[Tommy]

I'll add this bit of theory to back up Bill's comments about tuning. Imagine two cars moving down the same road at 60 MPH. They are identical except one has a 408 Windsor built to 450 HP max, and the other has a 520 FE built to 744 HP max. As it takes far less than max HP to move at that speed, both engines are producing the same power at whatever RPM, throttle setting and gearing that takes (e.g., 70 HP). If both engines are efficiently tuned to extract the optimum amount of propulsive energy from the fuel they are consuming, they should be burning about the same amount of fuel per minute. Thus the engines should be shedding about the same amount of leftover heat through the coolant system every minute. If the cooling systems in the cars are the same but one engine is running hotter than the other, then it must be because that engine is consuming more fuel to generate its 70 HP and the excess fuel is going to produce heat rather than propulsion. . . . In other words, an engine optimized to produce 744 HP at peak RPM may not be optimized to efficiently burn fuel at 2200 RPM, with the excess fuel going to produce heat rather than propulsion. The solution may be to tune or modify the engine to be more efficient at the power levels commonly used in street driven cars.

Here is one example. To make big HP numbers with big engines, builders typically use really big carburetors capable of providing enough air at peak RPM. Big carbs require more air flow to generate enough signal to properly meter fuel to the engine. Such combos often do not run well or efficiently below 2500-3000 RPM, where most street driving occurs. Having your engine dyno tuned with air/fuel ratio readings under cruising conditions might reveal whether you would benefit from changes to your current fuel system.