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Thread: wont go past 7psi

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Posts: 21-30 of 47
2009-12-30 21:11:36
in the piping by the BOV welds. vacuum lines.... everywhere
2009-12-30 21:14:24
I know what im talking about like ive dealt with turbo cars since I was like 12 granted im only 18 I build them and work on them everyday. This one just stumps me.
I found out I have the stock actuator on and i mean like bone stock never been changed and i think the spring in it is only rated for a weak 8-9 psi I found this on another forum:

The reason why you would buy the HKS actuator is to hold boost better. On the stock T25, boost will fall off as much as 3-4 psi, and the HKS actuator makes it so that you only lose about 0.5-1psi instead of several lbs of boost.
The boost controller is useless past 5,000rpm with the stock actuator, because if you have it set at like 12psi, then after 5k rpm, you'll drop down as low as 8-9psi. Seen this with my own eyes and i have a redtop w/stock t25.

The problem with the stock actuators is that the springs are not as strong, expecially since it is older. SInce the spring is weaker, it actually starts to open, regardless of the boost controller that you are running. The boost controller does not hold the wastegate shut, it keeps the boost signal from reaching the actuator which would normally open it. The boost controller is basically a bleeder, but a very precise one.

If you got the HKS unit, you would be able to hold the boost longer, with or without a boost controller.

Like Alex said, the stocker bleeds off boost at higher pressure due to the back pressure pushing on the actuator puck and the spring not being able to hold the puck against the housing.

If you only add the HKS actuator, your top end will imporve from the turbo holding the boost longer on the top end. We have done this to MANY SRs. You can see it happen on the dyno when you are logging the boost.
2009-12-30 21:24:43
is this correct?
if so Im going to try a 300zx t28 actuator and see what happens
or an actuator off of a TD04
2009-12-30 21:40:03
No, that is not correct. All that sounds like a bunch of BS if you ask me unless they are only dealing with "bleed" type manual boost controllers (which are notoriously finicky).

If you have a normal ball-and-spring manual boost controller (I noticed you said it has a pin-hole leak in it. That is normal and needs to be there.) then you shouldn't have any problems making boost, especially after removing the boost controller from the situation.

Your wastegate doesn't need replacing unless it's completely broken. (Which it very well might be.)
I've been leaning towards a boost leak this whole time. We all think it's a boost leak.

You say it's not a boost leak. Are you 100% sure?

If it is not a boost leak then it could be a few other things that people have mentioned already.
It could be that the wastegate diaphragm has torn (although that usually causes overboosting) or for some other reason the wastegate has failed.
It could be that the pre-load on the wastegate is poorly set and the gate is not closed all the way at rest.
It could be that you have a huge exhaust leak before the turbocharger.
It could be that your boost gauge is broken, or the signal to it is incorrect.
It could be something else.

You need to do some thorough tests and use your intimate knowledge of how turbocharger systems work to diagnose the problem.
2009-12-31 00:19:33
check your boost gauge line, a few days ago a friend of mine and i installed a boost gauge on his b13 with a t25 setup, the car was runing strong but the boost gauge doesnt move athing, so we proceed to chek the line that was the problem.
2009-12-31 02:40:51
but ive road in 240s w/ sr's on 10 12 and 14 psi I know what it feels like and I have a digital boost gauge not the crappy kind the max ive hit is 8.6 psi.
so Idk whats going on w/ it
I removed the actuator completely a few minutes ago but it started to rain
once it lets up I will try and put a different one on and see what happens
the guy that had the motor before rebuilt it and put a brand new turbo on it but reused the actuator so im going w/ that considering whatever the reasoning was behind the rebuild
2009-12-31 02:43:07
oh and actuator off a TD04 doesnt bolt up correctly found that out a moment ago.
but the TD04 actuator has a spring instead of an arm
w/ these two actuators maybe I could use the old actuator (if I can get the arm out) and replace it with the spring not sure if it will make any sort of difference nor am i sure if the arm comes out. First time w/ internally gated turbos
2009-12-31 02:58:23
the arm doesnt come out. I would just put air to the wastegate and see if it works first.
2009-12-31 03:28:50
yeah the wastegate works already tested it under pressure
2009-12-31 03:31:54
Then your motor has a pressure leak somewhere.
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