KILLER-LS1

iTrader: (18)

Guys, it was at the dyno shop all day today trying to get my car tuned. it would never make over 6psi on the wastegate alone, even with a 17lb spring. here is my setup:

408ci
gt91 w/ T4 .96 a/r from forced inductions (he said it flows plenty for my motor)
turbosmart pro-gate 50mm wastegate with 17lbs of spring pressure
AEM boost controller

So we tried every combination of boost controller settings and nothing worked... I was on the phone with turbosmart most of the day, and judging by the tests they had me do, it seems like the WG is fine. we pressure tested the cold side, and there were no leaks. The motor runs great, and is making good power for the boost level that its at. by cranking up the boost controller, we could get the boost into the low teens, but the controller was MAXED OUT.

the only thing left is the turbo... when I got the T4 flange, i noticed that the clearance between the turbine blades and the inside of the wheel was pretty large. I also have the t6 flange and the clearance is MUCH MUCH less. it is a very tight tolerance between the housing and wheel on the T6 housing. I asked jose@forcedinductions about this and he said that the T4 was fine. Im worried that there might be a little too much clearance, causing the turbo to spool slowly. The tuner kept telling me how slow the turbo was spooling.

I remember reading a thread about someone who got a bad exhaust housing, but i cant remember the details. does anyone have any input or advice on this??

gsxr1k2

iTrader: (6)

My first thought is why a t4 on a 408? My spool time with my gt91 is outstanding.

Fbodyjunkie06

iTrader: (10)

banana in the exhaust pipe?

blackmagicturbo

iTrader: (2)

is your b.o.v. holding ? what exhaust? down pipe size etc?

98Camarod

iTrader: (43)

Did you try it without an air filter? What dyno? How much boost are you seeing on the street?

MUSTANGBRKR02

iTrader: (91)

Try removing the boost controller and try running on the gate. Also check all of your vacuum lines to your wastgate/BOV and make sure they are split or soft.

slow67

iTrader: (2)

Also check for exhaust leaks.

KILLER-LS1

iTrader: (18)

Yes, the BOV is holding. It has a 4" downpipe dumped after the k member. It had a 7" long k&n filter on it, and it was a dyno dynamics dyno. It sees 6-7 pounds on the street

eviltwin_1987

iTrader: (18)

Boost leak? Have you ever ran this turbo on a different motor setup?

DrTurbo

iTrader: (3)

That GT91 will easily make more then 6psi...lol. Block the gate and BOV and see what she does. Just becareful cause it will boost to hell and back. The other thing is, I would definitely think about switching later to a T6. A T4 housing will work, but it simply won't flow what a T6 will.

hellbents10

iTrader: (10)

I agree sounds like a boost leak to me. Should make a lot more then 6psi even on a unloaded dyno.

SPRAYED 01

iTrader: (22)

I have the same thing going on. Makes about 8psi off an 11lbs spring,max out the aem controller and I get 11psi. My tuner thinks back pressure on my comp 80/79 with a 1.32ar housing. I'm not sure whats going on.

mr_biscuitz

iTrader: (22)

Mine has seen 22lbs on a 404 with t4 gt91. Theres something else going on cause mine would def make more boost just havent tried. I plan on swithching to the t6 sometime soon.

mr_biscuitz

iTrader: (22)

DR. TURBO you have a pm....

KILLER-LS1

iTrader: (18)

hmm i have the AEM controller too.

I just did a test. I drove the car WITHOUT the boost reference lines hooked up. it made 15lbs until I let off the gas. I talked to turbosmart and they think that there must be a ton of backpressure forcing the valve open. They are going to sell me a bigger spring to help me keep it shut.

Dr. Turbo, does this seem accurate? Im just surprised if thats true because you guys recommended that I get the T4.

gsxr1k2

iTrader: (6)

I run 2.5" piping and a 50mm turbosmart gate with a t6 gt91 and with a 14 spring i can only make 11.9psi. I had to run my eboost up to 30% to achieve 14.5psi.

JAX04

iTrader: (17)

How big is your down pipe if you dont mind me asking? Also, do you have a picture of the merge and where the wastegate comes off at?

SOunds like alot of backpressure.

98Camarod

iTrader: (43)

He said it's a 4" downpipe dumped after the k member

JAX04

iTrader: (17)

Guilty as charged, i dont always read everything or miss something when typing from the phone.

DrTurbo

iTrader: (3)

Lots of people are running the T4 version with those size motors. Also the T4 was recommended cause you must have been space restricted, as we aren't fans of T4's on big motors at all, but sometimes you have no choice. T6 will always get the nod over a T4 any day of the week, but not many folks can fit a 5" downpipe through.