I just read a post by "88transam5.0" He said that his compression ranged from about 205-215 PSI. Then Jester and Ede said that that was fine.

Now comes the confusing part. Summit Racing told me yesterday that a normally aspirated V-8 should have NO MORE than 165 PSI. Then they said that any engines that run hiher than 11.5 to 1 compression or 165 PSI are seriously risking detonation and fuel octane boosters or expensive racing gas mixtures will be needed My engine is 160 PSI.

My compression is 10.7 to 1.
So what is with the drastic PSI difference?

 

There is a big difference between static compresson (9:1, 10:1, 11;1, etc), and dynamic compression (165psi, etc). The cam profile is the biggest factor in that. A smaller camm will bleed off less pressure as the engine rotates, creating a higher PSI reading. That measurment is the actual compression your engine sees, and is what matters when it comes to gas octane.

however, there is no set guideline for where you need a given octane, there are too many other factors. What heads, engine temp, spark timing, etc. 10.7:1 is pretty high tho. Detonation is something you can hear, if you do hear it then a higher octane gas or retarding the timing is in order. If you don't have a problem, don't fix it.

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