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Location:
Adelaide
Registered:
July 2002
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boost creep help pls!
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Fri, 18 March 2005 11:00
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hey
wacked on a 3" dump pipe to the mr2 ct26 turbo along with full 3" pipework and now i cant hold boost, i used to be able to hold boost with no probs, maybe a 1psi creep when reving up to like 6-6500
but now if i set the boost to be like 10psi it will get there by about 3000 but by 4200-4500 it has started to creep and by 5500 has hit boost cut at 14psi this is a pain in the ass as i really wanted to hold 12psi. i've looked at on here and on the mr2 sites the mr2oc.com and the slender.mine.sumthing site and found lots of ppl with similar problems but no one seems to offer a fix. im pretty sure the problem is not with the wastegate not flowing enuff as it was doing a fine job before but is it possible that the wastegate is hitting the inside of the dump pipe and so its not opening fully?
ive heard that putting a restrictor in the boost controller to wastegate actuator line may help the problem?
ive got a FCD, which is basically a 10k pot and a resistor, and also a MBC from flynn.com its a bleed type valve but with the stock exhaust i was able to hold 12psi with out to many probs. the TVST thing has been blocked up and the extra plug on the wastegate has been blocked up as well.
Cheers for any help
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Location:
Adelaide
Registered:
June 2002
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Re: boost creep help pls!
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Fri, 18 March 2005 23:17
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Hi mate-yeah, it does sound like a W/G problem. Once you whack a decent exhaust on sometimes you can improve the efficiency of the turbine so much that to stay at your set boost level requires more gas to be bypassed than the W/G can flow. (I have seen this specific problem on a CT26 before actually.)
There are a few of things you can do.
1-check that you are getting the full travel on the gate flap.(if not and you free it up-check and see if it still happens)
2-pull off the turbine housing and have a larger hole bored for the gate and a bigger flap put in there.
3-bore out the back of the turbine housing for more clearance from the wheel to the housing-this drops the efficiency of the housing/turbine system, but is really a step backward and is bandaid.
4-put a restriction in the exhaust to reinstate the backpressure you got rid of with the new exhaust as a temporary measure to get you by.
5-put a pressure reg in the signal line to the BOV and set it to just under your W/G setpoint. That may bleed off just enough boost to keep things under control.
Basically though, if it isn't #1, then enlarge the W/G-it isn't that difficult or expensive.
I'm in adelaide too, so give me a buzz if you get stuck, I've got access to most of the stuff needed.
Cheers
Sean
Eden Hills
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Location:
brisbane
Registered:
December 2004
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Re: boost creep help pls!
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Sat, 19 March 2005 05:35
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yer i got the same problem i hold 10psi to bout 4k then it clumbs to 12 by 6000rpm
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Location:
Adelaide
Registered:
July 2002
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Re: boost creep help pls!
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Sun, 20 March 2005 22:31
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crap
its the wastegate not being able to flow enuff, stupid toyota.
ok now for the fun bit, pulling the turbo off, whos got a 4 poster hoist??? hahaha
i think ill just live with it.
berad what kinda setup you got? coz mines creeping a lot more than yours, what boost controller are you using? still using the stock dump pipe?
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: boost creep help pls!
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Sun, 20 March 2005 23:25
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have you tried putting your boost level back to stock? Do you still experience boost creep then?
If not then possibly your cheapest solution is to use a programmable electronic boost controller. With one of these you would be able to have the wastegate pressure source controlled in a variable manner based on RPM etc, meaning that you can keep the 10psi boost level down at low loads by restricting the boost source to the wastegate actuator, and then allowing more of that boost source thru at higher RPM to counteract the boost creep.
Of course if you still have a boost creep problem with stock boost setting (ie, wastegate connected DIRECTLY to boost source), then you will need to look at getting the wastegate size increased, or running an external wastegate  Importbitz has some DAMN GOOD PRICES on some..... they are one of our sponsors too.
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Location:
Adelaide
Registered:
July 2002
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Re: boost creep help pls!
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Sun, 20 March 2005 23:33
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with the bleed valve fully closed ie straight thru from compressor to wastegate actuator i *shoud* be making 7psi as that is the stock spring pressure on the wastegate BUT it creeps to 10-11psi by 6000rpm
mmm external wastegate....doh! need a new exy manifold to.
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: boost creep help pls!
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Sun, 20 March 2005 23:43
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you dont necessarily require a new exh. manifold for an external gate!!
There are a bunch of MR2 guys (and gt4 AFAIK) in the states who just make an adaptor plate for the turbo flange which gives another flange for the external gate and of course the flange for the turbo. I dont know if my explanation makes sense to anyone other than me.....
anyway, with the setup you have now, a programmable electronic boost controller would be able to curb your boost creep problem, as with the wastegate line fully open you are still at a desirable boost level.
To explain in lamens terms, a programmable electronic boost controller is like a bleed valve which you can vary at set engine load points 
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Toymods Vice President
Location:
Sydney
Registered:
May 2002
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Location:
Sydney
Registered:
October 2003
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Re: boost creep help pls!
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Mon, 21 March 2005 00:07
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That's good to know Josh! I'm about to get a custom exhaust (inc dump) made up. I'll definately tell them to beware of this problem.
Do you mean that the flap pysically hits the pipe or that there is a pressure build up in the wastegate area that stops it opening fully?
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Toymods member
I supported Toymods
Location:
Rydalmere, NSW
Registered:
May 2002
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Re: boost creep help pls!
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Mon, 21 March 2005 00:09
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I might have the same problem on mine, because my boost level doesn't taper-off at higher RPM's. It keeps going onto about 15 or 16Psi whereas I believe the standard pressure for an ST205 with twin 20mm internal wastegates (what I have) is no more than about 11Psi.  Would this be a boost creep problem? I also have a custom dump-pipe made to suit a 3" system and it's made to shape around the standard GT-Four turbo flange. As far as I can tell, the wastegate actuator isn't hitting anything... 
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Location:
Adelaide
Registered:
July 2002
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Re: boost creep help pls!
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Mon, 21 March 2005 00:12
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got the dumpy off ebay, generic stainless steel puppy. its REAL pain in the ass to pull it off to check but i had a look at the stock pipe and im like 99% sure that there is more room for the flap in the new pipe than there is in the stock pipe.
still not sure how a EBC is going to work tho, for example i'm at 4500rpm making 13psi of boost, MBC is set to 10psi, wastegate, i assume, is fully open yet boost is still increasing with rpm
how do you make the wastegate flap move, like say ive got the dump pip off so i just pull on the arm coming from the actuator? should there be a lot of resistance?
cheers
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Toymods Vice President
Location:
Sydney
Registered:
May 2002
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Re: boost creep help pls!
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Mon, 21 March 2005 00:34
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I'm talking about the actual flap touching the inside of the dump pipe, generally it catches on the flange but sometimes the pipe comes across to early and that's where it hits.
As to the EBC question. Your post earlier says that without the MBC you can get the car to only hit 10-11 PSI. The idea behind an EBC working for you is that it is able to be mapped so you can have the controller having no influence at all in the higher revs where you have creep issues but also have the controller allow you to run higher than actuator pressure at lower revs.
Do you have the T-VSV disabled and disconnected?
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Location:
Adelaide
Registered:
July 2002
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Re: boost creep help pls!
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Mon, 21 March 2005 02:15
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ahh i get ya, so with the MBC even after it has hit the set boost limit say 10psi even when its creeped to 13 the wastegate is still not fully open and an ebc would put all the boost pressure to the wastegate
i have to take the car back to get the bolts tighted on the dump pipe as i cant get to them, ill have the guys take off the dump pipe and see if it is catching anywhere. If it is, its dremel time 
on the wastegate actuator there is two lines, now if im standing on the passenger side of the car looking at the compressor side of the turbo the line from the wastegate actuator that is on the left, closest to the turbo is the one i ahve the MBC on the other one closest to the engine is blocked up with a hose and bolt. the line coming from the t-vsv is also blocked with a bolt.
glad i picked the hardest car on earth to work on..not
thanks for all the help guys
hey witzl will your boost controller thingy mabob be any good for this prob?
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: boost creep help pls!
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Mon, 21 March 2005 04:07
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yeah the boost controllers i have will do the trick, as you can limit the pressure seen by the wastegate down at low RPM, then increase it at higher RPM to get a resultant nice flat boost curve.... with a little bit of time and fine tuning
i would still be inclined to check the whole wastegate flap thingies as josh suggested - he knows lots more about 3S-GTEs than i think i do!! Cheap insurance really
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Location:
brisbane
Registered:
December 2004
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Location:
Newcastle
Registered:
June 2004
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Re: boost creep help pls!
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Mon, 21 March 2005 06:25
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Mine generally runs 10psi and creeps to 11psi. No biggie really. I'm gonna crank it up to 14psi soon, hope it doesn't creep much there!
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Location:
Adelaide
Registered:
July 2002
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Re: boost creep help pls!
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Mon, 21 March 2005 10:54
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interesting what dump pipe u using cycle??
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Location:
Newcastle
Registered:
June 2004
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Re: boost creep help pls!
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Mon, 21 March 2005 11:26
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My cat is bolted straight onto the turbo. Dunno if its a hi-flow cat (my guess is no). One day when i have money i'll get a propper exhaust.
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