I would expect it to be in a range over 12:1 compression. The stock 5.3 pistons are dished the 6.0 you would put them on would have flat tops, plus the cc diameter is smaller than the bore. Then if you have any aftermarket cam I would really worry about valve to piston clearance. By the time a machine shop reworked the 5.3 heads for larger valves, seates and expanded the cc to match the bore size it would be expensive.
But I dont know of anyone thats done it and it would be interesting to hear about it, Im shore you could get them to flow really well with an aggressive port job and they would probably have alot of velocity.
Hmmm...

What are the major differences between the 5.3 and 6.0 heads obviously cc size and larger ports.
Are there any other major differences? Valve angles, location of valves, spark plugs, injectors?

 

LQ4 doesnt have flat tops. A worked set of 317's would flow a lot better than 5.3 heads would. 317's have a bigger int valve too. Injectors are 24.7lb/hr just like a 5.3.

 

Are you sure the 6.0 heads have bigger valves ?

 

Exh is the same, intakes are different. Last I checked the 5.3 was 1.89 and 1.55. 6.0's are 2.0 and 1.55. I should have worded my sentence differently on my last post.

 

flow isnt everything hogged out heads will flow great and not perform, hell you could stick a 3" pipe on there and flow alot

tea heads from thier website

5.3 stage 3 intake-319.6 exhaust-276
$1,679.80

6.0 stage 3 intake-334.0 exhaust-277.1
$2,262.45

The valves are slightly larger on the 6.0 intake side .003 the exhaust is the same. For the money Id take the 5.3 and the velocity is probably better why do you think the f body guys use them and not milled 6.0 heads

 

Because I dont think you can safely mill enough off of the 6.0 heads to get a good usable CR. LS1 has same port size as the 5.3 head. The 6.0/LS6 is a superior cast.

 

I didn't rip you off. When I sold them to you the going rate was at ~$200. Just like Randy said, that's how much I bought mine for. I'm not one to screw anyone so please don't try to give me a bad name.

 

Exactly as put, WORKED OVER heads. Stock vs stock, no way I would do the swap. Again, the basic head castings are all the same for the GenIII motors. You can shave/remove material much easier than adding it. This is why the aftermarket guys use the 4.8/5.3 ( #862 ) truck heads as a starting point over the larger CC LS1 and LQ4/9 ( #241, 243, 853, and 317 ).
The valves are smaller in the #862 castings due to the tighter bore diameter ( 3.78" vs 3.898" and 4.00" ). You would get "valve shielding" with the smaller bores and cause reduced airflow and turbulence when the valves get too close to the cylinder walls.

 

I was kind of joking.

 

with the exception of the intake valve i don't believe there is any real change the the port causing a restriction. if you check around you'll find the 5.3 heads are a pretty good gain on the 5.7L applications. i think a 5.3L head on a 6.0L with the correct intake valve machined in would make more power than the 6.0L head let alone with some port work. it's not worth it as a straight forward swap, but well worth it with some minor work.