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Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Just a thought...
Say if I swapped my stock WUR on my n/a for the one with the vacuum and plugged that baby onto some manifold vacuum....do you think it would richen the mixture at WOT with my auto kickdown....to give me some impressive gain....or perhaps flood my plugs and just be plain old silly?

Tiny
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*****1981 - 924 - Auto - London, UK******

Smoothie · Posted: Fri Feb 29, 2008 8:11 am Post subject:

I'm pretty sure it wouldn't do anything.
As I understand it, the "vacuum" line on the full load enrichment WUR is actually for sensing pressure rather than vacuum. -So you'd need a turbocharged or supercharged engine to put that type of WUR into enrichment mode.
[Scrap all that yellowed-out nonsense. See the ** post below.

]

Here's the load enrichment WUR -

Pressure delivered through vacuum port 3 pushes diaphragm 10 down, decreasing spring pressure 7, which in turn allows diaphragm 4 to drop. [The normal, at rest and at 0hg vacuum state of the WUR is as shown in diagram "b".] This increases fuel flow through the WUR, dropping control pressure, which allows the fuel metering barrel in the fuel distributor to rise, and that increases fuel flow to the injectors, enriching the mixture. [When vacuum is high, as at idle and part throttle, vacuum pulls diaphragm 10 up to lean the mixture as shown in diagram "a".]
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Ozzie · Posted: Sat Mar 01, 2008 9:32 am Post subject:

on the other hand if you increase pressure wont it force diaphragm 4 closed?
Where if you decrease pressure the fuel pressure would force no 4 open?
Suppose it depends on the size of 4 & 10 working against each other and the spring.
A good question is - what is manifold pressure at WOT for a turbo?
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Smoothie · Posted: Sat Mar 01, 2008 11:50 am Post subject:

Yeah, apparently the fuel pressure above diaphragm 4 is more than enough to negate whatever air pressure is applied from below it.
Maximum manifold pressure is in the area of 0.43-0.73 bar from the factory (unmodified), depending on market, model year, and engine-turbo-wastegate condition.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Ozzie · Posted: Sat Mar 01, 2008 1:47 pm Post subject:

In PPC magazine (jan 2008) it actually says to instal later type of pressure regs with a manifold pressure connection. How applicable it is to the NA is unknown.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Smoothie · Posted: Sat Mar 01, 2008 4:11 pm Post subject:

**- Ya know, after looking at that diagram again, something pretty obvious occurs to me now.. In diagram "a" diaphragm 10 must be being lifted up by vacuum. -Then in diagram "b", at 0 hg vacuum (WOT), 10 would drop down by that inner springs' pressure...so you wouldn't actually need positive manifold pressure to put that type of WUR into enrichment mode - it would happen starting at approx 0 hg vacuum or a bit before. Duh!

-So I'll have to change my mind on that need for turbocharging or supercharging. It should provide enrichment at WOT with an NA engine.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Ozzie · Posted: Sat Mar 01, 2008 4:30 pm Post subject:

It should work cos how much pressure down is that bi metal strip gonna make?
On a NA that is all that pushes it open when cold.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Smoothie · Posted: Sat Mar 01, 2008 11:33 pm Post subject:

Actually, both "a" and "b" in the above diagram were showing the bi-metal spring in its' warmed-up position - when it's not affecting the valve.

This one depicts the cold, and warmed-up position of the bi-metal spring -

_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Ozzie · Posted: Sun Mar 02, 2008 8:45 am Post subject:

My point is - if a bi metal strip can open a WUR (fuel assisted) then vacuum should have no trouble.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

tuurbo · Posted: Sun Mar 02, 2008 9:35 am Post subject:

This is very interesting. Smoothie - are you getting these great illustrations from a Bosch manual? They're pretty clear and in color unlike the Porsche manual ones...

Ok so if I have a WUR from an NA, it won't work on the turbo, is that correct?

Smoothie · Posted: Sun Mar 02, 2008 12:32 pm Post subject:

They're from "Bosch Automotive Electric/Electronic Systems" ("out of print") shown at the bottom here -
http://www.sjmautotechnik.com/books/boschbooks.htm

This one's very good too -
http://search.barnesandnoble.com/Bosch-Automotive-Handbook/Robert-Bosch-Gmbh/e/9780837615400/?itm=1
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Sun Mar 02, 2008 12:34 pm Post subject:

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Thanks for your excellent input guys. I'll try to get a hold of one and try it out and post my results.
I was just panning for gold/HP while looking through the Bosch book by Probst. =]
Tiny
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*****1981 - 924 - Auto - London, UK******

tuurbo · Posted: Sat Mar 08, 2008 1:24 am Post subject:

Maybe one of you guys can answer this: How the heck do you GET AT the WUR from up top to remove it?

Should I move the coil? Start pulling things off? Or what?

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

Remove the coil and dislocate your wrist. I think I used my stubby ratchet.
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WeiBe (1987 924S 2.5t) - 931 S3