FWIW I had 800 at the wheels with 20 pounds of 93 and methanol on a forged 346 LS6 with stock heads and a stock LS6 manifold. A huge intake isn't all that necessary when you're ramming the air in there....

 

Ls6 intake flows less then truck intake

 

Someone get George the nobel prize...

 

Vortec, its a Magnum 76/65 (or 68, I cant remember).

I understand the intake isn't ideal on top the 4.8l, and that ET will probably increase with a stock intake back on. However, I think we all can agree (maybe) that the intake isn't the issue for the current problem: "more boost, slower ET" as the truck ALREADY went 11.59sec @ 115.9mph on 12-13psi.

Current Game plan:
-Currently rigging up another mechanical boost gauge to see pre-intercooler pressure: See how efficient the intercooler is - should have results tonight.
-I'm heading to the track on Sunday, and will try three new 1->2 and 2->3 shift points (6000, 6300, 6600) and see how ET is affected which should show if the exhaust housing or downpipe is causing some issues.
-If time permits at the track, I'll change the wastegate spring back to the 12lb spring (from the current 15lb spring) with the 11.59sec pass tune, and see I can't replicate a similar time slip.

Future Game plan:
-I will be changing the valve springs to duals, but they'll take a couple days to get here.
-I may do a 4" down pipe but I don't think that's the issue, and neither do you guys it seems...


Anything else?

Thanks again for the help and suggestions!

 

Triple 12 in a 4.8 id try shifting 5700 sad part is thr holley at that rpm isnt doing squat

 

I would argue the intake isnt hurting him either. Once the turbo gets singing the intake becomes less important, especially on a small cube engine. You know this George

I think your downpipe is fine for that turbo. Measuring pre-turbine backpressure would also be telling as well. Willing to bet you are close to 3:1 at your shift.

 

Ill argue as it is....make most power NA and add boost youll always make more power

Dyno that combo NA bet makes less then stock for most of graph


His a 4.8 its down on power as is add that intake and loses all down low...he needs down low

 

Think we have been over this before. The intake is definitely hurting it. I think that turbo and dp should not choke up at that low of psi on a 4.8L but I could be wrong. I think like George said the timing is killing it and 11.1 afr is pig rich for pump gas. Put a methanol kit on there and run 16~17 deg of timing. Springs could be tired but still should be good to 6500 RPM or so with small valves unless they are really jacked. Also look at spark plug gap and if tune is pulling timing for iat, or adding fuel somewhere. Spark plug gap should be around .024'' max. I have been low 10's at 130 mph at 4850 lbs with a 6.0L, stock intake, same camshaft, same springs, TC76/68 turbo, with a 3'' intercooler, and full 3'' dp and muffler, 91 oct with meth inj. I ended up stepping up to a 3.5" DP and picked up a little but was not huge. I know I need to upgrde but Truck still has the little 3'' core intercooler and has been mid 9's at mid 140's mph with it lol.

 

You added boost but took timing away.
That's a trade off isn't it?
No need to back timing off unless seeing knock or issue correct?

"Q" trim is a 68mm wheel.

3" down pipe has seen over 705hp to the ground.
Stage 2 intercooler is an entry cooler.
I don't think you've maxed either out.

There's always room to improve is it cost effective.

 

Results! Although I'm not sure how conclusive they are.

I gapped the plugs to .024. Tapped into the pre-intercooler intake piping and tied that to my regular boost gauge, and plugged the now open port on my vacuum block.

1) Seemed there was a fairly large disparity between the boost gauge and HPT MAP (part throttle acceleration the boost gauge showed 3-5psi whereas HPT showed 80-100kpa). WOT showed ~200 kpa on HPT and 19psi on the mechanical boost gauge. Would it be expected, or is it drastic that the pressure pre-intercooler is 4-5 psi higher than what the intake is seeing? With the 50 degree weather, IATs stayed relatively cool during pulls.

2) Comparing cyl/air and delivered torque through 2nd gear:
Last Week:
cyl/air range: 1.54 g/cyl tapering down to 1.47 g/cyl at 6900rpm (shift point)
delivered torque: 560ftlbs tapering down to 517ftlbs at 6900
Today:
cyl/air range: 1.66 g/cyl tapering down 1.57 g/cyl at 6900
delivered torque: same as last week at the track

3) Recorded HPT boost seemed slightly more stabilized than I've seen it on this psi.
4) Recorded AFR was .1-.2 leaner than typical - meaning the engine is getting more air?

Conclusions (?):
1) May have fixed a boost leak caused by the boost gauge line off of the vacuum block.
2) Engine may be getting a little bit more air, resulting in small power increase.

At the track tomorrow, I'll try different shift points (5700, 6000, 6300, 6600) and see what the differences are. Not sure if I'll get to try and replicate a mid 11 second pass by dropping the boost back to 12-13psi and increasing the timing.