I'm looking to swap out the pistons in an LS2 shortblock I just received. I want a forged piston with a -4cc valve relief. I would REALLY like to use the stock rod and the stock bore. I'm going to spray the car and I'm also running a heads/cam combo that will require cutting the pistons. I wouldn't have a problem cutting the pistons, but I'm not sure how well they will hold up to the nitrous with a relief cut in them. I would feel better just puting a new piston in it. Is there a piston that will work for this application?

Info or a part number would be great.

Thanks!
-Biz

 

I believe the stock rods use a .945 wrist pin. Most of the aftermarket pistons use a .927. It may be hard to find good pistons that will work with the stock rods.

 

Well ****. This build is just getting better and better.

 

For the amount of money you are looking at spending you might as well put some forged rods in there. When ever you put new pistons in you are going to have to rehone the block to get proper ring seal. Stock rod bolts suck. If you decided to do just forged pistons it would be retarded not to swap the rod bolts at the same time. That's going to cost you at least $80.

If you shop around for pistons look for something like a 4.005 bore, 3.622 stroke, for stock 6.098 rods with a .945 pin. You can then use Scat I beam forged rods 6.098 length, .945 pin, with ARP rod bolts from Speed Inc. They only cost $299.99. That way you're really only spending an extra $219.99 on putting in forged rods at the same time. You'd be kicking yourself if you didn't later down the road.

Why if your are using a -4cc dish would you need to cut an additional valve relief in the piston? Even if you did why not get a larger valve relief piston to start with?

Here's what I'd build if I was you.

Pistons = Wiseco K398F3 = 2618 material, 4.005 bore, 6.098 rods, 1.304 compression height, for a 3.622 stroke = $535
Rods = Scat I beams = 6.098 length, .945 pin = $299.99 OR extra money = Scat H beams = 6.098 length, .945 pin, ARP 2000 rod bolts = $529.99
Crank = Stock cleaned up

Get everything rebalanced, honed, align honed, and you're good to go. If you have an extra $200 I'd put ARP main studs in. Your block has to be align honed for those.

I was messing with a compression ratio calculator and that setup that I just put together, .005 out of the hole, and .055 compressed thickness GM gaskets the compression ratio comes out as:

70cc Chamber: 9.894436516622516:1
69cc Chamber: 10.001511846508816:1
68cc Chamber: 10.111196634690188:1
67cc Chamber: 10.223587447781734:1
66cc Chamber: 10.338785676683289:1
65cc Chamber: 10.4568978416548:1
64cc Chamber: 10.578035920838879:1
63cc Chamber: 10.702317704360208:1
62cc Chamber: 10.829867176355531:1
61cc Chamber: 10.960814927538708:1
60cc Chamber: 11.095298601186698:1
59cc Chamber: 11.233463375748254:1
58cc Chamber: 11.375462487632586:1

What heads and cam do you plan on running? I don't really see why you'd need an extremely large valve relief unless you were building something with a n extremely large cam.

 

I would be cutting the stock pistons not the forged ones. The -4cc relief would be plenty for what I'm running. I also already have ARP rod bolts. I'm just on a pretty tight budget. I wasn't going to run forged pistons at all, but the ones in the motor have detinaton marks. So, I'm looking to replace them.

I'm running a set of Patriot Heads 2.055/1.60. The heads are milled .035, so that puts the chamber at about 58cc.

I'm running a comp custom grind cam, 236/248 601/615 110+2

 

May have something better to offer, i'm sourcing 6.098 rods/ .945 pin bore rods, H beam with ARP rod bolts, $299.

basically the features of an Eagle H beam for the price of Scat I beams.

 

Then, just buy a set of the Wisecos that I listed. They'll work on stock rods and have a decently sized valve relief in them. If I were you though I'd save up and put some forged rods in at the same time. $300 isn't that much in the grand scheme of building a car.

^ Nice! I wish I would have known about those before I got scammed on here trying to buy a set of Scat H beams.

 

I think he was planning to cut the stock pistons to -4cc, if I am not mistaken.

 

^ He can do either. You can fly cut the stock pistons or get aftermarket ones. Plenty of people spray on fly cut pistons. Obviously it isn't going to help structural integrity when spraying, but it'll be fine as long as you don't go crazy on it.

 

You have a PM.

 

im running mahle forged with a -4cc valve reliefs and on stock rods they are 4.010 sized

 

I've found a set that are a 4.00 bore. I don't want to do anything more than a hone to the block.