DJH

I need to replace ONE piston on a very low mileage LS6 engine that has TRW 7053P .030 pistons. I'm told that this is now a Speed Pro piston L2349F +30. My quandary has been finding out if it's a replacement for the old TRW listing or is it an exact match. Some say new technology allows the pistons to run tighter in the bore or the valve clearance cuts may be larger etc. but I'm mostly concerned about weight, land dimensions, pin bore etc. etc. Can I readily substitute a Speed Pro L2349F +30 in place of the old TRW 7053P .030? I got great forum feed back on what caused my problem so I know someone knows this as well. Thanks.

ghostrider20

If the replacement piston is a tad heavier, you can lighten it by removing some material from the back side.

I posted a link to Arias in the other thread. If they don't have, or are unable to make what you want, they may put you on the right track.

Westlotorn

I saw the post in your other thread showing you an ebay TRW piston for sale.
That piston is the old design. It is not skirt coated with Moly Coat. If it had the skirt coat it would be one of the more modern pistons. I would buy that piston and have it checked out. It should work. If it does not match you will be looking for a set of 8 pistons.
Do an internet search for your one piston by the Sealed Power part number. There used to be 3 or 4 companies that collected old parts for resale. I think Agge Equipment was one. Might be Egge, sorry I have not chased them in quite a while.

DJH

I completely missed the post showing an ebay TRW piston 7053P .030 piston for sale. I will review the posts and hope it's still there. thanks

GOSFAST

If you aren't able to work it out I have a set of those original Speed-Pro's on the shelf if it'll help?

Contact me with an e-mail Theengineshop@aol.com

Thanks, Gary in N.Y.

P.S. I would rather not split the set I have but would give you a fair price on the set of 8!

DansYellow66

It is Egge.

65tripleblack

I had one damaged cylinder bore some years ago and a destroyed piston. I asked the machinist to overbore that ONE cylinder to clean up and used the next size larger piston on that ONE bore. I asked him to carefully weigh the new vs the old piston and match their weights before giving me the new piston/rod assembly back for installation. There was never any problem and the engine remains well balanced.

Easy Rhino

This is interesting and I have never heard of this being done (at least on a street engine).

Given some folk's tendency to measure intake manifold volumes down to the nearest tenth of a cc (about .02 or 2% of a teaspoon amount of volume), can you shed some additional light on the affect of one larger cylinder - in effect a larger "pump."

When you say next larger size I'm guessing that .010 was all it took to clean it up? At 4.010 vs 4.000 (just guessing here how far into the bore you were after this) that is only .25% difference. So I'm guessing that the amount of power difference would fit into that realm of "noise" and be no more significant than other "noise" problems, at least in a street engine?

Why not bore out all of the cylinders to the next size while you're in there? Cost of pistons and the bore?

427Hotrod

It's a common practice in warranty replacement stuff and repairs where cost is a consideration. It will work and once the head is on you will be the only one who would ever know the difference. You don't even want to get into discussing what some Super Stock racers have been known to do. They will build a cylinder as the "inspection" cylinder...the rest may have longer stroke, bigger bores, more compression...different cam lobes on different cylinders etc etc etc.

The engine doesn't care..it just makes more power in the other holes.

JIM

Robert61

Back in the 80s we built race v6 Buicks for a particular track. They checked the same cylinder for CCs. We built these for different people. The one cylinder was 4" bore the other 5 were 4.125".

cardo0

Well I am guessing here but I think your LS6 is a 11:1 compression version. The Chevy power manual lists the stock piston for that version LS6 as part #3976013 but no +0.030" overbore part number! for a replacement. So what you have is a already aftermarket piston in the TRW 7053P .030. If TRW no longer produces these you will have to find a substitute.

If you find one with matching compressed height and similar dome IMHO all you need is to do is get the weights close like 10 grams but 5 grams would be much better. BTW i bought a nice digital food scale at Costco recently that measures with an half a gram.

Good luck.

65tripleblack

Engine had less than 5000 miles on it when the heads I ordered, and SPECIFIED EMPHATICALLY minimum valve spring height were delivered with less than I specd. Started the engine and dropped a valve destroyed the brand new head and one bore. The head supplier made good with one new head and some $$$.

It was my idea to save an already new engine and my machinist didn't buck the idea or grumble in any way. I went from 4.030 to 4.040 on that one bore. Can't specify the torque difference on that one cylinder but negligible I'm sure. Another thing that machinists often do is to offset grind throw journals. Sometimes they are not all EXACTLY the same so some cylinders have longer stroke than others. Same difference, torque wise.

The effect that one bore slightly larger than another would have on the crankshaft would fall within the same range or less than the difference in "rich" cylinders and "lean" cylinders on old school engines. It would also be similar to uneven spark strength due to fouled or dirty plugs.

If you're thinking about torsional loading on the crank, then any uneven loading due to a single overbore is negligible.

The important consideration is the weight. Getting the balance weight is KEY!

Westlotorn

I have seen OEM pistons at .005 and .010 larger in one bore to fix a bad block. I have also seen one rod journal or one main journal slightly small with a .0005 or .001 larger bearing to fix that one journal. They did not scrap all out of spec blocks and cranks they usually fixed them creatively.