One of the parameters that has the most effect on power is the compression ratio of the engine. While the ideal compression ratio has a lot to do with the intended use of the engine, and the octane of the fuel you'll be running, more compression will make more power in nearly every application. The proper compression ratio depends on factors such as combustion chamber and piston design, but even a good street engine should have a minimum of 10:1 compression to make decent power. In our Engine Challenge, we've seen engines with compression ratios as high as 12:1 still run great on pump fuel, but for a street engine limited to 93 octane gasoline, 11:1 is a more reasonable limit.

There are many ways to raise the compression ration of an engine. Generally, Mopar engines produced after 1972 had the compression lowered to meet emissions standards by placing the piston below the deck of the block at top-dead-center. In addition to reducing compression, this also makes the engine more prone to detonation. As a start, we recommend a piston/decking combination to get the piston as close to the top of the cylinder as possible, improving compression and the efficiency of the combustion area. Domed pistons will also improve compression ratio, but are generally not as efficient as flat-tops because the dome prevents even distribution of the burning mixture, again hurting power somewhat.

Building an efficient and powerful engine is one thing, feeding it with enough fuel and air to work properly is another proposition. By increasing cubic inches and compression, and adding a bigger cam, we'll usually need to increase the induction volume as well by adding a larger carburetor and a more efficient intake manifold. Again, proper selection of these parts depends greatly on the size and performance level of the engine you're building. Generally, a warmed-over street small-block will require at least a 750-cfm carburetor, and big-blocks can require an 850 cfm or larger carb to achieve their potential. Factory multiple carb induction is a viable option if you can find it, but we tend to prefer the simplicity and drivability of a single four-barrel setup. Remember to match the rpm range of the intake manifold to the rpm range of the camshaft you selected, and also remember that you need to expel the additional gasses you're putting through the engine. Factory manifolds and exhaust should be replaced by quality headers and free-flowing duals for your new engine to operate properly.

Auto Performance Engines