440 compression difference

[02silverpile]

All, I am considering going from a 426 to the 440 kit. However I live in Michigan and we are only like 1000ft above sea level. I am trying to compare the 11:1, vs. 12:5:1 piston. I think with the 11:1 you need to run a 50/50 mix of premium and 110. Would you need to run 50/50 or 100% race gas with the 12:5:1. I will also be running a +6 timing key. I also have a thinner base gasket so the compression will be slightly higher. Thanks.

[bwamos]

11:1 you wouldn't have to fully mix 50/50. But the timing advance probably does require it.

I garantee with a 440 (more heat) @ 12.5:1 w/ a timing advance and a decent cam you are certianly going to need to run full race fuel of the appropriate octane.

More importantly you are going to need heavy duty head studs, and maybe even a stronger rod.

[02silverpile]

Am I even going to notice a difference if I dont go to 12:5? I mean some people go to a bigger compression to bring up psi. But since im combining it with a timing advance key. I think it might be like pulling a pin on a grenade. So am I going to notice a loss with my setup going down to the 11:1? Thanks.

[2muchquad]

Take it from an expert.The 12.5 to 1 piston can run on a mix of race gas.Its gonna be harder on bottomend as far as stress on the rod etc but compression is where you make your power.Thats why a ot of the 4fiddys are running 13 and 14 to 1 and higher!If your building a trail scoot then stay around 11.5 to 1 or so.Me i like a monstrous mid hit so i'll gamble with the high compression:D

[GPracer2500]

Originally posted by 2muchquad
Take it from an expert. The 12.5 to 1 piston can run on a mix of race gas....

But wouldn't that depend on which fuels you're mixing, what cam you're running, what elevation you're running at, what the terrain is, what the temps are, and other things??

[Colby@C&DRacing]

The 12.5 piston in a 400ex with a mechanical timing advance needs more than a 50/50 mix at 1000ft it will ping. With out the timing you can run less octane but that timing really creates heat.

[02silverpile]

Colby, and 2 much quad. Thanks for the info. Yes this will be built mostly for the trails, but I do like to hillclimb, and drag race. I have a full build 426 now, and im just contiplating going to the 440. Michigan is about 1000ft above sea level. I know the timing could cause an issue with the bigger compression. The lower end is all stock. So should I stick with the 11:1 or 12:5. Im thinking in both cases the 11:1 requires 50/50, and the 12:5 requires pure race gas. The gas cost doesnt phase me, or the convience. Its just since I do trial ride If i wanted to go on a long ride, I couldnt because 110 isnt available along the trail. I need to compromise on the setup soon. Any aditional advice will help thanks.

[2muchquad]

Loose the timing advance key.Stay under 12 to 1 and get you a nice cam.;)

[oldskoolex400]

Loose the timing advance key.Stay under 12 to 1 and get you a nice cam.

thats it right there