i wouldn't blame it all on the manifold. look how many people push these things with stock manifold. parish 9sec car all stock 5.3l with zo6 cam. there are many more.

 

Disclaimer: The following is JMO. I am no expert, didn't stay at a Holliday Inn Express last night, nor have I ever had a turbo vehicle. I just read a lot and have formed my own opinions. I will not get upset if someone proves me wrong, I am just learning here. With that being said. LOL

I know the truck manifold is not totally to blame, cars are prone to poping #7 too. It's the front inlet design all together that's the problem..... We probably wouldn't have to push the AFR down to mid 11's under boost if the rear cylinders didn't lean out so much. It would be interesting to know what the AFR of each cylinder was. I'd be willing to bet that the rear cylinders are seeing a more lean condition than the front cylinders just due to the flow of air in the manifold. If you richen up enough to keep #7 alive, your front cylinders are most likely way richer than they actually need to be..

 

Anyone have any idea why it would be hitting a wall at 4400 rpm? afr was not changing nor was boost.

 

In order to do on a cyl.- by - cyl. basis, you would have to use more sophisticated( read expensive $$) software than HPT, correct? Like a FAST, Accel, Motec, etc. Then, you could change to compensate the #7, right? Leavin the others alone in the meanwhile.

 

No idea, kinda let my *** start takin' in that last post. haha

 

If u have fragged internal parts, that could limit. If it's ok, somewhere there is a bottleneck. Back when the TPI's were out, they ran out of breathe @ a certain RPM. I'm not gettin into manifold design, yada yada, but it was known GM designed that piece for the 305 rather than retool for the 350. They choked it. Or like a 112 on a 6L. Limits can be found. I'm w/ the others, pull the head. If u don't, & ****'s in pieces, it'll just lead to more damage. At least that way, you'll know what u r up against. Repair, build the snot out of your existing 5.3, or go build a 6L. Pay now or pay later.

 

If #7 were being chocked by the manifold...wouldn't it cause this cylinder to run rich? All cylinders should have the same injector PWM for fueling at any given RPM. FWIW I have spoken to some experienced LS1 mechanics about issues with #7 popping ringlands and they were of the opinion that inadequate coolant flow around #7 is the cause of problems with this cylinder. Not trying to start a pissing match, just trying to throw another probable cause out there. I'm here to be educated and share any and all information concerning this problem. For anyone on the edge and and pushing the limits of this engine, piston #7 has always been a concern.

 

I found a used '05 5.3L with only 12,000 miles on it for $1200 so i might just do that. Would an edelbrock Victor Jr. Ls1 intake (#29085) kill my bottom end a lot?

 

I'm not sure where I could have a bottleneck. Guys put quite a bit of power through these engines and i have twin turbos that are a bit on the big side i think, 3" mandrel bent dual exhaust, no cats, and my intercooler is supposed to be good for 1000hp.

 

The working theory is that the air flow design on the manifold puts more air into #7, but the fuel is calculated by the average of the bank (via o2s). So the average means that #7 is always lean and #1 is always rich.