SPARKY WRX

I have been reading a lot about the dawes MBC on the forums, but carnt find an answer to my problem. If i fit a dawes device to my 1994 wrx and keep the boost as standard (0.8 bar) do I still need to check air/feul ratio, exhaust temps, knocking, inlet temps & injector pulse widths/duty cycle. etc.????

thanks Mark

Katana

Not needed mate as you aren't altering the boost.....yet.

SPARKY WRX

THANKS, BUT I READ THAT IT INCREASES THE BOOST AT LOWER REVS AND HELPS SPOOL UP.? IS THIS THE CASE?

Katana

Well, yeah but it shouldn't really matter much anyway. Its only a tiny amount anyway.

[Edited by Katana - 11/22/2002 3:36:42 PM]

SPARKY WRX

Ok mate thanks. but what amount of higher boost could i run without the need to monitor the above.

Katana

The minimum thing before I even think of going for a higher boost is a Dawes AFR. I know most old WRXs (like my MY93) runs rich but I wouldn't take any chances if you know what I mean. Try it at 1 bar to start off with first once you've got the AFR. It should be okay.

SPARKY WRX

ok thanks, ill give it a try.

LB4

Katana .... How do you measure the boost with a Dawes? ... does it have a graduated scale on it or something, so you know what its set to, or do you have to fit a boost gauge?

Gary

dhorwich

You need a boost gauge, and you can turn the dawes in to increase boost pressure and out to lower the boost pressure..!!

See here:

http://www.dawesdevices.com/boost.html

Dan

LB4

cheers Dan

Katana

LB4, I wish they had it. But every car is "unique" and it just won't work. I don't think there's any mbc that has that feature come to think of it, unless you get an electronics boost controller.

RRH

The need to monitor the AFR with a Dawes is because of the way the Dawes handles boost. Under certain circumstances the Dawes may produce full boost at part throttle; the ECU is blind to this and cannot adjust fuelling accordingly and there is a chance it could run lean (not enough fuel to support it).

It would be prudent to add an AFR if using a Dawes, even at standard boost pressure. It is essential if you intend to up the boost.

Once you fit the Dawes it will be very hard to resist the temptation to increase the boost. The Dawes at standard boost pressure will give you a smile all on its own, increasing the boost will make you grin like a cheshire cat!

If you do it right, and keep your eye on the gauges, it will be the best £50 you've ever spent!

hope this helps

simon

Katana

Problem is the Dawes AFR only works on WOT.

john banks

A Knocklink would be a good idea

The Dawes is a very cheap way to blow up your engine if you get it wrong.

SPARKY WRX

Why does the AFR only work at WOT and can you get one to work at any throttle position.????

Why does the dawes give you full boost at part throttle under cirtain circumstances, how can this be avoided, "dont want to tweek the throttle out of a bend and find mysely facing the other way in a ditch"!!

My wrx has done 129,000 Km (79,000 miles) will it cope with the dawes.

cheers Mark.

Katana

Your car is still a baby. As for why, ask john, he basically invented it for the scoobs.

SPARKY WRX

any comments John?

john banks

Wouldn't say I invented them... I did popularise a free version in the Scoobynet community.. but it was little that was new. AFR only works in open loop conditions - ie when the ECU is not using a closed loop adjustment using the lambda sensor to keep the mixture at 14.7:1 for catalyst efficiency and emissions/economy. Most ECUs go open loop with any significant boost (some at 0 PSI, some at up to 5 PSI).

The Dawes produces excess boost on part throttle because it is a closed loop control device (although pneumatic) which will stop most of the pressure on the wastegate actuator until its spring is overcome by boost pressure. Since a turbo's transition from not very much boost to potential full boost (it is a recirculating process which is a bit excitable and uncontrolled - like an explosion in some ways) is very abrupt depending on throttle position, this is why a ball spring MBC is a nightmare to drive in some situations. Increasing the bleed hole dumbs it down, but go much over 1.5mm and it ends up as basically only a bleed valve.

SPARKY WRX

cheers John