Compression - Octane, In 400

[Sled_Dog]

I have heard 9.5:1 is the max recommended on your standard pump gas(92-94).  I want to run 10:1 at least in my 400.  Anyone know what I would have to run with 10:1? 10.5:1? 11:1?

[pupp1]

92 to 94 octane should be fine

[roshteaux]

I have a '69 Firebird OHC6 250 Sprint with 10.5:1 comp. and I run a blend of 93 pump gas with VP C-12 racing fuel with an actane rating of 110. It wakes this motor up and actually performs much better being a pur hydrocarbon fuel and actually cleans the motor as it burns. If you have access to some...try it!        

[punkin]

Spark timing and cam timing and cam profile play a big part in your question. Adding octane alone doesn't make power but it does let you run a more aggressive timing curve and compression ratio by preventing predetonation. Some big cam profiles can help bleed off low rpm compression but they usually drive like a dog in street cars until you get the up into the power band but at that time, if the rest of the motor can't live and make power in the upper rpms then it's all a waste of money. It's a balancing act and an exersize in properly matching all the components to work together.

Higher compression also beats on crank bearings even a little detonation only makes matters much much worse. I'd have to ask why you're set on a higher compression ratio?

On the other side, I have to admit that when I was younger, I had done this and can tell you that it is "possible" to run high compression on the street if you're willing to live with the inefficiencies that result in making it "streetable". I have but don't recommend, run a 455 bored .030 over with #12 heads. This makes for about 11.5:1 or so compression ratio (maybe more but I don't remember exactly at the moment). Huge cam, retarded 4 degrees and spark timing set way back. The thing ran like a pig but hey, it was "streetable" by some definition.

Good luck