St185 boost/turbo question

dvsone

New member
Hi guys,
I have a 1990 jdm st185 and i have just fitted a kinugawa 3071r turbo to it with a fmic. The turbo came pre installed with a 1bar actuator spring but i am only getting 7-8psi. I have the vac line to the tvsv blocked off which i thought would allow it to run on wastegate pressure.
So my question is do i still need a boost controller installed for it to reach wastegate pressure or should it be hitting the 1 bar boost as is and i have an issue somewhere with my setup?
TIA
 

grip-addict

Active member
If it's a 1 bar spring then that should be your base boosr pressure. You need to make sure the waste gate door is closing fully, if it's partially open you'll really struggle to build large amounts of boost .
 

dvsone

New member
If it's a 1 bar spring then that should be your base boosr pressure. You need to make sure the waste gate door is closing fully, if it's partially open you'll really struggle to build large amounts of boost .
Thanks mate that’s what i thought just wasn’t sure exactly how the tvsv works and if just blocking the line from actuator to tvsv was enough to allow it to run on wastegate pressure.
The wategate door is definitely closing fully i checked that before installing the new turbo.
I have smoke tested intake and exhaust and have no leaks and double checked cam and base ignition timing all ok.
Not sure why it is only seeing 7psi boost 🤔
 

grip-addict

Active member
Couple other things coming to mind. A really big boost leak can impact the performance substantially. A boost leak tester is about a 50 dollar buy, And you can make them for less. They're very useful tools.
An exhaust leak could also be causing this for you but I'm guessing you would notice because it would sound like a helicopter taking off if it was so bad you couldn't get past half a bar of boost on a 14 lb spring.
Lastly, there's the possibility that the wastegate actuator is just crappy. Do you have a way to regulate down .5 bar of pressure and put it on the wastegate solenoid? Maybe you got sold the wrong spring or there's a problem with the diaphragm in there or something...
 

dvsone

New member
Couple other things coming to mind. A really big boost leak can impact the performance substantially. A boost leak tester is about a 50 dollar buy, And you can make them for less. They're very useful tools.
An exhaust leak could also be causing this for you but I'm guessing you would notice because it would sound like a helicopter taking off if it was so bad you couldn't get past half a bar of boost on a 14 lb spring.
Lastly, there's the possibility that the wastegate actuator is just crappy. Do you have a way to regulate down .5 bar of pressure and put it on the wastegate solenoid? Maybe you got sold the wrong spring or there's a problem with the diaphragm in there or something...
Yeah i have a smoke tester that goes up to 7psi and have tested the intake system and exhaust both are leak free.
I do have a 1.5bar spring to go in once the car goes to the dyno but do not want to put that in now. That would be way too much boost on standard ecu and injectors lol

I might open up the actuator and inspect that it is all ok.

I have noticed that there is no vacuum on the line that runs from the top of the valve cover to the throttle body so i think there is a blockage somewhere there but as far as i know this is just pcv related so shouldn’t be effecting boost.
 

Monachopsis

Member
With the stock ct's if you throw one bar you may only see 8 psi, I have heard and seen people solve all 'boost' problems not related to leaks by just slapping in a good ol' boost controller as most actuators are typically more likely to leak even if they have the spring you want. It was on some skyline fourm but yea, dude only was seeing x boost level with y (numbers leave me at the moment) spring, after installing a controller he finally did see y boost.

It's a nuclear option as boost controllers are also delicate and temperamental but something to consider seeing as you lack leaks.
Side question i was looking at that kinugawa unit, let me know how it runs.
 

dvsone

New member
With the stock ct's if you throw one bar you may only see 8 psi, I have heard and seen people solve all 'boost' problems not related to leaks by just slapping in a good ol' boost controller as most actuators are typically more likely to leak even if they have the spring you want. It was on some skyline fourm but yea, dude only was seeing x boost level with y (numbers leave me at the moment) spring, after installing a controller he finally did see y boost.

It's a nuclear option as boost controllers are also delicate and temperamental but something to consider seeing as you lack leaks.
Side question i was looking at that kinugawa unit, let me know how it runs.
Yeah i did read somewhere that if you block the line to the tvsv it will run low boost in all gears instead of just 1st & 2nd unless you install a boost controller but i wasn’t sure if this still applied with the aftermarket turbo or mot.
I’m going to double check the actuator and spring installed just to be sure but if i can’t work it out i will put a boost controller on and see how that goes.

It was a really nice kit from kinugawa and bolted up perfect. On initial test drives it feels a lot more laggy than the stock setup but that will also be from the large fmic vs the top mount w2a. I will let you know how it goes/feels once i get the boost sorted
 

Monachopsis

Member
Yeah i did read somewhere that if you block the line to the tvsv it will run low boost in all gears instead of just 1st & 2nd unless you install a boost controller but i wasn’t sure if this still applied with the aftermarket turbo or mot.
I’m going to double check the actuator and spring installed just to be sure but if i can’t work it out i will put a boost controller on and see how that goes.

It was a really nice kit from kinugawa and bolted up perfect. On initial test drives it feels a lot more laggy than the stock setup but that will also be from the large fmic vs the top mount w2a. I will let you know how it goes/feels once i get the boost sorted
Sounds good! Odd question, you trying to get rid of the the old w2a? I'm in the market for one
Yea rather than rebuilding the turbo I wanted to run the kinugawa with the 11 sts or whatever they call it. Good to know it bolts nice and it seems like it could be faster to spool given the billet wheel.
 

dvsone

New member
Sounds good! Odd question, you trying to get rid of the the old w2a? I'm in the market for one
Yea rather than rebuilding the turbo I wanted to run the kinugawa with the 11 sts or whatever they call it. Good to know it bolts nice and it seems like it could be faster to spool given the billet wheel.
I ended up getting the 6+6 blades with sts for better low end torque since i plan on doing some tarmac rally events.

I haven’t decided if i should sell the w2a setup yet or keep it incase i want to put the car back to stock later. I did some searching ti see what they are worth but couldn’t find any for reference so i just boxed it up and put it away haha
 

grip-addict

Active member
Where is your wastegate getting the boost pressure signal from? It should be directly from the compressor housing and not elsewhere on the motor. The factory VSV should not be in the loop so it does not impact boost pressure.
 

dvsone

New member
Where is your wastegate getting the boost pressure signal from? It should be directly from the compressor housing and not elsewhere on the motor. The factory VSV should not be in the loop so it does not impact boost pressure.
Yeah i have the line straight from compressor to wastegate actuator a d it is a new vacuum line so not perished or anything
 

dvsone

New member
This might be super dumb but i rotated the turbo actuator face to get better clearence and less crimping on the vac lines when installing the turbo. It is possible that i mixed the lines up in doing this. Is there a specific in and out and could this be my boost issue?
I will double check when i get home but just occurred to me
 
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Gert

Active member
If I read correct you are having an internal wastegate. So, just to test: unplug the hose to the wastegate, block it off and take her for an drive.
So with no boost going to the wastegate, the door keeps closed and you should see maximum boost.
Note: very dangerous this, but only do this in first or second gear, that should be enough to determine if the car can make boost at all. If not, there is an other problem! But again, take vary care with this testing, otherwise you can smoke an piston.

Once we ported the wastegate too much and I was not able to reach maximum boost in any gear.
 
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