I have 180psi cylinder pressure on my rebuilt engine. I am having some problems with pinging and detonation and I have the timing retarded. I am running 8 gallons of 91 octane with a bottle of Lucas octane booster that treats 25 gallons. I have perfect quench, aluminum heads, polished cambers and pistons, with the hot spots taken down and I am running as cold of plugs as I can get.

Octane booster in a bottle really doesn't do much. What does your advance curve look like? Where is your timing now? Are you jetted lean?

I have 185 psi and I don't have any problems with 91 pump gas. I have aluminum heads too. I run 36* of timing.

Are you running lean?

to hot or to lean. did you check yur timming tab to make sure ts right with the balancer?

well i know lean can cause that. i just wanted to know if my compression was with in the abilities of 91 octane. the octane boosters sure helped but they cannot get rid of the ping. i have some larger injectors i am going to put in it.

i didnt notice you said 91. that will rattle my motor. 93 is fine though

Try to set up some kind of cold air/ram air intake setup so you are not sucking hot engine compartment air.

This 65F1005.0's brother. Unfortunately in Tulsa premuim is 91, but I have heard rumors of 93 at one station in the suburbs of Tulsa.

His engine is actually a stroker motor with an EFI setup. We think there may be a problem with his timing advance controls and hopefully when we get that remedied the detonation will be under control. Neil (65F1005.0) started classes in Wyoming at Wyotech on Monday and will be gone for 9 months...hopefully I can get his truck running better for him before he returns. Thanks guys.

I'm running a SB with J's and 205 cyl psi on 93, but i have a fresh air intake, heat crossover blocked, Carb spacer, 32 total, very cold plug, high stall, ect.. ect.. 180 should be fine with 91 if everything is correct.

check the actual total timing on it. its probably up in the 40's after 4000 rpm.

i had 185 psi with the 284/484 cam and i ran crappy california 93 octane in it and it didnt ping. Well it did BEFORE i figured out the stock distributor kept advancing after 3000 rpm due to the heavy spring in it

Check this out: http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html

The engine that I built for my brothers car has 185 average PSI and he has to run 95 octane. His car weighs only 3250 with him in it and has 4.30 gears. I think the heavier the car with the lower numerical rear gear ratio is going to have a worse pinging problem that if the same engine was in a lighter car with higher numerical number gears in the rear like 4.30s. Many factors outside of quench, cylinder pressure and coolant temperature need to be taken into consideration when asking about the right octane for a given combination. I personally think that 180 PSI for the most part is too high for 91 octane. Can it be done?...Yes with the right combo....but not for most.

What EFI system??
Is the distributor advanced locked??
Is the distributor phased properly??

Can you tune the advance on the system you're running?

Make sure your not sucking oil from an intake manifold leak. They will rattle like crazy if that's the problem.