Muscle Mustangs & Fast FordsHow To Engine
2006 Ford Mustang GT Compression Ratio Comparison
Testing The Effects Of Increased Compression In A Supercharged Three-Valve Mod Motor.
Why not just change the blower pulley? It would be significantly cheaper, right? We hit Dezotell with that question. "Sure, it's cheaper and easier to swap a pulley. We actually did that on this car and it was still a bit lazy, which was due to the low compression. Lower compression ratios can be safer, because there is less chance for detonation, but they lack cylinder pressure and make less power as a result.
Another benefit of raising compression is the increase in power without turning the supercharger to a higher impeller speed. In a blower application, it takes engine power to turn the supercharger, so the less work the engine has to do (in regards to getting more cylinder pressure), the more you will see at the rear wheels. Another byproduct of increased boost pressure is a hotter intake charge temperature. We aren't saying that increasing the blower speed is a bad thing, but there are other ways to achieve increased power.
On the dyno, Dezotell modified the tune slightly for the higher compression by adding a little more fuel. That was done to help cool the intake charge, which is often necessary with higher compression. He also reduced the ignition timing significantly from the baseline of 19 degrees to 15 degrees. The result was 560 rwhp and 526 lb-ft of torque, which equated to gains of 22 rwhp and 44 lb-ft of torque at the peaks. The torque curves were also noticeably different, and the engine makes power as if it were a completely different combo. Average power was increased by 28 rwhp and 36 lb-ft of torque.
In total, upping the compression ratio increased the cylinder pressure and Gelles' Mustang picked up great power and torque as a result, not to mention much-improved tip-in throttle response, which is nice in any street-driven vehicle.
According to Dezotell, adding compression has been worth 140 rwhp in one application, but that was a race engine. For the street crowd, adding more compression will change the dynamics of your Mustang and keep you out in front of the local track bully.