If that were true I would have 5.3 forged flat top pistons in my hands at this very moment but I have yet to find any and If someone points some out to me I doubt they would be under $500 dollars and I can get stock 4.8 pistons and a new set of rings for under $450. Plus I dont need forged. I wont be spraying or going FI. So I wont be much over 400hp on motor anyways if I even get there cause I can only go so big with a cam in Cali.

 

4.8L connecting rods are most definatley a different length. 6.240" vs. the 5.3's 6.098".

 

Thats what i thought.

I also thought since the 5.3 pistons didnt push out of the block as much, if at all, compared to the 4.8?

 

so would the length difference explain why 4.8 protrudes from the cylinder wall? If that is the case and the 4.8s would fit then I would be fine with the 5.3 rods.

 

maybe i dont know for sure.

 

Neither of these engines have pistons that come out of the hole. And if they do, then its minimal, under .010". Given the factory gasket thickness and the amount of rod stretch I'd say they are pretty close to zero decked. If not then the piston would hit the head.

Where did you get the data on the compression height of the 4.8 and 5.3 piston?

 

Stock 5.3 pistons come out of the hole .007"

 

Yep, I measured mine at .008 out of the hole when I had the heads off.

 

Ok, so it is under .010", but if both pistons have the same CH, then it should be an easy swap as long as you keep your 5.3 rods. As for calculating the CR, you need to get the volume of the dish in the piston. If you're feeling ambitious, you could back calculate to get it since you know everything else like head cc's, gasket thickness, bore etc. Once you get the dish just eliminate from the equation and you'll get the theoretical CR with the 4.8's flat tops.

 

you'll be under 12:1 and good to go
LPE GT2-5 cam, lt's, fast intake and you should be around 380 with the 5.3

Honestly though if your going through all the trouble of completely disassembling the motor save for a stroker kit in the end you'll be thankful. Thats why everyone says go with the 6.0 its alot easier to make power with more cubes at lower rpm(smallercam).