geeteego

iTrader: (1)

OK, long and short of it:

BEFORE
2004 GTO LS1
Prior Dyno: SLP UDP, DiabloSport tune, SLP catted LT's, Bassani catback, K&N CAI
338rwhp, 347rwtq

AFTER
Same car, same dyno: STS GT76 turbo with tial 38mm wastegate and 4# spring (no controller), FMIC, DevilsOwn Methanol injection (2-nozzle), Comp cams 116LSA 228/235 cam, SLP UDP, HPTuners 2bar MAP SD tune, Kenne Bell BAP, Walbro 255 intank, Nasty Performance fuel rails, 60# injectors, stock manifolds with JBA midpipe.

360rwhp, 389rwtq.

WTF happened? Piping on the turbo (hot and cold side) is solid, no leaks. Turbo spools, but "feels lazy" to tuner. Car revs pretty slowly, and looking at the dyno curves, 0-4000rpm makes 20hp/40lb-ft less than baseline as above. 4000-up car starts to act like a turbo's there, but we all know that a big cam and turbo on a 346ci motor should be 80hp north even at 4psi.

The car this setup was on previously, with a GT67 turbo, made 533 to the wheels at 7.5psi.

What's wrong here? Any and all input will be taken to heart and checked.

Thanks!!!
-Ronnie

fenix999

iTrader: (17)

WTF!?, yea something seriously wrong there i wouldnt know what to tell you unless i saw the car or knew what exactly was done to the car mechanically...as in who did the install and maybe they missed something easy. As far as numbers go, the only way that would happen and you only gain 20hp is if you had the biggest boost leak in the entire world and you didnt know it. Maybe its in a weird spot b/c dam thats a BIG difference...Just curious- What size are the headers and exhaust pipes running up to the turbo?? hope you get this figured out man!

geeteego

iTrader: (1)

Everything done to the car pertaining to the motor is listed. Exhaust is factory manifolds connected to JBA catless mids, connected to the turbo piping. I don't see a boost leak anywhere...

Saleen91

If you're running a 4# spring did you see 4# of boost?

If so, get a boost controller and turn the boost up.

geeteego

iTrader: (1)

I don't want to turn the boost up until I find out why a large turbo (even at 4psi) and a camshaft gave me 22rwhp.

It saw 4psi of boost @ the turbo, but up front (dash gauge) spiked to 4psi and dropped off pretty quickly (I am assuming opening of the wastegate).

All parts professionally installed.

Saleen91

What's the A/R on the turbine housing? My guess is that with such low boost your motor is dealing with the exhaust restriction to the point that it's hurting the dyno numbers until your turbo spools and starts making some boost.

I know my motor is a total dog on low boost, but turn up the boost some and it totally changes.

geeteego

iTrader: (1)

That sounds more reasonable...it's a .70 A/R

EDIT: .91 backhousing.

ALLBOTTLE

iTrader: (13)

t3 or t4 flange?

Regardless that is tiny for a 76mm.... you shouldn't have anything smaller than an .80 a 96 would be best.

1320

iTrader: (6)

well thats a problem.....4 psi @ the turbo.....measure at the intake manifold. and why would it fall off if the waistgate opens? Its job is to maintain a boost pressure. Your not talking about a blow off valve are you?

4 psi? intercooled? water/ meth? timing? Did you pressure check the system or are you assuming no leaks cause all the clamps are tight?

geeteego

iTrader: (1)

T4.

BOV, sorry. Intercooled as described, DevilsOwn meth, but not until 10psi.

No pressure test. Just checking clamps, and as I read, that's not a great way to tell.

RW99

Somebody suggested to me once, and I think it's a great idea, to fab up a couple of end caps for your pressure side from PVC and install a fitting on one of them that you can hook up a compressor to. Set the compressor to 20 psi and you'll find your leaks for sure.

As previously mentioned, that A/R sounds all wrong for a T76. Any chance you can get your hands on the previous T67 to swap in... just to confirm that your problem is/isn't the turbo?

Patrick G

iTrader: (14)

Moved from Advanced Tech section.

Pro Stock John

iTrader: (34)

You should make 350-370rwhp just n/a, so maybe you have boost leaks.

geeteego

iTrader: (1)

RW, great idea, and the backhousing is indeed a .91.

Patrick, thanks. Originally posted in wrong section like a true n00b.

PSJ, to your first comment, agreed. That's why I'm here. Could be a boost leak.

Any chance the cam could be a tooth off, not throw codes, and cause the whole deal to act lazy like this?

RealQuick

iTrader: (14)

I wouldnt even think along those lines. You need to figure out why boost jumps to 4 and then drops off back to what? Back to N/A (0 psi)? Thats the problem you need to sort out.

RealQuick

iTrader: (14)

BTW, where does the BOV reference line go to on your setup (before the TB or after)?

onfire

iTrader: (17)

no boost in the manifold equals no power. 4 psi gate spring is too small....after the pressure drop from the piping and ic you might have 1 to 2 psi left....not worth tuning....put an 8 lb sping in the gate, make sure the meth is off and hopefully you'll see around 6 psi in the manifold after all the sts piping....then start the tune...with an ic you don't need meth until you go over 10 psi

geeteego

iTrader: (1)

OK, good. I knew it shouldn't the problem, but I had to ask. The guy that put it together is top-notch and has done 100's of LS-based cars.


BOV reference is after the tb...plugged into a "log" with other vacuum lines into it behind the fuel rails.

geeteego

iTrader: (1)

Meth isn't set to hit until 10psi.

The riddle is becoming clearer...so in essence I have a big, noisy exhaust restriction until I put a 8# spring in and see some boost to the intake.

JAvenger007

iTrader: (9)

Where is your WG reference? If its referenced off your brake booster then the psi drop from the intercooler wont matter, the WG will still run a full 4psi.
Do boost leak test. Did you say the boost guage is showing 4 then dropping off completely? How is that when it seems to become stronger around 4k rpm?

Where is that T76 most efficient? I still think it should be making 400+ on only 4psi with cam. 533rwhp with T67 and cam is some good #s at 7.5psi.