There's no problem running the 5.3L heads on a 5.7 bore size. TONS of LS1s have some mildly ported 5.3 heads (with bigger valves) and put down very solid numbers with them. When I go to a 5.7 (this year) I'll either go to some 243's or have my 706 truck heads worked over. Lost of aftermarket porters use the 5.3 castings with great results.

 

The engines are internally balanced therefore the 5.3 crank and the 5.7 crank each have different part numbers though they have the same stroke. The 5.3 heads on a 5.7 will raise the compression which in turn would raise the power, but, also, raised the possibility of detonation. I would recommend reading, "How to Build High-Performance Chevy LS1/LS6 V-8s". It covers the Gen III 4.8 through the 6.0 Vortec truck engines. In "Car Craft" magazine, April 08 issue, (I think), there is a very good article on a junk yard 5.3 with just a cam change, running a carb putting out over 400 hp.

 

you can add me to the 5.7 iron block list I just need to find a good priced piston.

 

Thats not that big of a feat to be honest... I'm sure thats rated at the crank, not the wheels... 400 RWHP out of a 5.3 with no power adder is the white elephant though...

 

No kidding. Haha. That's like 460hp at the flywheel. It's a task for LS6's to do that, let alone a 5.3L.

 

go look in the dyno section at LA TOMBSTONE's post to see a white elephant

 

and?? numbers... just numbers...

I had a dyno tell me that I was making over 340/380 BEFORE I did a cam and a good tune... you can make any dyno spit out any number you want. Its a tuning tool...not a dick measuring-tape...

Props to him for the numbers.... I suppose... but 400 with the mods they have listed there isnt going to happen... "Junkyard 5.3 with a cam change and carb" isnt going to cut it, not for 400 REAL Hp