Boost droping off

[BHDave]

I've recently installed a pnuematic boost controller to my lightly modded stock turbo R32 GTS-t.

Problem is that the boost pressure doesn't hold all the way but starts to drop at the top end.

I haven't done any testing yet but I think it's either the wastegate spring is too soft and is allowing the wastegate to be pushed open or the BOV is leaking.

Opinions please.

[red17]

Have you had your car dyno'ed? Because that will give you the best idea of whats happening. How much is it dropping off?

To give you an idea of what its normal turbo behaviour. My standard RB20DET turbo will peak at 11.5 pound at 4200 rpm. After that it drops off slowly to a low of 9.23 at 6250rpm.

The stock turbo is not efficent enough to produce the same amount of boost through out the rev range. It "runs out of puff" as it were.

A turbo will not hold the same amount of boost to an infinite RPM. If that were the case we'd all be shopping for the smallest turbo we could find so we could shove 18 pound through it with no lag. Of course thats not the case.

Turbocharger efficency and how it works is a tricky subject, and something im nowhere near qualified to speak specifically about. But im sure theres others on here that know all about impeller air flow, fin design, housings etc..

Red17

[Jay95R33]

In some cases, a good 3 inch dump pipe will reduce the back presure in the higher rev ranges and reduce that boost drop off.

But as suggested, turbo eff, and wastegate spring can and will contribute to it too.

J

[rob77]

When I have a working scanner I'll scan my dyno sheet. At 4800rpm my boost drops off from 12.5psi to 10psi immediately, within probably 50-100revs and then slowly tapers off from 10psi to about 9.5psi by 6630rpm at which peak power is reached. Its quite odd and has something to do with the NVCS, hopefully once I remove the ECU and fit something else up it'll get rid of the problem.