ok i have read a lot of different thoughts on this but got a boat 2002 Avalanche 5.3 Vortec 4x4 706 heads dish pistons. i have a set of 799 heads milled 30 thousands. swapping the 706 for the 799 better flow so im adding flat top pistons { what sorta of compression you think I'm at? } stock truck cam . Question would i need valve relief spots in the pistons with a truck cam stock?

 

As to the original question, that would be a No. The 4.8 used flat-top pistons, 706 heads, and the same cam as the 5.3, and didn't need VRs. The LQ9 used flat-top pistons, heads that located the valves at the same height as the 706 heads, and bigger cam; and didn't need em. You'll be fine.

Your CR will probably be somewhere slightly higher than the L33, which was right around 10.0. So, call it 10.3 as a starting point, more or less.

 

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