I am looking at another engine and trying to figure out if this is a 5.3 or 4.8.What will identify witch one it is?Thanks,Mark

 

Search!
Only way to tell is crank and rod casting numbers. Not sure on what the numbers are(search)

Also 4.8 has flat tops, 5.3 has dished pistons.

 

If you dont have the donor truck there to inspect, pulling the pan is the easiest way to determine for sure 4.8 or 5.3

I tried to measure stroke with a piece of wire to determine if my engine was 4.8/5.3 and couldnt get a consistent measure. Had to pull the pan anyways to swap to Fbody and checked the numbers then

 

There's enough of these sitting in junk yards in wrecked trucks that I'd say you're best off just getting one that way. Then you can just check the VIN.

 

As common as they are, Ive still never seen one on any of the local yards. All private sellers or regional salvage

 

Remove a spark plug place cylinder at TDC and look in the cylinder with a flash light. I also scrape the carbon off the top with a wooden dowel rod makes IDing it easier. Its pretty easy to see the differance. The 4.8L will be flat and 5.3L will be dished.

Now the newer 07 GMT900 Gen IV's are all flat tops now. Also some Gen III HO 5.3L had flat tops as well. These are easily ID as they have the 799 or 243 heads!

Really only way to ID the newer Gen IV ones is via the VIN or pull the pan.