I have a 5.3L LM7 motor and it has the leaky 706 heads. Picked up a set of 243s off a 05' GTO. Plan is to mill them down to 59 or 60cc chambers (.030" IIRC) and just bolt them on using the yellow springs the 243s come with and the stock 5.3L LM7 cam and stock truck intake and TB.

That should bump compression just slightly and gain a few hp while solving my coolant issue. Anything else I should look out for?

 

What exactly do you mean by "leaky 706's"

 

I assume he's talking about head cracks and loss of coolant. That's what prompted my LQ4 swap.

 

Some of the earlier 706 heads were ****.I have the newer batch of 706 heads and they are fine!Thats what I've been told.Could be wrong though! Mike

 

You are correct, I have 5 5.3 liters at home that were pulled from a GM dealer because of faulty casted 706 heads...

 

I have not verified that my heads are actually leaking but there was a smell of coolant in the exhaust. I added 3 cooling system tablets to the coolant and let it circulate and that all but took care of the problem. It isn't using much coolant at all, but I figure with some 243s laying around from another project...a quick mill and valvejob will give me a better head to use when I pull these off. At that point I will verify if and where the 706s have a problem. FWIW... my truck is an 06 silverado with an LM7. So I would assume these are the later 706 heads. :dunno:

Mainly just wanted to know if milling .030-.035" off the 243s would put me in the correct range. I'd like to bump the compression up just slightly from the 9.5:1 that the stock heads give at 61ccs. The 243s are 64.5ccs and it is roughly .007 per cc so a .035 mill should put me at 59.5ccs and raise the compression up to 9.7:1 or so.