3B venturi tune for turbo boost

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I’m just about installing turbo to my 3B and try to learn how to adjust the inline fuel pump the right way. I’d like to keep the economy and avoid increasing fuel to the power band where it’s not needed, but there should be the possibility to get all needed fuel when floored.

I have never seen or heard told here that the venturi nipple is turned or the hose of it is manipulated.
AC9E7F68-9BFD-4363-8097-BFF42AD14676.jpeg


I have read that turning it 180° would help quite a lot by giving much more fuel under the boost. Normally it reduces fuel when higher rev’s ”ram air” through the nipple starts to push the diaphragm back in the vacuum chamber. Charged air is heavier, so the fuel compensation starts too soon and in the wrong direction. By turning the nipple to the opposite direction allow the fuel delivery increase to the end. The rev limiter is not working properly because of that. The position of the turned nipple is told to be very accurate (the angle and how deep the nipple is). About 1.5 turn more inward might be about the right.

The other solution is install a bleed valve between the hose or drill about 2-3 mm hole to the hose near the fuel pump.

The diaphragm spring may need to stretch or shim longer, or change longer spring because of the increased vacuum, otherwise the rod may not keep in the max fuel position when needed.

Also some of you said that the timing should retard few degrees, but I’ve heard that by advancing it the consumption and power is the best.

Thoughts?
 
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I also ordered a Mercedes spring part no. A0010740393 for the diaphragm:
 

BreckenridgeCruiser

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Maybe I'm not understanding, but the venturi reads the difference in the pressure before and after the butterfly valve. It doesn't care how much pressure there is, just how much the difference is. When you have it full open, there is no difference so the fuel is fully adjusted (because of the spring). With the valve closed, the diaphragm is moved to reduce fuel adjustment. As you open the valve, pressurized air reaches both sides of the diaphragm based on how much the valve is open so total pressure shouldn't make a difference. If it did, it'd be so miniscule and probably not detectable on these old tractor engines.
 
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It doesn't care how much pressure there is, just how much the difference is. When you have it full open, there is no difference so the fuel is fully adjusted (because of the spring).
Yes, but because of the orientation of the nipple the boosted pressure force is stronger than the diaphragm spring.
 

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In other words... The spring pushes the rack to full fuel when the pressure on both sides of the diaphragm are equal (valve fully open). When half open, the pressure difference will push the diaphragm to change the fuel load.

I do not see how the position of the nipple changes the air pressure on one side of the diaphragm.
 
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The natural position of the rack is full throttle. The lower nipple’s vacuum by the butterfly valve pull the rod back to minimum at idle. The other nipple push it same direction by ram air. That ram air is greater than vacuum when boost come up, at least at part throttle, so the fueling is not linear = too lean. Turning the nipple helps the rod move more like it should be when boosted.
 

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There is no vacuum... Just less pressure than full.

Think of it this way... When the valve is closed, there is boost pressure pushing on one side of the diaphragm, and no pressure at all on the other. When you open the valve 1/4 open at 10psi of boost, then the pre-valve pressure is 10psi and the post-valve pressure is 1/4 of 10 so 2.5psi. this means there is a 75% pressure against one side of the diaphragm.

If you have 20 psi of boost, the diaphragm sees it the same. It now is 20psi on one side and 5psi on the other with a 1/4 open valve which is still 75%.

If the nipple somehow changes the air pressure being applied to the diaphragm, then it may affect the rack, but if the hole in the nipple is not somehow restricted with a regulator of some kind, pressure is pressure and the air will flow to the diaphragm side at full pressure. If you turn it so the hole is smaller, it may delay the pressure building by a second, but at constant valve position, it will eventually catch up.
 
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There is 2 nipples exposed all the time. If you turn the upper upside down, it starts to cause vacuum too while the air mass/boost increases.

Well, but it’s proved and called good thing to do when turbo is installed. Seems to be very common mod here in Finland.
 

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Unless I'm missing something, it should make no difference. I've been on this forum for a long time and had a turboed B series for a long time and no one has ever mentioned this mod. Mechanically, it should not make any difference.

I'm not trying to be a dick, just trying to save you time and effort with a mod that should not make any difference at all. If you get measurable difference I'd love to be proven wrong. Let us know how it goes.
 

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Okay... I think I see what's going on... Are you sure you're not thinking about adjusting a 13BT? The stock turboed direct injected engine has a diaphragm on the boost compensator, where adjusting can affect fuel level based on boost.

The 13BT has a completely different injection pump than the 3B so any suggestions for that engine will not work on yours...

The butterfly valve and diaphragm on the 3B is designed to adjust the fuel based on throttle position (therefore no cable directly to the pump like 13BT or HZ/HDT).
 
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No, 3B here and that’s done for several 3B. 13B-T is ultra rare here.

Here is one writing from our local forum: (translated into English by google)
Adjusting them with nipples is a matter of aerodynamics, i.e. the original purpose of its upper nipple is probably that when the velocity of the air flowing past it starts to be high enough, the dam pressure starts to push it downwards with the vacuum created in the vent pipe. And since there is an overpressure with the supercharger, then the mass of its passing air is also larger, so it starts to reduce its supply before its time.

That is, the purpose of turning the upper nipple is to create a small vacuum at the mouth of the nipple where the effect is opposite. And then because of this, the maximum revolution of the controller no longer plays as it should, but for the inspection the revolutions must be adjusted, for example, with a stopper placed under the accelerator pedal.

And the position of its top nipple is then pretty accurate, that is, how many turns it is in, and what position that hole is in there. That is, moderation to adjust. Usually it is then in place when you can no longer spend time under the hood.

After that you’ll need to drill about 2.5 mm hole to the upper hose or install some relief valve with that amount of leak.
1643702114468.jpeg
 
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I've been on this forum for a long time and had a turboed B series for a long time and no one has ever mentioned this mod.
Same here, I wonder why, that’s why I that is why I brought this up.

BreckenridgeCruiser said:
If you get measurable difference I'd love to be proven wrong. Let us know how it goes.
Well, a little change of plan, I’m thinking that I’m trying to get this thing (BJ42) ready on the road first and drive it without the turbo next summer. Still lot more important to do. But next winter then. The turbo (Holset HE221W) is coming backwards (turbine to the front), never seen that but let’s try.
 
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No, 3B here and that’s done for several 3B. 13B-T is ultra rare here.

Here is one writing from our local forum: (translated into English by google)


After that you’ll need to drill about 2.5 mm hole to the upper hose or install some relief valve with that amount of leak.
View attachment 2910939

Interesting picture.. it appears to be an attempt to introduce a degree of configurability into the vacuum differential provided by the two hoses to the governor housing. I can see where they were headed.
 
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I also ordered a Mercedes spring part no. A0010740393 for the diaphragm:
Got it:
FDF640AC-194F-4AC2-B674-8443404E5FB1.jpeg

26B00163-322C-440A-89F5-DA735F6F719E.jpeg


It was cheap (from LLL Parts):
NoNameQuantityPrice ex. VATPrice inc. VATSum inc. VAT
1A0010740393 (MERCEDES-BENZ)1€1.95€2.36€2.36
2Handling fee1€1.65€2.00€2.00
3Delivery - Economy1€4.13€5.00€5.00
 

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So it definitely looks like a homebrew blow off valve to lessen the pressure on the upper side of the butterfly valve. It would be linear though, and if large enough just lose pressure from the turbo system like a leak.

I'm not sure a stiffer spring would affect much of the fueling since there is air pressure on both sides of the diaphragm on the 3B unlike a boost comp that only has pressure opposite the spring.

It might make it add fuel a little bit earlier, but only at wide open throttle in my understanding of the system.
 

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