I just got my 6.0 in. It's an LQ4 I rebuilt. I used stock rotating assy. I got a new set of gmpp 799 headsfrom a guy. It has a truck cam, new ls7 lifters, ls2 trays, the stock pushrods and lifters. It didn't run very well on the way home from my dad's place where I installed it. It makes a noise that comes and goes. Its a fast repetitious hollow sounding thump or I would say it as "booke booke booke" that sounds like its coming from the intake. Any idea what that might be? I'll record it when I can and post it but like I said, it comes and goes. Also, my right catalytic converter was glowing on the way home. wtf is up with that? I'm sure I'll learn more when I can start tuning but I could really use some help figuring out this noise.

 

Sounds like your car is running really rich, this would cause the cat to glow red hot (in conjunction with excess air) . The sound your explaining could be pre-detonation or backfiring in the intake due to the same reasoning...

Try pulling your 02's and see if your car seems to run better in limp mode... Could also be a plugged cat, but I would start by pulling your 02 sensors and see if it drives worse, better or the same.

What all else has been done to this 6.0?

 

It does kind of sound like a backfire into the intake. It will be good if it's just running way too rich. I can fix that if I didn't damage it on the way home.

I didn't do much to the 6.0. Just a basic rebuild. Cleaned up stock pistons, new rings and bearings. I ran across a good deal on a new pair of 799s. I used psi springs. The cam is small. It's a sdpc cam, something like 216 220 on 111. It should be a lot stronger than the 4.8 it's replacing.

 

Here's the noise this morning. This is just at idle, but strangely, I noticed that it didn't accelerate with the engine on my way to work this morning.

 

It's the evap! I didn't hook the hose up to it but it was plugged in so it was trying to purge. Duh!

 

LOL. I was about to say it sounds like air popping like a compressor. Glad you found it.