boost spiking to 20 psi

I just got a 1997 gs-t for $4100. the car is in show room condition. not one scratch or ding. carbon fiber hood, boost and air/fuel gauge, and a manual boost controller, 3'' turbo back with a cat. and a hks ssqv with recirculation kit. anyways, the boost is set at 15 psi when I punch the throttle the boost spikes to 18-20 psi then comes back down to 15 psi. the car has the stock t25 turbo. Is 15 psi to much for the stock turbo? Im not to sure. thanks

Run the balls off that t25, it won't hurt it. :wink:

i've heard 18 is the most... pretty much toping out the t25...

EDIT: But i wouldnt chace it, 15psi is good for me as of now... on this turbo

I want to turn the boost down but i don't know how. I could probably figure it out but the intake pipe is in the way so i can really see it. I looks like I can adjust it with a wrench. but when the boost kicks in I can hear the turbo so loud pretty much over the exhaust. making that high pitch sound.

Your gonna need to install a manual boost controller so you can adjust your boost.

it has a manual boost controller

He has one, it said in his first post. ;) IIRC, the t25 efficiency is just about maxed out at 15 psi and after that, you will start to knock due to the extra pressure. I would turn it down to like 12 and see where it spikes at. Also, boost spiking is a result of wg creep right? How do you fix that?

He has one, it said in his first post. ;)
Opps, my bad. When he said it looked like he could adjust it with a wrench I thought he meant something on the turbo. lol

Also, boost spiking is a result of wg creep right? How do you fix that?
Bigger wastegate should fix it up nicely. Another thing that contributes to boost creep is an exhaust that is too restrictive, although that isn't the problem in this case.


It is also possible that the internal wastegate isn't operating properly and opens too slow.

not bad for $4100.

:werd:

Porting the o2 housing helps too right? I wouldnt get a manifold mount wg unless you are going to be running a bigger turbo. I'd just port the bitch a bit and see what happens.

I will post pictures when it stops raining and I washing the car.

how do I test the wastegate to see if it is working properly? If there is a way. How do I turn the boost down with a manual boost controller? Is it as easy as twisting the knob?

Yes, just twist the knob to and test it... To check the wastegate, I'm not really sure how you would go about it. I guess just pull the turbo off and see if it give you any problem to move the wastegate flapper manually? lol

ok I was wondering what was the max boost allowable for a 1997 eclipse GS-T spyder with a stock turbo, i am installing a manual boost controller and dont want to blow my engine.

ok I was wondering what was the max boost allowable for a 1997 eclipse GS-T spyder with a stock turbo, i am installing a manual boost controller and dont want to blow my engine.
Safely you can run about 42psi if you have balls you can set it to about 55psi.

Safely you can run about 42psi if you have balls you can set it to about 55psi.
:lol:
Maybe on a built motor with the head o-ringed. :wink:


Ok,seriously though... Your stock t-25 can only produce like 16 or 17psi at the most... If you crank up your boost though, you are gonna need to log your engine sensors so you don't get knock... If you get knock then you need to turn your fuel up a little bit.

Well, your getting boost creep from what Ive read at posracing.net ( thanks kevin ) reason is because of the bigger exhaust is flowing too much and overpowering your wastegate. Basically you need to port the o2 housing and wastegate, then you can turn boost up or down.

Well, your getting boost creep from what Ive read at posracing.net ( thanks kevin ) reason is because of the bigger exhaust is flowing too much and overpowering your wastegate. Basically you need to port the o2 housing and wastegate, then you can turn boost up or down.
I thought that too restrictive of exhausts is what causes boost creep because the exhaust gases can't escape the system quick enough causing pressure. And the only other place it can escape is through the turbine causing it to build more boost and thus receiving the term "boost creep"... Or have I misunderstood it all this time?

Well from how kevin explained it, when he put on a 2.5" exhaust on a 14b, he spiked to about 21psi...same thing happened to me with a 3".

Well from how kevin explained it, when he put on a 2.5" exhaust on a 14b, he spiked to about 21psi...same thing happened to me with a 3".
How much boost do you have it set to?


I sure hope Kevin visits this thread, cause I sure would like to know which theory is right... :uhoh:

I had it set to 15psi before I put on the exhaust, then it jumped to about 20 after

Boost creep is when te wastegate doesn't open enough (or is not big enough) therefore there is less resistence through the turbo. A bigger exhaust makes it worse cause there is even less resistence after the turbo yet it remains the same for the wastegate. I think the best fix would be to port the flapper hole, or get en external waste gate, boost spike is diferent but i'm not sure how exactly, i think it's more of a sow response from the wg cause the boost to momentarilly "spike"

Spiking is pretty normal with an MBC, and the pattern you displayed seems pretty standard. I blew my T-25 running 17psi for 2 months (ok ok...the car was practically begging for an upgrade so I kinda...helped the stock turbo...u know, lol ). Keep the boost at 15 if you dont plan on changing the turbo any time soon.

Mine is now spiking to ~18 and then decreasing to/below 15. It's wierd. Need a MBC.

EZ explained it correctly. THe thing to consider is which way will the exhaust gasses want to go (path of least resistance). With a freer flowing exhaust but the same crappy internal gate, the exhaust gasses are more likely to ignore the wastegate and go through the turbine, which produces more boost, which produces more exhaust flow, which wants to go through the turbine even more, producing more boost, and so goes the cycle.

Spike a function of the WG's but probably more so the boost controllers abililty to react quickly to rising boost. Small turbos like the t25 spool so quickly spike is very common. EBCs tend to really shine in this department ;)

The maximum boost I Would run on a t25 is 16 psi. I found that going above that doesn't add any performance on pump gas. If it spikes to 17-18 psi but quickly falls to set boost of 16 psi, I wouldn't worry about it. MBCs are going to give you some amount of spike. To fix the creep read about the porting stuff on my site. The vast majority of it can come from porting the WG exit area of the turbine housing and not even touching the flapper hole. But, creep is extremely unlikely on a t25 for two reasons. One, the turbine is so restrictive the wg looks like an atractive option for the exhaust gasses. Two the turbo doesn't flow enough to creep over 15 psi at high rpm.

So a nice external wg would fix boost creep even if your dumping it back into the exhaust?... Or is it better to let the wg dump atmosphere?

So a nice external wg would fix boost creep even if your dumping it back into the exhaust?... Or is it better to let the wg dump atmosphere?
That's personal opinion, i don't think there is much of a performance gain with dumping, but it does sound pretty damn good.