225 ProMax ideal compression?

[ssv1761982]

How much compression are you running on the 225 ProMax and still using pump premium?
The only other mod is the rod slots have been opened a bit.
Stock heads are 125#.

[LakeFever]

Ive done some digging on this. Seems there are three head gasket thicknesses and the promax comes with either the thinnest which is 1mm iirc or the second thinnest which is 1.5mm. The 2mm version is for fishing motors. Seems the standard set up for a promax is 91octane, 23-25 degrees timing. Seems the 23 is safe, the 25 is safe’ish. More squeeze or timing advance than this requires race gas. Hopefully someone who knows more will chime in thats all info i read that i am passing along

[DangerNewb]

I've run 140psi on 93 pump gas. I seem to recall that equates to 28cc head but I could be way off on that. Whoever cut or will cut your heads should know.

[rjdubiel]

35 or 34 CC should get you 140-145. 28CC is high comp race gas needed. Stock is 38 cc and 125 ish on a healthy engine

[DangerNewb]

35 or 34 CC should get you 140-145. 28CC is high comp race gas needed.

Thanks for clarifying. Wasn't sure on cc. But pretty sure 140 lbs is ok for 93.

[rjdubiel]

What I would do is order some 844R75 head gaskets if you wanted more comp but not sure you will really feel it that much. Maybe....

EDIT
found this here, not sure if it is true, but I doubt a gasket change is going to do much anything for you. You should have 1 MM gaskets now as that is stock on PM.

If you want from a full 1.25 mm gasket to a .75 mm gasket it would be the same as reducing the chamber size by 3.2 CC's (3.55 inches x 2..54 / 2 x same x 3.1416 X .05) . 1 mm to .75 would be 1.6 cc's. Smaller the chamber size you start with the more significant the cranking pressure difference. The smaller the chamber you start with the more it will change the finished compression.

[tunnelmike]

I've run 150lbs for years on 91 with Klotz 333 and never had an issue. Would turn a 32 Cleaver 7300 for miles.
All the guys I run with are running 145-150 on 91 also. Highest no ethanol octane available here.

[ssv1761982]

I've run 150lbs for years on 91 with Klotz 333 and never had an issue. Would turn a 32 Cleaver 7300 for miles.
All the guys I run with are running 145-150 on 91 also. Highest no ethanol octane available here.

That's what I was looking for. Thanks!

[doug vaughn]

what would be a safe head cut/ 90 unleaded a 225 pro max/ thx

[KIRCHNER]

what would be a safe head cut/ 90 unleaded a 225 pro max/ thx
.o3o

[doug vaughn]

thx / Doug

[gmorgan]

I run 165 psi on my ProMax and use 93 octane ethanol and one ounce of Aces to every five or six gallons. I also run AmSoil HP synthetic oil mixed 40 to 1.