PonchoFan

A friend has an ,04 Avalanche with a 5.3 that's losing a gallon of coolant every 2k. Chevy wants $3300 to replace the heads.
I have a set of LS1 haeds off my '98 TA with PRC Gold springs and new seals.
Wiil they fit and what effect wpuld they have on compression?

SuperSport01LS6

iTrader: (3)

they will fit just fine but you will drop .4 of compression which is nothing really. but you will benifit a little with the bigger valve size on the ls1 head compared to the 5.3. should make for an easy swap

SuperSport01LS6

iTrader: (3)

i forgot only problem is that you have perimeter bolt valve cover..he has center so that wont work at all

JBIRD02

iTrader: (4)

Those heads should fit just fine. You will lose a little compression though. As far as the valve covers go, just swap out to the center bolt style. It will be much cheaper that paying $3300

PonchoFan

Would Cometec .040 gaskets make up for the compression loss and would they require shorter pushrods?

SuperSport01LS6

iTrader: (3)

Yes and yes but I know for a fact that you cant put them on his truck unless you get perimeter valve covers with the perimeter coil pack brackets you cant put his valvecovers on your old heads it just wont work. lookup 98 heads vs 99-02. find pictures and then you will understand a lil better let me know

PonchoFan

Perimeter valve covers not a problem.

Sales2@Texas-speed

iTrader: (5)

That drop in compression is NOT what you want for a DD truck! The 5.3L trucks come off the show-room floor with about 9.5:1 static compression, and that LS1 head is going to bring that even lower like stated. Compression = torque! You need that bottom end and mid-range torque to move that heavy truck!