STS Turbo/Waste gate question?
STS Turbo/Waste gate question? I had my car dynoed the other day on a Dyno Jet Dyno. The guys who own the shop are primarily blower/ nitrous tuners so they aren’t real knowledgeable with turbo tuning. My car has a forged 6 liter with an iron block, Agostino racing heads (I bought them used and don’t have any flow numbers), turbo cam and a STS GT 70 turbo with a stock STS waste gate. The dyno graph shows it making good power up to about 5500 RPM and 9lbs of boost then the waste gate opens and the graph flattens out and starts to drop. It made 530 RWHP and 505 RWTQ. The owner of the shop said he adjusted the waste gate as far as it would go and it wouldn’t make any more than 9 or 10 lbs of boost. They are suggesting I get a new waste gate to correct the problem. The question I have is why is it falling off at 5500 rpms when the waste gate starts to bleed off boost? They ran my engine up to 6500 rpm and from 5500 to 6500 rpm it lost power. Do you all think a new waste gate will fix the problem? I know it will make more power with more boost but why is it falling on its face at 9 or 10 lbs of boost at 5500 rpm and not making more power at a higher RPM? By the way it’s got plenty of fuel and they played with the timing and no matter what they did it didn’t help. As soon as the waste gate opens it starts losing power. I’ve seen cars running less boost make power up to 6500 RPM so why is mine dropping off at 5500?
TECH Senior Member
Joined: Nov 2001
Posts: 10,341
Likes: 1
You could put an MBC in the car. Sounds like there is a 9# spring in the gate and you are running out of turbo above that.
Running the MBC will allow you to turn up the boost but you'll still get that drop off in the higher rpms if your AR or turbo is too small.
Running the MBC will allow you to turn up the boost but you'll still get that drop off in the higher rpms if your AR or turbo is too small.
Did you not get any boost controller with the kit? When you say the guy adjusted the WG, what does that mean? There is no adjustment in a TiAl wastegate except for spring changes (I am assuming you got a TiAl, because that is what I got with my kit). Does it have the manual boost controller with it? If you only got a 5lb spring in your WGA, then you can get a fairly reliable 10psi out of your system with a boost controller (I'm thinking this might be what you have if you have the manual boost controller right now). If you got an 8lb spring then your can get up to 16psi. So, the upshot is that you need to find out what spring you have in your wastegate and if you don't have a boost controller, get one.
This is what I got with the kit.
GT 70 Turbo Upgrade
Additional components to match up with GT70(4" intake pipe, bigger filter, other pipes)
Electronic Boost controller 0-15 psi, this thing is a switch that changes it from 5 psi to what ever I have the manual spring set to. Won't go higher than 10 psi.
65# injectors
Walbro Fuel Pump
TiAl Blow off Valve
Methanol System for over 500 HP
I asumed that they said I could adjust it between 0 to 15 psi but it won't go above 10.
Could the spring be weak? Is the Electronic Boost controller they sold me junk?
Thanks to all!
GT 70 Turbo Upgrade
Additional components to match up with GT70(4" intake pipe, bigger filter, other pipes)
Electronic Boost controller 0-15 psi, this thing is a switch that changes it from 5 psi to what ever I have the manual spring set to. Won't go higher than 10 psi.
65# injectors
Walbro Fuel Pump
TiAl Blow off Valve
Methanol System for over 500 HP
I asumed that they said I could adjust it between 0 to 15 psi but it won't go above 10.
Could the spring be weak? Is the Electronic Boost controller they sold me junk?
Thanks to all!
Originally Posted by CHRISPY
You could put an MBC in the car. Sounds like there is a 9# spring in the gate and you are running out of turbo above that.
Running the MBC will allow you to turn up the boost but you'll still get that drop off in the higher rpms if your AR or turbo is too small.
Running the MBC will allow you to turn up the boost but you'll still get that drop off in the higher rpms if your AR or turbo is too small.
Thanks
The dynojet probably isn't loading the engine enough to maintain any more boost. I set my boost controller to hold 8#'s on a dynojet once, and when I went to the street it boosted over 14#'s. Try a dyno capable of loading the engine, or just see what happens on the street before fixing a problem that may not exist.
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Originally Posted by gametech
The dynojet probably isn't loading the engine enough to maintain any more boost. I set my boost controller to hold 8#'s on a dynojet once, and when I went to the street it boosted over 14#'s. Try a dyno capable of loading the engine, or just see what happens on the street before fixing a problem that may not exist.
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TECH Enthusiast
Joined: Mar 2004
Posts: 697
Likes: 0
Originally Posted by gametech
The dynojet probably isn't loading the engine enough to maintain any more boost. I set my boost controller to hold 8#'s on a dynojet once, and when I went to the street it boosted over 14#'s. Try a dyno capable of loading the engine, or just see what happens on the street before fixing a problem that may not exist.
Ok, you have the same set up as mine boost controller wise. You have a wastegate with a manual boost controller that is switched on and off by and air solenoid. Are you sure they adjusted it all the way? You should be able to turn the boost pretty high with that system. To see what spring you have, you need to hook up one air hose from the output of the turbo nipple to the nipple on the wastegate that is closest to the turbo. Disconnect the other line to the wastegate. Do a quick pull on the street in at least 2nd gear. See what boost you get. Note what your boost guage reads with the car off and add or subtract that and that will be what spring you have (if you have no boost leaks). I had a boost leak at the power brake booster line where the tee for the blow off valve was placed because it melted in the heat from my headers. Anyways, check for leaks if the boost is low. In fact check all your clamps for leaks and any hose that can have vacumn or boost on the engine just to be sure. Good luck.
I think he needs a bigger wastegate spring!
Its not that the spring is weak or deffective
the wastegate just needs a different spring to work
with a 15 psi controller.
the stock sts blow off valve holds around 5 psi
so to see 9 psi with a boost controller all the way out and
the stock spring in the wastegate out is right on!
I have a 7 psi spring in mine and after the pressure drop of
the intercooler I get 5.5 psi to the intake with my switch off.
with the switch on i would only be able to make around 10 lbs
of boost with a 7psi spring and my controller max'd out.
look at it this way.....
if your setup can make 5 psi with the stock spring in the
wastegate your only going to be able to see around 9-10 psi max
with that spring and the controller max'd out. this might be the
wrong way to look at it but if the top of the wastegate can
only see 5 psi you can only add that much more pressure to
keep the gate closed a little longer
so you can only double the psi your system makes with the
controller on and max'd out.
http://shopping.lightningmotorsports...ate-p-692.html
they have many springs available! i use the green one...
I have experienced the same thing with my setup!
change the spring before yah throw in the towel on the valve
Its not that the spring is weak or deffective
the wastegate just needs a different spring to work
with a 15 psi controller.
the stock sts blow off valve holds around 5 psi
so to see 9 psi with a boost controller all the way out and
the stock spring in the wastegate out is right on!
I have a 7 psi spring in mine and after the pressure drop of
the intercooler I get 5.5 psi to the intake with my switch off.
with the switch on i would only be able to make around 10 lbs
of boost with a 7psi spring and my controller max'd out.
look at it this way.....
if your setup can make 5 psi with the stock spring in the
wastegate your only going to be able to see around 9-10 psi max
with that spring and the controller max'd out. this might be the
wrong way to look at it but if the top of the wastegate can
only see 5 psi you can only add that much more pressure to
keep the gate closed a little longer
so you can only double the psi your system makes with the
controller on and max'd out.
http://shopping.lightningmotorsports...ate-p-692.html
they have many springs available! i use the green one...
I have experienced the same thing with my setup!
change the spring before yah throw in the towel on the valve
Last edited by 98Ztwentyeight; May 5, 2006 at 05:50 PM.
