st215 boost drop

[hldqn]

hey all. ive had a search on the site and asked a few people who know a little about cars but havent had my question answered so thought id pick your brains.

I had been looking at gtt wagins for a while a test drove a couple and only noticed this in one other wagon.

i have a boost gauge and when accelerating the boost goes straight to 1.2 bar at 3000rpm and then tapers off to aorund 0.6 then builds back up as the revs increase, making it back to 1.2 bar around the 5500 mark. the drop seems quite extreme and wierd and i would like to know if anybody else has experienced this or if it is a problem. I have installed one of thoose cheap hks bov coz the stock one was shot and a mate had it lying around. apart from eliminating a rattle it hasnt improved the situation. the is also one of those GO FAST BITS inline taps which i have spent some time slowly adjusting but only plays with the boost peak and doesnt effect the drop.
There is also a wierd rattle that could possibly be the wastegate??? as it coincides with the boost drop.
Maybe someone could drive it at the next wednesday meet and see what they think.

If anybody can help me with this i would much appreciate it.

thanks

[sergei]

Rattle? Does it make it sound like a tractor? Check for black soot around the exhaust manifold. You might have warped manifold.
I say get rid of the taps, restore boost control to factory.
And use at least 95 gas in it....

[hldqn]

true i forgot that they warp manifolds, nah no noticible tractor noise but will check anyway. yeah going to get rid of that gay tap...dont know how to use it anyway. i always use bp 98 around auckland. other than that 95. never 91. thanks for the reply ill check the manifold and post what i find. anybody else got any suggestions?

[rmf55]

surely its the wastegate sticking? there has to be a problem with the actuator or something, or as sergei says, the manifold is leaking pressure out so the pressure getting to spin the turbine fluctuates.

[Santa'sBoostinSleigh]

do a search, fivebob did a post about this a couple of years ago - its common happenings on a GT-T, mine does it to - peaks about 14-15PSI, then tapers back to ~11PSI, then will sometimes climb back up to about 13 depending on load/revs

[hldqn]

cheers for the heads up guys. done a bit more research now and think i know what i gotta do.

[cat007]

cheers for the heads up guys. done a bit more research now and think i know what i gotta do.

yeah - what you have to do is: take the boost tap off!!!

You'll detonate - and grenade your engine in no time....

[AW11 Turbo]

what was the problem here???

i think i have the same problem:
viewtopic.php?t=78957