Pro Touring Math - Horsepower and Mileage
So, how much horsepower?! The ratio here is horsepower per cubic inch or hp/ci. On a budget it's really easy to get one horsepower for every cubic inch out of a small block Chevy. That means 350 horsepower. Not a bad start.
The less weight that horsepower has to pull the quicker it can accelerate your car. In one version, a car, or is that 'rocket' they made in the sixties called the Shelby Cobra had an extreme weight to horsepower ratio at about 5.57 pounds per horsepower. This was a tiny race car with a thumpetty Ford big block of a type not even made anymore. Specifically, it weighed 2282 pounds and made 410 horsepower. I'll compare those numbers to a '91-'92 GMC Syclone truck which is about as close to a sports car as trucks come. It's got about 12.85 pounds per horsepower. I'd say shoot for something in between. A little extra weight helps stability at very high speed, and going too far with the hot rod tricks of putting your car on a diet can make it less safe in an accident. Those things said, less weight and more horsepower mean quicker acceleration and car weight loss even helps gas mileage. By the way, taking some weight off the front end of a rear wheel drive car can help handling. So you've now got one more excuse for pulling a worn out big block on an old Chevelle and replacing it with a small block. :-)
A very important consideration in a pro touring car is the miles per gallon ratio. If you plan on driving this car on actual tours or even across the country it sure is nice to have some decent mileage on it. A 350 ci small block is a pretty good compromise here between power and mileage. At least it is in my opinion. There are a couple things you can do here to improve the mileage.
An overdrive transmission helps when you are at cruising speed by lowering the rpm's, revolutions per minute or speed the engine turns while maintaining the cruising speed of your car, say 55 or 65 mph on the highway. The other thing is to have mileage friendly gears in your third member or rear end. 3.55 to 1 gears are a compromise between acceleration and mileage. With an overdrive transmission with a final gear of about .70 to 1 you might even go to a lower gear (higher numerical) of something like 4.10 to 1. With gears that low, you had probably have some pretty good tires or your acceleration might go up in tire smoke. Of course you could go with even higher gears (lower numerical) or so and get even better mileage with your overdrive transmission. Might save you some money, too because that's probably what's already in your rear end right now. You can use that strong transmission, especially good is a standard transmission, to accelerate, and use the overdrive gear when you're cruising. With my budget buildup of my Camaro this discussion is a bit moot. I'm pretty much going with what I've got in both transmission and rear end.
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