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Very simple, allows me to switch back and forth from my MBC to ECU control while I drive. I love the low-end torque of the MBC but it gives me tractions problems and lower gas mileage. Instead of trying to explain it all I made this diagram.



(All black lines are pressure hoses and the colored line is the electrical power)

Parts Needed:
12V solenoid
A few cm/inches of hose
2 tee fittings
Some electrical wire and a switch

The differences between the MBC and the ECU are very apparent. The MBC has much better torque up to ~3400 rpm but above that the ECU gets pissy and retards timing, the power feels very flat from then on to redline. When the ECU is in control low-end torque is about 40 ft-lbs lower (proven by dynos) and max boost is only 18 psi. The top end however feels much stronger and continues to push me into the back of the seat. It is interesting to note that above 4000 rpm the T25 turbo can only manage 16 psi, so even through the MBC and ECU are supply the same boost pressure the power outputs are very different.

The next question is obvious, how to work the switch to get the best of both worlds. It would be a hassle to try and switch it every time I ran it up the rpm band. Maybe if the switch was mounted on the top of the stick shift, but I really don’t want to start cutting that up. Maybe an electrical switch tied into the rpm signal?

Eric
 

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Brilliant idea, Eric.

As per your own post, it's probably best to have it triggered by RPM's.

One question though. When the boost selenoid is activated, will it act like there was no MBC installed? The MBC will still leak some vacuum and may influence the amount of vacuum the boost selenoid is aiming for, or will the ECU compensate for that?
 

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Eric,

Interesting stuff, which I will try to get some time to wrap my head around and give some feedback. My brains's too dead at the mo having spent all day ripping out my bathroom and (finally) starting on the tiling after having done all the wiring and plumbing...

Mark
 

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Interesting idea but I'd like to see how well it transitions from mbc to apc. W

ould you see a sharp rise or fall in boost (and thus power) at the switch over point?

Andrew
 

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Definitely an interesting idea, Eric! Like Scaero owner, I'd wonder whether the transition would be fast enough, but I'd tend to think that (esp if you could tie in the changeover automatically to the RPM signal) it would be able to be done without any significant drop in boost. Try it and let us know how it goes....
 

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interesting...
there is a company in blackpool doing something similar but they have a 3 and a 6 level boost switch which must work in a similar way..
for the price (£150) I do not imagine it is electronic map sensor controller !!
I think they are called motorsport developments btw
 

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(emerges from bathroom, swearing...
)
The difficulty I see is not where to derive your signal to switch, but the mechanics of the switch itself. An instaneous cut over from one to the other is likely to be harsh as you've no way of knowing how far open the ECU will have driven the APC solenoid. My suspicion is that because it is sensing it has no control, it will be applying minimal boost, so at the switch over point you would suddenly get a reduction in boost, and then a rise again.

That, of course, assumes an instantaneous switch over and that the valve is the electrical equivalent of break before make ie port 1 is closed before port 2 opens. If (as is likely) it's not an instantaneous switch, then you have a situation whereby there's no pressure getting to the actuator-so boost could rise to fuel cutoff point if it got stuck in this condition. As a safety measure you could install a Dawes device in a separate line from the compressor to wastegate, therby limiting your maximum boost

The alternative of having a "mixing" valve that you can alter the rate of actuation on may be the best compromise. The problem with this method is that you can end up with both devices trying to bleed pressure off, resulting in a sudden increase in boost. However, if you get the actuation time right- short enough to avoid a rise in boost, long enough for the ECU to realise it's in control and adjust, I would say that this is the best route.

HTH
 

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I agrre that the idea is quite interesting. But in my thinking, I do not think that it can be made to work so well. My reason is that the ECU will have to readjust itself constantly.

From my experience of running a mbc and then switching back to ecu control, the ecu was not very fast at adapting itself back. It could be brought back to full boost in one run, however, the boost was always dialed way back and did not do a full recovery until at least 3 or 4 seconds of full throttle. If this were to happen as you switched from mbc to ecu control, you would be shifting into the next gear before the ecu could recover back to full boost.


I agree that it is worth a try but I think the ecu doesn't readapt quick enough.

Good luck!
 
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