doww301

iTrader: (10)

Hi to all:
I’m replacing my stock ls2 bottom end with some upgrades. Crank has a divot of about .002” and also some marks on the journals due to the failure of the mellings oil pump I previously used. But, if it weren’t for the divot I wouldn’t have it turned as the rest of it is ok. I plan on doing .010/.010. And, I have the following replacement parts in mind:

Wiseco # PTS523AS – Forged small dome (+4cc) with valve reliefs. Compression of 11:1 with stock ls2 heads. I have ported ls3 heads so I’m guessing I should be somewhere around 10.5:1 – or maybe a little higher with rods that are .002” longer than stock.

Eagle 6100M3D Forged H beams – use standard .945” pin and are 6.100” in length vs stock of 6.098”.

.010” undersize clevite 77 PTFE coated “H” series mains and throws.

My main question is: Will the pistons be ok concerning “through the bore” measurement by adding -.002, or, in other words, causing the pistons to be raised .002” higher in the bore than stock pistons are as I will have connecting rods that are .002” longer? The wiseco pistons have a comp height of 1.335” and a +4cc dome. If everything I have read about these is correct the valve reliefs in these pistons should accommodate the larger ls3 valves. My cam is fairly conservative: 224/236 on a 114 +4. With this setup I had almost .120” of ptv on the intake side and about .135” on the exhaust with the stock flat top “meh” pistons that come from the factory. And, of course I’m gonna check these specs again with my dial gauge when I re assemble the engine. I’m wondering if anyone has had any experience with anything like these pistons installed in an LS2 while using a moderate or larger cam – especially if you also have L92 or LS3 heads. If so, would you please chime in and tell me what your PTV numbers look like. Also, any good general advice on how/why this setup either will or wont work would be greatly appreciated as I need to buy the right parts the first time. I have looked at other wiseco, diamond, and a few other brands of pistons. To be honest, the ones I’m considering are about $420 vs $750 to $800 of the typical -3cc flattops that are available. Also, my CR would be about 10:1 tops with my heads and most of these other pistons. I know I could mill the heads along with using the more expensive pistons but I really don’t want to go there. Also, I’m not sure I need the more expensive pistons as my car will be mostly daily driven and once or twice a year to the track at the most. Anyhow, some good advice about this would be greatly appreciated – Thanks!

KCS

iTrader: (20)

Save yourself some headache and measure the bearing ID before you have the crankshaft turned .010". If you just hand the crank over to be turned, you're pretty much stuck with whatever clearance you get as a result. If you know what journal diameter you need to get the clearance you want, you can give the crank grinder those numbers to turn the journals to.

The .002" extra rod length probably won't matter. It just depends what your deck height will be and how far out of the hole you need the pistons to be to get the quench you want. If you're wanting to run stock head gaskets, they're about .051" thick so you can safely run the pistons .015" out of the hole for .036" quench. That's about as tight as I would feel comfortable with.

If I were you, I would look at different pistons. I personally have not had good luck with the cylinders in used engines cleaning up with a light hone. They usually need to go to a .005" larger bore at least to clean up, especially if honed with a torque plate. If you do stick with the Pro Tru pistons, I suggest you verify that the pistons come with rings from whomever it is you're purchasing from. I bought the same pistons in a 4.030" bore size and they did not come with rings.

doww301

iTrader: (10)

thanks for the come back! uh, I actually have determined to have the crank turned to get to my bearing clearance goals. For some reason I just didn't write it down in the post - long week at work. I probably will want to use the tru pro pistons just for cost if anything, but you make a good point about the cylinders. I will look to see if they make one in a 4.010 or 4.020. I know scoggins dickey says don't go over .020 even though GM claims you can go .030 and still be safe - though I don't want to put that to the test. I don't plan on going FI or nitrous but still would prefer to find a set of 4.010 slugs and leave it at that. I really appreciate the info on the piston height. its good to know I can use those rods and be ok - I previously used the cometic .040 head gaskets with the stock rods but after removing the heads I discovered they were pushing a micro amount of water - not enough to cause any problems - YET but that would probably change sooner rather than later - I have a set of .051's setting on my shelf but I'm actually disinclined to use them - I even ran moroso ceramic cooling system seal on my first heat cycle thinking that would be enough, then I flushed it out and installed the antifreeze. So, I probably will use gm gaskets if I can with whatever overbore I end up with. Again thanks for info!!

KCS

iTrader: (20)

The LS2 blocks will go to 4.030" in an NA application. That's what I was originally building but I learned the block had been previously decked and ended up using flat top Wisecos with a 1.30x" compression height and a 6.10" rod. I sold that shortblock to build my 440ci combo, but the guy I sold it to says it runs perfectly.

I don't think the Pro Tru's are offered in a 4.010" but you may be able to have them done straight through Wiseco for a small fee.

Have you considered hypereutectic pistons? There are some really nice options out there that have considerable advantages over the Pro Tru's, especially in a daily driven application like what you've described.