Big Block from Hell Series..
Part 7 ... Cooling Hell's Fire
by Hib Halverson

Out here in L.A., when we’re not getting a tan, sitting in traffic jams, breathing smog, burning south-central or bouncing off walls during earthquakes; one can pickup "L.A. Weekly" and read the stuff on which leftist, vegetarian, fashion victims thrive. The only thing I like in this rag is a great comic strip, "Life in Hell" by Matt Groning who also does TV’s "The Simpsons."

This comic always gets me thinking about the Big-Block from Hell series. After the problems of Part Six (see VETTE 2/92); you’d think the troubles with our modified, ’71 big-block coupe were over…but nooooo; once again, up jumped that devil!

Last spring, my girlfriend and I took BBfH on a desert outing with the Pomona Valley Corvette Association. Halfway back, at a gas stop, she quipped, "Ah, your car has a bit of a problem." Coolant was dripping over her nice clean tennie-runners and onto the floor…the heater core had sprung a leak.

As an emergency field repair, I bypassed the heater while wondering, what of rest of the cooling system? (Good question to ask in the middle of the damn desert!) It was original and we had increased its load with 50% more horsepower…more jumping devils?

The following week, an inspection showed the radiator in marginal condition. I also found the radiator core support rusted our, a problem with the ’69-’72s. Additionally, the main section of the fan shroud was cracked. Obviously, the subject of this installment of BBfH is cooling system repairs.

The first task was to replace the heater core with a new, Chevrolet unit (p/n 3014900). This is a job anyone can do to their Corvette, however, the Chevrolet Service Manual was sparse on facts about the job. A Motor manual covering early ’70s cars has better information.

Much Ado about Core Supports

There were four core supports used from ’69-’72. To differentiate, measure across the radiator opening:

1) 19" hole p/n 3966591–low-performance, small-block, manual, no air

2) 21" hole p/n 3966597–all w. L88, ZL1, early ZR1, ZR2.

3) 26" hole p/n 3966594– small-block, air

–hi-po, small block, M20/M21 manual, no air

–small-block, automatic

4) 27.5" hole p/n 3966596– big-block, M20/M21 manual, auto

All of these are discontinued Chevrolet parts, however, a derivative of #4 (p/n 339176, introduced for model year 1973) was available. If you use it on a ’69-’72, you accept any cosmetic differences and drill two 1/4" holes to mount the fan shroud.

First, we hunted for a serviceable used core support. None was found. We looked at repairing the existing piece by removing rusted sections and welding in new material. Not. A better idea was a reproduction. Numbers 2-4 can be had from Eckler’s. As the Big-Block from Hell is a ’71 coupe; we ordered p/n 25155 which replaces Chevrolet’s 3966596. It’s identical to the original part and bolted in with no problems.

With an engine like the 525 horse 454 in the BBfH, no ordinary water pump will do. Stewart Components sells high-performance and racing water pumps. We chose a their Stage 3 unit (p/n 31103), an excellent choice for aggressive street driving or competition use. It’s available in big-block and small-block versions and features: a 3/4-in. bearing which can take 5-times the loading of a production bearing and a billet steel, dual pattern fan hub that is adjustable to for pulley position. To reduce cavitation, the impeller and pump casting are selected for minimum separation. The Stage 3 has a built-in, cam stop which takes cam thrust on engines with a roller camshafts. Lastly, Howard Stewart’s Stage 3 pumps include grade-8, socket-head bolts.

Installation is straight forward except for one thing. If a stock timing cover is used, the pump’s bottom four back-plate bolts may need to be replaced with button-head screws that are provided with the pump.

Big-block water pumps have either 3/4-in. or 1/2-in. fan pilots. Do not replace a pump having a 3/4 pilot with one having the 1/2-in. size! Before ordering from Stewart, measure the pilot on your old pump and have that data when you call. Howard Stewart makes his pumps either way.

Cooling on a Diet

Our choices were to repair the stock radiator, install an identical replacement or go to an aluminum unit. We decided on aluminum, however, we didn’t use the L88/ZL1 variety as they were manufactured with 30-year old technology and are not as efficient as contemporary aluminum radiators. In a street application, even when a fan shroud is added, they offer marginal cooling at low speeds. Besides, if we could have found an NOS piece to buy; our budget wouldn’t have tolerated the 1000-1200 bucks!

Our solution was an aluminum duplicate of BBfH’s stocker and for that, we went to Griffin Racing Radiators.

"No problem," the Griffin folks said, "We do that all the time. Send us your stocker. We’ll have you an aluminum facsimile in about three weeks." They went on to say that Griffins are used in all types of racing, including Winston Cup, and are popular in the street rod and muscle car hobbies.

"We are the ‘Burger King’ of the aluminum radiator business," Griffin told us, "because you can ‘have it your way.’ There isn’t a radiator made that we can’t duplicate in aluminum."

Griffin advantages are lighter weight and better cooling. The weight thing is pretty obvious…aluminum has less mass than copper or brass. With an iron big-block under the hood, any dieting up front helps. A not-so-obvious cooling advantage comes in its construction. Griffins have larger tubes that are closer together ie: more tubes per inch of radiator. This makes for an increase in "fin-to-tube" contact, so more heat transfers to the fins and thence to the atmosphere. According to Cory Nagle, this can be up to a 30% increase in cooling capacity. When the BBfH’s 454 is run hard, the aluminum radiator’s higher efficiency will cool its increased horsepower.

Griffin radiators are built with 4043 aluminum. The core is furnace-brazed and the tanks are heliarced in place. The size, mountings and hose connections duplicated the stocker, so installation was a snap.

We installed an Eckler’s radiator core support seal kit (p/n 25691) and radiator-to-hood seal (p/n 25746) on the new core support. These prevent air flow from bypassing the radiator and are an important, but sometimes neglected part of the package. A set of Eckler’s radiator cushions (p/n 25683) were installed in all four radiator mounts. Then, we slid the Griffin radiator into the lower mounts and bolted on the upper mounts. A new lower radiator hose was added.

Next, we dealt with our cracked fan shroud. The correct piece for a ’71 , non-ZR2 454 is no longer available from Chevy, nor can it be had as a reproduction. However, Eckler’s does market a shroud for ’73-’75 cars (p/n A9887). This unit can be altered for the ’71 application with the following procedure: 1) drilling holes at the top to fit the upper mounting bracket. 2) use of the stock shroud’s lower extension, and 3) trimming of the ’73-‘75 main and ’71 extension shrouds for fit. With the fan shroud problem solved, the BSE guys added the water pump pulley. Once they installed and properly tensioned the drive belts, then added a new upper hose; the engine was ready to run.

Air management is an important part of cooling any big-block. That’s one reason Chevrolet changed a lot of the cooling system pieces for MY1969. The aerodynamics of the ’68-’72 nose are such that some cooling air flow must be channeled from below the front end, upwards and through the two cut-outs in the lower fascia at left and right of the vertical bumper sections. Most ’68s will not have these cut-outs. If you don’t have them, unless 100% original is your thing; we suggest adding them. Production Corvettes used a plastic "chin spoiler" that altered aerodynamics just enough to enhance air flow into the cut-outs. Any ’68-’72, particularly air cars and big-blocks, lacking that piece will run hot under certain conditions.

For the Big Block from Hell, we prototyped a road racing style air dam. The reason for that is as much aerodynamics at speed as it is good cooling. Later in the series, we’ll built a more attractive unit, but for now, you get to look at our proto.

There is a ground clearance compromise with an air dam such as ours. Speed bumps, intersection dips and the like must be traversed slowly to prevent banging the air dam. If you don’t want that problem, install a new, production-type chin spoiler from Eckler’s (p/n A2983).

Initial testing consisted of normal driving and showed that coolant temperatures were no different than with the stock water pump and radiator. The southern California area is famous for traffic congestion…forget the "Golden State." It’s now the "Smog and Traffic State." If a big-block is going to have trouble on hot days; it will be in the bumper-to-bumper stuff. As this is being written in late July; we have plenty of hot. The Stewart pump, Griffin radiator along with the sealing and air flow management pieces from Eckler’s all seemed to do their jobs. We never saw over 210F

Our Biggest Fans.

After a few of months, we decided to remove the stock cooling fan and shrouding and go to an electric set-up. There’s absolutely nothing wrong with the clutch fan or Eckler’s shrouding. However, front suspension modifications we will do in a future part of the series will interfere with them. Going electric is just a case of planning ahead.

We looked at two production Corvette electric cooling fan systems: the single fan used on 1982s and the dual fan assembly used on 1990-’96s. We picked the current arrangement because it had two fans, adapted to the Griffin radiator with ease and would provide space for our future modifications.

The late C4 fan assembly consists of the following Chevrolet parts:

2ea 22074984 bracket kit, elec. cooling fan
2ea 22088786 motor kit with bracket (22104439)
2ea 22088717 fan kit, elec. cooling (22098785)
2ea 22082538 nut
1ea 14104898 shroud (10157958)
8ea 11505023 screw
8ea 11514290 nut

First, we modified the fan shroud: 1) additional openings were cut for better airflow. Compare our pictures to a stock unit. 2) some cars may require removal of material along the shroud’s bottom edge to clear the front antiroll bar. 3) depending on the type of bracketry you build, the edges of the shroud closest to the radiator may have to be trimmed. You don’t want the shroud to actually touch the radiator. There should be 1/16-in. or so for clearance. The shroud is made of a reinforced, rubber-like material. Because heat melts the stuff, be careful with cutting or trimming using whiz wheels, etc. which generate friction. A better choice might be a carpenter’s plane. You can even do it by hand with a sharp knife.

We made brackets from aluminum flat- and angle-stock to hold the fan assembly to the core support. Securing the fans was done with screws and bolts. We removed the top four bolts holding the core support to the front end and loosened the lower two. The core support was pivoted forward slipped the fan assembly in place.

The bolts were installed and tightened then we added a fan control unit (p/n 3647) made by Hayden, Inc. It consists of a temperature sensor that you install into the radiator fins or attach to the inlet connection, a relay, a control that is adjustable for "fan-on" temperature, a wiring harness and instructions. The sensor actuates the relay and the relay controls the fans.

The wires going to the fans were connected through the relay to the same junction block that feeds BBfH’s MSD ignition amplifier which, conveniently, is just in front of the radiator. We couldn’t find production connectors for the fans, so we called our friend, Scott Leon, in the Corvette Development Group at the GM Desert Proving Ground. We figured "Scotty" would know where to get that stuff as his summers are spent testing Corvette cooling hardware. Interestingly, Leon told us that those connectors are the same as fuse holders for late-model, spade type fuses. Sure enough, at the local auto parts emporium we found two of them! We set the Hayden controller to kick the fans on when coolant reached about 205F.

There may be some cars out there having low-output alternators. Check the stamping on the unit’s case. If you have a 42 amp unit and are going to an electric fan(s); we suggest switching to one with at least 60 amps output.


Now, it’s late September, and like when we tested back in July, searing hot weather is nuking Southern California. Finding 100+ heat was as easy as driving around the block. The LT5 electric fans work very well. On the hottest day of our test (105F), we found heavy traffic on the northbound I-5 caused by one of L.A.’s frequent big-rig wrecks…excellent bumper-to-bumper stuff with long idle times.

We never saw over 215F. As the electric fans were our final cooling system change, we took the Big-Block from Hell for a hard run over the Angeles Crest Highway north of the L.A. basin. Now, "The Crest" is renowned by sports car freaks and crotch rocket jockeys as an excellent venue for get down and dirty, fast driving. On a day where it was hot even up in the mountains (about 95), I ran the car as hard as its ever been run since we built the new engine. The coolant never got over 180F. That moderate temperature at high speed says much about Howard Stewart’s water pumps and the Griffin radiator. We’re definitely cool!

In the next installment of the Big Block from Hell series, we’ll add an engine oil cooler. We’ll also plumb the cooler and the fuel system with braided stainless-steel lines.


Chevrolet Motor Division
see your local dealer
Eckler’s Division of Smart Choice, Inc.
PO Box 5637
Titusville, FL 32783-5637
Griffin Racing Radiators
100 Hurricane Creek Rd
Piedmont, SC 29673
Stewart Components
Box 5523
High Point, NC 27262


So…What Are You Going to Put in that Radiator?

Aluminum is more susceptible to corrosion than is copper or brass, so an important consideration with an aluminum radiator is what coolant to use. Chevrolet and Griffin recommend a 50/50 mix of water and antifreeze in any radiator, aluminum or otherwise.

For better results with a 50/50 mix, add a bottle of Red Line "Water Wetter™". This product comes in liquid form and contains a wetting agent along with an anticorrosive chemical package similar to what is in GM Dex-Cool. The wetting agent reduces the surface tension of the coolant such that it adheres better to the engine’s water passages making the cooling process all the more effective. The anticorrosives keep your cooling system clean and free of rust.

While Red Line Water Wetter can be used with mixes of antifreeze and water it also can be used with the 100% water many race cars use for coolant. Good old H2O is a more efficient coolant than mixes of water and antifreeze. Though a 50/50 mix increases the coolant boiling point by 11F, some racers take water’s better cooling and rely on cooling system pressure alone for boil-over protection. In an all-water system, a radiator cap with a 15-18 psi pressure relief, at sea level on a standard day, will make for a boiling point of 257-269F…more than enough protection for an engine running 180-210F nominal coolant temperature. As for altitude; boiling point drops 2 for every 1000 feet, so your pretty safe up to about 7000 feet. Above that, you may want some antifreeze or a higher relief pressure.

Racers use 100% water because the higher efficiency of an all- water cooling system allows a smaller and lighter radiator. That, with the 30% additional efficiency of an aluminum radiator allows further "downsizing." Combine all this with a lighter aluminum water pump and you have significant weight reduction.

Using all water with aluminum parts typical of race cars sets up a potentially serious corrosion problem. That’s where Red Line Water Wetter’s anticorrosives come in. They retards electrolysis and corrosion such that all-water coolant can be safely used with aluminum radiators and aluminum engine parts. Though 100% water and Water Wetter are a good choice for a race car and they also have potential for use in street vehicles. For more info on Water Wetter: Red Line Synthetic Oil Corp.,6100 Egret Court, Benicia CA 94510, 800 624 7958, .

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