telling the difference between

[pitslayer]

ive always wondered this, and just thought about posting it. but how do you tell the difference between a genuine MBC/dawes device, against a bleed valve?
ive been looking on the net, and to me they both look relativly the same, just wondered thats all

[apeman69]

When I was looking to buy my MBC I was confused by this also. It seems that all manufacturers tend to mention 'valve' somewhere in their info and this was misleading me a bit. From my research I could not find a bleed valve for purchase at the time I was looking. The usual suspects (e-bay sources, Turbosmart etc) seem to be producing ball and spring type manual boost controllers.
From what I found these are not bleed valves. A bleed valve is open all the time to some degree and the adjustment you can make is to the degree of openness(!?).
The ball and spring type MBC (Dawes device) is virtually the same as a bleed valve apart from the fact that the spring produces pressure on the ball which effectively closes the valve or opens it depending on the pressure coming down the vacuum pipe. Once the gas is at a certain pressure (determined by your adjustment) the ball will move and the path through the Dawes device will be open. The adjuster on the MBC just shortens or lengthens the spring by pressing against it (making the spring harder or softer if you like) and this effectively determines the pressure at which the ball will move and thus allow the gas to move through the device.

Try this link for some info:-
http://www.boostvalve.com/infofaq.html

Having said this I cannot work out how the fcuk mine works because it is not the traditional L shaped Dawes device design.

In fear of hijacking your thread can anyone more knowledgable have a think about this and let me know.
Here's my thread from when I was trying to fit the thing and it will show you what it looks like:-
http://www.clubvr4.com/forum/showthread.php?t=31684

The t-piece block has a ball and spring mechanism within it which moves depending on the pressure from the boost source (red tipped inlet pipe). The movement of this ball just opens the path to the adjuster which then does I don't know what. This must have some sort of pressure regulating system within it too, linked to the vent hole maybe. How can the boost then get past the ball in the t-piece and off to the actuator? I've thought about this a couple of times and short of dismantling (with a hammer) the thing I'm stumped. Anyone able to shed some light? When I checked the t-piece block I found that the ball would only move one way and it's movement opened or closed the route to the adjuster part of the MBC. What's going on?????

[apeman69]

:inquisiti 55 views but no comments?
Did I get it right for a change then? :inquisiti

[Kenneth]

By looking at the thread you linked to, it looks like your boost controller is a bit of a hybrid.

edit: after re-reading your post it seems to do the stupid thing and bleeds off after the ball and spring.
I would think this makes it rather touchy to adjust.

Go somewhere and buy a lighter weight spring, put it in and see if it makes a difference.

Because a wastegate can partially open under low pressure, the ball and spring prevents any pressure from being applied until the boost pressure overcomes the ball and spring pressure.


There is not always any visual way to tell the difference between a dawes and bleed type MBC, however it tends to be that a bleed valve has 3 openings in it. One for the boost reference, one for the wastegate and then one to atmosphere.
A dawes device only needs a very small (i.e. 1mm) hole to bleed off pressure from the wastegate line.


As an aside it usually isn't very hard to modify a bleed valve to be a dawes device as this is how I did mine.

[pitslayer]

yeh, ive got the pics you sent me on how to do one, but was more curios on if there was a difference :)