LS6

Can LS7 piston be used with the LS1 connecting rod?

sandragnx

iTrader: (82)

LS1 rod=6.098 LS7=6.077.Wrist pin also different size and ls1 pin is pressed ls7 floating.

LS6

I want to use the LS1 connecting rod with a piston sized for a bore of 4.125".

How to know the LS1 piston dtailed information (Compression hight, pin diameter, skirt length, etc...)

Thanks...

dfinke23

I prob don't need to say this considering you may be asking about an LS7 "sized" piston rather than an actual GM LS7 piston, but the GM LS7 is a cast piece of junk. It is only appropriate for a stock, or slightly modified configuration.

KCS

iTrader: (20)

You could, but you need some machine work to make it happen.

The LS1 rod has a .945" pin and the LS7 piston uses a .925" pin. A machine shop could hone it to .945" and use it with an LS1 pin, unless the length is different.

The compression height is something like 1.175", so with a 6.098" rod and a 4" stroke crank, you're sticking the piston roughly .033" above the deck. You would either need the pistons cut down to reduce compression height or use a thicker Cometics gasket to get quench distance back to a safe level.

For what you're paying a machine shop to do all of that, you may as well buy the correct rods/pistons.

KCS

iTrader: (20)

I wouldn't call them junk. The OEM pistons have some great technology built in them, they're just not as strong as the forged pistons.

LS6

I bought a junk LS1 block, where local machine shop will do dry re-sleeving, where currently I'm experementing the re-sleeving. I would like to use the stock crankshaft & connecting rod since they are good condition and I want to test the block if it is sound well as N/A. This machine shop is known to do sleeving alot on LS1 block with alot of sucess.

The block will be topped with L92 heads, where I will be milling the head to about 0.040" to pump the compression up.

The original LS7 Piston compression hight is 1.173"
1.173" (LS7 Piston C.H.) + 6.067" (LS7 Connecting Rod) + 2" (LS7 Stroke /2) = 9.24" Block Hight.

The original LS1 Piston compression hight is 1.331"
1.331" (LS1 Piston C.H.) + 6.098" (LS1 Connecting Rod) + 1.811" (LS1 Stroke /2) = 9.24" Block Hight.

Option 1, if I used the LS7 piston on stock LS1 connecting rods & stock LS1 crankshaft:
1.173" (LS7 Piston C.H.) + 6.098" (LS1 Connecting Rod) + 1.811" (LS1 Stroke /2) = 9.082"
Difference Between Block High and Rotating Assessmbly = 9.24" - 9.082" = 0.158"


Option 2, if I used the LS7 piston on stock LS7 connecting rods & stock LS1 crankshaft:
1.173" (LS7 Piston C.H.) + 6.067" (LS7 Connecting Rod) + 1.811" (LS1 Stroke /2) = 9.051"
Difference Between Block High and Rotating Assessmbly = 9.24" - 9.051" = 0.189"


Will there be difference in compression ration in option 1 & 2? I think this 0.158" & 0.189" will be added value since I'm milling the heads and will protect the valves heads from hitting the piston, but on the other hand, there will be cost of honing the rod to pin correct size for the 0.158" while in the 0.189" does not require. Please any other thoughts ...



Thanks after all

S10xGN

iTrader: (11)

No, these are very poor combinations. There are reasons for the piston to be at (or near) deck height. With 66cc heads and a completely flat-top piston, option #1 results in a 7.59 CR while option #2 shows 7.24 CR. Even if the engine were to start and run, performance would be abysmal...

COPO9560

You might want to talk to your machine shop. I don't believe you can dry sleeve an LS1 for a 4.125 inch bore as they are the only ones with coolant between the individual holes and factory liners are thin. LS2 and later blocks are siamesed between bores and can accept a larger liner. Key is the liner OD, not ID - LS1 just does not have enough metal there.

Only real option for LS1 block and 4.125 bore is a wet sleeve. This is a much more difficult install and probably a local guy is not the best choice for this. RED or ERL would be a good choice but be advised this is not a cheap job.

LS6

You are right about LS1, but if you see LSA sleeve, they use dry sleeve on LS1 very sucessfully and as you menstioned the OD is the key.

LS6

I tried to find out piston having bore of 4.125" and the pin diameter 0.945" and the compression hight of 1.331", but no sucess.

It seem that no one done a engine of bore(4.125") X stroke(3.622") with connecting rod of 6.098" before...

Thanks...

3pedals

iTrader: (3)

if you replace the rods with 6.125" aftermarket rods, your piston choices may be better

MikeFSKSpeed

iTrader: (37)

What he Said ^ and for the amount of machine work to make a set of LS7 pistons work, you could have had ROSS or JE make you a custom forged set. though I think there's a few problems outlined in this combination.

LS6

I have approched one piston manufacture for a custom made and waiting for their answer. Today, the LS1 block is sucessfully dry sleeved in the shop. I can not confirm the block integrity is sound well unless I put under load and start the engine. I will see soon how it goes.

If I can not find the 4.125" piston's, I think I will go with the LS3 Piston's. I want to see the sleeving integrity is sound good and to use the engine for high RPM. Could you please elaborate more about the combination issue...

Thanks...

LS6

Update:

I went with the LS3 piston (4.0845" bore) with the same pin diameter of LS3 stock and compression hight of 1.330". The machine shop ensured with this re-sleeving, I can go to 4.150" as maximum, but the 4.125" & 4.15" bore piston's are not avilabe as shelf items.

I will be later on my next project ordering a custom pistons of 4.15" bore.

LS6

This is the junk block after sleeve installation. The Block cost me $ 130 USA. The sleeve cost $100 USD (8 QTY), machine shop cost $ 240 USD, Psitons cost $ 413 USD (8 QTY), Piston's ring's cost $ 130 USD (for 8 Piston's)