mck08 Posted October 28, 2009 Report Share Posted October 28, 2009 Hey guys, I have an 08 Shee - fairly stock (FMF Fattys, +4 timing, K&N, 310 mains and run on 98 octane pump gas) and as we know the factory comp. ratio is 6.5 : 1. I am planning to weld and machine the stock head and want to know what compression ratio I can go to, or finished head cc's, and still run my pump gas. What's with 6.5 : 1 anyway - that's gay!! Any help would be great. Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted October 28, 2009 Report Share Posted October 28, 2009 (edited) with the effort of welding/ machining, your better off just getting a cool head. Id take advantage of the dollar and buy one from one of the site sponsors. That way you have a head that has better cooling characteristics and interchangeable domes. i havent worked out the proper C/R with the smaller domes, so i cant tell you what that is, but with 20cc domes @ 165+psi with +4 adv you would be getting very close to the 98 limits. (94oct U.S ) Edited October 28, 2009 by dirtydownunder Quote Link to comment Share on other sites More sharing options...
blowit Posted October 28, 2009 Report Share Posted October 28, 2009 6.5:1 is the corrected compression ratio which is what Japan uses for engine calculations. It is a more relative number than swept or uncorrected. That is why the number looks low.. Brandon Mull Engineering Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted October 28, 2009 Report Share Posted October 28, 2009 yeah, you're thinking of the 6.5:1 like a car's comp ratio. the 6.5:1 is the corrected or trapped compression ratio like blowit stated, which is the cylinder volume from the roof of the exhaust port and everything above divided by the volume above the piston when its @ TDC. Quote Link to comment Share on other sites More sharing options...
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