Boost fade

[asshanson]

I have a 96 Tsi with a 3" exhaust and an FP T-28 turbo. I run about 18 lbs of boost, but it doesn't hold - it fades to 14 by redline.

I've checked for boost leaks, 99% sure there isn't one. I've changed boost controllers, same thing happens. I actually tried a broken boost controller too and it didn't limit the bost, so it went to 25 almost instantly at 3500 rpm and I let off.

What else can cause this? I assume the T-28 can hold over 18 until redline, so I doubt that's the issue.

Any ideas???

[scheides]

Fill with c16 and unplug the wastegate...see how high it goes!

Ok, don't do this. You could try some sort of electronic boost controller that'd try harder to keep boost high all the way to redline.

[Kracka]

A T28 is more than capable of holding 18psi to 7000 RPM. Do you have a major restriction on your intake track? Really dirty air filter? Stock IC piping? Stock BOV? When doing the boost-leak test, how high have you tested it to?

BTW, unless you have a FMIC on your car you should not be running that much boost on pump gas, especially untuned. Do you have the fuel to support it (pump, injectors, etc.)?

[94talonawd]

List all of your mods please.

[1ViciousGSX]

Look at your complete intake & intercooler system and look for a restriction. What are the measurements of your frontmount?

The reason I say this is because a friend of mine bought my old turbo set-up from me and installed it on his 1g (2.0 w/2g pistons, Comp cams). Made good pump gas power at 18 psi until around 6500rpm, kept loosing power quickly after that. Since I was doing the tuning for him with DSMLink over the internet, I couldn't see his set-up. Fuel was good, 18 psi at the intake all the way to 7500rpm. We kept trying to figure out where the power was going for the longest time. I knew he had a front mount, but I couldn't remember what size. Finally I got him to put a boost gauge on each side of the front mount and make some runs. He found at 18 psi at the intake manifold he had a 1.5-2.0 psi restriction at the intercooler. Meaning his turbo was pumping more boost to keep the intake psi up. No need to look any further. Another front mount is on the way.

[Super Bleeder!!]

but most good front mounts are semi restrictive. the air has to bump into something to transfer the heat.

[CornFed2.4]

what about upgrading the wastegate actuator spring
here the link to Forced Performance website and the page where you will find the info and parts
http://linux.forcedperformance.net/merchant2/merchant.mv?Screen=PROD&Store_Code=FP&Product_Code=WAT28DSM17psi&Category_Code=DSM

[Kracka]

^ If multiple boost controllers aren't working that probably won't help (unless their is something wrong with his current wastegate).

[CornFed2.4]

I dont think the t-28's come with the upgraded wastegate actuator though.So why would that not be it, did you read what it said. Describes his situation to a T

[Kracka]

I doubt his flapper is being forced open by exhaust preasure at only 18 psi with a 3" exhaust. Its possible I suppose, worth a shot if all else fails.