is 11.2:1 compression too much for 91 Octane

67cuda360 said
Thanks Clinteg,
so the bore and stroke you mentioned there are based on a stroked 440 (500cui) correct?

I'm just trying to wrap my head around if the car that I'm looking at (that has this engine) will run on the fuel I have available here. Like you mention 91 octane might not be enough (not that we'd know for sure until we try it LOL).

The current owner mentions that the car seems to have some rattling under load, so I assume this is pre-ignition and I'm trying to figure out if It would be possible to tune this out (timing, curve and carb setup) or if something more drastic is needed to make it run on 91 octane.

How much difference would a thicker head gasket make you think, or maybe porting and polishing the heads would make a difference (not sure if this is already done).

I guess the only other way (and probably best way) to reduce compression would be to go with different pistons, but I'm not sure if the current cam would work with anything lower than 11:1.

ha ha, questions, questions, questions LOL.

Yes I looked up what a 500 CI stroked 440 was (I wasn't familiar), as in what stroker kit that would be with rod length, stroke, etc. That's why I was saying I'm "assuming" those numbers are correct on the stroker setup because that's what I came across. If there's rattling under load, it might be safe to say that there's some pre-ignition/detonation going on. From reading, it sounds like 8.5:1 Dynamic is about where you want to be for 91 octane (with Al heads). Does he run 91 in it? Has he ran race fuel in it to see if the rattle goes away under load? That would be a good indicator of knowing what fuel it needs (for the timing he has it set at). And doing what EL5DEMON340 said along with pulling the timing out of it would probably help. If the guy has the timing fully advanced, with hot plugs, then yeah it's probably going to ping under load with 91. For example, I pull my timing down to 28 degrees on 91 octane and advance to 34-36 on 110. I also run NGK-7 plugs which are a colder plug. It could be as simple of a fix as pulling the timing out and running a thick head gasket. If that doesn't work, then either a cam change would be in order or piston change. Here's a long detailed read about Dynamic CR: http://cochise.uia.net/pkelley2/DynamicCR.html.