I regret not running 10.5:1 however I think 10:1 is good enough for now. I would never put 12.5:1 on a evo. I don't even think the motor would stay together under boost. That would have to be wicked high cylinder pressure. Unless he has 12.5:1 pistons and a 5mm head gasket.

Mikey

 

You have 93oct where your at?

 

no 92 and e85. I'm v7 dual map too

Mikey

 

a few years ago people thought the same about 10:1. heck, a lot of people still do!

 

Yeah but thats when peopel were running 9 and 9.5:1...I could see maybe 10.5:1 or 11:1 but at some point your decreasing the amount of volume you can force into the engine. So I would think your gonan decrease overall power.

10:1 @ 24psi will more than likely make more power than 12.5:1 @ 16psi

 

when i tell people that i plan on 10:1 and 35+psi they freak out and say there is no way the motor will stay together. they are old school and think 8:1 is the highest you can go.

 

I agree to a certain point... However I think 10.5:1 is prob the best and works good on 93. If I redid my motor it would have 10.5:1 pistons and a 159mm rod instead of 156.

Mikey

 

Ya one of the guys I work with has a built SS and he saw my 675 at 37psi and asked if I had 8:1 and I said 10:1 and he called bs and said not possible.

Mikey

 

I run 33psi but only on e85 lol. I have e85 readily available to me in kansas but I am from CT so when I go back home on leave and stuff to see my family I have my map switching to run on 91 just to make it so I can always fill my car

I think 12.5:1 is a bit excessive I mean corvettes run like 11.5:1 I believe nad they only run like 6 to 10psi when boosted.

 

when it comes to knock resistance and combustion efficiency, you cant compare an evo to much except a honda. lsx motors are inefficient knock magnets in comparison.

 

that is also like twin turbo lambos. they run 12:1 but they only boost 4-5 psi on two 6262 and make 1500hp.

 

honda motors are way better than the 4g63, at least the heads. hard to compare a honda to mitsu for that reason.

Mikey

 

but compared to nearly every other motor around, the 4g63 is still at the top.

 

I wouldn't say they are way better, they excel in certain areas but the 4g63 is one of the best motors ever made imo. But even still 12.5:1 and more than say 12psi is gonna be trouble. And like I said your moving a lot less total air and fuel...there for less power.

 

i come back in the thread and say still to damn high.