sorry about that last post my keyboard fell and in the process i entered my topic...
Anyways..
my set-up is as follows
sir2 with a garrett t-3 (from a saab, anybody know the specs),greddy fmi, ...bosch bov....If you need more info let me know..
When i had this turbo and piping (no intercooler) on my old engine (d15b7) it would boost to 5.5psi and hold steady, since i've swaped it to my new engine it will boost to say 8psi then drop off about 2-3psi.I had the intercooler modified and pressure tested so i know that it's not that, i've checked all of the connections and they are tight, there are no leaks anywhere.I have also tried 4 different waste gates (one of which worked fine on my buddy's car and held it at 6psi up to redline).I'm at a loss, i have no clue where to look.
any idea's would be greatly appreciated...
I also have a manual boost controller, when i'm using it i adjust it to 8psi which it holds until about 5,000 rpm then that is where it starts to drop and continues to drop up to redline.If i remove the boost controller the wg opens at 6psi holds steady until about 5krpm where is drops off to about 4.5psi (gradually).In both cases it drops to about 4.5 - 5psi.My inital thought was that it was the wg (the boost was actually spiking to 6psi then droping to 4.5) where the wg can control the boost, but why would it hold at 6psi on my buddys car and 5.5psi on my old engine.BTW he has the same set-up as me.
I bought a tial wg but was unable to use it because as i found out the hard way it won't fit under the hood with the drag manifold...

 

the EXACT same thing is happening to me. does anyone have an answer?

 

Is the bosch valve leaking...they are flaky

 

I don't know, it is a possibility.i know a while back the bov got stuck open, so it may not be sealing properly....thanks for the idea......i'll look into that

 

What is your set-up

 

crvtec
custom log manifold
rebuilt saab t3 turbo (.42 compressor a/r)
homemadeturbo.com custom intercooler
1st gen dsm bov welded to i/c pipe

1st gear.... hardly any boost, too quick i guess
2nd gear.... boost but it starts to die off at high rpms
3rd gear.... same as second
4th & 5th.... reaches max of 4lbs. and stays there

u think the turbo is just too small and cant put out enough air at high rpms?
any help, turbo experts?


[Modified by TurboCRVTEC, 12:44 AM 11/12/2002]

 

[QUOTE]crvtec
custom log manifold
rebuilt saab t3 turbo (.42 compressor a/r)
homemadeturbo.com custom intercooler
1st gen dsm bov welded to i/c pipe

1st gear.... hardly any boost, too quick i guess
2nd gear.... boost but it starts to die off at high rpms
3rd gear.... same as second
4th & 5th.... reaches max of 4lbs. and stays there

u think the turbo is just too small and cant put out enough air at high rpms?
any help, turbo experts?

....................your set-up is simular to mine (same turbo) but you have a b20 block instead of the b16.
1st gear does the same exact thing as your car but 2-5 act all the same....boosts fine until about 5k then drops off........it's the only thing that is keeping me from getting hondata and runing better times at the track...

 

u using internal or external wastegate?

 

lol,im using a saab t3 also,almost same problems here too,im boosting to 10 psi with it though using a mitsu wastegate actuator.it boosts extremely fast up to 10psi by atleast 3k rpm,then by 5 or 6k it starts falling off to about 7 psi and stays there.i think the turbo can not push enough air to keep up with the 10 psi im trying to get from it,before i added the intercooler it seemed to stay at 10 all the way through.but i would think puishing 6 it should keep up with no problem at all.

 

internal wg.....

 

What engine are you using

 

I'm going to go out on a limb here and say that perhaps the turbo is too small for the engine and you're approaching the surge limit of the turbo above 5000 RPM...

 

your turbo is off the saab slant 5?

 

any specs on the trim?what about the engine (saab) is it feasible that the turbo is just to small for the b16a?It just can flow enough to get through all the piping and intercooler?When i pulled it off the car i remember it being up top of the engine and close to the intake maifold