VE table is stock, but your engine has mods which affect volumetric efficiency, the engine controls are going make incorrect assumptions as to the amount of air entering the engine. Some rookie calibrators use other methods to fool the engine controls into delivering the right amount of fuel. This may result in an inconsistent AFR when in PE and it does not address the effect an inaccurate main VE table has on part throttle drivability.

To get the VE table right, be it on the dyno or on the test track, you have to write a temporary calibration to the ECM which disables the MAF sensor, has the high octane spark data in the low octane spark table and is an open loop cal. You, also, have to set-up your wide band to send data to HPTuners and you need to program VCM Scanner to compute and display "Lambda error" which is the difference between the air:fuel mix the calibration commands compared to what the actual air:fuel mix is according to the wideband O2S.

Based on wide-band data we took with VCM Scanner, during several test sessions, we incrementally altered the Main VE table. Once we had a "final candidate" written into a new cal, we restored MAF sensing, spark tables and closed loop fuel control.

While our WOT air:fuel mix was more consistent because of the RC Engineering injectors and the revised Primary VE table, it was now a tad rich so we took a little fuel out, across-the-board, then tested again to find the engine at 0.85-0.86λ from 2000-6200 rpm and the maximum injector duty-cycle at about 85%.

Getting the main VE table in shape, first, makes any subsequent calibration changes made to enhance drivability easier to accomplish. The end result is a car that runs well when your foot is flat to the floor but also runs well at high-part exiting turns.  
Image: CHpg Staff

During this test session, we were running straight 91-oct gas in very good (sea level, 68°F) air. In VCM Scanner data, at high manifold absolute pressure (MAP), I noted consistent knock retard (KR) between peak torque and peak power. To verify it was real detonation and not false knock, I added some Rockett Brand 100 Unleaded Racing Gasoline and detonation was reduced. So the engine would run with less KR on pump gas, In the main spark table cells around peak torque at high MAP, I reduced the spark advance by 2° then dropped the surrounding cells by 1° and tested again. KR was reduced. Finally, I increased the rate of knock retard decay–how quickly the system puts timing back in after a KR incident ends–by 50%.

Both those changes improved the knock retard situation on pump gas. With the dip in the spark curve around peak torque and faster KR decay, when using pump gas, which is the vast majority of the time, the car ran better.

The last major calibration issue we worked on was mass air flow. Some who know enough to be dangerous about tuning minimize the importance of getting the MAF tables right, but know this: much of the computation the ECM makes about fuel flow depends on measurement of the air flow going into the engine. Some might be familiar with the adage: "garbage in–garbage out." That certainly applies to MAF cals. If you don't have the MAF cal right, you won't have the engine's fuel delivery correct.

Why do we need to optimize the MAF cal? Anything you change ahead of the MAF sensor affects the accuracy of the data it sends. The Tom Henry RS has an Whisperlid aftermarket air filter top, a Green Filter and the stock air intake resonator had been removed. All of that makes for a change in how air gets through the MAF sensor.

Work with the MAF calibration can be a little tricky because the ECM toggles back and forth between the MAF sensor data and plain old speed/density computation anytime the engine is in a transient condition–for example: throttle opening changing and the ECM adding fuel–when that happens, the ECM may disregard MAF data and that can effect data you're scanning. For that reason, whether you're calibrating on the dyno or the test track, how the vehicle is driven is key. The smoother you are during acceleration testing the better.

Once again, we set up HPTuners VCM Scanner to read lambda error then configured VCM Scanner's histogram function to show that error for each MAF frequency cell. You also have to force the engine to run in open loop and zero the fuel trim values. You will not obtain accurate data if you don't do that.

We did our MAF testing in several sessions divided into high throttle opening and cruising. It took a while but we got are MAF Lambda error down to ±.02, far better than the .08-.12 we started with.

For more on how to learn basic tuning, read a sidebar by clicking here.  

SS Hood

We've always wanted an SS hood for the Tom Henry RS. We spent a couple of months trying to find an original SS hood but gave up once we saw the cost. Even damaged SS hoods were going for 700 bucks.

Clearly, the best choice for our budget was a fiberglass reproduction. After researching the market a bit, we went with the SS hood RKSport sells. One  reason why we picked the "RK Competition Ram-Air Hood" (PN 01011104) is the way it's made. Tom Baker, RKSport's Director of Marketing, told us, "All our hoods are hand-laid, not gunned or infused. The fiberglass is sealed with marine grade gel coat and the hoods ship 'paint-ready'–they just need a light scuffing and primer before they're shot with paint and clear coat. They're all manufactured at our facility in Murrieta, California."

The RKSport hood came out of the box nearly ready to paint. Image: CHpg Staff.


Before any significant finishing work was done, the guys at Diamond Finish Auto Body, test fitted the hood on the Tom Henry RS. 
Image: CHpg Staff.

Besides the look and how they are made, another reason we picked the RKSport hood is the cold air ducting inside the O.E. SS hoods is reproduced on its underside. The hood scoop is functional with incoming cold air split between two ducts which channel air to the our Whisperlid air filter top.

The test fit confirmed RKSport's "first-time-fit". Image: CHpg Staff.

The final work on the Tom Henry RS was done at THR's West Coast development facility so we had RKSport ship the hood to our bodywork specialist, Diamond Finish AutoBody in Santa Barbara, California, for installation and painting.

At Diamond Finish, during a test installation before any sanding, we found the fit of RKSport's reproduction of the SS Hood to be quite good. The only significant difference came at the left front corner of the panel. To get the panel gap correct at that spot, we had to shim the left side of the front fascia up about an 1/8-inch. The RKSport hood is not drilled for the stock hinges' locating tabs. While ten minutes with a drill will fix that, we asked Tom Baker why there were no holes for the tabs. He told us that if one bends the tabs on the hinges flat, the rear of the hood has a much greater range of adjustment as to its position in the hood opening, so they leave the tab holes undrilled figuring installers will do that and have more adjustment–smart guys at RK Sport.


A small amount of sanding and priming was done to the edge of the hood at the front. Image: CHpg Staff.


After that, it was into Diamond Finish's spray booth for a coat of white and then a clear coat. Image: CHpg Staff.

The crew at Diamond Finish sanded and primed the hood then shot it with Arctic White. After painting, the hood was installed using the lower pressure struts RKSport includes with the hood. A laser-cut, polished, stainless steel grille, also, comes with the hood and is installed over the hood scoop opening. The polished stainless didn't look good on a white car with a black front grille insert so, we had our long-time coating vendor, Extreme Performance Heat Coatings, put a satin black coating on the grille.

Not only did the RKSport Competition Hood do much to toughen the THRS's look but its functionality was shown in our road testing. Image: CHpg Staff.



In fact, the Tom Henry RS came out looking "tough" from just about any angle. Image: CHpg Staff.

For-Real Ram Air

With the new hood, I decided to retest with the wideband O2 to see if the hood made any difference in airflow into the engine.

Oh boy, did it ever!

I was astonished to find that at highway speeds, the RK Competition Ram-Air Hood increases air flow through the MAF sensor by 5-6%. In fact, I had to, once again, tune the high end of the MAF table in the calibration because, at high throttle openings the engine went lean–Lambda .89-.92. Once we did that, the WOT air:fuel was back at the ideal .85-.86λ we like to see. Too bad we can't properly duplicate the airflow into that hood on the chassis dyno. I'd love to see how much of a change in power output that hood is worth.

After the hood installation and some final cal work, it was back to WesTech's Superflow Chassis dyno. Image: CHpg Staff.

  Back at Westech Performance Group for some final numbers, it was hot day. As knock retard hedge, I added enough Rockett Brand 100 Unleaded to bump the octane to 93. In three runs on Westech’s AutoDyn, we were at 0.84-0.87 λ. We, also, made our best SAE-corrected, rear-wheel power and torque yet: 244.9-hp@5750-rpm and 234.5lbs/ft@4700-rpm, SAE-corrected. That is just under 17-rwhp and 14-rwlb/ft torque more than we did in our last chassis dyno test in Part 5–a significant improvement. Using a .82 correction for driveline loss, that's about 299-hp and 280 lbs/ft, SAE, at the flywheel. Not bad for a 3.8-liter V6 which started at 200-hp.

Next, we ran some quarter-miles at our test venue. We use a Vericom VC3000 Performance Testing Computer to measure the car’s performance. Vericoms have three major components: an accelerometer, a crystal clock and a microprocessor. The first two measure acceleration and elapsed time and the third calculates velocity every 1/100 second. Knowing the velocity and the time enables the VC3000 to calculate distance every 1/100 second.

Suction cups or, for some models more powerful vacuum cups, attach a Vericom to the windshield. It can be installed in less than a minute. It runs on an internal battery or off the car battery via a 12-volt power cord. An “OBD2” cable is available so the Vericom can recored engine controls data along with vehicle dynamics data.

The VC3000’s accuracy and dependability is such that it is used as a braking test device in traffic accident investigations worldwide. Vehicle manufacturers, tire companies, law enforcement, transit companies and training academies all use them. Vericoms are approved by the Federal Aviation Administration to measure runway friction. A test of a runway’s traction–or lack thereof– is information required for pilots of commercial aircraft landing in bad weather. Vericoms are widely used in the United States for that purpose.

The unit’s accuracy is 1% in time, g-force, speed and distance. In acceleration testing, the difference between a Vericom time and drag strip clocks is typically .2 to .4 sec. and comes from the VC3000 not having a “roll out” delay before timing begins. The later model of the Vericom, the VC4000, does, in fact, have a “roll-out correction” which defaults to 12-inches but can be user-adjusted for other values.

With the Vericom in the Tom Henry RS we headed for our test venue. In three quarter mile passes, we averaged 15.22/96.90. To equate that to drag strip timing, we’ll subtract .3 sec. for the lack of roll-out to get: 14.92 No doubt, if we were going to do another part of the series, we'd trade the stock 3.23 axle ratio for a set of 3.73s  then put some drag radials on and have a 13-second car.

Finally, we took the Camaro to a California Smog Check station and had it tested. The engine tested clean by a significant margin.


The Tom Henry RS's final engine modification was nitrous oxide injection from Mike Thermos' Nitrous Supply. We installed a "Sportstar Universal EFI Dry Manifold Kit" (PN NS06100) and a "WIde Open Throttle Switch" (PN NS25633). The Nitrous Supply Dry Manifold Kit is for engines with electronic throttle control and a vacuum-controlled, return-type fuel system, however, because this kit is not specific to a V6 Camaro, there were extras–mainly fasteners, some 3/16 fuel hose, an extra 7-ft. of AN-4 nitrous hose and fittings–necessary to get it working.

With the Sportstar Kit, nitrous is injected just downstream of the throttle body's MAF sensor. Extra fuel is supplied through the injectors by increasing fuel pressure when the system is active.

Nitrous Supply's Mike Flynn at work on our throttle body. If you are very careful, nozzle mounting can be done with a hand drill. The TB material is thin so, to ensure the nozzle doesn't back out, use a thread locking compound such as Permatex Medium-Strength Thread Locker Gel. After nozzle installation, thoroughly clean the TB to eliminate any metal chips. Image: CHpg Staff.


It's critical that the nozzle point to the rear of the TB. If it does not, nitrous oxide can "bounce" off the sides of the throttle body, causing errant mass air flow sensor readings resulting in significant problems with fuel delivery. Take a fine-point Sharpie, mark a line on the top of the nozzle then tighten the nozzle until the line points to the rear.  Image: CHpg Staff.

The discharge nozzle has to be installed in a specific spot in the throttle body. While it is a task which can be accomplished by a DIY with a drill press, we decided the job was better done by Nitrous Supply. We pulled off the throttle body, visited Nitrous Supply and had Mike Flynn install the nozzle. Inside the discharge nozzle is the nitrous jet.

Nitrous nozzles have SAE 37° AN04 connections to which our braided stainless steel  covered Teflon hose attaches.
Image: CHpg Staff.

We put the nitrous oxide cylinder in the cargo well behind the rear axle. Using some wood we bought at Lowes and the two bottle brackets that come with the kit, we built a mount which held the bottle securely but could, also, be easily lifted out when the space was needed for cargo. Our bottle holder accepts either 10-lb or 15-lb Nitrous Supply cylinders. The positioning of the bottle in the brackets is key to optimal performance.

We built a wooden frame, painted it flat black, bolted Nitrous Supply bottle mounts to it and viola–a removable nitrous bottle mount which fits nicely in the Camaro's cargo well. We installed the Nitrous Supply 10-lb bottle into the mounting rings. Image: CHpg Staff.

Under pressure, nitrous oxide is a liquid. A nitrous bottle is made such that its siphon tube extends to a point on the bottom of the bottle opposite the center of the label. The idea is to orient the end of the siphon tube such that acceleration keeps the end of the tube covered with liquid nitrous oxide. On a bottle, such as ours, located perpendicular to the vehicle centerline with the discharge valve on the driver side of the car, orient the label so it is 30° from vertical towards the front of the car. That puts the pick-up end of the siphon tube, 30° towards the rear from the lowest point of the bottle.

Next, we assembled the "solenoid module" by installing a Nitrous Supply solenoid on each end with the solenoid tee and the nitrous pressure regulator in the center. We screwed the solenoid module to the bracket that comes with the kit and mounted that on the driver side, front subframe rail, above and just behind the front stabilizer bar mount.

We used the stock power steering reservoir bracket to hold the pair of Nitrous Supply solenoids and the regulator. Image: CHpg Staff.


This is the solenoid/regulator assembly once the power steering reservoir bracket is reinstalled on the left front frame rail. Image: CHpg Staff.

We ran the AN-04 braided stainless-steel-covered Teflon hose from the solenoid module, along side the fuel and brake lines which run down the driver side of the floorpan, to the back of the car. In several places, we attached the hose with zip ties. In places where this nitrous feed line runs near our headers, we insulated it with Design Engineering Heat Sheath (PN 010419). The hose included with the kit was not long enough, so we added a Nitrous Supply, four-foot, AN-04 extension. To get the hose into the cargo bay, we temporarily removed one of the two plugs in the bottom of the cargo well and ran the hose through the hole. To keep the sharp metal edges around the hole from cutting the hose, we sliced a three-inch piece of plastic hose from our scrap bin lengthwise and slipped that over the AN-4 where it touches the edges of the hole. We removed the screw holding the left corner of fuel tank's aluminum shield, tucked the nitrous hose into the void between the tank and the shield then replaced the screw. Finally, we dropped our custom-made nitrous bottle mounting in the well and connected the nitrous hose.

The Nitrous Supply Sportstar EFI Kit is known as a "dry system" because only nitrous oxide flows into the throttle body and extra fuel comes through the fuel injectors. To meter that extra fuel, nitrous oxide at greatly reduced pressure, is fed to the stock fuel pressure regulator (FPR) which causes fuel pressure to rise from the approximate 50 psi normal for a 3800 V6 to 65-70 psi.

We mounted the Nitrous Supply "WOT box" on top of the driver-side wheel house just behind the underhood fuse block.
Image: CHpg Staff.

The reduced nitrous pressure fed to the FPR is accomplished in two steps. The first takes place in the nitrous regulator between the two solenoids. From the nitrous regulator, we ran fuel injection hose across engine compartment behind the cooling fans then, up to the top-right-front of the engine and along the right rocker cover to the rear of the engine. We installed the Nitrous Supply pressure tee into the hose which runs from the intake manifold, around the back of the intake plenum to the fuel pressure regulator. The tee comes with a .042-in. jet in it which bleeds off some of the nitrous flow from the nitrous regulator, further reducing the pressure applied to the FPR. The size of this jet can be varied to change the air:fuel ratio when nitrous is flowing–smaller jet, more fuel pressure; bigger jet, less fuel pressure.

The pressure on the FPR generates more fuel flow, provided the fuel system has been modified for adequate flow at the higher pressure level and we accomplished that with the Racetronix fuel pump (PN PN F99-FPKG-2) installed for Part 4 of this series. Some DIY's don't understand the relationship between fuel pressure and fuel pump capacity. If you raise the pressure, the pump's fuel flow limit decreases. If that decrease goes below the engine's greatest required fuel flow, the engine will go lean at high rpm. We raised the the engine's need for fuel flow through our engine mods, then we raised the system pressure. That overtaxed the stock fuel pump. Hence our switch to a Racetronix.

The plumbing of the nitrous bypass and the fuel pressure regulator gets a little bit complicated but the system works quite well provided the fuel system is capable of the extra flow the nitrous oxide system requires. Image: CHpg Staff.

 Any nitrous oxide system uses a relay to control the solenoids and Nitrous Supply's system includes a 30-amp relay which we mounted on the front of the inner fender. We wired the load side of the relay to the battery and the solenoids.

We attached the Nitrous Supply Wide Open Throttle Switch–"WOT box" for short–on top of the left inner fender. It triggers nitrous injection for an engine without a mechanical throttle linkage by sensing throttle position sensor (TPS) voltage and energizing the nitrous solenoid relay just before maximum TPS. This voltage varies depending on the engine. Using our shop's Fluke 88V DMM we measured the TPS #1 voltage at wide open throttle and it was 3.30-3.32v, so we adjusted the WOT Box to kick the primary nitrous solenoid on at 3.28v. Finally, we connected the box's output to the line side of the nitrous relay.

Next, we removed the cap from the fuel rail's fuel pressure connection. Then, using a tire valve core tool, we took out the Schrader valve core. Once the cap and valve were gone, we installed the nitrous kit's extension tube, which adapts the kit's fuel pressure safety switch to the AN-04 connection on the fuel rail, and screwed the switch in place. Finally, we wired the fuel pressure switch between the secondary solenoid and ground and routed the switch wires along side to the hose running down to nitrous regulator. When the system is energized, the primary nitrous solenoid opens and nitrous oxide flows through to the nitrous regulator and up the hose to the tee and to the FPR. When the fuel pressure rises to 65 psi, the safety switch closes energizing the secondary nitrous solenoid which opens, allowing gas to flow to the discharge nozzle and into the throttle body. The fuel pressure switch prevents nitrous oxide flow until adequate fuel pressure exists.

The Nitrous Supply fuel pressure safety switch is installed in place of the fuel pressure test connection on the end of the passenger side fuel rail. If you remove a rubber plug on the top of the switch, you can adjust its trigger pressure with a hex key. The default setting is 50 psi, but it must be readjusted to turn-on 3-5 psi above a V6's nominal fuel pressure range of 48-52 psi. The best way to do this is test the engine's fuel pressure per the Service Manual, then use a calibrated air source to set the switch 3-5 psi above the pressure you read. Image: CHpg Staff.

Nitrous Supply includes a generic toggle switch for arming the system, but we decided a neater installation would be a second fog light switch (PN 10273879) in the panel above the radio as an arming switch. We ordered one from the Tom Henry Racing parts department, removed the plug originally in the panel and popped the switch in place. After that, we installed a push button, momentary switch on the gear shift lever just below the shift knob and positioned such that when the driver's hand is on the knob, he can flick a thumb down and push the button.

We ran a hot wire from the fuse panel to the master switch, then to the button and from there, though the fire wall to the WOT box. To get nitrous, the arming switch must be closed, the throttle must be wide open, the driver must push the button and the fuel pressure needs to be up.

These are the features we like in the Denso Iridium Power spark plug. Image: CHpg Staff.

The last step in preparing the car for nitrous was to install a fresh set of Denso Iridium Power IT-20 spark plugs. We've used Densos since the start of the Tom Henry RS series. We like the Iridium Power design because it's a combination of the best of Denso's two product lines, the iridium-tipped plugs it makes for car companies–General Motors being one of them–and its track-proven racing plugs. A key feature of this Denso is the small, 0.4-mm iridium center electrode. The advantage of an iridium electrode over one made from more traditional platinum is better durability and lower resistance. Another obvious characteristic of the Denso is its ground electrode which is cut-back, tapered and grooved. The small center electrode and unique shape of the ground electrode give the spark maximum exposure to the incoming, air/fuel charge. In short, we think the IT-20, which is a heat range colder than stock, is the best spark plug choice for 3800s in street high-performance and mild racing applications. For track only applications, we'd use the even-colder, IT-22.

With all this nitrous hardware installed, it was time to take the car out for a little test run. Did it work? Damn right! When we shifted into second gear, then squeezed the button–boom! We got a serious, nitrous-fortified, kick in the ass.

The next step was to verify the tuning of our newly installed Nitrous Supply system. Testing with the Innovate Motorsports LC-1 found that when the nitrous was working, the engine was a bit rich–0.73-0.76-λ so–with some tuning, the nitrous hit would be even bigger.

One more time on the WesTech dyno, this time with spray, had us just short of 400-hp. Image: CHpg Staff.

We decided the nitrous flow was likely adequate but, because the air:fuel was rich we weren't getting the full benefit. We needed to lean the engine out to the 11 or 11.5:1 suggested by Nitrous Supply and, with the Nitrous Supply Sportstar EFI system, you can do that by decreasing fuel flow during nitrous operation.

First thing we did was test what kind of fuel pressure we had when the nitrous system was enabled. We installed our Waekon digital fuel pressure tester (PN 48165) and went for a road test. When we squeezed the nitrous button and–wow–97-psi fuel pressure! No wonder the engine was rich on the bottle.

With the nitrous oxide system operational, additional fuel flow comes via higher-than-atmospheric-pressure applied to the FPR diaphragm. The size of the jet in the tee determines that pressure. Ideally, you want the air:fuel ratio with the nitrous system operating at about 0.80-lambda. That is a little rich, but you need that richness to compensate for inconsistent distribution of nitrous oxide in the intake manifold.

We started by doubling the diameter of bypass jet to .081-in. Fuel pressure was still too high. We went up to .091-in. and finally to .110-in. Fuel pressure was now at 70-lbs. Air: fuel with nitrous oxide working was finally hovering around .79-lambda.

We rolled the Tom Henry RS on Westech's Superflow Autodyn for the final time. Because the engine with nitrous oxide being injected is more prone to detonation, we put a 2:1 mix of Rocket Brand 100-oct Unleaded Racing Gasoline and pump gas in the tank and let fly. On nitrous, the car made 316.3 hp at the wheels at 5775-rpm and 325.8 lbs/ft at the wheels at 3630-rpm, SAE-corrected. Those numbers work out to 385-hp and 401 lbs/ft torque, SAE at the flywheel. A 75-shot indeed! Actually, it's an "85" shot and more than enough nitrous oxide for an engine with a stock pistons and rings. Peak torque moving down 1000 rpm is a function of the increased cylinder pressure in the mid-range which nitrous oxide can provide.

 Image: CHpg Staff.

Once again, we installed our Vericom VC3000 and did some more quarter-mile tests. With nitrous, the our Camaro went 13.65/100.43.

THRS Chassis dynamometer test history
Rear wheel power, SAE-corrected

1)  162.3-rwhp–Stock

2)  173.5-rwhp–Stock with Flowmaster exhaust
3) 206.0-rwhp–DeGroff ported big-valve heads, Comp Cam, Extrude Honed intake, Extrude Honed stock exhaust manifolds, Flowmaster exhaust, Z-Industries reprograming.
4) 212.9-rwhp–DeGroff ported big-valve heads, Comp Cam, Extrude Honed intake, Dawson Headers, Flowmaster exhaust, Z-Industries reprograming.
5) 219.1-rwhp–DeGroff ported big-valve heads, Comp Cam, Katech Valve Springs, Extrude Honed intake, 1.8 rockers, Dawson Headers, Flowmaster exhaust, Z-Industries reprograming.
6) 228.3-rwhp–DeGroff ported big-valve heads, Comp Cam, Katech Valve Springs, Extrude Honed intake, 1.8 rockers, Dawson Headers, 3" cat converter and S-pipe, Flowmaster exhaust, Z-Industries reprograming.
7) 244.9-rwhp–DeGroff ported big-valve heads, Comp Cam, Katech Valve Springs, Extrude Honed intake, 1.8 rockers,  RC Engineering injectors, Dawson Headers, Flowmaster exhaust, in-house reprogramming.
8) 316.3-rwhp–DeGroff ported, big-valve heads, Comp Cam, Katech Valve Springs, Extrude Honed intake, 1.8 rockers,  RC Engineering injectors, Dawson Headers, Flowmaster exhaust, nitrous oxide, in-house reprogramming.

Farewell to the THRS

Clearly our Extrude Honed intake manifold, RC Engineering injectors, Mark DeGroff heads with Manley Valves, Comp Cam, Katech Valve Springs, Dawson Headers, Flowmaster exhaust, our ECM programming and the hardware from Nitrous Supply all work very well.

After five years, it's time to turn-off the lights and shut the door on the Tom Henry RS. We've learned a lot about how to improve performance and tune a 3800 Series II V6 for high-performance street use and modify the fourth-gen Camaro chassis for better handling and braking. We hope you have too.

If you enjoyed this series, let us know. If we hear from enough readers, we might do an encore. Finally, we'd like to thank all of our project sponsors for their support of the Tom Henry RS project.

Project Sponsors:

Baer Brakes
Brush Research
Calibrated Success

CarTech Books

Denso Products and Services America
Design Engineering
Fikse Wheels
Fluke Corporation
Goodyear Tire and
 Rubber Company
Inland Empire Driveline Service
Innovate Motorsports

Bosch Automotive Service Solutions  (formerly  SPX Kent-Moore Tools)

Bosch Oxygen Sensors
Nitrous Supply
Porterfield Enterprises
Procar Seats
Raytek, Inc.
RC Engineering
Red Line Oil

Rockett Brand Racing Fuels

Summit Racing Equipment
The Tuning School
Tom Henry Racing
Year One Muscle Car Parts, www.yearone.com
Westech Performance Group
Motorbooks Inc.
Wheelskins Inc.