I have a 353 tpi with iron heads and flat top pistons with 2vr. The engine is 90% together and was measuring for my CR and came up with a 9.75:1...Higher than I was aiming for. I could buy a different head gasket and get it down to 9.67:1. Will these numbers ping on California premium? I also have a 224/230 durration cam xr276hr if that helps. And an aux cooling fan relay so I can have them both kick on at lower temps.

 

It shouldnt with that cam. Just be careful on timing and put in a sparkplug thats 2 steps colder than stock.

90-92 tpi cars had flat tops and should have been near 9.5-9.7 to 1 with stock cams and ran on 87-89 oct just fine

 

Thank you. You just ended a stressful 2 days of head scratching! I'm a total dunce when it comes to spark plugs. How do I find or know if a spark plug is colder than stock coppers

 

Need to find an application guide for a stock car, basically find what brand part number is recommended for stock L98. Then find what that stock heat range is for that brand and then learn their numbering system for different heat ranges. Lol i use ngk plugs and i believe they recommended a heat range 4 for stock. For my 11:1 aluminum 383 i ran two steps colder and on spray i think i went 3 steps colder than stock. So heat range 6 and 7 respectively.

Yours should be ok with heat range 5. Can always adjust later to find sweet spot

 

Okay I spent an hour looking through the spark plug books at work and came up with the NGK 2771 (2 step colder split fires) and the ac delco R42ts (one step colder). "they stopped making the r41ts in America." I like AC Delco better... So is it a for sure thing that I shouldnt use a 1 colder and I need to do the NGKs

 

1 colder should work.