Does anyone know why the boost pressure in my MY99 drops of at high rpm? The car runs 14psi up to about 6000rpm the as the revs continue to rise the reading on the guage tails of down to about 10/11psi at 7000rpm.Is this normal if so what causes it?

 

David,

I think you are lucky in that of the 2 MY99's rolling-roaded at the last dyno day peak boost was 14 psi which falls to 12/13 roundabouts 4500-5000rpm.

I believe also the ECU starts to knock back the boost at higher rpm.

I've increased mine so it peaks at about 17 then holds 16ish until 5000rpm where it starts to drop again. Will see the results at the next dynoday.

 

David,

This is due to the size of the turbo (it is smaller than the earlier Imprezas) which means less ultimate flow but with the benefit of reduced lag.

I have a 94 WRX (with a larger turbo) which
boosts all the way to the redline - but nothing happens below 3500rpm.

If you look at Paul Strong's "Dynomite Scoobies" site (start.at\dyno) with the power plots for a wide selection of Imprezas, you can see this represented graphically.

In day-to-day driving, I would say that you have the better arrangement as power is more readily available when you want it!!

Thanks

Gavin

 

Hi
When my car was standard it had 14 psi with a drop to 10/11 psi at about 5800 rpm.
This must be the ECU, as the turbo can easily boost at 17psi at 7000 as mine does now.
Bob

 

Hi there...

Alot is down to the ECU... hence by fitting a boost controller the pressure will remain right upto redline (if required), but remember to look at fuelling.

You will be working the turbo harder.... which inturn generates more heat..and could cause pinking...

J.

 

I had exactly the same problem on my MY98. Mine was dropping from 14 to about 10 at 6000 RPM. My dealer changed the boost control solonoid and now I hold 14/15 and it drops back to 12 (I used to get varying peak boost as well so I suspect the valve was faulty). My friend checked his MY99 and he holds about 14 and drops to 11/12. So I think this is normal behaviour but it appears from my case that it can be affected by the solonoid.
The settings do seems to vary between cars and the only real solution seems to be to let PE spend the 4-5 hours doing the re-map to set up everything specifically for your car. Dearlers don't seem to have rolling roads or the necessary equipment to diagnose these variations.

.Richard