Ryhno’svette

I’ve got a question for you experienced LS builders, this is my my first LS rebuild . I’m rebuilding a 2002 5.3 LM7 and I just got it back from the machine shop. He had to bore the block .020 Over and turn the crank .010. So now I’m beginning to buy parts to put it back together. I also bought a 2008 5.3 pretty cheap from marketplace because it had 243 heads on it. So I noticed when I pulled the heads from the gen4 that it had pistons with valve reliefs in them but my gen3 did not. So I’m getting ready to buy new .020 over pistons and i need to know if my new pistons need valve reliefs in them or not? Any advice from you experienced builders I’d really appreciate it so I can build this engine the correct way . Thanks

Fast355

Things get a bit tight with a 2.00" valve and a big cam, the reliefs will give you added PTV clearence. Personally I would use the GenIV rods and piston design. The Gen IVs as well as some later Gen III had full floating wrist pins rather than pressed pins.

In some instances the reliefs will also help unshroud the valve a bit during the overlap period. For added PTV clearence as well as the unshrouding effect since most of my overlap period is with the piston at or near TDC, my SBC 383 has Weisco forged flat tops with 2 deep dished valve reliefs. With only 0.041" between the piston top and bottom of the chamber, a larger than stock 2.02/1.60 valve package, and cylinder head for good quench and a 1.7 rocker for 0.578" lift giving quicker valve lift throughout the curve, it helped with the PTV.

Ryhno’svette

Thanks for the information I appreciate it. Yeah I was thinking about running Gen4 style pistons and rods.