Boost spike to almost 20psi?!?!?

[DSMvroom]

I just got my autometer lunar boost gauge today and installed the vacuum hose.

At idle the car is at -15 vac . . . OK
smoothly depressing the accelerator to WOT . . . boosts up to ~12psi . . . OK
mash on the gas in 1st or 2nd gear . . . boost spike to almost 20psi!!! . . . NOT OK!

Why is this happening?

I haven't done the BCS restrictor mod, and the only mods I have done are hardpipes and a new bov.

when I mash on the gas it spikes to almost 20psi and then slowly settles towards ~12psi

From my searching the only things I've found are related to people doing the BCS mod on 2Gs and that the solution is a boost controller.

I figure this will help me also, but could it be something else too??

p.s. I did buy the car used "as is" so I don't know and havent checked if the previous owner had done the BCS mod, but the car was completely stock everywhere else so I figure the previous owner hadnt done jack 5h!7 to modify the car.

 

[saw wave analog]

if its just hitting 20psi for a second its nothing to worry about, investigate your wastegate actuator for loseness or kinked hoses or whatever.. my car spikes to 22psi from 18 during shifts on stock fuel and its not a problem because its for such a tiny amount of time. if you are spending more than just a flick of the needle there id be more worried about it

 

[DSMvroom]

o yea it is definitely over 16psi for longer than a second. once i mash it goes up drastically fast up to almost 20 and then slowly descends down towards 12psi.

Though it is probably important to note that at redline of 2nd gear it hasnt gone down to 12psi. Its hard to pay attention to both the road and the gauge but it looks like when I hit redline in 2nd it has only dropped down to about 14-15psi.

 

[Lazer RS]

my friend once spiked to 30 psi on a 14b with manual controller, flames shot out his exhaust.. he pulled over and looked everything over and nothin blew, never happened since.....kinda off topic but i had to tell

 

[ZenkaiRacerDsM]

You can hold 14-15 psi to redline in 2nd gear on a T25? How? When I have my controller set at 17psi my boost falls to like 9-10psi at redline in 2nd! I hope it holds all the way when I install my 14b.

 

[realhp=turbo]

Would it be a blow-off valve problem? It would seem to me that it would be, because the blow-off valve is what maintains somesort of a constant pressure, Theroetically. I would look first at the bov to make sure that it is releasing at the proper pressure level. My two cents.
mike

 

[cfisher]

boost controller works wonders!

 

[Bjeezy01]

Would it be a blow-off valve problem? It would seem to me that it would be, because the blow-off valve is what maintains somesort of a constant pressure, Theroetically. I would look first at the bov to make sure that it is releasing at the proper pressure level. My two cents.
mike

The BOV works off vacume pressure, not boost pressure. So installing a new BOV would have no effect. Boost spike comes from the output side, not the intake side....o2 dump, checking the WG, and a boost controller will help fix a spike. But for you, I would say the BCS is whats cousing it, try taking it out, and just running the line from the compressor to the WG itself...this might help it. But I would get a MBC, they are one of the cheapest mods for our cars, and they work wonders.

 

[kobykris]

A T25 won't hold boost like that, sorry.

But either way, you might have a kink in your wastegate vaccum tube or some other problem that is not letting the wastegate open when it should.

 

[saw wave analog]

?

my t25 had no problem holding 15psi to redline. it sucked up there but it was making boost. of course it only lasted a month that way so it doesnt much matter.. moral of the story? the t25 is a peice of crap and you need a mbc!

 

[bhop]

Mine spikes to about 18-ish, for just a sec, then drops back down to 14 or so, then drops even more around 4k... I would love to buy a new turbo, but without a job, i'm screwed..

 

[DSMvroom]

listen to this guys . . .

i disconnected the battery to hook up the electronic side of the boost gauge so that it would glow that cool green that it should.

Just to note, I've recently (since before i installed the boost gauge) had my CEL on because of p021 iirc which is a TPS error.

So of course when I took the car out for a spin the car was in open loop and the CEL was off.

During the entire time that the CEL was OFF, it never boosted above 15psi EVER.

As soon as the CEL came back on and the car started running in closed loop, there go the spikes! All the way up to almost 20!!!

wtf?????

 

[nurseryboy]

My car also spikes to around ~20psi for a few seconds when giving it a lot of gas. I have the stock T25 as well. I would say it stays up around 20 for about two or three seconds, and then starts going back down to 12-14 (it seems to jump back and forth between them). (Also, it is an automatic, so shifting doesn't effect it much). I have just contributed this to the fact that I have opened up the intake and have a header and 3" exhaust from the turbo back.

1) Am I correct in assuming that this is a boost creep of sorts? (as a result of the modified exhaust)

2) Is it normal to have the psi to change back and forth, even while keeping the gas steady?

Also, if the turbo is above around 10 psi, it "screams". I don't really know how to describe it with any other word. It is pretty loud. I don't notice a loss in power or anything. It seems more of an audiable thing than anything.

3) Is this something I should be worried about?

Sorry for asking my own questions, but since they are closely related, hopefully the answers to these questions will help the thread starter as well.

Thanks,

Matt

 

[Bjeezy01]

to answer you

1) No, boost creep should actualy start going away with exhaust modification...if you have an exhause, and "headers"(I think you mean downpipe) then you are on the right path, but you may wont to look into an o2 with a dump, those seem to help a lot

2) Boost can shift at WOT depending on RPM's and the turbo itself, but either way its better if it has a constant PSI, the screaming could simple be that some of your IC pipes are loose, and at higher PSI it is leaking through a small bit(which will sound like a load scream)

3) I know they set the T25 at 15psi stock, but thats really its max....So going beyond if for a second or two is not good, but might not be bad either, if you are not running a MBC invest, if you are, then maybe looking into an o2 with dump, You can pick those up for about 135+...

good luck

 

[nurseryboy]

Thank you very much for your reply. It was very helpful. I just have a few replies/questions to your replies.

1) I actually have a Pacesetter (..yeah, I know) header, and a 3" downpipe, as well as 3" cat, and 3" pipe from the cat. So everything should be pretty open below the turbo, except for the o2 housing (?). But that wouldn't cause the boost spike, correct?

2) I had the IC removed and cleaned, as well as a gromet at the top of the IC. Maybe everything isn't completely tight. Do you think that could cause the "screaming"?

3) I have the DejonTool MBC-2B boost controller, although I haven't adjusted either stages at all. Maybe turning it down a little would help control the spike?

Thank you very much for your help on this. I hope I am staying on topic here..

Matt

 

[saw wave analog]

im going to have to be a dick and say that just about everything bjeezy01 said is wrong


1- boost creep starts to APPEAR with exhaust modification, and since you say you have full 3" piping off of the stock 02 housing i am willing to bet thats at least part of the reason you are getting the creep. if you took a look at the stock o2 housing you will see that the wastegate path is very small compared to the main exhaust outlet. this isnt so much of an issue when you have the stock restrictive ass piping and cat on there because the pressure difference isnt that great, but when you open up your exhaust you are creating a much easier path for your exhaust gasses to take.. and if you were exhaust, would you rather go out the nice big hole leading to a nice big 3" pipe, or would you take the tiny little wastegate hole and have to fight your way through there. since you are getting more flow out of the main exhaust outlet (causing the compressor wheel to spin faster, sucking in more air, pushing your boost beyond where you want it) and less out the wastegate (allowing the turbine to see more energy from all the extra gas flowing across it) you have a hard time controlling boost, therefore you creep. a ported stock housing or better yet a tubular aftermarket one should help a lot. i would suggest porting the wastegate passage on the turbo itself but the t25 is a peice of shit and not worth the time, especially since it sounds like its dying on you...



2- the screaming you are describing could be a boost leak, but if you are leaking enough to where it is making a loud noise you would most likely feel a difference in power and the studdering that is normally associated with boost leaks. more likely is your t25 is on its way out due to the fact that you are spinning it much faster than it can handle. 20 psi is guarenteed to kill that turbo very quickly, mine lasted about a month at 18psi, a buddy of mines lasted a few months, another friends lasted a bit longer that that. check your compressor wheel for shaft play, likely the screaming sound is actually the blades hitting the housing as they spin. mine did that for a few days before it died completely, be prepared to buy a new turbo soon (one with a ported and oversized wastegate flapper preferably, to help out with the creep you are getting in your 1st question)

3- the t25's stock boost is not 15, it was 11 psi on my car with the bcs removed.. ive heard anywhere from 10-12 but definately not 15. its possible that it would spin faster on an aftermarket exhaust but none of this really matters anyway since you are modded.


so, to sum it all up, be prepared to get a new turbo very soon, get one that is ported, get a tubular o2 or a ported stock one, and you will be set. also, another thing to check is the hole on your mbc.. if it is clogged that could also cause your boost to fly past the setting you want at first.. but much more likely is your stock wastegate flow situation.

 

[nurseryboy]

Ok. Thank you as well.

So if I would turn down the MBC, would that keep the boost from going up so high (even with creep/spike), and help prolong the life of the turbo? I know it's a T-toosmall, but I cannot afford another turbo at the present time. If I could, heck, I'd run that T-25 till it kicked the bucket just to put it in it's place

Thanks,

Matt

 

[saw wave analog]

i hate to say it but its probably a lot closer to kicking the bucket than you would like, hopefully im wrong.. but mine had 33k miles on it when it died, 31k of those miles it was unmodded being driven by a 50 year old lady.. its just a crappy turbo in every aspect, but yes, if you want it to last i would turn the boost down.. though judging by your post where you said its screaming i am thinking its a bit too late. pull the intake pipe off the compressor and check for oil in there and shaft play, it takes 5 minutes to do and you will know if its on its way out or not for certain

 

[DSMvroom]

solved my problem by installing a hallman pro

no more spikey!

 

[TurboDSM86]

pardon my ignorance but how in the hell do you get your t-25 to hit 14/15 psi at redline? i just dont see that happening...it sure wont happen for me.

 

[ZenkaiRacerDsM]

Maybe if you set it to like 25psi it will only fall to 15psi at redline?

 

[DSMvroom]

i dunno how mine was doing it but it was spiking up to almost 20psi and slowly went down as rpms increased, but only dropped to about 16psi even then.

But anyway it's not a problem anymore because now it boosts up to 15psi all the way to redline. Never spikes and doesn't fall either.