Forcefed86

iTrader: (4)

Measure the back pressure. Simple peak and hold tire gauge works in a pinch and is dirt cheap. Whats a "T67"? Exhaust housing and wheel diameters?

Patrol402tt

Turbos have been proven on a near identical setup and pull through fine

Back pressure test is next on the list. If there is excess back pressure still need to find the cause, springs, cam timing etc

svslow

The springs are about the same as a PAC 1218.

JoeNova

Cam specs?

Bad Apache

This sure looks like another cam timing thread, unless those springs don't match the provided spec sheet.

Forcefed86

iTrader: (4)

Retarded cam won’t stop it from revving, severely over advanced cam might. I’d think you’d smack the intake valve before getting is so advanced it wouldn’t rev like that though. That would also show up on a compression test I’d think. If the engine spits out some super high cranking compression numbers....

The fact that it will make 20lbs makes me think it isn’t an exhaust restriction. With my exh dump closed it necks my exh system down to 2” I couldn’t make over 5lbs with it closed on a 370.

I’d check the push rod lengths and get a known good spring in there. Was the head milled a lot? What push rod is in it now?

Also I don’t know about those turbos being "proven" with china 60mm compressors and a 58mm exh wheel in a t3 housing. Especially on a stroked 6.0. What are your current cubes? 408?

Those are small exh wheels/housings and compressors for your setup IMO… like WAY too small… and then some. Get a back pressure gauge on there I bet its high.

H.P.Ranch

When you call to get specs on springs be sure to tell them your valve size. I think those heads have the heavier 2.08 intakes 1.60 exhaust manleys.

ls1_chevelle

iTrader: (9)

We will find out once he gets back to use with some backpressure numbers. It should be through the roof if its choking the engine back that much.

OP, can you post pics of the setup??

You say fueling is fine but what MAP sensor is on the engine combo? Is your tuner stumped with this as well?

ss454327

iTrader: (10)

Those springs sound WAY too light...you need some more aggressive springs on there.

gametech

iTrader: (1)

I agree, but with the graph he posted so heavily smoothed, it ruins potentially good data that could more directly point to the issue.

coltboostin

90% chance its valve float, or an ignition timing issue. Just because its good with a light at idle means dog dig for where its at with a given RPM. You could be losing sync, the triggle wheel could be warped, any numebr of things could be fuckering it up.