Big Block from Hell Series..
Part 2 ... Cylinder Head Art and Science
by Hib Halverson
In this second part of the Big-Block from Hell series, first, we are going to finish assembling the short block, then we will examine proper modification of oval-port, big-block heads for street high-performance use.
Short block wrap up
When we left Edelbrock in Part One, preliminary short block operations were complete and our engine assembler, Mike Eddy, had installed the crankshaft.
The chamfer on the big end of each Crowerod must face the outside of its respective rod bearing journal and Bill Miller Engineering pistons must have their domes oriented correctly. Thus, four rod/piston units are assembled one way and the remaining four the opposite way. This all sounds pretty damn complicated but, there is an easy way to get it right. Just remember: the numbers on the rods' big ends go to the outside and the domes go to the outside, too; or as Mike Eddy says, "nado" for "numbers and domes outside." Apply Red Line Assembly lube on the wrist pin and the rod's small end, orient the rod and piston such that all is "nado" then slide the wrist pin in place. Pretty slick, eh?
To retain wrist pins, BME pistons use four Spiralocs. They're devilishly hard to install. Use your fingers to slightly spread the ends of the Spiraloc apart then, with a rotating motion, feed it into the pin lock groove. You must do this four times for each piston. It comes with experience is all I can say…while Mike Eddy did six pistons, I was only able to assemble two.
The Big-Block from Hell's 454 uses a Childs and Albert ZGS piston ring set. "ZGS," an acronym for "Zero Gap Second," denotes C&A's torturous-leak-path, second ring design. A ZGS ring does have a "gap" but it consists of two overlapping steps with an inner boot "back seal". Use of ZGS rings with properly prepared cylinder walls will pay off in reduced cylinder leakage. (author's note: this article is reproduced, for the most part, as it was printed in Vette Magazine back in 1991. There were, in fact, serious problems discovered later with the ZGS rings and they will be covered in a future part of the series.
The oil ring goes on the piston first. Make sure the two oil rail gaps are positioned
opposite each other and that the ends of the expander butt together 45degrees from either
of the rail gaps. The ZGS "inner boot" is installed in the second ring groove
followed by the ring itself. The assembly must have a minimum of .005" back groove
clearance and its gaps must be opposite each other. If back groove clearance is lacking,
you have two choices.
1) Use the ring without the inner boot. The effect of the ZGS ring will be reduced but not eliminated or
2) have the second ring groove on your pistons machined for more depth. Last to go on is the plasma/moly-filled, ductile iron top ring.
Mike Eddy determined last month that we would use Childs and Albert, .001" undersized rod bearings. The Crowerrods were fitted with upper bearing shells then the piston skirts and the rings were given a light coat of Red Line Break-In Oil. The rod/piston units were installed in specific cylinders (selected last month) using a B&B Performance tapered ring compressor (p/n 4145). Superior to "squeeze-type" units, B&B Compressors taper to your exact bore size, are made of hard-anodized aluminum and come in a multitude of diameters. The piston can be driven smoothly by hand through the compressor and into the cylinder. The rod caps were fitted with bearings, installed onto the rods and had their bolts torqued to 65 ft/lbs.
The camshaft will be a critical factor determining whether or not this engine will meet its power and drivability goals. An Edelbrock Torker-Plus hydraulic lifter cam (p/n 5062) will replace the Melling 396-S used previously. Compared just by duration and lift, the two appear somewhat similar.
|Stock Chev. 3883986||Melling 396-S||Edelbrock 5062|
|Duration at .050" lift~Int./Exh||213o/217o||222o/235o||224o/232o|
However, the 5062 has significant differences: 1) a moderate lift increase to which the big-block responds particularly well 2) more rapid valve opening and closing rates. For a given duration, the valve will be open a greater amount 3) although it works well in any oval-port big-block, the Edelbrock cam really shines with cylinder heads that have been mildly ported and polished and 4) to capitalize on the interaction between intake manifold and camshaft, the Torker-Plus was developed in conjunction with Edelbrock's Torker 2-O manifold, which we also will be using.
The camshaft was treated with G&L Coatings' DFL0221 dry film lubricant then burnished with a Standard Abrasives General Purpose Brite-Rite pad. G&L DFL0221 and its preparation before use were discussed at length last month.
Mike Eddy spread Red Line Assembly Lube on the lobes and bearing journals of the 5062 then slid it in place. Installation of an Edelbrock True-Rolling Timing gear set (p/n 7810) finished the job. Next month, once the rest of the valve gear is fitted, we will discuss the camshaft checking process.
The last short block assembly tasks dealt with the oiling system and Mark Gray stepped in the do the honors. He began with a Milodon oil pump (p/n 18760) that was prepared for use by coating the interior of the pump body and its gears with G&L DFL0221, chamfering the area were oil flow transitions from the pump body to the output line and shimming the pressure relief valve spring .025-inch. The pump was then fitted with a B&B High Strength pump drive shaft (p/n 6508) and a special Milodon oil pump pickup (p/n 18465) designed to work with a Milodon oil pan we will install later. The pickup is a heavy press fit into the pump body and also bolts to the oil pump cover so welding it into the pump body was unnecessary. A B&B Oil Pump Stud Kit (p/n 3400) was fitted to the short block and a Milodon windage tray (p/n 32200) was attached to the ends the main bearing cap studs.
This tray requires trimming where it mounts at the oil pump and the nuts used to fit the tray to the main studs must have their height set. The best way to do this is first, fit the tray at the pump, then lower the oil pump and windage tray into place as a unit. Hand tighten the rear nut, set the height of the lower tray nuts then add lock washers and upper nuts tightening them to 35 ft/lbs. Tighten the oil pump stud nut to 65ft/lbs. With that, Mark Gray covered the short block with an engine bag. We will be back to it in Part 3.
Cylinder Head Preliminaries
The reasoning behind porting, polishing and custom valve jobs is simple. Those techniques reduce resistance to flow in and out of the combustion chamber. Anything done to enhance flow makes the engine more efficient and powerful. Thus, the heads are another big factor in how well the BBfH 454 will perform.
Mark DeGroff's Cylinder Head Service and Machine Shop is one of those small, unique firms whose work is as much science as it is art. DeGroff learned the cylinder head craft at Valley Head Service for almost 20 years ending as General Manager in 1980. In ‘81 he opened his own operation and has never looked back. His three-man shop offers personal service and attention to detail that is difficult to find but expected by many Corvette enthusiasts.
From the BBfH 454, we want plenty of low-end torque and a 5500-6000 rpm power peak so we are using the stock, 1971, low-performance, oval-port head castings (DeGroff calls them "truck heads"…such abuse we take in the name of bringing you a great engine project!). Why "Lo-Po" heads? Well, first they're cost effective…like, we already had them…also, their smaller intake port volume is well suited to a stump-puller, six-grand big-block.
Mark DeGroff's port and polish strategy would be to moderately increase air flow by:
1) an increase in both intake and exhaust valve sizes,
2) porting of the valve pockets
3) smoothing of the short-side radii of both intake and exhaust ports and
4) streamlining and polishing of both the intake port entries and the exhaust port exits.
This combination, an excellent compromise between power increase and cost, is known as a "street port and polish".
The castings were hot tanked and pressure checked. Mark then inspected the valve guides for excessive stem-to-guide clearance. The guides in cast iron big-block heads are quite durable. Even our high mileage units showed no significant wear. We would leave them untouched. Next, to check if the head gasket surfaces were parallel to the planes of the head castings, Mark carefully measured the height of the gasket surface on each head at the three locating pads that Chevrolet uses to index all of their machine work. One head was acceptable, the other was tapered approximately .010". Lack of parallelism would be corrected later.
Our DeGroff heads will be fitted with larger diameter, Milodon Megaflow Competition intake (p/n 45115) and exhaust (p/n 45135) valves. They are made of stainless steel, have stock diameter stems, hardened tips, hard-chromed stems and swirl polished heads. The area of the stem just above the head is of reduced diameter to improve air flow.
The valve seats were bored out to fit the L-88/ZL-1 sizes of 2.190" and 1.880" respectively. Next Mark rough finished the new valve seats with a Kwik-Way valve seat grinder fitted with a 45o stone.
Mark set the valves in place and made the initial seat depth measurement. Additional small amounts of seat grinding were done to set depths within .010". This is necessary as valve seat depth affects porting around the seats and polishing of the combustion chamber. Valve seat depth will get a fine adjustment during the CC'ing process.
We cannot overemphasize the importance of experience in head porting. Inexpensive do-it-yourself or "home" porting kits are available containing some of the tools and materials that those who port heads for a living use. However, these kits contain no "instant expertise." We suggest, unless you have substantial porting know how or a large supply of castings, a flow bench and many hours to spend on the learning curve; that you skip the home porting kits and have professionals do the work.
Mark DeGroff begins porting with the intake valve pocket or "bowl," as the experts say. This area is enlarged bringing its diameter out to just under the valve size. Next, the intake port short side radius is blended and smoothed. This is a critical flow area as it is where the floor of the port curves down to the valve seat. The port entry is not enlarged as we want only moderate cross-sectional area to keep flow velocity high for good mid-range torque and sharp throttle response. Intake manifold port matching is usually done at this point, however, Edelbrock recommends the Torker 2-0 be used without port matching.
Big-block Chevrolet exhaust ports have, relative to the intakes, poor airflow characteristics. Some of the flow improvement we need will come from the 1.88-inch valve. In addition, to bring the exhaust/intake flow ratio from the 65% of a stocker to around the 80% considered appropriate for street high performance or racing engines; port work similar in nature to that done on the intakes was necessary.
Intake and exhaust port surfaces are polished using different techniques. Intakes are finished with rotary stone in the die grinder which leaves a surface that is noticeably dull and rougher. In pre-flow bench times, everything was near-mirror finish. Flow testing done in the '60s and early '70s discovered that with intake ports, this finish was detrimental. A very smooth port wall causes much turbulence restricting flow in the main part of the air stream.
If the intake port wall is finished such that it is smooth, but not "very smooth" the slight roughness actually decreases turbulence and allows a "boundary layer" of smooth air to form next to the wall. The main part of the air stream can "slide" over this boundary layer and air flow numbers improve.
Conversely, Mark DeGroff polishes the exhaust ports to near-mirror finish with his die grinder fitted with a 60-grit Standard Abrasives sanding cartridge roll. Port wall finish is not important as velocity in the exhaust ports is about four times that in the intakes. A very smooth finish reduces carbon build-up on the exhaust port walls.
The combustion chamber walls were altered to match the profile of the cylinder tops in the block left last month after the block was relieved. After that, Mark polished the combustion chambers using Standard Abrasives 60-grit "SocAtt®" sanding discs.
Valve Job and CC'ing
The first step here was to machine the head gasket surfaces to correct the lack of parallelism discussed previously. The head with the problem got a .012" angle cut and the other "straight" head took a .002" cut. Mark DeGroff explained that the surfacing operation is concluded before grinding the valves and valve seats as the final valve seat depth measurement and the combustion chamber displacements depend on this parallelism.
The value of a multi-angle valve job to a set of street high-performance or racing heads is undisputed. It is a critical factor to improved flow at low valve lifts. The ideal situation would be to have smoothly radiused valve faces and seats however, there would be no place for the valve and seat to seal. The next best thing is a series of straight cuts at a number of different angles. The angles are selected so the air flow will "see" the angles as nearly a smooth radius.
With our DeGroff heads, the intake seats get 45o, .060-inch wide cuts and the exhausts get 45o, .080" cuts. This is done with a 45o stone on the Kwik-Way valve seat grinder. Next, the valve depths are measured again and, if necessary, the seats are ground slightly to get depths within .002" of each other. Finally, all valve seats get a 60o under cut and a 35o top cut. The valve faces are ground on a IDL valve grinding machine. The intake valve has a 45o, .060" wide face cut and a back cut of 35o. The exhaust valve gets a 45o, .080" wide face cut followed by a 25o back cut.
Valve lapping is next. This time-honored final touch, optimizes the seal between the valve and seat. An ultra-fine abrasive paste known as "lapping compound" is spread on the valve face. The valve is put in place and spun using a suction-cup-with-handle device. In addition to honing the seats and faces, the lapping compound leaves behind a gray haze giving a final indication as to the quality and positioning of the valve-to-seat contact area.
It is necessary for all the combustion chambers to be of equal displacement. To get to this point, each chamber must have its displacement measured then, if their numbers vary too widely, adjustments must be made to equalize the numbers. The largest chamber is selected then, the remaining seven chambers have small amounts of material removed such that are all within 0.25 cc of each other. Our final average chamber displacement was 113.5cc's.
No serious cylinder head modification shop works without a flow bench to simulate and measure airflow through intake and exhaust ports. Mark DeGroff has a Superflow 110 flow bench he uses to do R&D and spot check his cylinder head work.
The first step was actually taken before Mark made any changes. After cleaning one of our castings, he flow tested the stock ports. All big-block heads, excepting the Bow Tie aluminum race head (p/n 10051128), have two different intake ports. The "good ports" aim directly at the valve. The "not so good ports" are shorter but curve to clear pushrods. Proper intake port flow testing procedure is to flow test the bad ports. You can figure that the good ports will always be better.
On the Superflow 110, our DeGroff heads showed a 12.3% average increase in intake flow and a 30.6% average increase in exhaust flow. The difference in increases is because the stock intake ports are quite efficient, considering their port volume and valve size, where as the stock exhausts are not as good. Thus, the street port/polish procedure has a more pronounced effect on the exhaust port. Admittedly, a small additional increase can be had with porting the intake further, but it would come at greatly increased cost.
Cylinder head flow comparison c/n 3993820
|Valve lift (inch)||.050||.100||.200||.300||.400||.500|
|Stock Chevrolet "bad" intake|
|Air flow (cfm)||18.5||35.4||72.5||113.3||129.9||139.5|
|DeGroff modified "bad"intake|
|Air flow (cfm)||20.6||41.6||86.0||118.2||143.1||156.3|
|Stock Chevrolet exhaust|
|Air flow (cfm)||13.4||25.8||52.7||71.9||87.9||95.2|
|DeGroff modified exhaust|
|Air flow (cfm)||16.7||33.5||70.9||95.6||113.3||128.6|
All these numbers mean much to cylinder head aces like Mark DeGroff. They sit around at parties talking about how they got such-and-such a port to flow three more cfm at .825 valve lift. However, with most of us Big-Block drivers, what counts is how we feel when we hit the loud pedal! We'll find out how good Mark's work is when we put the Big-Block from Hell's on the dynamometer in Part 4 of our series due in the November Vette.
Flow testing complete, it was time to deburr the inside and outside of the heads. Particular attention was paid to removing casting flash, rust and scale from oil drain-back holes and coolant passage openings. The castings were then thoroughly cleaned and blow dried. Cylinder head assembly began with the installation of new B&B Performance rocker arm studs (p/n 3615) and the set of Chevrolet pushrod guide plates removed during the disassembly process in Part 1.
Next the valves' stems were coated with Red Line Assembly Lube and fitted to the heads. Edelbrock retainers (p/n 9731) and Stem Locks (p/n 9611) only were set in place to allow DeGroff to check the valve spring installed height. We are using Edelbrock Torker Series Valve Springs (p/n 5762). They go with the 5062 camshaft and must be installed at 1.870". Mark found that the installed heights in several locations were .060-070" too low, a problem typical of stock heads. Low installed height will have valve spring seat pressure above the Edelbrock specification of 110-120 lbs. This causes excessive pressure on the cam lobes at valve opening and possible premature camshaft wear. The solution was time consuming but nevertheless, necessary. DeGroff machined the valve spring seats such that the installed height of all springs was the desired 1.870".
After a repeat visit to the solvent tank, it was back on the assembly bench. The Milodon valves were reinstalled and as our heads had been previously equipped with Perfect Circle valve stem seals, a new set was put in place. The Edelbrock springs were checked for open pressure (int. 290 lbs@.527" and exh. 300 lbs@.553") then installed followed by retainers and locks.
To improve oil drain back, areas exposed to engine oil were painted with General Electric "Gyptal" armature paint. External surfaces were sprayed with Chevrolet orange. When dry, Mark DeGroff put the heads in plastic bags for shipment to Edelbrock. Next month we will detail the rest of the engine assembly process.
Rancho Santa Margarita, CA 92688
|Bill Miller Engineering
Carson City, NV 89706
|Crower Cams and Equipment Co.
3333 Main St.
Chula Vista, CA 92011
2700 California St.
Torrance, CA 90503
|Mark DeGroff's Cylinder Head
Service and Machine Shop
18736 Parthenia Unit 2
Northridge, CA 91324
|Red Line Synthetic Oil
6100 Egret Court
Benicia CA 94510
On to Part 3