That magnum you speak of is a q trim with the bigger 67.5 or 68 mm turbine exducer. On my 6.0 it felt out of steam at 12-13psi as well. But on a 5.3 it will go up several more psi and still make power apparently. That little 3" down pipe isn't helping either. But anyway I say it's about done for. Time for a 75mm exducer turbo. (83/75 Borg) or the 87-81mm turbine

 

Or twin 62's with twin 3" down pipes and all the way back......

 

I wonder if its time to clean the intercooler. I've never had oil in the turbo even though my crank vents to there. But when I took the filter tube off the Inlet to swap motors it was covered in oil. Odly the motor, for the first time ever, had also used a quart of oil on the trip from here to AR.

 

Hpt guy look at my other thread please. https://www.performancetrucks.net/fo...7/#post5090799

 

Seat of the pants is hard to say what's going on.
The 3" dp is fine till you get past 650hp-700.
The bov should not be a ls to push open if you have boost on both sides. Unless you have a huge boost difference from one side to the next. Because you also have the spring in there.

The whoosh noise could be a leak, or the suction on the filter, or an exhaust leak. That's only leaking at the hi boost.

 

How about when under WOT and the boost reaches the gate set boost, then it will open to dumb exhaust. Isn't it going to create this sound?? mine does that and I feel it stays flat when it does. Is this normal?

 

Turns out that pid uses max torque table which maxes out at .64 and on high boost I'm maxing out the normal timing table which is 1.24 max. That's why it shows almost no difference.

 

A tc78 on a 6.0 should pull strong to 15-17psi. I had a t76 with the bigger compressor housing but same size exhaust wheel and it died at about 16psi on my 6.0L. I did gain quite a bit going from a 3 inch to 3.5 inch downpipe at that boost level. You also need to keep your rpms below 5,600 with that turbine on a 6.0L over about 10psi. That setup was good enough to run high 10's with a 5,200lb raceweight on street tires.

 

I have rear heat and a/c so not much more than a 3" can fit. Another reason I want twins.