my brother has a 90 trooper with a 2.8. here is his question from another forum that I figure would get a better response here:

"I am trying to see if anyone knows if you can bore a 2.8 .120 over.
I know a 3.1 is a stroked 2.8 and a 3.4 is a bored 3.1, I was wondering if you could bypass the new 3.4 block by just putting oversized 3.4 pistons in a 2.8.
If anyone knows please help. thanks"

I'm wondering if there are other things that would help in the power dept without going to a 3.4 (aside frome the normal bolt ons and exhaust and stuff, which he already has). For instance, can the heads from the 2.8 be reworked to flow like the 3.4?

TIA

Paul <img src="/forums/images/graemlins/cheers.gif" alt="" />

Wouldn't a running 3.4 be less priced than new 3.4 pistons and the 2.8 machine work? I just don't see the point?

Not a good idea, far in excess from recommended oversizes. You can bore it out to at least 040" safely and install a 3.1 crank and appropriate cast-iron-head 3.1 pistons. You'd end up with something around a 3.2.

With the 3.4 HT crate motor's cam, valve springs & retainers, plus 1.6:1 roller-tipped rockers, Holley Big-Bore/GM 4.3 TBI and bored intake, it should be a very strong runner.

There is a company that touts a 2.8 block overbored to 3.4 specs, but at that point the cylinder walls are so thin that they have to sonically test each block for thin spots. The 3.4 block is a lot stronger than a 2.8 and a better platform for performance mods.

BTW the 3.4's heads are the same as what's used on the Trooper 2.8 or Rodeo 3.1. Typically with casting #'s that end in "884". Some gains can be made by port-matching the intake manifold to the heads, but don't mess with the "vane" in each intake port.

You can turn the 2.8 into quite a revver with performance bolt-ons, but what you're really looking for is more low-to-midrange torque, and the largest gains are going to be made by using the 'stroker' crank.

Check out this article if you haven't already:

http://www.4x4wire.com/tech/60degreeV6/?

HTH.........ed

he's having trouble finding a 3.4 for less than $600 with less than 100k. pistons aren't expensive and he knows people who can give him a break on the machining I guess.

so if they make overbore pistons for a 3.4, which is essentially a bored 3.1, wouldn't the cylinder walls be an issue for the 3.4 as well? and if so, why do they make overbored 3.4 pistons?

cam and roller rockers are on the list, and he got a 4.3 tb and is boring the intake right now I think.

thanks for the info so far!

The 3.4 block is a totally new casting, designed with the larger bores in mind. So, even if you overbored a 3.4 .040" (or whatever arbitrary overisize), the cylinder walls would be no thinner than a 2.8 bored out .040".

I used Sealed Power pistons for my 'Stroker' project. You can get them with teflon-coated skirts. The teflon coating allows for very tight piston-to-bore clearances, eliminating the dreaded GM 3.1 piston slap and skirt wear issues.

I can testify that with cyl's bored to the tight end of the mfr's specs, the pistons were a snug fit indeed. But the motor is real tight and doesn't burn a drop of oil.

Part # for the pistons I used: Sealed Power H562CP .75MM; the "CP" in the part # stands for "Coated Piston".

I have a nice set of 1.00MM (.040") pistons, same brand, that I snagged off eBay Dirt Cheap. These are awaiting a Project-to-be-Named! That one will see the performance cam and other goodies and should be very Sweet. <img src="/forums/images/graemlins/cheers.gif" alt="" />

well we talked today and I think he's gonna try to find a 3.1 crank, go .060 over, cam, rollers, etc. i'll fwd the pn's to him and see what he thinks. good thing is, when he does find that smoking deal on a 3.4, he can swap lots of stuff over.

trying to get a pic from him too. his troop is pretty sweet. suspension lift, trimmed, 35's (ie, the need for some extra power), two tone OD green/flat black <img src="/forums/images/graemlins/smile.gif" alt="" />