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NorCalAnthony · 01-12-2015, 05:38 PM

+1 If you aren't going to be swapping in a cam shaft while you're at it then I can't really see it being worth the trouble or money.

The 243/799 heads are the same castings that were originally used on the LS6/LS2’s engines and were later put on the higher output 5.3’s. The higher output 5.3’s also had the flat top pistons though so if you’re planning on swapping them to your LM7 with the dished pistons then you would need to have them milled around 0.030” to get your compression ratio back up near stock. They are a better flowing head than the 706/862 heads and also have a larger intake valve which is all a big part of why the newer engines make 30-50 HP more than the older ones.

FWIW I have a 5.3 LM7 from a 2000 Yukon XL and will be using a set of milled 243 heads to compliment my new cam shaft. Depending on how many miles your engine has on the clock you may want to replace some other wear and tear items while you have everything exposed. My engine has 146xxx miles on it so I’ll also be replacing the lifters, push rods, valve springs, timing chain, and oil pump along with the bolts and gaskets. If I were swapping the engine without making any changes I wouldn’t bother replacing any of that stuff but since I’ll have everything taken apart anyways I think it’d be silly not to.

01-12-2015, 05:38 PM	#3
NorCalAnthony Registered User Join Date: Jul 2014 Location: Lincoln, CA Posts: 208	Re: ls/lm head question. +1 If you aren't going to be swapping in a cam shaft while you're at it then I can't really see it being worth the trouble or money. The 243/799 heads are the same castings that were originally used on the LS6/LS2’s engines and were later put on the higher output 5.3’s. The higher output 5.3’s also had the flat top pistons though so if you’re planning on swapping them to your LM7 with the dished pistons then you would need to have them milled around 0.030” to get your compression ratio back up near stock. They are a better flowing head than the 706/862 heads and also have a larger intake valve which is all a big part of why the newer engines make 30-50 HP more than the older ones. FWIW I have a 5.3 LM7 from a 2000 Yukon XL and will be using a set of milled 243 heads to compliment my new cam shaft. Depending on how many miles your engine has on the clock you may want to replace some other wear and tear items while you have everything exposed. My engine has 146xxx miles on it so I’ll also be replacing the lifters, push rods, valve springs, timing chain, and oil pump along with the bolts and gaskets. If I were swapping the engine without making any changes I wouldn’t bother replacing any of that stuff but since I’ll have everything taken apart anyways I think it’d be silly not to.