necrocannibal

iTrader: (5)

Its a 383 car. 317s with brand new springs. 224 .595. 114 cam, not the best I know. Huron Speed kit with a billet 76mm. Heres the graph. Falls on its face at 5500 everytime. Looks good until then and boom, plummet. Anyway here is the graph. Any insight or opinions? Every dyno looks the same.

NoorJ

what springs? Also that is real rich, but not causing your issue

necrocannibal

iTrader: (5)

Brand new Comp 26926-16 shimmed .030. Did this before the spring change. I don't think the a/f is accurate so pay it no mind.

redss82

What 76 turbo specs? Are you hitting your target psi and holding?

necrocannibal

iTrader: (5)

.96ar. Held 15 psi all the way through once hit hit full boost.

NoorJ

what plugs and gap?

necrocannibal

iTrader: (5)

TR6s. Not sure in gap but they were installed by a very reputable shop.

Hank Peabody

iTrader: (2)

383 at 15psi with 75mm exhaust wheel might be very high back pressure, that might be the issue.

Power seems a little low for 15psi, is the timing really low or doing anything weird? Getting knock and pulling timing above 5500 rpm?

necrocannibal

iTrader: (5)

Could this be a cam issue?

necrocannibal

iTrader: (5)

That part I do not know but my shop told me that turbo and that motor would work well, spool quick and make good power. Now you have me wondering. I do have a dyno sheet of 703 at 16 psi but it was a different dyno.

So you think it might be too small of a turbo? The install shop said at 16 psi it was like 3 to 1 back pressure but didn't know why. Maybe the turbo b is too small causing all of this. Hmmm

Hank Peabody

iTrader: (2)

I have a PT7675 that is probably the same size as your turbo on a 6.0. I have LS3 heads but I went from a 220/220 cam to a 224/230 cam and it seems to run a little worse up top, I suspect its back pressure related. I feel like a turbo this size would work better with a small cam like an LS6 but I could be wrong, all speculumation!

necrocannibal

iTrader: (5)

Would a bigger turbo fix this issue? Kind of want to go bigger anyway.

Hank Peabody

iTrader: (2)

And look at Stock48s truck, at one point he had a BW S400 with the same size turbine I think on his 6.0 truck and he made a lot of power/went really fast at a lot of weight, so it might not be completely turbine related. He does run a smaller cam in his stuff to so that might be part of where I am getting my small cam theory for small turbines.

Strange the shop was surprised by 3:1 bp on a tiny turbine on a 383. That shouldn't surprise anyone really.

Confirm its really a 75mm turbine, but .96 kind of points to that.

And its not like its running particularly bad, just doesn't peak very high. We are pretty fickle these days about power....."why am I only making 630whp??" You'd never have heard that 10 years ago

Moter

iTrader: (20)

can you post up a log file?

Kmspeedie

iTrader: (1)

well yea nowadays factory cars get faster n faster so we gotta keep up!!^^
and OP, i feel no doubt you have back pressure problems causing it to poop out

Hank Peabody

iTrader: (2)

My guess is yes. 76mm compressor is fine but needs more turbine, and more cowbell.

necrocannibal

iTrader: (5)

Sorry I don't have that .

necrocannibal

iTrader: (5)

I was told to do camshaft and lifters to fix this. Id gladly put a bigger turbo on it instead.

LILHEMI

needs more turbine for sure.

Hank Peabody

iTrader: (2)

Do a bigger turbo then. If it really is a 75mm turbine (you need to confirm) then no matter what else you do your not going to carry power further than you are now without a bigger turbine. If you have stock pushrods, replace those too, dual springs and shimmed will really push stock pushrods.

Look at dyno graphs for LS1 and 76gts on google and most graphs look like yours. Mine does too. Still runs great but doesn't peak very high on the dyno, nothing wrong with the setup unless you just want more.