What's the highest CR you can safely run with pump gas?

[harrisonm]

I have a moderately build 340 (right at 375 HP) with iron heads, 10.5 compression, headers, 4 speed, and I run 34 degrees total timing. I always put an octane booster (usually 104+) with each tank on 92 octane (that's all I can find), and my car runs great. I guess I could run an experiment and not use octane booster, but why mess with success.

 

[toolmanmike]

I have a moderately build 340 (right at 375 HP) with iron heads, 10.5 compression, headers, 4 speed, and I run 34 degrees total timing. I always put an octane booster (usually 104+) with each tank on 92 octane (that's all I can find), and my car runs great. I guess I could run an experiment and not use octane booster, but why mess with success.

They run so much sweeter with octane. Depending on what cam, pistons, distributor curve and heads you have, you might be able to use 93 octane without much detonation. You could always run your tank close to empty and put a few gallons of 93 in, test beat it and drive it easy back to the station if it pings. (or take your octane booster with you) It would be interesting to find out the results. tmm

 

[sireland67]

This is why we are having this discussion, my friend!:coffee2:

With the heads you have throw some KB 243 in it.
They will put your static compression down to about 9.0 depending on the cc's of your heads.
You will be able to run pump gas with no issues.

 

[GEO]

I have a moderately build 340 (right at 375 HP) with iron heads, 10.5 compression, headers, 4 speed, and I run 34 degrees total timing. I always put an octane booster (usually 104+) with each tank on 92 octane (that's all I can find), and my car runs great. I guess I could run an experiment and not use octane booster, but why mess with success.

My 340 before the new build had 11-1 and iron heads and timing set at 35degrees total.

It liked 104+ and I mixed a bottle to 10 gallons of gas, with out it it lacked power and dieseled when turn it off . Never did ping on pump gas , but it didn't like it

 

[C300]

Ask a local, or good engine shop this question. I (thought) I new EXACTLY what I wanted. Built circle track engines, boats and jets too. Had Just moved to Washington state. Ordered a Stroker kit for my 440 From Hughes Engines. Wanted 10.6-10.8 compression, have Ported RPM heads. finalized everything, he liked my combo and I took his suggestions. I have an Arizona Phone #. When he saw my WA. shipping address he said wait a minuet, The gas is so bad up there that combo wont work on the crappy 92 octane gas you have up there ! Had to pay extra for Custom Diamond pistons, 9.89 to 1. A little lower, but zero decked the block and, done right, just as good. He spent the time (HIS TIME) to hook me up so I'd have what I want and will be happy. He spent extra time when he could have just sent me in stock parts. That make me want to order more from them. even if it's a little more $. You can drop 15k into an engine and if done wrong, be left at the light by a ricer ! Good luck ! C300