WUR part# compatibility?

[Tim Hancock]

My 79 SC has a Bosch # 0.438.140.072 which is for an 1980 SC.
It does not have vacuum ports on it. I understand how the WUR is supposed to enrich the mixture at WOT on a 78/79SC. A friend offered me a 0.438.140.033 (1976/1977 part number) to try. I am supposed to have a 0.438.140.045 for a 78/79 SC.

Does anyone know what difference is between the .033 vs the .045 WUR. I would guess that there is some sort of difference but maybe it would work OK? I am most interested in ensuring that I get enough enrichment at WOT. The present non vacuum WUR seems to work OK for warmup issues, I just think I am being short-changed at WOT conditions.

[Paulporsche]

Tim,

I can't post the graphs for you, but I can tell you the control pressures as shown.

The .045 unit has a cp @ 10C of 1.6-2.05 bar and a warm @ 40C of 2.75-3.4.

The .033 is 10C .6-1.05 and 40C 2.2-2.6 bar.

We know the problems of too high a cp. I guess w/ too low you would be too rich, although that might be overcome by knocking the plug upward to get a higher cp by about 1 bar or leaning the mixture.

I am currently doing this w/ my car w/ good results.

[Tim Hancock]

Paul where did you find this info and do you know the values for the .072?

[Mysterytrain]

Paul,
Do you have the specs for the 045 replacement which is 911-606-105-09. I would be curious to know what the 20 degree C pressures should be. Are the graphs in the Bentley?
Thanks, Ron

[Paulporsche]

Tim and Ron,

The values for the .072 are in the Bentley manual for SC, p240-14. The ccp @ 10C is 1.475-1.975 wcp @ 40 is 3.25-3.75 bar.

The values for the 09 are in the book "Troubleshooting Guide K-Jetronic" which is a Porsche handbook that came w/ my car, which is a 77. It shows graphs for some of the WURs for 76 and 77 models.

The .09 values @ 20C are 1.05-1.45 bar.

[Tim Hancock]

Thanks Paul, I will check out my Bentley (duh, I'm so stupid). I do not have the other book that you mentioned for the .033, so thanks so much.
I should be able to make some logical decisions armed with this info.

[Paulporsche]

You know, it's funny, but w/ the amount of range built into the graph, the variation you can get thru plug knocking, the variation available by turning the screw @ the bottom of the WUR, and the wide range of CO available thru the mixture control, you ought to be able to get these engines to work using almost any of these WURs.

Knowing what your target cp should be and having the gauge would help, although I have set up my engine w/o knowing what the cp should be (because of mods) and using an Audi WUR by doing some plug knocking and mixture tweaking. And I figured out that when I tried Randyrap's gauge (thx, randy) I had it hooked up wrong for ccp so I didn't get an accurate reading anyway!

I'm not trying to brag here. I just mean to point out there is a lot of adjustability in this system and that the feedback from the car gives you a lot of info that you can use to set up these things.

[Mysterytrain]

Thanks Paul, interesting thats a very low value (rich) and was about where I found it fresh out of the box..I'm up at 2.1 at the moment (which is the old 45 spec) but I think I liked it better around 1.9

[Paulporsche]

Ron,

I remember we were talking about your cold starts & warmups. It seemed to me @ the time that you might be still a little lean.

I think the thing is use what works. Why just follow the graph for a poorer result. Especially if emissions regs are not important. Unless we have a brand new rebuild, we're talking about 25-30 yr old engines and components here.

BTW, I wonder what the effect would be if we put a resistor inline for the WUR like we are contemplating for the AAR. It seems it would lengthen the time for which the mixture was richer, which might be another way to fine tune the curve (graph) for engines that needed it because of age (carbon buildup) or mods, or if a replacement WUR were used, if plug knocking and enrichment and AAR tweaking were not enough to do this.