What compression ratios do people usually run on 360-420bhp engines? I'm just building up an egnine at present so have the opportunity to get the pistons machined down.

Up till now I've been running 7.7:1 on a 4x4. With the new build and the ported head I'm wondering if it's still worth retaining the lowered compression or whether people run standard compression on much higher power outputs than was the case back when my current engine was built up 5 or 6 years back. What do people think?

 

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The usual ratio is around 7.5:1/7.56:1 Anything over 440/450bhp IMO the 7.2:1 is the easy way!

Am i think right in your gonna be runng a a big blower? A .63 T34 runs out of puff at 400ish and a T4 is running out if steam on 403's at around 440bhp