Lack of boost

[totle]

Hi,

My car has lately less boost. I thought it has come and go between 0.8 and 1.0, but not driven the car that active. NOw I have prepared for a DE event, so tested out the car today WOT.

Boost table is set up for 1 bar.
0,7 wastegate spring. Tial wastegate. Now it boost on 0.8-0.9 bar.

My guess is air leakage somewhere, probably wastegate membran.

Any suggestion?

Could it also be boost solenoide?

Will try to increase boots table and see if it I get more boost.

[JFairman]

If you can blow through the bottom pressure line on the wastegate either the diaphram is shot and leaking or the valve guide is worn out. It's difficult or it may be impossible to get parts for the original wastegates so replacing it with a 46mm Tial is the next option.

Around 9 years ago I found an original diaphram for the factory wastegate on the classifieds for around $35. I'm glad I have it in case I ever need it.

I also have a new Chinese Tial copy I never installed and it looks like it's really well made. Especially for only $79. Tial springs fit it too. I put a green Tial spring in it. It even came with a really nicely made chrome plated wastegate tailpipe. I sold the pipe for $50 around 7 years ago.

FWIW, it looks like the website I got it from is still active...
46mm WG Performance Racing Products for International Sales from SSAutochrome Inc.

[dap930]

If your boost control solenoid is plumbed so it vents to atmosphere with no power to it (failsafe mode), disconnect power to it and check boost pressure with just the wastegate spring. If the boost pressure is somewhere in the range you are seeing, then the solenoid valve, wiring(power, fuse) or computer output could be the issue.

[TheRedSlantnose]

Is your intake connected to the throttle via a rubber boot/90-degree elbow? Assuming it is, it may have loosened up somewhere and could be causing a small air leak.

I had that problem at the beginning of the year, only my case was more major; the 90-degree elbow came loose and sprung a leak at the top of the throttle body, causing my car to lose over half of its boost, dropping all the way down to 0.4 bar.

[T77911S]

the elbow usually gets soft and colllapses.

if the diaphragm leaks wont the WG stay closed?

valve guide wore out on my factory WG. i am questioning my tial but everyine says they leak some.

[infraredcalvin]

Originally Posted by T77911S

if the diaphragm leaks wont the WG stay closed?

Which results in an overboost condition...

[totle]

Yes of course, you are right. Failed diaphragm would cause in over boost. My bad

When solenoide has no power, it boost 0,7 as the spring stiffness in the WG

[totle]

Found out why boost was lacking.
My guess was that there was an air leak somewhere.

After inspecting around for broken/cracked hoses, I noticed one screw on the turbo compressor housing was missing. The threads was broken, so decided to remove the housing insert a helocoil.
When removed I also noticed that the silicone seal gasket had blown away.

No wonder there was less boost :-)

[totle]

Or maybe the Garrett GT35r does not have sealing gasket?

[JFairman]

I don't know about the GT35R but I do know the Garret GSX 61 which is built on the Garret TO4Z has no backplate seal like the 3K K27 turbos have.

So... I'm going to guess the GT35R has no big silicone o-ring seal around the backplate like the K27 turbos have.

The current day Garret turbo backplate and compressor cover interface is machined to a much finer degree of precision than the old K27 turbos. No o-ring seal is needed there.

[MikeD930]

Gaskets are not used in turbine/compressor housings on Garrets. Hopefully one missing screw contributed to loss of pressure. Are there any signs of contact between the compressor blades and housing? Also, suggest to check all intake plumbing (condition of hoses and clamps) for leaks.

[dap930]

The GT3582R does in fact have an orange silcone o- ring seal at the compressor housing to backplate, or at least mine does. I screwed mine up adjusting the compressor housing angle when I first put it on the car. I have a new GTX3071R and it does not have a seal between the compressor housing and the backplate. I just used a thin coat of bearing grearing to help seal that area.