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Old 09-12-2002, 11:14 PM   #1
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Exclamation Boost Creep...

Well, I finally installed my boost gauge. I had my Hallman MBC installed for almost a week tuned by the butt dyno. To my surprise I was running .09 Mpa. Not bad to be tuned by feel. At least I didn't go too far with the boost. Now that I have a gauge I tuned it to run about .11. It won't quite reach .11 in 1st gear(from a rolling punch) because the gear is so short, but 2nd and 3rd it holds .11 pretty well. The problem is in 4th and 5th gear where the load is greatest. I reach .12 Mpa in 4th just by giving it a little gas. So, if I'm not mistaken this is called boost creep. I asked a friend of mine if it could be the manual boost controller, he said no. He told me that if the boost is set to a specific psi and it creeps up when under more load then the wastegate is failing to do it's job accurately.

To sum it up, what do I do to control boost creep?


BTW,

.11 Mpa= 15.95 psi
.12 Mpa=17.40 psi

Oh yeah, I have no mods done to my car except the mbc. I have yet to hit fuel cut with the boost set this high. Am I asking for trouble, or can the car withstand this much pressure? A turboback will be installed within a couple weeks.

Thanks.
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Old 09-12-2002, 11:33 PM   #2
amelnikov
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don't let the boost get that high at part trottle. If you see that the boost is getting up to 10 psi at part trottle, either let off or floor it. Tune your mbc with pedal to the metal so to speak.
At part trottle you are running too lean and that's why you are getting higher boost.

Alex...
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Old 09-12-2002, 11:49 PM   #3
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Alex, I understand completely. I need to know why the boost creeps and what I can do about it...

Will an electronic boost controller fix this problem or was my friend right?
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Old 09-13-2002, 12:09 AM   #4
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Default Help me out guys!

I need some help guys. I don't want to tear my car up. Give me some info!
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Old 09-13-2002, 12:37 AM   #5
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bump
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Old 09-13-2002, 12:56 AM   #6
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I can answer part of your question.

Not fully understanding the turbo concept and generally being a dumbass, I bought a bc from a friend (he'd bought the TXS stage 2 and decided he didn't need the auxilliary bc that came with). Installed it and got so excited that I decided to try it out.

On the flat area where I was, I was getting 17-18+ and got scared (not even fully understanding why I was scared...turns out my friend had left it wide open) so I stopped what I was doing and started home.

On the way home is a nice climb and on the way up I completely forgot why I was going home in the first place and gunned it (not even full throttle (partial throttle creep, oh my). The car bucked like it had been shot with a .50 cal and the CEL went on.

When I got it home I immediately got on the i-club to have my butt spanked by all my local WRX friends. FRIENDS DON'T LET FRIENDS OVERBOOST.
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Old 09-13-2002, 02:42 AM   #7
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Quote:
Originally posted by New IP
Alex, I understand completely. I need to know why the boost creeps and what I can do about it...

Will an electronic boost controller fix this problem or was my friend right?
I wouldn't go as to say you have a boost creep issue. What you are experiencing is the fact that turbos produce more boost at higher load. That's why you get lower boost in lower gears and higher boost in upper gears. Boost creap is wnen the wastegate cannot contrlol the boost at all and the boost keeps going up and up and up...
What I would recommend is to tune your boost by doing runs in 3rd gear. Set the boost to about 14 psi. This way you will still get about 12 or so psi in 1st and 2nd and should be around 16 psi in 4th and 5th. And stay out of part trottle boost.
Seriously if you want to aleviate part trottle high boost you will need a sofisticated electronic boost controller or a 2 stage manual boost controller. The first will cost you an arm and a leg and the second will set you back$5-$35 for parts and some elbow greese. I personally have been using ball and spring type mbc ( granger vlave) for over 30K miles and I'm too lazy to add a second stage solenoid that I have laying around. I just learned to keep my eye on the boost gauge and when I see that it goes higher then 10 psi for more them a couple of seconds at part trottle, I just floor it or let off depending on situation. Flooring it always brings the boost back to where it's set and adds fuel to keep the egt's in check.

Alex...

Alex...
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Old 09-13-2002, 03:41 AM   #8
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your boost is creeping because of your stock downpipe, get a downpipe which has room for the wastegate to breath more freely.

jeremy
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Old 09-13-2002, 07:35 AM   #9
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Boost creep occurs when the wastegate cannot divert sufficient gases from the turbine usually at high revs. This is not a problem with a TD04L. You have not proven that you have boost creep until you wire the wastegate open or disconnect the actuator arm and then demonstrate sky rocketting boost at the top end. Otherwise it is not boost creep.

Your problem is that you haven't set up the MBC correctly. Set it for the boost you want when driving at WOT in top gear with the car hot. Accept the lower boost in lower gears as a consequence of lower load.

The part throttle issue can be virtually solved by putting a 0.04 to 0.06 inch bleed hole in the MBC after the ball spring area. This is a cheap ass hybrid MBC.

The load calculation is based on TPS and MAF, hence it will run lean and too advanced at part throttle full boost unless you do the above.
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Old 09-13-2002, 09:51 AM   #10
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Quote:
Originally posted by john banks
Boost creep occurs when the wastegate cannot divert sufficient gases from the turbine usually at high revs. This is not a problem with a TD04L. You have not proven that you have boost creep until you wire the wastegate open or disconnect the actuator arm and then demonstrate sky rocketting boost at the top end. Otherwise it is not boost creep.

Your problem is that you haven't set up the MBC correctly. Set it for the boost you want when driving at WOT in top gear with the car hot. Accept the lower boost in lower gears as a consequence of lower load.

The part throttle issue can be virtually solved by putting a 0.04 to 0.06 inch bleed hole in the MBC after the ball spring area. This is a cheap ass hybrid MBC.

The load calculation is based on TPS and MAF, hence it will run lean and too advanced at part throttle full boost unless you do the above.
So can I just buy a profec B and run 15.5 in every gear? Isn't it smart enough to pull back the boost when there is a greater load?
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Old 09-13-2002, 10:10 AM   #11
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I've not played with the Profec B but I suspect you won't get identical boost in every gear unless you can map per gear (eg AVC-R) AND you make enough load to reach the target you want in lower gears. Live with it?
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Old 09-13-2002, 10:25 AM   #12
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Some relevant info:

related thread

John;

I am EXTREMELY interested in your comment about the LOAD calculation. Has this been confirmed? Do you know the formulation for the calculation? How much is reliant upon TPS and how much is reliant on MAF? VERY VERY interested in this info.

JC
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Old 09-13-2002, 10:36 AM   #13
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I don't have the actual calculation as it is hidden inside a load of assembly language which has not been fully decoded by Ecutek, but I have seen the old shape and WRX making full boost at part throttle and then adjusting the AFR depending pretty much on TPS. On the older ECUs I have experimented by disconnecting the MAF and TPS sensors in turn and looking at the load points accessed from the fuel and ignition maps live.
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Old 09-13-2002, 10:48 AM   #14
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like it was said above boost creep is the W?G's failer to flow enough ehxt gasses away from the turbine wheel. The TDO4l has a very nice turbine housing and a poor DP. A person above pointed this out but was not fully explained. The W/G fires on to a flat part of the DP flange and this is good and bad. Good B/C this forces the gasses to cut in front of the exiting gasses from the turbine and this causes pressure on the back of the turbine wheel. this will force more gases past the w/G and not the turbine BUT it comes at a cost. when higher boost levels are seen the mani pressure is much higher and the gases coming off of the turbine wheel are really moving with force. they are much hotter and if tuned right the heat is at it's max in the scroll of the turbine and this means that it's expanding. this causes and low befoire the turboine and it must be filled while the turbine spins out a hard twisted ehxt pulse. This is a higher pressure then what is coming from the W/G so it will flow less. this in short sucks more in to the turbine and makes for more boost. The W/G has reached it's ability to flow any more and it's cross section area is filled and it's to hard to make the bend int he turbine. All this will effect boost control.

With the added DP the common ones I have see and what we build have a big mouth around the W/G area and the out of the turbine. This helps to get the W/G gases past the area where the pressure is form the turbine wheel and exit a bit more down stream. this larger area also helps with lowering the pressure on the turbine and W/G so the effects are a lot less. or not noticed as much.

So as you see amny things are in the question but as for MBC's Hallman MBC is a good unit, used hundreds and we sell some thing called the Joe P ( same s&^T) and they all work as well as the EVC EZ and profec B and such. I am a fan of spring rates not $1000 boost controlers. the worlds fasters cars mostley run just spring rate as failer is not a option and K.I.S.S. rules.

Hope this helped.
BM-
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Old 09-13-2002, 10:59 AM   #15
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Quote:
Originally posted by john banks
I don't have the actual calculation as it is hidden inside a load of assembly language which has not been fully decoded by Ecutek, but I have seen the old shape and WRX making full boost at part throttle and then adjusting the AFR depending pretty much on TPS. On the older ECUs I have experimented by disconnecting the MAF and TPS sensors in turn and looking at the load points accessed from the fuel and ignition maps live.
Don't leave me hanging man, how much did you find TPS affected the LOAD vs the MAF sensor? Some examples would be very helpful. BTW, your knowledge has been a HUGE help to me in figuring out this damn ECU. Thanks,

JC
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Old 09-13-2002, 11:10 AM   #16
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With the MAF disconnected it runs like a dog and doesn't respond at all well to the throttle so I was careful, did not want to grenade my motor. But blipping the throttle did make it traverse the load zones up to about 1/4 the way across the map. With TPS disconnected it ran badly when blipping the throttle but again traversed the map. With MAP disconnected it ran perfectly. Backed up by findings that full boost at anything above about half open throttle is fuelled for appropriately - hence the bleed on the MBC.

Hence my conclusions why the load is based on TPS AND MAF - with both connected it got further across the map for a given throttle snap.

Your cars may be different and there was talk of different fuel pump voltages for different throttle positions, although it may just be that there is TPS input that was not realised?

The thing is, improvements to VE will be only partially compensated by a MAF setup that also uses TPS. So full boost at under half throttle is a bit too much
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Old 09-13-2002, 12:15 PM   #17
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Quote:
Originally posted by john banks
With the MAF disconnected it runs like a dog and doesn't respond at all well to the throttle so I was careful, did not want to grenade my motor. But blipping the throttle did make it traverse the load zones up to about 1/4 the way across the map. With TPS disconnected it ran badly when blipping the throttle but again traversed the map. With MAP disconnected it ran perfectly. Backed up by findings that full boost at anything above about half open throttle is fuelled for appropriately - hence the bleed on the MBC.

Hence my conclusions why the load is based on TPS AND MAF - with both connected it got further across the map for a given throttle snap.

Your cars may be different and there was talk of different fuel pump voltages for different throttle positions, although it may just be that there is TPS input that was not realised?

The thing is, improvements to VE will be only partially compensated by a MAF setup that also uses TPS. So full boost at under half throttle is a bit too much
John, Thank you so much. That has to be one of the best pieces of information posted on this web forum that I have read to date.

Now (and realize I am oversimplifying the LOAD determination dramatically) but it seems to me that TPS affects the RPM's but can also offset the MAF readings by about 25% from the MAF-only based LOAD determination. This means that by full boosting at part throttle you could be underfueling by as much as 15-25%. I can see now why it is reported by some as a problem and perhaps not by others because it would really depend on how you drive the car... Hence, your comment that:

Quote:
full boost at under half throttle is a bit too much
"bit" being the key word... It is all beginning to become very clear to me now. Basedon what you have just told me, I can see that there is an absolute ton of misinformation posted on this forum.

On a related note, do you have any DD logs of your car running just an MBC? I would be very interested if you do. Email me at jcb@cbcl.ca if you do.

Thanks again,
JC

PS - my apologies for getting off topic a bit.
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Old 09-13-2002, 12:25 PM   #18
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I have quite a few, but with big turbos and not with repeated part throttle runs with controlled variables (very difficult to do) so not very interesting. Also how do you do two runs with the same throttle? So I have a painting by numbers style map fill in for knock correction and timing and drive the car. Smooth transitions across the map seem to do the job nicely. Subaru did the part throttle quite well, so I only adjust the full load areas and fill in the other bits smoothly.

Since I have a narrowband lambda I cannot give you precise AFRs for part throttle full boost, but if you use too small a bleed hole on the MBC it just does not drive right on part throttle. 1/4 throttle full boost just does not feel or fuel correctly so I just avoid it. Present setup gets full boost at over 50% throttle openings and you can set the boost you want with your right foot. No high EGTs.
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Old 09-13-2002, 03:28 PM   #19
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Just a confirmation that you won't get the same boost level in all gears with the Profec B.
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