[mark e]

Some of you will know I've had real grief with my BB turbo hitting silly boost levels (2 bar quite easily!) as it spins up too quickly for the software to react and contain it. I've been searching for a solution for a while now (slugging the software didn't help), and a while back I tried using a Dawes Device in parallel with the APC solenoid, but that didn't seem to work at all well and I never pushed it further.

Having given the matter due thought over the last few months I decided to try again and it works!

Basically you tee the input end of the Dawes in to the C line, and the output end of it in to the W line.

In order for boost pressure to rise above base, the APC solenoid effectively holds back the boost until the desired level and then opens slightly to let boost through the the wastegate. Thus there is in effect a pressure differential across the C and W ports. By placing a valve that opens at a pre-determined pressure (enter the Dawes) I have effectively capped the maximum pressure differential across the APC solenoid, and thus max boost

I soldered up the little bleed hole in the Dawes as it was not needed in this application.

There we go- a use for a Dawes/MBC that's actually guaranteed to protect your engine!

Here's the plumbing, which I'll tidy up once it's had a thorough test:

[edit] And of course, this means I should be able to get the software "de-slugged" for an extra bit of responsiveness

 

[wrighar]

Well done Mark.

That's exactly what we want, extra safety in our massaged Saab.

Andrew.

 

[peter messenger]

dont you just love this site.

 

[1989agoodvintage]

WOW! Nice job there Mark.

 

[wrighar]

Mark,

Are you going to demonstrate a Dual MBC setup for those of us with the slow spooling non BB turbo's

One for rapid boost rise, while retaining APC control and you max over boost prtection...

Andrew

 

[mark e]

Hmm... that's an interesting one Andrew, and I must admit I have contemplated it myself. Basically it would involve inserting another Dawes in the C tube between the T off "protection" Dawes and the APC solenoid.

Or, alternatively, if you weren't using APC but a 3 port MBC, you could plumb the Dawes the same as I have shown to provide overboost protection.

Or, put another way, whatever APC/MBC set up you run, if you fit a Dawes in parallel, directly across the C/W hoses, you will have an adjustable max boost limit.

Meanwhile, my ECU is away to have the sluggishnes removed...

 

[ylee coyote]

I have a spare one if anyone is interested in doing an expt....

 

[grentarc]

spare MBC or BB turbo???

 

[briancatt]

Me! Me! I am so cheesed off with this problem and have tried everyhting preumatic and mechanical...its just the really quick surges it can't keep damped, its fine after a few seconds. How do I get me one of those....

BTW I would love for someone to respond to my question re TCS and ABS lights coming on a start up, being reset by switching off while in motion, or after a short stop. Is it the electric pump under the TCS resevoir??

Best,

I have a spare one if anyone is interested in doing an expt....[/b]