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Old 11-17-2002, 08:38 PM   #1
rex n effect
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Default I get 1.1 bar boost spikes with stock boost control. Is this dangerous?

Hi,
I recently installed a vishnu uppipe, samco intercooler hoses, and a TurboXS turbo back exhaust. I installed a couple gauges too(Omori electronic boost and EGT). I notice that at WOT in 4th and 5th gear, right around 3000 rpm, I get a boost spike sometimes to 1.1 bar for about a second. Could this be detrimental to performance? Could it cause the ECU to pull timing? Why does it happen? I didn't have the gauges when the car was stock, so I don't know what the boost curve looked like before. By the way, I get 1 bar of boost at 2,500 rpm in 5th. I don't think it did that when stock! I'm very satisfied, but I'm just curious about the spike.

Thanks
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Old 11-17-2002, 09:39 PM   #2
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Hmm.. I think it is definatly something to be concerned about, but if your car is running rich like my car is with the stock ECU it will probably be ok. 1.1bar is 15.95psi just as a reference so you are nearing the threshold of the stock turbo. I doubt you need to lower it, but with the FBC you don't have that option to play with the settings. You can always buy an MBC/EBC and lower the boost settings etc.
edit: In most cases the boost setting will be higher in the higher gears. It has to do with the load on the engine+the actual duration of the gear eg. In my car in 3rd gear I am at .1bar at WOT, but the pressure rises as I go into fourth, and by 5th gear it is actually at 1.1bar for a second or two before slowly dropping as the rpms increase.

If I had one of those fancy EBC's I could probably tune out the spikes etc.

Last edited by PaulRex; 11-17-2002 at 09:44 PM.
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Old 11-17-2002, 09:51 PM   #3
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That doesn't sound right, is it possible you have a leak in one of the vacuum lines on the turbo side? I believe TurboXs' ABC basically does this for you with adjustability, all it does is not allow the ECU to see the full amount of boost your by bleeding some of it off before it gets to the FBC so your ECU thinks your running 13.5 psi since that's all it's sensor is telling it it's seeing. Bottom line check for leaks in your vacuum lines and make sure the restictor is still in place. You didn't happen to do the 3/16th mod did you? Let us know what you find. Another possiblity is the boost gauge is off what are you idling at with the AC/def off. The only problem you may see is knock being cased by a lean condition but it's doubtful when your only peaking at 16 psi.-James
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Old 11-18-2002, 12:38 AM   #4
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Quote:
I believe TurboXs' ABC basically does this for you with adjustability, all it does is not allow the ECU to see the full amount of boost your by bleeding some of it off before it gets to the FBC so your ECU thinks your running 13.5 psi since that's all it's sensor is telling it it's seeing.
That doesn't quite make sense? The FBC is an electronic bleed device (PWM run solenoid), it doesn't measure anything. Your MAP sensor does the reading, and it is hard to bleed anything off the MAP sensor as it is bolted directly to the inlet manifold.
That is why I built an electronic circuit to "remap" the MAP sensor voltage, to do what you described above(ish).
What you described is a problem with sticking a bleed valve on the FBC system, in that the factory controlled boost will peak more quickly but the "closed loop" nature of the FBC will quickly try to keep that boost in check. Changing the diameter of the little brass restrictor will alter the boost characteristics too (too small will cause "peaks" which can also cause oscillations in higher gears as the factory system stuggles to keep the boost level at whatever it is trying to achieve), so check that it doesn't have some junk blocking it up (although it sounds to me like your small peaks are nothing to worry about, it is fairly normal).
R's
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Old 11-18-2002, 01:52 AM   #5
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I hit 1.1 bar 100% bone stock except samco hoses. Not sure how it happened but I'm sure it lasted for .0001 seconds
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Old 11-18-2002, 08:27 AM   #6
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It is perfectly normal given your setup, and perfectly safe as well....
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Old 11-18-2002, 08:55 AM   #7
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I had some spikes like that using the FBC. I was not to worried, but reset my ECU and everything went back to normal.
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Old 11-18-2002, 10:10 AM   #8
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i have the same exact thing .. ..
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Old 11-18-2002, 10:40 AM   #9
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Is is the exhaust causing this? Or does it happen with stock exhaust as well?

Will you get any boost creep with this sort of setup?
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Old 11-18-2002, 01:51 PM   #10
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Its a result of less backpressure courtesy of your up and downpipes, coupled with the factry bleed system, which is inadequate even on a stock WRX. A good ball and spring MBC, or better yet, a good EBC will solve this easily.

Adam
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Old 11-18-2002, 03:08 PM   #11
rex n effect
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A MBC will solve the problem? I thought that might make it worse. I'm pretty sure there's no leaks anywhere. For some reason, I thought 1.1 was higher than 16, so I was worried. If it's only 16psi for a second, it's probably nothing to worry about, right? I run fairly low EGTs too, so i'm pretty sure the car is running rich. I have the vishnu MBC and unichip tuned for stage 0 w/turboback, but I was waiting to put it on until I'm comfortable with the setup.

Thanks!
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Old 11-18-2002, 06:24 PM   #12
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look on your muffler tip- soot?

wot the car does tend to run rich

the one problem revisited over and over agiain wiht a mbc is partial throttle high egts

speed safely

Brian
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Old 11-18-2002, 08:11 PM   #13
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Quote:
Originally posted by tonymy01

That doesn't quite make sense? The FBC is an electronic bleed device (PWM run solenoid), it doesn't measure anything. Your MAP sensor does the reading, and it is hard to bleed anything off the MAP sensor as it is bolted directly to the inlet manifold.
That is why I built an electronic circuit to "remap" the MAP sensor voltage, to do what you described above(ish).
What you described is a problem with sticking a bleed valve on the FBC system, in that the factory controlled boost will peak more quickly but the "closed loop" nature of the FBC will quickly try to keep that boost in check. Changing the diameter of the little brass restrictor will alter the boost characteristics too (too small will cause "peaks" which can also cause oscillations in higher gears as the factory system stuggles to keep the boost level at whatever it is trying to achieve), so check that it doesn't have some junk blocking it up (although it sounds to me like your small peaks are nothing to worry about, it is fairly normal).
R's
Tony
Can you explain to me how the MBC works then , I may have misunderstood this in a thread I read a while back. Basically it bleeds pressure off to fool something, what is it fooling, the FBC?Why is it that pulling the hose to the FBC or bleeding air off the line to it gives you more boost? btw why is this normal? Is my car a freak because with Samco intercooler hoses, a free flowing uppipe, downpipe, and muffler I didn't see more than 14.5 psi.

Last edited by jjunior887; 11-18-2002 at 08:20 PM.
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Old 11-18-2002, 09:52 PM   #14
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The way an MBC works is like this-
The FBC gets totally disconnected and you cap off the FBC hose so that no air gets in there.

Your MBC should have two nipples on it(like most women I've met); On one nipple the an hose connects the MBC to the wastegate actuater, and the other hose connects to the high pressure connection off of the turbo. Essentially what any MBC ball&spring or just a bleeder does is bleed off air to the atmosphere diverting it from the wastegate actuater. The Wastegate actuater has a line connecting it to the actual wastegate inside the turbo on the exhuast side, it opens up the little flap that lets the excess air go out with the exhuast to keep your turbo from just spinning as fast as it can and also keeping the boost pressure down.
The MBC gets between the Turbo pressure outlet and the Wastegate and bleeds some air off, the wastegate actuater has a spring in it with a preset level at which it will start to open; On WRX that level is around 7-8psi(that is the most boost pressure you would get if you did not bleed any air off)

Wastegate<<---MBC<<----Turbo high pressure nipple

An EBC works the same way only using a system more like the FBC with a dual solenoid that will pulsate open and closed etc. to control how much air gets bled off. Hope this explains it.
Paul
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Old 11-18-2002, 09:55 PM   #15
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Thanks for clearing that up for me, I never intend to use a MBC but I figured it would be nice to at least know how it works. -James
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Old 11-18-2002, 10:34 PM   #16
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I have a quick question, My friend has a 02 WRX and he went to a shop that have a wrx there, the guy told him that the turbo can run 30psi??? can this be true? also my friend got a MBC and he had a spike up to 22psi. where did u guys hear that the turbo can only make 17psi? where can I read about this. thanx!
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Old 11-18-2002, 11:03 PM   #17
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M///Scooby: You haven't read a lot about turbos on i-club I take it?
The turbo may be lucky to reach 30psi (although I really doubt it, mine while playing with high boost fuel cuts managed to touch about 22psi before I panicked and backed off the throttle), but it would be blowing so much hot air that your engine would detonate to death (or pull so much timing that your horsepower would be down, your engine heat up, piston melt due to severely retarded timing and severe inlet heat etc).
Look at the efficiency charts for our turbo, and you will see that 14psi is at maximum efficiency, 17psi is a *little* down on efficiency (but OK at certain RPM ranges). Anything beyond 17psi, especially in the higher RPM (hence higher flow requirements) is pushing the turbo way out of its efficiency range. This is why some of the VF series (VF-24/28/30) doesn't have THAT much more maximum boost than ours, but has an extended efficiency range (and flow rate) and thus produces cooler air (and better flow) at the expense of spooling up a little later due to its larger size. Not only that, but the factory fuel cut trips in at about 17 to 18psi (well, here in Aus..)

There is a thread here in i-club comparing a whole bunch of turbos. Look at that one for the charts.
Hope this helps.

As for the MBC question, Paulrex describes it well.
The MBC "fools" the diaphragm spring that less boost is hitting it, just like the FBC fools it, but the FBC uses a lookup table and then does adjustments on the solenoid based on the MAP (pressure) sensor readings, where as an MBC is typically just a manually adjusted hole, or a manually adjusted spring. You can't have a MBC in line with the FBC, as the FBC really only works well with short hoses connected, and the ECU manages to work against what your MBC is trying to do (unless you adjust it to out of the maximum adjustment capability of the FBC, but then you are really just running the MBC....)
I don't want to confuse this thread too much more, hopefully you can understand all that!
Here is the thread regarding changing the MAP voltage to allow the factory system to up the boost without MBCs etc (so pretty much follows the "tapered" factory curve, but slightly more aggressively).
http://forums.nasioc.com/forums/show...hreadid=167448
R's
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Old 11-18-2002, 11:26 PM   #18
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hey thanx for the info, I was just wondering, and yes I am new, and looking to get a wrx in a month or two, so I just want to get to know the car as much as possible. thanx again, Oh and also can you tell me what "bump" means?
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Old 11-19-2002, 03:06 AM   #19
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Quote:
Originally posted by WRX Power
I hit 1.1 bar 100% bone stock except samco hoses. Not sure how it happened but I'm sure it lasted for .0001 seconds
Mine would get that high once in a blue moon also.
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Old 11-19-2002, 03:35 AM   #20
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Spikes are nothing to worry about. Overboosting is only a concern when it's holding too much boost.

Ryan
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Old 11-19-2002, 03:36 AM   #21
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"bump"?
In what reference?
Hit another car, hit a speed hump...
or...
to bump the thread to the top of the list so more people can read it/answer it (if it drops off the bottom of the list, sorted in date order, no one will read it).
R's
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