I tore apart my bro's '01 4.8L truck for a cam install along with new lifters and noticed the pistons are flat with just a small hole no more than 1/8th of an inch wide on the center left of each piston.
While I was installing everything my friend was doing a H/C swap on a 5.3L truck; which I noticed the pistons seemed to be smaller(IDK) and were dished similar to the LQ4's(see pic) Ive seen before.

Why the difference in pistons, I thought the 4.8L had lower compression than the 5.3 which have similar heads I assume?

 

I thought that the compression was the same, but I'm not sure. I do believe that there is a different stroke between the 5.3 and 4.8, and a different wrist pin location.

 

4.8s have flat top piston 5.3 have dish and the stroke is different by like .30

 

compression is similar between the 2 but the the rod length and stroke change between the 2 displacements. This requires a change in piston design to keep the compression simillar. If you want to bump the compression use a 4.8 piston with the 5.3L
Try this on for size... LOL All the math has been done in this post...

https://www.performancetrucks.net/fo...7&postcount=25

 

Exactly, this was answered in a recent post, let me look for it and I will post. The 4.8 pistons are the exact same as the 5.3 H.O. (L33) pistons, same compression height, same dome displacement. FastBrick is correct, smaller volume displaced in the 4.8 requires a smaller volume at TDC to achieve identical compression ratio. Since the 4.8 and 5.3 (standard output) share the same combustion chamber volume, the 4.8 needed to reduce the total volume in the cylinder at top dead center, thus pistons with less dish (flat tops) than the 5.3.

 

click the link I posted above... I saved you 4 pages of BS

 

BTW to street demon2k3... those dots on the side of the piston indicate the forward position of the piston in relation to the block. The center is just a casting or machining mark left be hind

 

Beat me to it!

 

I decided to make it a little more clear too...

 

According to JE pistons this is incorrect. All LS rods are 6.098 inches in length except for the 4.8L truck engines and the LS7. The 4.8L rod is longer at 6.298 inches to allow GM to use the same compression height between the 4.8L and 5.3L even though, as we’ve seen, the 4.8L and 5.3L pistons are not the same.

Here is where i got this information. Everything You Wanted To Know About The GM LS Engine Family | JE Pistons


4.8 Specs
4.8 stroke: 3.268
4.8 rod : 6.298
4.8 deck height: 9.240

5.3 Specs
5.3 stroke:3.622
5.3 rod: 6.098
5.3 deck height: 9.240

Now do the math: the centerline of the cank is half the stroke of couse and the deck height is measured of the centerline of the crank.

5.3 Stroke 3.622/2 = 1.811
4.8 Stroke 3.268/2 = 1.634

5.3:
1.811 + 6.098 = 7.909
9.240 - 7.909 = 1.331 Pin Height

4.8:
1.634 + 6.298 = 7.932
9.240 - 7.932 = 1.308 Pin Height