cannot make over 10 psi of boost

[camcojb]

well, one by one I've handled the little issues of a new car and I'm pretty much down to the final one or two on my list. Since I finished the car it will not make over 9.5-10 psi of boost, in any gear up to 6200 rpm or so.
Here's what I have:
402 LS2 turbo-specific build, ET Performance 245cc heads, PMC sheetmetal intake, Nelson Racing headers, twin T67-76RE Precision ball-bearing turbos with twin 44mm Tial wastegates and single 50mm Tial blow-off valve. The 3.5" in/out intercooler was in the car when I bought it and the old motor could run 15+ psi of boost without issue. I have 3" mandrel bent downpipes and full 3" mandrel-bent exhaust out to the rear of the car.
The wastegates started with 13 pound springs and I run a manual boost controller on top of that. I swapped to 19# springs in the gates and tried with and without the boost controller, no change. I added a boost line to the top of the wastegates directly off the turbos, no change. I shimmed the blowoff so it cannot open, no change. I removed the air filters and then the inlet tubes (3" mandrel-bent) and no change. I pulled the inlet/outlet tubing out of the intercooler to see if there was a rag inside or something stupid, nothing. I swapped from the W2W turbo roller custom cam back to the stock LS2 Z06 camshaft; picked up idle vacuum, but no change in boost.
The turbos have .81 exhaust housings, but spool fine. Even if those were too big once it made boost it should go nuts. My laptop shows 160-165 kpa which matches my boost gauge at 9.5-10 psi, so I believe the boost reading is correct. The car runs great, but I'd really like to be able to make more boost. I am out of ideas at this point. I've spoken with Precision and Tial, no answers.
The boost comes up fine and then it's like it hits a wall and stops at 10 psi; that's why I thought the gates or blowoff were opening, but apparently not (I know the blowoff isn't as it's shimmed shut). The only other thing I can think to do is add a boost gauge off one of the turbos before the intercooler just to see what it shows. Does anyone have any other ideas?
Jody
https://static1.pt-content.com/images/pt/2008/09/ls2engine-1.jpg

[shmoov69]

Sounds like a leak to me. Surely the exhaust isn't too small and not letting it breathe?.. What is the EGT's? Does it nose over when it gets to 10? Like it wants to go more, or does it just kind of "run out"?
Hmmmm......?

[camcojb]

Sounds like a leak to me. Surely the exhaust isn't too small and not letting it breathe?.. What is the EGT's? Does it nose over when it gets to 10? Like it wants to go more, or does it just kind of "run out"?
Hmmmm......?

it's a 3" mandrel bent system that was on the car when I bought it. It actually acts just like the boost controller is set at 10 psi; it goes smoothly up to there and then stays, engine doesn't lay down.

It actually runs pretty hard, probably 550-600 rwhp. It's just that it has so much more potential if I could get it to make 15-16 psi like it was built for.

It does show 15-16 psi of boost right off the turbo before the intercooler, so my next step is to remove the intercooler and bypass it to see what if anything changes. Bummer is it's quite a job to get that out of there; bumper, grill, supports, etc all have to be removed first.

Jody

[GBodyGMachine]

I would guess there is something plumbed wrong. Like the reference line going to the waste gates. Where do they get their boost signal from?
JEff

[Hawaiian turbo]

How do you know its 15# right after the turbo's? And where are you getting the boost references from(laptop,gauge) same place?

If you can get supplied pressure(CO2, compressed air) to the top of the gates, about 15 to 20 #, and see if that raises the boost. Just don't over boost unless your running race gfas or Alky injection. Sounds like the gates are opening too soon.I've had rated springs NOT at the rated spec before.

[camcojb]

I would guess there is something plumbed wrong. Like the reference line going to the waste gates. Where do they get their boost signal from?
JEff

from the outlet housing of the turbo to the top of the wastegate on each side. The boost controller goes to the sides of the wastegates, gets it's reference from the intake plenum.

Jody

[camcojb]

How do you know its 15# right after the turbo's? And where are you getting the boost references from(laptop,gauge) same place?

If you can get supplied pressure(CO2, compressed air) to the top of the gates, about 15 to 20 #, and see if that raises the boost. Just don't over boost unless your running race gfas or Alky injection. Sounds like the gates are opening too soon.I've had rated springs NOT at the rated spec before.

I plugged into the outlet housing of the turbo on the drivers side, and hooked a boost gauge to it. I started with 13# springs, then added a second dual spring for another 6#'s, so it shouldn't open until 19#'s. Plus boost on top of the valves, and a manual boost controller turned all the way up. But I've tried it with all the reference lines disconnected also, same boost.

[camcojb]

well, I found 2 psi. The nice thing (for me) about getting older is that I can laugh at myself now. In my younger days I'd never post on a board about some stupid thing I'd done. :angel:
I built a plug and test fitting to pressurize the intake manifold. Hooked it up to 25 psi and found a big leak. In the throttle body there was (what I thought) a blind hole out the passenger side. I'd looked at it when I installed it, and it didn't go anywhere. Well, it does, goes out in front of the throttle blade. Not under vacuum, but a direct leak under boost. Thing is, you look straight at it and it looks like a blind hole; change the angle and you can just see a passage on the bottom side joining it. I tapped it for 1/8" NPT as you see here:
https://static1.pt-content.com/images/pt/2008/09/100_0354-1.jpg
That now gets me to 12 psi at the intake. I can also hear some slight leakage at the intake o-rings. Very small amount, but who knows how much that may add up to total. Trying to find a stock LS2 intake to try. Don't want to spend a ton of money as I'll never use it permanently, but it will bolt right on and fit my 90mm throttle body. It's also what I had on this engine in the GTO, and had no boost leakage. If someone has one let me know.

[Hawaiian turbo]

Glad to hear you found the problem. I also would have not posted the stupid things I've done when younger, but hopefully other's will learn from our mistakes.:cheers:

[camcojb]

Glad to hear you found the problem. I also would have not posted the stupid things I've done when younger, but hopefully other's will learn from our mistakes.:cheers:

thanks. I found one problem, but not THE problem. Still should be making 18+ psi at the current settings, so still looking.

Jody

[Hawaiian turbo]

Even after plugging the TB, you still can't build boost running the car , or are you using the the pressure tester you made?

[camcojb]

Even after plugging the TB, you still can't build boost running the car , or are you using the the pressure tester you made?

I plugged it and took it for a test run. It now makes 12 psi, so there's still some stuff going on. If that little hole is 2 psi, and I can hear leaking from the intake o-rings, then maybe there is another 2+ psi there. That's why I'm getting a stock intake to try.

Jody

[shmoov69]

Cool, it seemed like a leak to me since it still ran hard and just stopped. Did you pressureize the intercooler too?

[camcojb]

Cool, it seemed like a leak to me since it still ran hard and just stopped. Did you pressureize the intercooler too?

no, might try that next. I know there's some leakage at the intake o-rings, but it may not be anything significant. Swapping intakes next.

[GBodyGMachine]

Intake O-Rings?

[multiplex]

i guess its slightly more difficult with two turbos, but i would try to pressurize the system right were the turbos attach to the piping.

i did this on my setup and found some pretty massive leaks at the intercooler that i never knew were there, plus lots of smaller other leaks.

what type of boost controller are you running?

if you have a 19# spring i would bypass all of the controllers and plumb directly from the outlet side of the turbo to the bottom side of the wastegate. Leave the top side open.

[camcojb]

well, I found the reason I'm having a problem with the boost levels. The intercooler was not built for this power level, and simply won't support my airflow needs.
I have a 24" wide by 12" tall and 3" thick core with side tanks. So the unit has air flowing horizontally, which is very restrictive with that config of a core. If I could swap to a vertical unit, the same size core would be much more efficient as it'd be 24" wide and only 12" long. Unfortunately that won't fit without a complete re-doing of the front end of the car. According to Bell my intercooler config and size is only real efficient up to 400 hp or so............. :(
The tech at Bell guessed the exact boost drop of my combo just off the intercooler specs and boost level into the core; I didn't have to tell him. My plan is to bypass the intercooler for now and plumb the turbos directly into the throttle body and run water injection as I have in the past. It may not be ideal but it definitely works and I'm sure the power difference will be huge.
Thanks for all the help, it is much appreciated.
Jody

[shmoov69]

Sweet.....
Sucks.....
LOL!

Glad you figured it out!