piston questions

[Rootie524]

Ok..i have a couple questions about pistons. bare with me..haha.

it says on 60degreev6 specs for the 3.1 gen 2 (what i have) that stock compression is 8.8:1..if that's true..that pretty pathetic. So I'm looking to boost up compression with some new pistons. First questions..do they make aftermarket rods for my engine? ive got 100k miles on my current ones so at the very least i'd want to get new ones as well as bearings. so if you can point me in the right direction for rods and bearings that would be great.

i have found two different types of pistons:

http://wot-tech.com/shop/all/forged-3100-pistons/prod_262.html

and

http://www.mpracing.org/store/index.php?_a=viewProd&productId=457

the ones at WOT-tech seem more promising..the ones at mpr dont give any indication as to what the compression will be. so i dont really know. I don't plan on boosting the engine ever..im going to leave it NA..so is 10.5 or 11.5:1 over kill for NA?

also, with new pistons will i need different head gaskets for clearance? and if i got the WOT-tech pistons at say 10.5:1 compression..how much power could i expect to see from that? and can i run stock rings with either of the pistons i listed

lastly..can this be done with the engine in. all i have to do is take of the complete top end down to the block..take the oil pan off..work at the crank from the bottom and pound the pistons up and out..seems possible..

[robertisaar]

8.8:1 is correct for the LH0. considering the L82s run ~9.6:1, i would call 9.5:1 absolutely safe. 10.5:1 is probably fine if you're using any fuel better than 87 octane and 11.5:1 is probably going to require 93 or 94 octane at a minimum....

all of this assuming a stock cam and little/no tuning.

[Rootie524]

i've got a performance comp cam with upgraded valve train..soon to have ported heads and 28lb injectors.. so i should be good at 10.5:1 with 87 octane?

[robertisaar]

since you'll quite obviously need tuning to get 28lb injectors to work where there were once 16.7lb, you could probably get away with 87... probably not the ideal octane, but it should at least decently on it without too much knock.

EDIT: why exactly are you going to 28lb/hr injectors? i highly doubt you'll need to go that far.

[Rootie524]

what would you suggest? everyone i talked to said to get the 28lbers from a trailblazer and get those tuned. if i get it tuned correctly i wont run lean or anything..i just might not use them to their full potential

[robertisaar]

the problem with using injectors too large for an application has to do with how short of an injection pulse would be necessary to maintain a decent idle. i highly doubt you'll need 28lb/hr injectors for just a cammed/headwork 3.1... something along 24lb/hr(or possibly less) would be more ideal.

[Rootie524]

so i would probably have a shit idle if i went with 28lb?

[robertisaar]

you would likely either have WAY too rich of an idle due to a minimum pulsewidth that needs to be met, or you could attempt to bypass that and potentially have an unstable fuel flow...

i advise seeing what some other people are running with roughly the same setup and seeing what kind of duty cycles they are getting up to... wifey's GP has a 3.1 with stock injectors and they only ever reach ~48% duty cycle maintaining a 12.5:1 AFR at WOT.

[Superdave]

If it truly is a Gen2 engine then just pull the heads and swap on a set of head gaskets for a 3.1 Camaro. They are thinner and will get you up to about 9.4:1 on stock pistons.


19lb/hr injectors from an early 3400 would be plenty for this engine.

[Rootie524]

well its a large port 3100 in a 2002 malibu..im guessing small port is gen 1 and large port is gen 2..

what yeah camaro can i get the heads off of and what year 3400 has the 19lbers?

[asylummotorsports]

'94-'99 3100 SFI AND '96-'99 3400's had 19# injectors

[bszopi]

You have a Gen 3 engine. Gen 2 would be the actual 3.1MPFI engines (up to 1993). After that, they became 3100SFIs and Gen 3. So you already have ~9.5:1 CR.

[mickaz]

'94-'99 3100 SFI AND '96-'99 3400's had 19# injectors

are you sure about that asylum? because my beretta had lower injector then the 3400, and I have a 96.

[Superdave]

small port 3100's were like 17lb/hr


ok, so what i said before is null and void because you do not have a gen2 engine. You cannot use camaro gaskets on a gen3. Your SCR is also 9.5:1 stock with a gen3.

[asylummotorsports]

are you sure about that asylum? because my beretta had lower injector then the 3400, and I have a 96.

That is right off the information posted on THIS site!

If that is wrong then what shall I suggest?