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Discussion Starter #1
Tonight after fitting a 20p axle end (button) to the waste rod on the Aero I decided to try fitting a MBC between the W port on the APC and the wastegate to keep It clamped firmly shut until a low preset value (about 7.5psi) for a quick spool up.

It didn't work Horrible overboost spikes up to 20psi and safety cutout. from about 2500rpm, no APC control at all. I ended up undoing the adjuster until it came out and I could blow straioght through it.

Get the revs up a bit higher though 3500+ when boost and APC are normally up and running, and the boost it stable at 15psi as normal and controlled (apparantly) by APC.

Any suggestions?

Should I plumb it another way? I'm keen to keep some APC function.

Andrew
PS. backing the throttle off to keep 20PSI, the car sure fly's

 

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No suggestions on the MBC, but it's definitely a good idea to fit your towing eye for Anglesey (Goodwood insist on it) and I hadn't thought about the driving licence. Just as well you had.

While I think about it (I'll post this elsewhere if someone else doesn't), this is the checklist I've been sent for a number of trackdays:

<ul type="square">
[*]Helmets (available for hire at Anglesey, I believe?)
[*]Clothing covering arms and legs.
[*]Wheel nuts tightened
[*]All Fluid levels & caps replaced
[*]Car fuelled.ie Full
[*]Tyre pressures increased for higher speed
[*]Windscreen Cleaner
[*]Loose articles removed/secured
[*]Towing eyes (modern cars) Fit at beginning of day
[*]Zero tripmeter on arrival - if you wish to count laps.
[/list]

Oh, and MBC fitted, of course

Not fitted your "Baldwin Tuning" sticker yet, then? That would be good for another 10hp

Another frivolous post to increase my post count
 

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Frankly, I am a little curious to see how this could be plumbed so that APC is still working but with the MBC in line somewhere around the wastegate. Mine is non-Trionic of course!!

Regards,
John
 

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Originally posted by BillJ:
[qb]No suggestions on the MBC, but it's definitely a good idea to fit your towing eye for Anglesey (Goodwood insist on it) and I hadn't thought about the driving licence. Just as well you had. ..............................................................Another frivolous post to increase my post count      
 [/qb][/b]
LOL for about 5 mins, wife even came to read 'cos I was LOL'ing so loud
 

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Originally posted by Aero:
[qb]LOL for about 5 mins, wife even came to read 'cos I was LOL'ing so loud  
 [/qb][/b]
Didn't realise it was funny, but I'm just a nosey g1t

On the subject of the MBC, wouldn't fitting it in the "W" line just increase the boost once the APC valve starts to open?

I'd have thought what you need is a Dawes Device in the same location, keeping the wastegate actuator from seeing any pressure until the boost reaches a preset pressure, so preventing wastegate creep and accelerating spool-up.
 

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Originally posted by Griffin #341:
[qb]Mine is non-Trionic of course!![/qb][/b]
Any plumbing we arrive at should work for any version of the APC system, Trionic or not.
Having said that, I don't like the MBC/Dawes approach to fooling such a sophisticated system. My preference is to remap the system. Then again, I'm a software engineer...
 

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Discussion Starter #10
On the subject of the MBC, wouldn't fitting it in the "W" line just increase the boost once the APC valve starts to open?[/b]
This MBC stays shut until a preset pressure and then opens (sounds like a dawes doesn't it).

I was hopeing it would keep the wastegate clamped shut tight until about 7.5psi and then open fully so the APC operates normally.

When the revs and boost aree both well up it does work like this.

When the revs are low, and when the boost is rising from a low figure, it over boosts over 7.5psi (well over, 20+) and cuts out.

I think that the APC duty cycle is too short and that the post mbc ball valve vent hole is dumping the pressure that sould be opening the wastegate.

When at higher starting boost and revs when the apc is normally working harder, it is able to control the boost with the vent hole (and it did at the correct 15psi).

Does that make sense?

Andrew
 

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There are 2 types of mbc - a bleed valve (3 port) and a ball and spring valve (2 port) of which the Dawes is but one brand. In general the ball and spring valves are known as mbc's and the bleed valves are known as..er..bleed valves.

As regards Andrew's problem, I think your diagnosis might be correct in that the boost is being vented before the wastegate is opening, due to a short APC solenoid duty cycle.

First try blocking the vent hole in the mbc. This might well work but it could give a variable response if any 'trapped' pressure keeps the wastegate cracked open. Trial and error will tell if this condition exists.

Alternatively try connecting the mbc in the hose between the turbo compressor and the 'C' port on the APC solenoid, again with the vent hole blocked. This should give a similar result (ie. boost is withheld from the APC solenoid and therefore the wastegate until the mbc preset is reached). Any associated problem of venting 'trapped' pressure would be taken care of in the APC solenoid (via the R port)

Might also be worth removing all the packers from your actuator since the mbc will be doing the job of any actuator adjustment and it might be that the packers are upsetting things (not sure how but just a thought)
 

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I basically agree with Bill's comments about the MBC but, of course, it is a trade off between sensible software control and manic low end BHP with the risk of a blow up.

A good example of why Bill has a point is that I recently removed the MBC for an experiment and found that it boosted HIGHER than when I had my MBC set for 21psi. This is probably because I've fitted water injection and the Speedparts ECU is now allowing boost to rise higher than it previously had without water injection.

However, at the moment I'm still undecided about whether to go back to a non-MBC set up or continue with the MBC (in line with the APC). I like the spool up in 3rd gear and above but in 1st and 2nd it is ridiculous regardless of whether it is wet or dry. As a result, lots of Bath has thick black lines from the exits of roundabouts and just after traffic lights

Alanb
 

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Originally posted by Alan_b:
[qb]As a result, lots of Bath has thick black lines from the exits of roundabouts and just after traffic lights[/qb][/b]
Sounds like you need an LSD. Roundabouts and drag-starts become a breeze. Nothing else is so much fun (well, while driving a car, anyway ). Then again, exploded transmissions and disintegrated driveshaft joints are a good hint to tone it down a bit...
 

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Discussion Starter #15
First try blocking the vent hole in the mbc. This might well work but it could give a variable response if any 'trapped' pressure keeps the wastegate cracked open. Trial and error will tell if this condition exists.

Alternatively try connecting the mbc in the hose between the turbo compressor and the 'C' port on the APC solenoid, again with the vent hole blocked. This should give a similar result (ie. boost is withheld from the APC solenoid and therefore the wastegate until the mbc preset is reached). Any associated problem of venting 'trapped' pressure would be taken care of in the APC solenoid (via the R port)

Might also be worth removing all the packers from your actuator since the mbc will be doing the job of any actuator adjustment and it might be that the packers are upsetting things (not sure how but just a thought)  [/b]
I think I may try the R port placement 1st setting a pressure cut off below 7.5 psi, that sounds more promising (and place a temporary tape accross the vent hole)

The packing washers on the actuator mount bolts is only to bring the base boost up to the correct level as the shaft has rusted solid so can't be adjusted (no thread left and very thin...)

As to blocking the hole while on the R port, I was tempted to do that today, but was unsure to the level of leakage available to the system to vent wastegate actuation pressuere away without the vent.

Andrew
 

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In theory, using this sort of MBC valve is not dissimilar to shortening the wastegate arm, thereby raising the base boost.

However, you can't set the valve accurately in isolation. It needs to be done in situ. It should be inserted between the W port of the APC valve and the actuator. Leave it fully open to begin with, and gradually close it until you achieve the desired effect.

The problem with overboost will be caused by the APC mapping which will expect a certain rise characteristic. In effect, it predicts the expected rate of rise and modulates the APC valve accordingly. If you do anything that affects the rate of rise, then you can give the APC problems. I would guess that is what is happening with you at low revs.
 

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Ive been watching some of these threads about overboosting and spiking with the dawes device, and have been wondering why so many ppl seem to be having these problems when ive had one for a while now and never suffer from it.

I think there are a few different views on how these things can be installed, I have a Dawes device which i actually got from the states a long while back.

I spoke to Darren the maker of the thing, and he advised that the best place to run the MBC from is off the turbo or off the manifold.

If you set it off the turbo you don't suffer from spiking cos you are close enough to the source for it to react quikly.

Running through the apc is only going to slow things down in my opinion, and by all accounts cause problems.

I am confused at why you would want to run a MBC (which in essence is a device to fix the wastegate at a certain pressure) thru the APC (which varies the boost pressure) ?? surely the MBC isn't going to work correctly if the source vacume is varying ?? causing it to spike.



Just my thoughts

Damian
 

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I am confused at why you would want to run a MBC (which in essence is a device to fix the wastegate at a certain pressure) thru the APC (which varies the boost pressure) ?? surely the MBC isn't going to work correctly if the source vacume is varying ?? causing it to spike.
 [/b]
The APC begins to open the wastegate relatively early as boost is still building, I suppose to allow for general day to day driveability for the masses and minimize wear and tear on the driveline. When using an mbc in conjunction with the APC system, the mbc is set to a lower value than max boost (say, base boost or a little above). The upshot is that spool up is greatly improved since the wastegate is held shut until the pressure set in the mbc is reached. At this point the mbc opens and effectively becomes invisible, allowing the APC system to do its job at the higher end of the boost range, controlling max boost with all its inherent safety features still functioning.

There are basically 2 ways to use an mbc:
1. Bypass APC totally and set max boost on mbc.
2. Use mbc in conjunction with APC to improve spool up and low down boost.

I'm am sure I've said this a least 3 times now.
 
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