17psi adj. wastegate dropping pressure above 4500rpm

[HartmanMS]

I have a 95 tsi awd with a t28 Killer turbo and a FP 17psi adj. wastegate. I took it to the track yesterday and the boost builds to 17psi then drops to about 12 by about 6500. I am running a vacuum hose from the turbo outlet nipple to the wastegate directly, until I can get by mbc put back together. Would this, in any way, cause the boost to drop off at higher rpms? Or could I just have a simple boost leak somewhere in the pipes? I was really disappointed with the times, because I got a 1.84 60ft. time, but ended up with a 14.17 @ 93.8 mph with the t28 killer and 3" O2 Elim. turbo-back. A few weeks ago I hit a 14.4 @ 92 mph with the tiny T25 at 15psi no adj. wastegate, with stock exhaust...please help me out!

 

[pneumo]

Did you also get the 34mm wastegate with your turbo? That could explain the boost drop. With a very free flowing exhaust the big 34mm valve tends to blow open slightly. Try running a line from the intake manifold to the wastegate actuator, instead of from the turbo outlet. That should give you slightly more boost, and help it hold into high rpm. The best solution is to get a MBC. It's also possible you have a boost leak too since many cars do, but I don't think that's your main issue.

 

[HartmanMS]

I do not have the 34mm gate flapper on the turbo. But I will definately try the manifold to wg hose idea. Would it be ok to just tap into the manifold/BOV hose for this?

 

[pneumo]

Yes, that will work. Just cut the hose at a convenient spot and add a T fitting. The boost should be a little higher, and it will still change with rpm, so plan on getting a boost controller sometime.