it is not really that the power drops off at 3500 rpm it peaked on the dyno at 5100 but the boost peaks at 3500 or so and starts to do a slow drop off
for eg it peaks at 8.5 PSI at 3500 at 4000 it is at 8psi at 4500 it is at 7 psi at 5000 it is at 6.5 at 5500 it is at 6 PSI or sometimes lower

 

The gauge should be hooked to the intake manifold to monitor boost. Some minor drop after peak torque is normal. If you use the turbine housing to read control, then a intercooler can cause the readings you are getting. If that is the case, you could move your boost reference points to the manifold, or at least after the intercooler.

Kurt

 

sorry I may have missunderstood
the boost referance for the wastgate is off the turbo
for the guage and the Boost controller is off the intake manifold

 

Try moving the line to the wastegate over to the intake, or the pressure tubing after the intercooler then take the car for a spin to see if it changes.

Kurt

 

I'll throw this out there again.. Ussing the Turbo boost fitting can cause the loss of boost in the high rpm area's because the that vacuum port can not read the boost loss through the intercooler. This is why you use a reference from the intake itself

 

ok I will try that in a few minutes
thanks

 

Sounds like you need to take a Mityvac and hook it to the wastegate pressure line and see how much preload is on the gate.

 

I read someone saying the 38MM might be too small. I dont think thats the issue here neccesarily, but 38MM does seem small for an engine of this size. Much smaller engines have expirienced boost creep with 31-34 MM internal gates. I doubt the mitsu BOV is havng a prob at these pressures.

It sounds to me like with the old set-up the wastegate was simply getting blown open. As the exsaust gas presurized the mani-turbine housing at about 3500rpm, it got blown open. The solution might be some more preload on the wastegate actuator, but that only works on an internal gate in the3 way I am thinking of.

The new setup which hit 14.5 PSI sounds like the wastegate is not opening at all, which is what you expected. That makes sense despite the 7 lb spring, since the spring is not being counteracted by anything when you unhook the boost. What I think the guy meant is that if you ran strait signal with no BC to the WG, you would get 8PSI.


So maybe try to preload the WG actuator a bit more if you have the internal gate (does the T-67 even have that option?). I dont know how it works on your kit, but a lot of those allow you to screw the controll arm from the actuator counter-clockwise, effectively making the rod longer and pressing the WG closed harder against its port in the turbine housing.

If its an external, I dont get it. Those things should not blow open like that. I assume we are sure there are no leaks in that line anywhere?

Its almost certanly not a boost leak in a massive way, since you did test it without wastegate actuation and got great boost.

Oh yeah, and that makes sense too about where you get signal. Figure the air right of the compressor housing is at its hottest, so at that point your getting the highest boost pressure possible to signal the WG. As you go up the rev range that signal might just get stronger and stronger. So 5PSI at the mani is like 10 PSI where your getting signal, like the poster a few above me said.

 

well i moved the boost line from the turbo to the intake manifold and it makes about 2 pounds more boost but still falls off just as much
it was making around 7 psi @ 3200 before and now it is making around 9 PSI at the same RPM
so I turned the boost controller down 2 points and it is right back where I started
it may be a little better but not much at all
if any

 

oh and it is a External waste gate
it is a turbosmart 38mm

 

Exhaust restriction? On a previous post, be careful, if we relocate the wastegate's boost line from the turbo housing to the intake manifold, have large enough BOV(s) because the waste gate may no longer help bypass boost when we close the throttle. Do to a lesser boost signal at WOT, the waste gate may no longer open and when you close the throttle at high boost/RPM, it no longer senses this boost spike and it can do strange things. We had a customer who had it set up this way, it kept the throttle blade blown wide open when we let off, guess the rest of the story.

 

My wastegate is the same size and it works fine...

 

Darren, any progress on your setup?

Hope all is well,

Rich

 

well I change the way the boost controller was hooked up to the 2nd method that was supposd to allow more boost
it would not make under 10 PSI like that but it was still falling off to around 5 or 6 psi
so I changed it back and moved the boost referance to the intake manifold
this made a little more boost but not much and it still bled off

oh and when it was making 10 psi and falling I later remembered that the overboost protection was set at 12 psi and that it was supposd to be at least 2.5 psi more than the desired boost level
I turned it up to 14 psi and have not hooked the boost controller back up like that yet
I do not have the car right now. It is getting a dent fixed before I show in the Food Lion Auto fair but I should have it back tomorrow night

then I can continue to pull my hair out

oh BTW on last saturday it ran a 7.65 at 93 MPH
with a 1.84 60 ft
but I feel like it should be faster with 7 to 8 pounds of boost

 

It would if it held the 8 psi...

By the way, how's your Spec 3 running?

 

it is not a Spec stage 3
it is the stage 3+
it is doing great