I bought a motor over ebay about nine months ago to build up. Its done and in the truck. I was told that it was a 5.3, but after my recent trip to the dyno, i am beginning to believe elsewise. Heres a list of my mods.

Ported and polished heads(stockk valve size)
MTI Hammer cam 222/222 .566/.566 112lsa
Asp pulleys
Long tube headers no cats
ported throttle body and MAF sensor
Built 4l60e 3200 stall convertor

A/F ratio ranges from 13:1-13:4 throughout the pull.
I pulled it up to 6700 rpms and my maximum numbers i could pull out of the thing was 312hp and 315tq! What the hell is going on?!?
How can i tell if this motor is indeed a 5.3 or a 4.8?

 

Wouldn't the stamped block numbers tell you?

EDIT: or do both the 5.3 and 4.8 use the same block, I don't remember.

 

Yeah they do use the same block. It has both numbers on it

 

What were you hoping for? My 5.3 Tahoe made 236hp/284tq with a tune and cat back exhaust. You ported and polished and added a cam/pulley and got another 75+ hp. Doesn't sound too far off but I'm no expert.

 

You can check the displacement without removing anything but the spark plug. It requires special tools, but that's one route. They do it all the time in racing, so if you know some one in tech that helps.

The other would be to find the vehicle's VIN that the engine came out of. That would tell you a lot as well. I'm not sure where it is on the block though.

BTW, those #'s aren't that bad. Dynojet? 3rd gear? Locked TC?

 

Do you have any track times..? My friend's truck(rgvsierra) made 334 rwhp and 319 tq with a smaller cam and stock heads. Those numbers seem a little off to me. What were the weather conditions?

 

pull a spark plug-rotate till piston is at TDC on that hole-shine light in if you see a dished piston you have a 5.3 it will look like a cross sort of shape, if its flat you have a 4.8

there are other differences but I dont feel like pulling the book out and this way should be easy. Those numbers do seems slightly low also I have that exact same cam (but lpe), 5.3 and a 2800-3000 stall. Where is your power band at, when do you first notice it start to pull?

 

There's no mention of the PCM being tuned for your modifications. Has this been done? If not, hp and tq have been left on the table.

 

I actually think those numbers sound pretty good. My 5.3 made 222/240 stock. Yours is about 90/70 more than mine. Thats pretty good for what you've got. Did you dyno before the swap?

 

Dynojet dyno in third gear with the torque convertor unlocked.