BUT the dish in the 5.3 pistons let you run rediculas lift without having to fly-cut the piston.

 

You guys are totally overlooking the most important measurement on the piston itself. The distance between the wrist pin centerline and the surface (deck) of the piston. If you put a 4.8 piston in a 5.3 liter you would lose compression because the rod length is different. 4.8's have a longer rod and a shorter pin-piston deck height. If you put a 5.3 liter piston in a 4.8 it would come out the top of the bore. Good theory but will not work.

 

Doh I thought this was going to be a good upgrade.

 

Same block w/ a difference in stroke of .354. The rods in a 4.8 are longer? How much?

 

I said this a while back, but was told that the compression height of a 4.8 piston is the same as a 5.3 piston.

The comp ratio i get is 10.6:1, based on a stock 61cc head, no piston dish, stock .054" thick head gasket with 3.78" bore, 3.622" stroke, and the piston .008" out of the hole at TDC.

 

The 4.8L has a 6.278" long rod where the 5.3 has a 6.098" long rod. That means it's a .18" difference in wrist pin to piston deck height. I don't have a clue as to how far in/out of the hole a stock piston on a 5.3 is. You may be able to get by with this, however when building big blocks a lot of guys off the bat want to put 454 pistons in a 427 since they have the same bore, however this will not work because it's a .25" stroke difference and they use the same length rod. Thus needing a COMPLETELY different wrist pin to deck height.

 

Everyone is on the right track just hasn't done all the math. The effective rod lenght and pin height have to be considered with the stroke divided in half. Or at least hasn't posted it anyhow.

3.622/2=1.811
3.268/2=1.634

1.811-1.634=.177

Differences in rod length:

6.278-6.098=.180

The difference between overall piston height would be .003" which is the thickness of a hair. The 4.8 flat top would work fine in a 5.3 and would yield a compression of approx 10.38:1 as stated above. hope this helps. GM did the same thing when they produced the 400 sb back in 1970. Even though it required a larger bore piston they still kept the same pin height as the 350 but used a shorter rod in the 400. Go figure. It must cust more in production to change the pin height in the piston than to manufacture a new rod.

 

So, swapping piston heads off a 4.8 into my 5.3 will work?...giving me a 10.38:1 compression ratio sweet... I will add it to my "To do List."

I was thinking...how much will it affect Piston to Valve clearance? (Im going with a 220/220 .581 .581 112 cam)

 

It shouldnt change. The distance of the valve relief to the head would be the same as a 5.3. A stock 5.3 & 4.8 cam has similar lift if i'm not mistaken.

 

Yeah, they use the same cam.

191/190 .457/.466 114 '00up 4.8/5.3s
191/190 .457/.466 115.5 for the '99s

Sweet.