i did some tinkering around today with some 2.8 pistons on a 3.1 crank

the 2.8 piston will pop out of the bore .157 of an inch

well the pistons are thick enough for na apps u can fly cut them

heres how it works out

ok from the top of the ringland to the top of the piston measures

.330

so if we take off 157 that leaves us with

.176 left for the top ring land.more then enough material

now for the thickness of the piston before machining
.350

and after machining .193 thick at the thinest point

so it is possible now u just need to figure out base cr with 0 deck fith a flattop piston.and ur thickness headgasket of choice

 

Psst, look here. Secret's been out for a while. And I think you have an admirer or 2. LOL

 

never saw that and even on 60*v6 they had no solid numbers.
so today i took a stock 2.8 piston and measured it, then cut it down and remesured it and posted the numbers

im gonna go play witht he cr calculator in a bit and come up with possible cr options

the 2.8's can be milled to flatop, slight dish/recerssed or slight dome or popup style dome

so there are gonna be quite a few options here for high cr builds.
but anyone who does this should do this for an N/A only build the piston crowns would be to weak to be used under a decent amount of nitrous. a 50 shot prolly wouldnt hurt it but i deff would not go any higher

on a side note tom im going to cut a 3.1 piston in half and see just how thick the crown is.

the 2.8 has amuch thicker top ringland then the 3.1 piston
i wouldnt be surprised if that a milled down 2.8 piston didnt have a crown about the same thickness as a stock 3.1 piston

 

ok heres what i come up with

3.1 with cutdown 2.8 piston as above
this is with a .040 gasket

and this one
same as above but with .060 gasket

 

now the same as above except with a minus 6 cc dish milled into the piston and .060 gasket


and now the same with the standard .040 gasket


im not sure just how much material u would have to remove to get a -6 cc dish but i have 5 more 2.8 pistons at work i can throw in the milling machine or lather and cut some dishes into and try some diff configurations, afterwards i could cc each piston to come up with some solid numbers and combos to calculate compressions with domes and dishes on the pistons

edit

just to make u guys aware were it says dome in the calculator actually reflects dish volume
a positive cc number means dish
and a negative (i.e -6 would mean 6cc dome)

 

For the 3.1 or 3.4 guys who want to run turbos and forgings, you could machine a few thousandths off of a set of stock type pistons to get your compression ratio down to 8.5:1 or so.

Does anyone make stock style forgings for the 3.1 or 3.4 liter?

How thick would you surmize that the crown needs to be for boosted and non-boosted applications?

 

I don't believe there's any 3.1/3.4 forging offered right now. For f.i./n2o min thickness is .250", for na min is .150" with hypereutectics. You could strech it a bit with forgings, but keep it close.

 

forgings will run u about 100-125$'s per piston as they are pretty much a custom deal, so u could order them with ur desired cr from the getgo

 

The Fiero store has forged 2.8 pistons. That's all I'm aware of that's not custom order.