Jeep Strokers

OK, worlds dumbest question here. Which compression ratio do you go by to determine what octane fuel you may need? Is it the static or dynamic? I have seen numerous references to 8:1 DCR or lower to run pump fuel, but others showing I need race fuel @ 9.5 or higher. The setup I am putting together puts me at 9.6 SCR and 8:03 DCR. Guessing I probably will be good?

You should be fine for 91 octane, maybe 89. Of course you would start with 93 and see how efficient the fuel is burning. 91 octane typically requires a dynamic compression under 9.0:1.

Randy Bobandi wrote: ↑February 9th, 2022, 9:05 pm You should be fine for 91 octane, maybe 89. Of course you would start with 93 and see how efficient the fuel is burning. 91 octane typically requires a dynamic compression under 9.0:1.

Agree,
Only thing that I would add is a piston dish that has a reverse mirror image of the combustion chamber (same as a stock 4.0 piston) as opposed to a full circular dish benefits from a minimum/tight quench.

I’ve seen guys running the stock 12cc cast 4.0 piston with the shorter 258 rod combo with the piston .025-.030ish negative deck and struggle to run on premium gas with a 9.5:1 static compression ratio, where a piston .035 piston to head clearance (including head gasket thickness) can run s higher static compression ratio of 9.8:1 with the same octane fuel.

Russ Pottenger wrote: ↑February 9th, 2022, 9:53 pm
I’ve seen guys running the stock 12cc cast 4.0 piston with the shorter 258 rod combo with the piston .025-.030ish negative deck and struggle to run on premium gas with a 9.5:1 static compression ratio, where a piston .035 piston to head clearance (including head gasket thickness) can run s higher static compression ratio of 9.8:1 with the same octane fuel.

Exactly. Compression ratio is irrelevant if the combustion chambers are not designed properly. The hot spots in the poorly designed chambers will be the limiting factor.