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View Full Version : T-25 Boost Issues, Questions?

rednerd
10-24-2003, 07:51 PM
According to the turbo faq:
http://www.zilvia.net/f/showthread.php?s=&threadid=15874

About the T-25:
"With a cat, I would run no more than 10-12 psi. Expect about 220 whp."

I am running a high flow cat and 3" free flowing exhaust. I can run 10 psi all day long, but when I do drag runs at 13-14 psi I get wicked boost fall off at high rpm. By the time I have to shift I'm usually down to about 11 psi.

I've been messing with clamps, new vacuum lines and boost solenoid placement but the problem still seems to escape me.

Am I seeing an inherent design problem with the small t-25 and my high-flow yet still somewhat restrictive cat? Or should I keep looking for a boost leak / other problem?
double_jd13
10-28-2003, 05:51 PM
just read your post and wanted to know what kind of blow off valve or diverter your are using. Because it might be bleeding off to quickly (like if it is a diaphram style and its ripped due to higher boost). Or it is not rated for the higher boost you run at the track..

jason
rednerd
10-28-2003, 06:30 PM
I have a HKS SSQV. It is pretty new and I don't feel it leaking.

The problem seems to come and go. I notice it more after I have driving for an hour or so.


Thanks.
double_jd13
10-28-2003, 07:06 PM
Let me think a little more on the subject i have some other ideas, but there is a lot i havent checked yet. For the fact my roommates supra is having pretty much the same problem, around 17 lbs it bleeds off alot quicker than at 15 or 16. So if i come up with any two cent ideas ill throw them at ya..

jason
nismofeind
10-28-2003, 10:05 PM
what boost controller are you using??
rednerd
10-28-2003, 10:27 PM
The boost controller is a Greddy Profec B Spec-II.

I'm fairly certain that something must be leaking boost when the engine bay heats up. I've made sure all my clamps are tight, and I just replaced my exhaust gaskets not too long ago (I don't hear them leaking).

The engine will also lose 1 psi boost over 6K RPM when the boost is set higher than 10 psi.
nrcooled
10-28-2003, 11:41 PM
I have the same problem. To solve it I am replacing my actuator with the HKS unit which will hold boost beter at a steady 14lbs not to mention that it's only $55

From what I have picked up is that the t25 is horribly ineficient. When it gets hotter it doesn't hold boost as well. The t28 has the same issues
Joel 180
10-29-2003, 02:00 AM
14 psi is way out of the t25g efficency range. At high RPM the boost will drop and there is nothing you can do.
MazzyMan
10-29-2003, 06:14 AM
Originally posted by nrcooled
I have the same problem. To solve it I am replacing my actuator with the HKS unit which will hold boost beter at a steady 14lbs not to mention that it's only $55

From what I have picked up is that the t25 is horribly ineficient. When it gets hotter it doesn't hold boost as well. The t28 has the same issues

Yup...i rekon that its the accuator that ain't holding enough at high boost. A replacement would do justice if you intend to use that turbo for awhile longer.
240_keyy
10-29-2003, 03:12 PM
rednerd, I have the same problem. I boost to 14 and then it drops to 11. My two other SR friends were boosting 14 and when they got near redline they were at 11 or 12psi. That is just the T25 for you, it won't hold that much boost up high...
rednerd
10-29-2003, 03:35 PM
Cool thanks guys.

I might try the HKS actuator, or just save the money and pick up a better turbo this winter.

What do you guys think of the gt-28r series. I don't want to go with a top mount turbo it I don't have to but damn the gt's are expensive...
MazzyMan
10-29-2003, 09:07 PM
Was told that the S15s turbo would be the cheapest turbo one step upgrade and gives a nice result compared to our stock S14 one.
rednerd
10-30-2003, 12:22 AM
Aren't the S14 and S15 T-28's almost the exact same turbo?

I thought the only difference was a slightly updated turbine wheel.
MazzyMan
10-30-2003, 11:04 AM
Originally posted by rednerd
Aren't the S14 and S15 T-28's almost the exact same turbo?

I thought the only difference was a slightly updated turbine wheel.

Yes they both are T28s but ones a conventional bearing and the other's a roller bearing turbo. Looked at the turbine wheel and they kinda look the same.

Spool rate is much quicker and back end feels a little stronger.