JetMech99

iTrader: (3)

So the car was on the rollers today, and the tuner can't make power past 5k, tells me the turbo is too small?? I guess it hits 5k and the boost spikes and fluctuates then he backs out of it..... I wasn't there to see it for myself. It made 510 RWHP at 5200 RPM, but that's all he could spin it to.

So this post isn't here to bash the tuner, I'm just left scratching my head because I know guys here run these turbos. My reason for posting is to brainstorm and come up with a possible OTHER reason it won't make power past 5k. He never said anything about running out of fuel either.

Specs on the car are as follows:
Completely stock long block
M6 trans
80 lb Siemens Flow Matched
Racetronix 255 with the hot wire
Huron Speed non AC kit
Turbonetics TC 76 Hurricane series (68mm turbine, 76mm comp.)
Exhaust is dumped right off the down pipe so no restriction there

So are there ANY ideas on what else besides the turbo that may be causing my issue? Thanks so much in advance guys!!

JetMech99

iTrader: (3)

Could this be possible clutch slippage??

jridenour31

Hard to say without more info. Is boost creep the problem?

JetMech99

iTrader: (3)

He said it jumped from 8 to 12 right before he let off. Basically I am wondering if the turbine is too small for the stock cubes? When I know guys have and still do run these turbos.

Any other info that I can provide?

LT1RAY

iTrader: (21)

What wastegate do you have? How is the vacuum line ran to the WG?

JetMech99

iTrader: (3)

Turbosmart Ultra Gate 38mm. Vac line goes from the pressure side of the turbo housing to a manual boost controller (opened all the way, running on the 7 psi wastegate spring) to the wastegate per Turbosmarts instructions

dudeman

iTrader: (43)

What valve springs?

1fast bird

iTrader: (22)

Sounds to me like valve float also...

That turbo should do better than that before choking.

SPRAYED 01

iTrader: (22)

What springs? Also you can buy a cheap 60psi boost gauge, drill a hole in a o2 sensor bung plug,weld a barb in there. Put it in one of the cross over tubes or merge. This way you can check for high back pressure.

another thing is, do you have the air filter right on the turbo? or do you have a tube or 90 then filter? could the filter setup be shutting close.

LT1RAY

iTrader: (21)

I was thinking that as well.

JetMech99

iTrader: (3)

Stock springs, was hoping they could handle 8-9 psi. And yes, the filter is right on the turbo. 51,000 miles on the engine and springs.

evo462

iTrader: (27)

I made almost 650 on a turbo with that same 68mm wheel but a 1.15 housing and 44mm waste gate. Strong all the way to ~6K. Lots of others have used that exact turbo on LS1's with no issues. I would guess it isn't the turbo.

I am running dual valve springs and 10psi on low boost.

dudeman

iTrader: (43)

put valve springs and pushrods in it then take it back to your tuner.

something like prc double springs.

cory32690

Could fuel pump be getting close being its only single 255

SPRAYED 01

iTrader: (22)

Why would you even tryv to boost it with out springs? Especially with a small turbine and high bp.

itsslow98

iTrader: (18)

Valve springs and itll make plenty of power. Anyone who thinks a 7668 can only make 500hp on a 5.7 probably shouldnt be tuning.

BTW your about maxed out with that fuel pump so I would address that before wasting money on another tune.

oange ss

iTrader: (50)

are you running a boost referenced regulator ? That will help the single pump work better, I have no problem pulling to 6200 rpms on the street (boost starts falling off around 6000 rpms)

MIGHTYMOUSE

iTrader: (59)

agree on fuel pump and springs. no need to get crazy with the springs unless you plan a large cam in the future any reasonable single spring will do a great job for you.

.. and you needed a fuel pump before you started... and a regulator will only help the pump if you lower the fuel pressure.

redtan

iTrader: (5)

If this is purely just a tuner (and had nothing to do with the actual build) then I can see him just putting the blame on the easiest thing he could think of.

If this guy is also your builder that put this setup together then he's ether 1) blaming the turbo so he can sell you a bigger turbo upgrade unecessarily or 2) too lazy to actually look for the problem and just blames the easiest thing he can think of.

Troy5061

iTrader: (19)

Stock springs ain't gonna cut it, you need at least yellow or blue z06 springs. IMO you really should get at least PAC 1218s they're only $120 shipped from ws6store no reason not to. Like the other guys said it could be a fuel pump issue too although ive personally seen a single racetronix 255 make alot more power it seems to be a crap shoot some only make 550rwph and others make alot more.