1stgear

now i understand that you can have a tune from SCT that will tune your car for 93 octane, but how is that possible if the compression in your cylinders controls what octane you use.....how can you change a set compression ratio in the cylinder?

04BlueGT

You don't change compression, as it is fixed. However, you can advance the timing and/or play with the fuel curve to lean out the air/fuel ratio and gain hp.

For example, the stock GT has 10 degrees of advance (timing). I have a timing adjuster and I'm running 14 degrees of advance. However, I had to upgrade from 87 to avoid detonation. The extra 4 degrees leaned out my a/f ratio.