So I was doing some research today and found that the 1999 5.3L motors had 15 less hp than the 2000 5.3L motors (270hp vs 285hp). Does anybody know why there is a difference?

I'm swapping my 280,000mi 2000 5.3 out for a 18,000mi 1999 5.3. Its gonna **** me off if the new motor is gonna drop my power!

 

off hand i know that 2000+ have larger injectors and better tuning. Possibly even a slightly larger cam.

 

Damn!! I wish I would have known that BEFORE I swapped over the '99 injectors to my old manifold lol

 

You're not the first person thats done that, and you won't be the last.

 

with that much of a mileage difference, i'll bet the 99's making more power. injectors ain't that hard to swap - put the 00s back in

 

my 99 is a freaking turd as well,but i would speculate that the cam is retarded from the factory....
why do i assume this?
my 03 made 250hp and would walk all over my 99
my 99 made 260hp at the top of the "power band"
so do yourself a favor,install a cam, upgrade injectors and put it in a new fuel pump,im pretty sure the 99 pump is on the verge of its death soon.
basic bolt-ons of coarse.

 

I believe that the 99 cam is on a 115lsa vs 114 for 00, as well as the injector and tuning differences...

 

Well I don't have the $$$ for the cam swap right now. The engine swap is being rushed since I just found out I'm moving from FL to CA in a month. I do have a 02 5.3 I can rob the injectors from though!

 

man that drive from fl to ca will 4 sure break in that 99 5.3L ! what part of ca are you moving to ?

 

FWIW I've noticed a difference in stock main spark timing tables pre 2004 vs 2004 + on the 4.8.