I'm getting alot of pinning/detonation at WOT over say 4000+ RPMs. The car was dyno tuned but it always pings at higher RPMs at WOT. Tune has 8* base timing and 34* total timing. I have a WB O2 gauge and it doesnt go lean up top even at WOT. I was told by my engine builder that it was a 10.56 compression engine. Tonight I put the numbers in from my build sheet into a Compression calculator.

cylinder diameter - (4.040)
stroke length - (3.750)
number of cylinders- (8)
chamber in cc's - (63)
pistons- - (-6.8)
gasket thickness - (.041)

displacement - (385 cu. in.)

it comes up with a compression ratio of ........ 11.05739

So my question is what octane fuel does a 11:1 engine call for?? I've been running 93 octane with 34* timing and i'm pinning away!!!!

 

Take a couple of degrees out of the total timing and see what it does. You may have to bump up the octane a couple more numbers to keep it from pinging.

 

when I went down to 29* total timing I didnt hear it ping. I guess I'll be adding some high octane fuel to my fuel.

 

Also, you may need to look at dynamic compression, not static. I've heard that dynamic compression needs to be at around 8.5:1 for 91 octane, so you may be able to go a little higher for 93. Not too sure how you'd use that info but I know dynamic compression affects pre-detonation more than static.

I heard of a guy running 12:1 static compression on 91 octane because his dynamic was at 8.7:1

 

Not an exact answer, but educational for about a 10 min read---

https://www.thirdgen.org/forums/theo...legal-gas.html

https://www.thirdgen.org/forums/tech...78-octane.html

 

A little primer

http://members.uia.net/pkelley2/DynamicCR.html