Current set up on my truck:

2004 GMC Sierra 1500
4.8
Huron speed turbo kit and fuel system
E85 and 80 lb injectors
Dual 450 fuel pumps
Truck Norris cam kit (springs, retainers, etc)
Running 16 lbs of boost on this run 15 degrees of timing
AFR's around 11.0-11.2 under boost during the full run

My question is about the fall of on the dyno graph. Some runs, early ones, seem to pull all the way through and have no issues. Initially we were having some timing pulled due to IAT's but on this run I do not believe it did. My thoughts are that I am either having some valve float or too small of an exhaust. My exhaust is the huron speed 3" downpipe, then to the factory cat back which was replaced with an MBRP system. They call that cat back a 3" but ID is actually a 2 3/4". Also the MBRP muffler and another Vibrant muffler.



What are some thoughts?

 

Was this on the same transmission gear?

I normally see RPM on the x-axis, but not an expert on Dyno pulls...

🧐🤔

 

Yeah I don't know why it shows MPH instead of RPM...Truck is a 6 speed swap (T56 out of a GTO). Run was done in 3rd gear opposed to 4th because he was worried about the two piece driveline. Rear gear is a 4.56

 

Do you have the datalog of the runs and was the dyno setup for the 3rd gear pulls?

You didnt mention what size turbo nor what springs you have. "cam kit" doesnt give much info to go off of.

Would really like to see RPMs instead of speed as well.

 

I do not have the data log, I can try to get one driving on the street because you can feel it taper off. I do not know if the dyno was set up as such...

The springs are the BTR Beehive ls6 style springs. And the turbo it has is VSRacing Next Gen Billet 7875 T4 .96 Turbo

 

Boost controller or manual wastage? Got a boost curve graph for that run?

 

I'm thinking the valve springs are part of the issue, they're OK for an N/A setup. But I honestly feel like you need a good dual spring setup with it being turbo. I would inquire with BTR to get their input.

As for back pressure, try dropping the cat back on the dyno and running open down pipe. If it picks up, there's your answer.

My humble opinion, those two things should fix the majority of the issues you're having. Just guessing by MPH, it appears that you're falling off about 1000-1200 RPM early in the curve.

 

Can't make power through 2-3/4" pipe: ----- It's a STRANGLEHOLD, Baby.