Compression Ratio Survey

[FBSideoiler427]

What is the highest compression ratio you have employed successfully in your motors and the highest boost achieved reliably?

 

[441120]

boost

$0.02
I think low compression & high boost goes the fastest.
7.5:1 + 45 psi vs 9.5:1 + 15 psi, fuel being the limiter. Alky aside.
Less built in stress

 

[rodman99999]

Assuming you're using 92-94 octane pump gas: One pound of boost=about 4% HP gain, one point compression= about 2% HP gain. If you up the compression from 8.5 : 1 by one point(which ups the octane requirement), you have to lower the boost by about 2 PSI(to stay out of knock). That nets you a 6% reduction in HP. As posted: boost is worth more than CR(unless you're after mileage instead of speed).

 

[bison]

All of mine have been in between 8.5 and 9.0-1.0 in the last 8 years. All had iron heads and i run a lot of methanol and sometimes with pump gas. I run a few degrees more timing with high octane gas vs 93 though. The next one i do when i get my hands on a champion block will be 9.5-1 with ported aluminums. Compression+proper cam selection+boost=alot more hp than running low compression and high boost alone. There is no need to run more than 8.0-1 if you plan on low octane fuel and no methanol. BSFC gets a lot better with more compression. Most of the most potent TSM cars run at least 8.5-1. Some are reportedly over 9.0-1 with the 109 block. You need the best of everything if you want to run big numbers. Building a 9.0-1 compression 109 that revs to 6500+rpm is not cheap. Btw i run a minimum of 25psi boost.