geeteego

iTrader: (1)

It's hard to put the full picture in text...the falloff was ocurring when metering the boost from the dash-mounted pod.

When the boost was metered at the turbo, there was no dropoff at all.

The old setup on another identical car I would not have believed if I hadn't seen it myself.

JAvenger007

iTrader: (9)

Well that tells you the turbo is making boost, but obviously the leak is in the charge piping. Its not going to tell you anything until you hook that WG to the brake booster and monitor it.

1320

iTrader: (6)

I use a leak down gauge and plumbing lug. Some pvc, and some couplers and you can adapt to almost any turbo, then plug the exhuast. I always find leaks even on "good" cars. Your exhuast housing sounds like a .81 (not 91), which is fine. I run a .68 on a 72 and previously did on a p trim 76, on a 346 stock engine, it works fine. It run 10 -14 psi on 91 octane.

look for a leak, raise the boost, make sure the bov does not open under boost, start at about 11 degrees timing then tune from their (wot)

Pro Stock John

iTrader: (34)

Nicely summarized, if that is what Tom (onfire) is saying. Easy enough to try right?

geeteego

iTrader: (1)

1320, I bought this kit used from another guy with an 04. I'm an idiot when it comes to turbos, so I have to go by what I get from the tuner, LSxGTO and here. The guy that had the turbo before me says it is a .91 backhousing. The A/R # on the fan housing says .70.

I'm certain the stock 346 with that cam moves enough air to justify the 76, as discussed. I do believe now that there is significant loss between the a$$ end of the car and the intake (The downside of remote-mounted turbos...but I have seen them make GOBS of USABLE power).

I will try the system pressure test. It seems like a fail-safe way to know where the leaks are (everything I have read tells me there are leaks somewhere...TB, etc)

PSJ, I can't think of a more simple way. Beats hell out of pulling the timing cover and taking the whole mess apart.

I'll fill y'all in when I get it sorted out. Thanks so much for the sage advice and suggestions.

Zombie

iTrader: (2)

if this car has an intercooler make sure the reference line to the bottom port on the waste gate comes from a manifold source. I had a similar issue until I did this.

antivenom370ci

iTrader: (6)

Your wasegate is probly opening up causing exhaust to bypass the turbo. Just curious why would you waste your time with running 4 pounds of boost when you Have all the stuff to run at least a min of 6-8 it just sounds like a waste of precous dyno time. But I would check all the basics, compression test, Test fuel pressure, spray for unmetered air with break clean NOT carb clean rubber gaskets don't always like it. If worst comes to worse degree the cam or at least check the marks. I have seen several mechanics **** up It is very easy to do when your in a hurry.

Mike @ New Era

iTrader: (10)

Another thing to check that I have come across with the STS GTO kits is the snorkel intake (to prevent being exposed to rain water), it is absolutley horrible and will KILL your power , put a filter on the turbo and make a pull on the dyno and you will be amazed at the results .

Mike

geeteego

iTrader: (1)

Zombie, it's connected to a "log" that has multiple connections off the brake booster, manifold, etc...

antivenom, wastegate is functioning normally. Tied a string to it to see if exhaust was coming out under boost...nothing until 4psi. the reason for doing it with 4psi was that I was uncertain what spring was in the WG. The previous owner ran a MBC. Beyond that, I wanted to make sure everything was functioning correctly before I threw 10psi at it.

New Era, no snorkel on the car. Just a big 'ol K&N.

JAvenger007

iTrader: (9)

open up that WG and check the spring.
http://tialsport.com/prod_wg_38.htm
Click their PDF to see the different pressures. You should put the correct spring in there to begin with if its not already in.

mp928

IM reading this with great interest. I just went from the 60-1 turbo to a t-76 turbo and intercooler and went from 492hp to 390hp on my 04 GTO. The car just died at 5k with the 60-1 and now with the .96 ar T76 it dies at 5200. I did 6lbs spring and the 10 lbs spring and still couldn't get it over 400hp. I feel the pain!!!

Mike P

1INSANEGTO

iTrader: (13)

That spring is good for 8psi so why would it open?

1INSANEGTO

iTrader: (13)

Here is what you need to test the system for leaks

BoostJunkie

iTrader: (11)

Try a larger air filter, I had an STS Silverado I was tuning recently that was doing the same thing and the filter fixed it.

Zombie

iTrader: (2)

Do you have good valve springs? Sounds like symptoms of valve float, but it's tough to tell without a dyno graph.

mp928

Thanks, Ill try and get it posted tonight.

Mike P

geeteego

iTrader: (1)

All,

Getting it re-tuned tomorrow with a .8 bar spring. We're going Methanol @ 4psi-up.

There is also a conflict between the old Diablosport program that was in the car and the HP tuners program now in it. Set off a couple VATS codes and for a while the car wouldn't start after the build. So we'll strip it down to the base GM program and rebuild from there after the Diablosport program is pulled.

I think between that and the new spring, things will go just fine. I have new springs and pushrods so my valvetrain should be solid.

Boostjunkie, my air filter is pretty big already...I'll lose ground clearance if I go bigger.