piston question

[Brandon350]

First of all Hello all I am new to this site, and I apologize for my question which I searched and found several posts of similar questions but its still a little fuzzy to me. I am building a 2.8 for my wifes z24 and my question is what is the stock compression ratio? I would like to bump the compression ratio by swapping in less dished pistons in. I know flat tops wont work and I hear different things about what piston and what gasket to use. Can anyone clear this up for me. Once again sorry if this has been answered already.

Thank you

[Doubt_Incarnate]

your pretty limited. not a lot of 2.8's actually being done on here. if you have dished pistons, you have aluminum heads. your best bet would be to get a set of oem gaskets for a 2.8l S-10 (iron heads). they are thinner, and i belive that is the safest, least expensive way to do what your asking, a little playing in DD2K says you'll end up with about 9.44:1CR. price of new gaskets and bolts is much less than custom pistons. the other option is the pistons from an old 2.8 S-10 wich are flat on top, but sit far enough down the bore that with the aluminum head gaskets you'll get about 11.5:1, with iron head gaskets is over 12.5:1. thats calls for expensive gas, and moderate tunning.

the gaskets you get over the counter at a patrs store are going to be different than the oem parts (from a dealer) so you'd have to measure them up and compute from there.

[sharkey]

im guessing this is going to be mainly a stock rebuild with a few performance things.

stock compression is 8.9:1. there are some aftermarket pistons out there for the aluminum head 2.8l, but not much. your best bet if you want some nice pistons is to find a 3.1l crank, and you will now have the increased stroke. all that is required to build it as a 3.1l is the crank and pistons. this would allow you to get some nice pistons that are 9.5:1, and if you want to go almost 10:1, you can use ironhead head gaskets (s10, fiero, ect).

what other thing do you have planned for this motor??? are you going to be using a little bit more agressive cam, roller tip rockers, ect???

[Doubt_Incarnate]

i dont think you can use the 3100 pistons with the iron head gaskets, those pistons come .016" out of the block, and the thinner gaskets don't provide the "recomended minimun clearance". it comes to .026" where-as the "proper" is .035" piston to head. i remember there bing an argument about it elsewhere.

but he's right, the upgrade to 3.1L and the 3100 pistons are a good way to go. you get higher CR, and more displacment. for this you need a crankshaft from any FWD gm car with the 3.1l (90-94 z24) and pistons from a 95+ (berreta, century,) with a 3.1 (aka 3100sfi).

[Brandon350]

as for the rebuild I am going to go with a more agressive cam, Havent really decided on which one yet, roller rockers, I am fabricating up a set of headers, other than trying to bump up the compression thats about it. I was looking to get somewhere around 10.5 to 11.0. I also already looking into stroking it to a 3.1 but I figured since I already had the parts I would just stick with the 2.8 but the motor has been apart for some while and I see some rust formed on the crank and it would take quite a bit to take it off so I might just as well go with the 3.1 build.

So lets say I go with the 3.1 build, what would be the wisest piston setup to go around the compression ratio I am looking at? Also I am reading that putting a 3100 top end on the motor also flows better than my stock setup am I on the right page? I really dont have alot of experence working on 60 degree motors to know the difference between the generations. From what I gather first gen is the carb version like in s-10's, second version is what I have with the multi port, and third gens are 3100's is this correct? Thanks for all you help guys I appreciate it.
Brandon

[geoffinbc]

Your Pretty Close. Generations are defined by the heads for the most part.

Gen I is Iron Heads (regardless of injection system. Gen I saw Everything Carb, TBI MPFI and SFI)
Gen II is First design aluminum heads (was all MPFI)
Gen III is Second design of aluminum heads, block includes roller valvetrain (All SFI)

Take a look at the family tree

[Doubt_Incarnate]

for about 11:1 you could use the 3.1 crank, and the pistons from a 3.1 camaro. those pistons have less dish and should yeild about 11:1 if used with the 3400 ('99 grand am) head gaskets. the newer heads reqiure more than just a head swap, its a whole topend, heads, upper and lower intake, and the front timing cover. its called a hybrid swap, check this: http://www.j-body.org/frame.php?url=...iccrew.com/660

they have about anything you need to know about a hybrid swap, or just swaping a comple 3X00 into your J-body.

[GinoBeats]

Yeah there are a nice set of ironhead 3.1 pistons for sale on this board that would yield that compression ratio on your Gen II V6