Well I ordered the cheapest ones which is Eagle rods and Weisco pistons, I got the 8:1 compression. Is this bad? What would you suggest getting? Cuz alot of people were saying you will have to boost alot more, like atleast 25 psi. Is this true?

why would you have to boost 25psi? that doesnt make any sense, and how much did your package come out to?

He's saying he will have to boost more to make the same power someone at stock compression would be making... Which he is right, but you have a lot more room to tune and not blow it up... so i say more power to you... nothing wrong with cranking up the boost :-) Nothing beats turbo whine.

>Well I ordered the cheapest ones which is Eagle rods and
>Weisco pistons, I got the 8:1 compression. Is this bad? What
>would you suggest getting? Cuz alot of people were saying
>you will have to boost alot more, like atleast 25 psi. Is
>this true?

Peoples are saying in general that you make 5 hp average on each compression point, So I can assume that you loose the same amount for each reduction point if it's true you are loosing 1.6 point over stock, which could be around 7-8 hp loss with your rebuilt
but you also make 8-9 hp per psi on a 420a engine
So the math and you don't need 1 psi to compensate but you will have an engine that could be almost bullet proof if rebuilt properly

Alain

I have no dyno proof, but have been in numerous turbo cars with different compression ration pistons with the same turbo/fuel system etc. Mostly 4G63 cars.

Here is my guess on it.

If the turbo kit, fuel system and ignition are all the same. Basically everything identical(exhaust/intake etc.) I believe for every point of compression it takes 2 psi of boost to make up the difference. If I am running 10 psi on stock 9.6:1 compression it will make approx. the same power with 12 psi on 8.6:1 pistons. It will take 13 psi to make the same power with 8:1 pistons.

All will require approx the same fuel if the same maps are used for each setup. You will have less predetonation/knock problems with the lower compression pistons. This is not a problem at these low boost settings though. It will also require a higher initial rpm to get to your boost setting with lower compression pistons(turbo/boost lag). Once your full boost is achieved, the power output should be the same at a given rpm(say 5K rpm). I know many 1G turbo guys that have big problems with running a large turbo(60-1) with their low stock 7.8:1 compression pistons. Boost does not come on real strong until 5500 rpm and that only gives them roughly 2000 rpm to go before rev limit. I can see if you rebuild the head(aftermarket parts) and port it to really flow, use low compression pistons (8:1) and rev to 8500, your car will pull like a mad man. This setup is not very street friendly and can be disappointing if you cannot get those rpms high during a race.

I will rebuild with 8.6:1 or 8.8:1 pistons. My car is driven on the street/track/autocross and this is the best compromise. Basically I am just following with others have already done.

BTW: You could mill the head a bit while it is off and that would raise you back up to 8.5:1 or slightly better.

If you run a small turbo, the lag issue is not a problem. Just crank the boost up a few psi and call it good.

Off boost driving will suck no matter what turbo kit you have with low compression.

ahh just throw an afx under drive pulley in the mix you won't even know you have the 8:1 's ....
I running this same set-up ;)