way too high for reliable power on 91 octane reguardless of dynamic compression therory. Bla bla bla.

When the enigine is cammed right to make power the cylinder has high cylinder presure at speed. Usually highest at or near peak torque output.

A big bore engine like a 400 is more octane sensitive.

If you want a reliable max compression u should use on 91 octane consult one of the professional high perf marine engine builders.
They make big power on 91 octane and their engines last.
Standard marine premium is 91 octane and they know that works and what doesn't.

We're not talking about what works for 5 seconds on a engine dyno.

I'd estimate not more than a true 10:1 (even employing all the "tricks", with the cam you'll be using. 91 is not the same as 92 or 93.

 

Ya it just bumped out like .2 points cuz im goin with teh 3.8" stroke but ya i figured. Oh wellz, guess ill have to cash out for some 103/110 thanks fellas.

 

If you're stuck with 91 octane and just got to have high compression then the easy why to do it is to employ good design and let physics work for ya.

Do a search and research on Water Injection.

In the long run, its far $$$cheaper and easier$$$ to work within the laws of physics then working against them.

As good a place to start as any

 

Dude if you don't have to deal with emissions, go as high as you can until pump gas and detonation says no more..that is if you plan NOT to use nitrous.

 

Its really like this, i already have my pistons so this is the compression i will be going with unless i sell them and get some other ones. 2nd is if it can run on 91 octane with timing retarded 1 million degrees thats fine. I just need it to run on 91 so i can get it to the track, at teh track i can mix it with high octane and advance my timing. I have no way of towing my vehicle to and from the track which is the real reason i want it to run on 91. That water injection thing looked interesting but imma try to find a way around this with out it. How bout 91 with some of those NOS octane booster things on a serious note tho how many octane points those things boost?

 

those octane booster stuff...I dunno man, seems like sales gimmicks to me.

 

Me 2 thats y i dont wanna use the stuff, but then again i donno if somebody actually uses it and has experience with it id be willing to listen.

 

Devil: if you can't afford a truck and trailer to get the car to the track, how are you going to afford race gas on a regular basis?

Just get different pistons and do it right the first time.

 

I understand what you are saying but i think ill just leave it. Ill figure out something. Thanks for all the help tho fellas.

 

I would run a thicker head gasket and get a 160 * thermometer. You can get away with higher compression if you keep the heads cooled. Thats how us lt1 guys do it. We have reverse cooled heads so the coolant reaches the heads before the block. Im going with a 11.4:1 compression on 93 octane. Your dynamic compression ratio is really what matters and as long as the engine and heads are cool you should be ok.

 

Running a thicker head gasket would **** up my quench.

 

You could put a Fuel Cell in the back filled with 110..etc. And use a MSD Timing Controller. Up your compression, Drive around town on 91 with the timing retarded. If you want to have some fun, switch over to the fuel cell. And with a control **** mounted inside the car you can crank the timing up to what it runs best at on 110. Run your fuel line from the cell and the tank to a diverter valve and wire that up to a switch. And u can run off the tank or the cell with a flip of the switch.

 

True, but will it run on 91 at all even with the most rediculous retard in timeing.