[lust4speed]

H.O. Racing computed out horsepower loss at different compression ratios and had a graph plotting ratios vs. horsepower reduction. Getting to the punchline, a reduction from 10.25 to 9.25 was right at a 4% loss. Not only would you never feel that but add in a proper roller cam and not much more than gasket matching and you will easily exceed stock horsepower levels by a bunch.

An extreme example might be my old 67 GTO engine in my automatic street car. Started life as 335 HP. Wanted to build a regular gas cruiser so dropped the compression ratio down to 8.6:1 so it would run year round on 87 octane. Retained the 3.75" stroke and 400 engine was only .020" over. Small Crane hydraulic roller cam at 214/222 @ .050" range but with .536/560" lift. Nicely ported 670 heads along with port matched original iron intake, and 3" exhaust to the bumper. It made 298 horsepower at the rear wheels on the first chassis dyno and 297 on the second dyno during the Hot Rod Magazine testing session. That computes out to 366 flywheel horsepower on 87 octane regular gas from the pump.

We keep all the iron head street engines between 9.25 and 9.30 because of the lousy 91 octane gas, traffic, and hot summers in SoCal. Our club dyno day testing shows the majority of these iron headed engines to be between 400 and 450 flywheel horsepower with a few over the 500 mark.

So much better to lower compression and run a normal advance curve than push the limit and end up retarding ignition timing to curb detonation. Much better to have a 4% loss to start than push compression and suffer up to a 20% loss by having to drastically retard timing.