So I recently (11/14) swapped a 6.2L bottom end into my 2008 GMC Sierra Crew Cab. See here for the initial thread I started at the time: https://www.performancetrucks.net/fo...1500-a-533520/

I put some headers on it this past weekend finally and have been tweaking the tune to get things right in the AFR department and have noticed a couple of things.

1) Either I have an exhaust leak after the header install, or headers just really sound incredibly loud under load on these trucks. I can hear a very fast rattling noise almost like a misfire at WOT that drives me a bit batty because I cant figure out what it is. Retorqued header flanges...new gaskets...retightened all clamps....etc. Scanned for KR and misfires and nothing. Truck pulls like crazy, but just makes an annoying noise. I tried multiple times to get video, but the noise doesn't seem to come through.

2) I have not changed the WOT shift points and notice its shifting at like 5400 RPM. Seems incredibly low to me. My GTO shifts at 7K. I guess I never really noticed the stock shift points were so low. I have BTR springs, pushrods, and a Tick cam in it, so I plan on raising this a BUNCH....but....

3) My injectors are at 100% duty cycle with a 12.8:1 AFR at WOT at only 5400 RPM. Guess I'm in the market for some bigger injectors. Anyone know how much HP the stock injectors support? I can prob lean it out some but if you take the generally accepted max of 80% duty cycle into consideration, I'm going to need at least 36 lb/hr injectors just to be able to hit 6500 RPM in this thing.

All in all I am incredibly happy with the results, just want to get that noise issue worked out and get some injectors so I can wind it out a bit.

 

Well, the noise was an exhaust leak. New clamps and some Permatex muffler and exhaust sealant at the joints fixed it. Sounds awesome now.

Bought some LSA injectors for $125 on Ls1tech. Smoking deal. So my injector duty cycle issue will soon be a thing of the past.

Coming right along

 

Glad you found the source of your exhaust leak! I love this swap!
You mention 6.2 bottom end....
What heads and intake do you have on this engine?

 

Still using the stock 5.3 intake manifold and TB with 317 casting cathedral port heads. The heads were cleaned up with a valve job and BTR springs, but otherwise stock. I know how much flak I'll get for THAT little tidbit. LOL.

Realistically, this was going to be a very mild build from the beginning and I wanted it to be 87 octane friendly since it is a DD. Didn't want to spend the cash for rectangle port heads/intake. The short block only cost me $1500, then the cost of some lifters, cam, pushrods, and timing set. With heads and all, I probably have $2500 in the swap. I just made sure the cam would compliment the heads and went with it...

I'm a bit irritated with that exhaust leak right now. After I posted the above, we drove around town a bit, and by the time we got home, it was leaking again. Going to try a couple more tricks I read about like aluminum foil wrapped around the joint and maybe a stepped style band clamp. If that doesn't do it, I'll weld the damn things on. I hate exhaust leaks.

 

You'll get no flack from me! I think you've got a great driver for not a lot of coin.
Enjoy!