You may be building a hot rod to serve as a home for your big-block powerplant, but for maximum performance you have to keep your cool. An overheated engine can have far more serious consequences than just an embarrassing stop along the roadside to let things cool off—blown head gaskets, burned or tuliped valves, scuffed bores, and burnished piston rings are all possible if you keep driving when the temp gauge gets to the far side of “H.” The cooling system is usually the last thing on any performance enthusiast’s list of things to upgrade, but if you design and execute your system with a bit of forethought and knowledge, it does more than just keep you from overheating while cruising the local car show; it helps your Rat motor make more power.
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I again reference the Kings of Carbureted Big-Blocks, NHRA Pro Stock racers, to illustrate the value of proper engine cooling. Pro Stock racers do everything in their power to keep the engine cool before an assault on the quarter-mile. They use heat exchangers and portable refrigeration units in the pits to bring water temperatures down to 50 or 60 degrees F before each pass, and only run the engine long enough to drive it to the staging lanes, as required by the rules.
It’s an old wives’ tale (more likely an old husbands’ tale) that your engine has to be thoroughly warmed up to make maximum horsepower. That used to be true when all cars had stock carburetors that were jetted as lean as possible for best fuel economy, and before the introduction of synthetic motor oils. A cold engine requires a richer air/fuel ratio than a hot one, and that’s why street carburetors have chokes. The purpose of a choke is to richen the air/fuel mixture, and blade-type chokes do this by restricting the amount of air ingested. Lowspeed drivability is poor only because the carb is tuned for the proper air/fuel ratio when the engine is thoroughly warmed up. Modern high-performance and racing carbs are calibrated richer than stock, and EFI systems have coolant temperature sensors that richen the fuel delivery when temps are low.
Conventional motor oils are thick when they are cold, and the spinning crank and other internal engine parts have to wade through a pool of this thick liquid in the crankcase, so that warm, thinned oil offers less resistance than cold oil.
Synthetic motor oils can provide the lubrication necessary for even the most powerful big-blocks with much less viscosity, which reduces the parasitic drag on engine components. Less drag, combined with superior lubrication properties, make synthetics the oil of choice for any professional racer, (after proper engine break-in with conventional oil), and synthetic oils don’t need to be “hot” to yield maximum power from your Rat motor.
There is no such thing as keeping the engine “too cool” for best performance, so let’s look at how your cooling system can be designed to meet that challenge.
Big-block Chevy water pumps were produced in two lengths, short and long. Short-style pumps were used in passenger cars through 1968 and in Corvettes through 1974, while light-duty trucks had them until 1972. Long-style pumps were all standard rotation until 1988, when the serpentine drive belts were introduced. Serpentine belts rotate the water pump in a counter-clockwise direction, so the water pump impellers are curved the opposite direction of standard rotation pumps. If you are going to use one of the aftermarket billet aluminum serpentine belt pulley sets, you must switch to a reverse-rotation pump from a 1988-or-newer big-block.
Many aftermarket water pumps are more than just lightweight versions of the stock pump. They flow more water at a higher pressure and are able to cool your hot Rat motor better than the stock pump.
Electric water pumps offer several benefits for drag racing. First of all, they eliminate water pump drag on your engine. This may be as much as 15 hp, depending on the pump and pulley system used. The biggest advantage of electric pumps is that the engine does not have to be running to cool off after a pass down the quarter-mile, when temperatures are at their highest. Shut the engine off, leave the electric pump and fans running, and you’ll be ready for the next round of eliminations in a few minutes.
Most street cars use belt-driven water pumps, and the stock Chevy crankshaft and water pump pulleys work fine if you already have them. If you’re piecing your big-block together, it may be easier to find matching pulleys from the aftermarket industry. Companies like Billet Specialties, March, Moroso, and Tru Trac all offer aluminum pulleys for the bigblock Chevy. Remember to use a reverserotation water pump if you go with one of the serpentine belt systems.
Written by Tom Dufur and Posted with Permission of CarTechBooks