Looking to rechamber my head. What C/R should I shoot for 92 octane?

timstoys

Member
Jan 28, 2012
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I've got a ported 240 (at 73mm), Hot Rods +4mm crank, V4 reeds Lectron carb, custom made pipe and a rechambered head with I believe a 28cc chamber. I cut the head a couple years ago and wrote the chamber size on it but can't read it now. But I believe my C/R is to high. I've got it apart now and I'm ready to cut it again. What C/R range works best for pump gas and hard riding?
 
If it helps, Ive ran everything from 18CC to 29CC with good results. Your squish distance is very important too. .035 to .045 works well. I would just re-measure the volume of your head's chamber and start from there. That way you know. Go from there. What pipe is a custom pipe?
 
With a 28cc chamber I calculate over 10:1 C/R. With the pinging I'm getting I believe I'm way above what it cane handle. I cut a toroidal chamber in it and my squish is .040 to .045 widening from outside in. The pipe is a full custom mad by LED Performance in Gresham Or. Send me an email address and I can send ya a pic.
 
rule of thumb from the memory bank.
we like actual psi readings versus ratios
all using 32:1 fuel/oil mix

87 octane for stock compression
89 up to 150psi
93 up to 165 psi
50/50 mix of race fuel and 93 up to 185 psi
straight 100+ octane race fuel for anything over 185 psi

plug reads for signs of detonation should always been done when pushing these "limits"
 
For me personally, I have had 3 heads cut. I ask for 150psi for the pump gas I run which is 92 octane. I have two bikes at 175psi which I run 50/50 in. I have an engine on the bench that should be around 185psi. I will run C12/or VP110 straight in the engine.
 
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