Manual boost controllers

[Ken Keith]

Hi Trevor,

I've got some comments amidst your post, as well as at the bottom.

On 2 Feb 2001, at 11:41, Trevor Topley wrote:

> Hi everyone,
>                     in my response to turbo whine and the increased
> noise I have after removing the silencer before the IC, I mentioned my
> manual boost controller and bypass valve on my 90 200q. I believe it
> was follow up to this that has started this thread. There seems to be
> some confusion between a manual controller(Hallman, Redline etc)
> versus electronic control(Apexi, HKS, Audi wgfv etc). Phil I think it
> was said about seeing what happens when you feed 100% manifold
> pressure to the top chamber of the wg!! Exactly the same if you remove
> or clamp the hose to the lower chamber. Nothing relieves the exhaust
> flow to the tubo and boost builds very fast! 

I thought the boost in the exhaust manifold itself exerts pressure 
on the actual wastegate, which can open it, even without boost 
being applied to the bottom chamber of the diaphragm.  This is 
slightly different than what you wrote (although I'm sure the boost 
still builds faster than with the bottom chamber hooked up).  Is this 
true (that the WG won't open from manifold pressure alone, not 
acting up the WG diaphragm at all)?

> Now put an adjustable spring loaded ball bearing in the line to the
> lower wg chamber, preset it so that it lifts off of its seat at say
> 1.5bar, because the hose is small and short there is little volume.
> The pressure almost instantaneously goes to 1.5b at the wg and it
> opens - bang. There is no pressure at the wg until the preset level
> is reached, so wastegate cracking is no longer an issue. Boost
> drops, the spring loaded ball reseats. Boost rises again because
> there is a small bleed orifice in the line between the spring
> loaded ball and the waste gate, which relieves the pressure in the
> lower chamber allowing the wg to close. This is how the "ball and
> spring" manual controllers work. 1.5b will be there by 2000rpm
> accelerating at part throttle. Cruising at say 2500rpm, there is NO
> lag, touch the go pedal and it's 1.5b! It absolutely transforms the
> character of the car. Without the bypass valve it was very
> difficult to drive smoothly! Mine is a Hallman, purchased gadget
> for $55, but just a selection of brass fittings and some minor
> mods. Total cost with the bypass $200Cdn. I have been running upto
> 2bar for a year now(12,000 miles on a 115,000mile car, with no sign
> of it retarding, knocking or blowing up yet. It is pretty flat
> around here so the motor is never under load for extended periods.
> I have pulled plugs several times and they look good, exhaust tail
> pipe is black. Gas mileage is good too, 30mpg on long runs. Getting
> high boost without having to go to WOT is very nice, really feels
> like a V8. Obviously I am happy with it, and would do it again.
> Risks, certainly, I have an above average "feel" for the way a
> motor is running and would not reccomend this set up for any one
> who hasn't any. I never did find a reason why my maximum boost
> sometimes drops to 1.7b, and falls to 1.4 in 3rd gear at high
> load/rpm. Since it fixes itself, so far, I'm still thinking the
> problem could be internal in the wg. Any other ideas? 

Did you see the second stage of the manual pneumatic boost 
controller on an ur-S4 motor on the autospeed.com website?  They 
added a check valve going the other way (they have one way valves 
to regulate boost pressure reaching the wastegate).  The theory 
was that boost pressure was getting "stuck" under the wastegate, 
not allowing it to fully close.  When they added a check valve, it 
fixed the problem.

I may be misunderstanding what symptoms they were 
experiencing and fixed.  Also, it doesn't sound like you could apply 
that fix to you system without changing the way your system 
works.  And even worse, when I reread your post, I guess you have 
that bleeder in between the BB/spring and WG, so this probably 
isn't it.

Ken