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Guys-
(Also posted this on Pelican)
I drove my '91 964T to Rennsport from Denver in Sept - and my WUR was made adjustable by Leask a few years ago. When we got to sea level my AFRs were way off - cruise went from high 14's to mid/high 16's going from Denver to CA - which surprised me as I was under the impression the 964T WUR has altitude compensation. Talking to Chris Carroll in his booth he said he thought making the WUR adjustable disabled the altitude compensation.
Do you guys know anything about this?
Once in CA I used the fuel head (3mm) so that cruise was where it was supposed to be. Idle was a bit of still - and even tho I do use the O2 sensor, pulling from a light the engine was VERY finicky at clutch engagement - had to give it some revs or it would want to stall right at clutch engagement. Made even minor hill starts tough - clutch no happy.
I'm very curious to see answers on this...been considering having my WUR made adjustable, but if this is true...
Also curious how you managed to change the cruise AFR via the idle mixture screw, as my current understanding is that only controls the mixture at idle and once air is moving the meter, fueling is only monitored by system pressure>WUR>fuel head.
For those that don't go to Pelican - it _was_ determined that making the WUR adjustable disables the altitude compensation that is built into the 964T WUR.
So that's kind of a bummer. I just picked up an unmolested 964T WUR and will do some experimenting - maybe swap it in for road trips to low altitude or something...?
For those that don't go to Pelican - it _was_ determined that making the WUR adjustable disables the altitude compensation that is built into the 964T WUR.
My memory is hazy on this but I thought there was a separate component in the WUR that responded to barometric pressure. It wouldn't be any thing that would get altered in the process of making the WUR adjustable as I recall.
I'll have to consult the Posbt book on CIS.
Based on my experience driving to CA and seeing what happened to AFRs, combined with the feedback on Pelican - I'm confident the elevation compensation _is_ disabled.
From RarlyL8 (Brian B):
"This past weekend I pulled out a couple 964T WUR's and the technical manual for them. What I found wasn't good news. It appeared from what I saw and read that it would not be possible to modify a 964T WUR without eliminating the altitude adjustment diaphragm. To be certain of this I got ahold of BL* and told him the story. He confirmed that indeed the altitude adjustment is eliminated on the 964T WUR when making it adjustable."
*Note BL is Brian Leask - I trust that if he says its disabled, it is.
I find this to be very interesting - and info I would like to have known prior to making my WUR adjustable. While I love how I have been able to tune the car - losing the altitude compensation is a big trade-off (for me) in my opinion...
I'm going to "log" (or in 1991 911 Turbo with CIS speak - write down on a piece of paper) some cruise AFRs while driving in Denver and up at higher elevations. Then I'll do the same thing when I install a stock WUR in the spring - see how they compare.
Based on my experience driving to CA and seeing what happened to AFRs, combined with the feedback on Pelican - I'm confident the elevation compensation _is_ disabled.
From RarlyL8 (Brian B):
"This past weekend I pulled out a couple 964T WUR's and the technical manual for them. What I found wasn't good news. It appeared from what I saw and read that it would not be possible to modify a 964T WUR without eliminating the altitude adjustment diaphragm. To be certain of this I got ahold of BL* and told him the story. He confirmed that indeed the altitude adjustment is eliminated on the 964T WUR when making it adjustable."
*Note BL is Brian Leask - I trust that if he says its disabled, it is.
I find this to be very interesting - and info I would like to have known prior to making my WUR adjustable. While I love how I have been able to tune the car - losing the altitude compensation is a big trade-off (for me) in my opinion...
I'm going to "log" (or in 1991 911 Turbo with CIS speak - write down on a piece of paper) some cruise AFRs while driving in Denver and up at higher elevations. Then I'll do the same thing when I install a stock WUR in the spring - see how they compare.
This is all true.
The altitude compensation chamber is under the warm c/p plunger. The boost enrichment adjustment screw added by BL passes straight through it (I confirmed the chamber location with the Posbt book. It's the best CIS technical reference book I've found).
Brandon, before you drive with the stock WUR, you should check the control pressures on it. As little as 2/10ths of a bar will have a big effect on enrichment. You don't want to risk any engine damage.
You might be able to have CIS Flowtech make you up a new WUR if you are running non-factory settings.
Yeah - will definitely check control pressure prior to driving with the stock WUR. My only mods are 1 Bar boost and cat bypass - so fueling should be fine - in fact the issue I have here in Denver is getting it lean enough under boost. Leanest I've been able to get is 11.3 under boost - and that is with system pressure at low end of spec.
I'll have to keep that in mind about Larry - curious to see what AFRs will look like....
This is all true.
The altitude compensation chamber is under the warm c/p plunger. The boost enrichment adjustment screw added by BL passes straight through it (I confirmed the chamber location with the Posbt book. It's the best CIS technical reference book I've found).
Brandon, before you drive with the stock WUR, you should check the control pressures on it. As little as 2/10ths of a bar will have a big effect on enrichment. You don't want to risk any engine damage.
You might be able to have CIS Flowtech make you up a new WUR if you are running non-factory settings.
Hello Sir
Happy Holidays, where do I find Posbt book or can you send me a copy ?
So I wanted to close the loop on this - I did “log” my idle (with O2 unplugged) and cruise AFRs - in others words wrote them down on a piece of paper - at my home elevation - about 5300 ft and up at 9300 ft. With my adjustable WUR (no longer able to compensate for altitude) my idle went from ~13.6 to~12.3. And cruise did about the same. Went from ~14.8 to ~13.3.
So then I installed the unadulterated factory 964T WUR that I had CIS Flowtech rebuild for me - told them where I live and how much boost I run - then adjusted the shims in the fuel head so system pressure was middle of spec - and AFRs were darn near perfect out of the box. Did a super tiny tweak on the head to raise cruise AFR by about .2. Now when I go up to 9300 ft my AFRs are pretty much the same as at 5300 ft. Maybe down .2.
So anyway - super happy with the rebuilt factory WUR. For me - since I see large elevation changes it’s what my car needs.
Here’s a pic from last night did a 90 mile round trip dinner drive with a buddy - this was taken at 9000 ft.
11-29-2018, 05:47 PM
WUR - elevation changes
