4horseman

Hi,

I just purchased a supercharger and came across a short block rebuild that has forged pistons and rods. Has arp bolts so I think its stout. I already have the blower cam and 243 cnc ported heads.
As I looked into the specifics of the shortblock I researched the pistons and found that the rods used for it are 5.70 inch, I know the stock ls1 is around 6.098. Builder says it was built for forced induction.

Why would these pistons and rods be chosen over the stock ls1 rods . I verified that the block is a ls1 with a 4.00 x 3.622 bore and stroke.

Would I be making a mistake with this set up? Are there advantages to 5.70 inch rod because I cant find anything online so far about it.

Thanks

69ls6

I've never seen a 4" bore in a ls1. Cylinder walls get to thin..3.905 is the largest bore that I know of..

4horseman

I am going off the piston that was used in the rebuild. Summit PBP-12342-STD 4.00 bore 13.80 cc dish

Bore (in):4.000 in.
Bore (mm):101.600mm
Piston Styleish, with two valve reliefs
Piston Material:Forged aluminum
Compression Distance (in):1.560 in.
Piston Head Volume (cc):+13.80cc
Wrist Pin Style:Press-fit or floating
Pin Diameter (in):0.927 in.
Piston Ring Thickness:1/16 in. x 1/16 in. x 3/16 in.

sorry for the confusion.

stevieturbo

I'd find it almost impossible to believe any LS motor would be running rods as short as 5.7"

Likewise talk of a 4" bore on an LS1 block is just nonsense unless it has been sleeved.

I'd stay very far away from it

Turbo-Geist

Something seems off. The deck height of most LS1 blocks is 9.24". This is the distance from the centerline of the crank main journals to the block deck surface.

So if it is an LS1 block the deck height should be about 9.24" and the piston is generally 0.006" out of the hole.

Given from your data
Connecting rod length = 5.70", stroke = 3.622" Compression height = 1.560"

Assumumption
9.24" deck height if truly an LS1 block.

Solution
Divide stroke by 2 and add to rod length: 3.622/2 = 1.811", and 1.811 + 5.70 = 7.511".
Subtract this answer from the deck height: 9.24 - 7.511 = 1.729". So the piston compression height needs to be 1.729" vs your 1.560". Piston would be almost 3/16" below deck.

Input a standard 6.098 rod into the above example and now your compression height would need to be 1.331" vs 1.560", so the piston would be 0.229" out of the hole. Almost 1/4".

As you can see, something doesn't add up.

4horseman

Yes, hes checking it. I thought it was an lq4 but he swears its aluminum