That's the theory behind any of the boost controllers. In my case the one I chose actually is doing the job quite well. I've met the goal which was to restore normal boost. The car is noticeably more spirited.

...now just have to find some black silicone tubing.

That contraption worked very well on my 83 300D with the Garrette T3. I had to shim the spring as well as max out the adjustment to get boost up to spec. On my 85 with the KKK ?, the waste gate adjustment is easy without having to deal with that difficult to access retainer spring..

I had to remove the spring and ball as it was just too strong - never allowed the bleed valve to see any pressure to bleed off.

Manual Turbo boost
 

Hi Mach4,

Thanks for your post. I have a few questions.

1. You said in your last post you had to remove the ball and spring. Are those items in the waste gate housing? If so, how did you remove them?

2, Did the Vibrant come with good installation instructions?

3. Which model did you buy?

Thanks,

bsdguy

I spent less than $9. for a lpg ball valve and fittings,been using it 6 years.

Have you cleaned the banjo bolt for the ALDA manifold pressure signal? Pretty much not worth doing anything with the turbo until you've done that, and I almost never see anyone mentioning it.

It's on the back of the intake manifold. My 300D was pretty gutless and wouldn't ever shift into 4th, cleaned the bolt and fitting and it's like a whole new car.

No, sorry for the confusion, I wasn't clear. In the el cheapo boost controller housing there is a little ball and spring which is supposed to function as a check valve. It was just too strong and wouldn't allow bleed off so I just removed it. Just unscrew the hose fitting and it will fall right out.

As an update, mine is still working perfectly...though I detest the yellow silicone hose - just haven't gotten the motivation to get around to changing it :)

My boost is low.
I checked at manifold first.
Then on line from overpressure valve to alda.
Then on line to my 85's blue tranny vacuum gizmo.

I got low numbers (about 4-5psi). These with and without overpressure valve bypassed. I once saw 8psi but don't know why!

Today, I clamped the turbo bypass line partly closed using a small pair of vice grips. First setting added 1psi, then second got to 7-8psi. This was with boost measured from manifold port. I stopped at that point.

From this, seems that wastegate must leak or at least have some flow because restricting the bypass flow reduces the pressure.(from ~8 to 4 that the wastegate appears to open at)

Reading above and elsewhere, it seems some owners have just restricted the bypass rather than bleeding off in the manner that Mach 4's original unit did. Seems like the easier way to go. The Mach 4 unit appeared to be designed so that the boost could be adjusted remotely (from inside the car) - hopefully with vent directed out of cabin!

I have oil on exterior of the bypass line near the wastegate. Perhaps I have a leak there?

Next step is to replace the bypass line and see what that does. If nothing, I have an industrial needle valve that I could install in-line in the bypass or I could just use a lab-type hose clamp or buy a more suitable valve or buy a Chinese controller :) I may install my boost gauge permanently, IF I can find a neat way of doing that.

https://assets.fishersci.com/TFS-Ass...~p.eps-650.jpg

I used a similar setup on a couple of Merkur XR4TIs. What I was after was upping the boost from ~14 psi to 18 and both designs (used a different product on each car) worked as designed. The Merkur uses a Garrett T3 and 18 is about as high as you can go and still be somewhat efficient. I think this a cheap and proven way to up the boost pressure.

NB. I've been told the turbo diesels use a NLA T2.5, which I didn't know existed. While this isn't the OP's problem I'd be willing to bet that a T2.5 would be hugely inefficient much above the stock 12psi.

Found a good description of how turbo, wastegate, overpressure valve and alda interact (it's in the FSM!)
https://tinyurl.com/4875zz89

While replacing turbo to wastegate line, I pressure tested the wastegate by applying pressure with my brake bleeder. It took some pumping to get gauge to read at all. When I reached 4psig,and stopped pumping, it leaked back to zero. Repeated after first pressurizing the brake bleeder canister to 20, 15 and 4 psig and then cracking open the valve using this set up.

https://www.dropbox.com/scl/fi/59pdy...6eob85q01&dl=1

Same thing - quickly drops to zero with gurgling sound coming from waste gate. (click for video)

Seems the wastegate is leaking? Some questions:

1. I don't understand where the air goes if the wastegate diaphragm is leaking. Is there a vent? Or is the unpressurized side of the diaphragm open to the exhaust via line C in the diagram?

2. I don't understand, how manual boost controls work if the waste gate is not leaking. I can see that throttling line A can maintain a higher manifold pressure, but only if wastegate is leaking and there is flow through the wastegate. I have done that by clamping line A partly closed.

3. Not sure where, but I think I read something about putting a clamp on the wastegate? Maybe in attempt to seal a leaking diaphragm seal. Is that something some have done?

https://www.dropbox.com/scl/fi/wg91s...3t4e1u860&dl=1

Not sure anyone is still following this discussion, but I will continue anyway ;)

I don't understand Mach 4's post above. He said he removed the check valve, but the picture shows it still in place.

The Vibrant does come with a check valve, but they say it doesn't have to be used. Otherwise, the needle valve just fits on the line from the turbo to the wastegate and the needle valve throttles the flow. Explained in this video.

There can only be flow if the waste gate opens (or if like mine, is leaking :( ) With no flow, the wastegate will always see the manifold pressure regardless and will open at some low pressure we don't like. Then the needle valve will restrict that flow and allow the manifold pressure to build. With the check valve in place, it would have to open first before flow starts and would need to have an appropriate spring for the application. How likely would it be that those universal $20 units would have a suitable spring? Too bad the Vibrant is a bit expensive. A lot more than the hose pinch clamp I currently have :)

Or at least that is my 2c worth on how I think the in-line throttling type boost controllers work.

Question - Why the emphasis on silicone boost line? Not just here, but merc sauce sells that short piece of hose for about $25! It is essentially just an air line with a bit of oil perhaps and could get quite hot. But most fuel injection or diesel fuel hose should be able to handle that.

Not much interest in boost control these days ;)

Anyway, this is my <$3.00 solution (actually zero $ because I had the clamp!). Works perfectly. I used new heavy walled ~3/8" hose that I already had. Set Boost to about 10psig. (It had dropped to about 5psig). Will remove gauge now.

https://spectrumed.ca/en/tubing-clamp-hoffman-screw-1

https://www.dropbox.com/scl/fi/ra2y0...6zcfznrb9&dl=1