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patkeefe patkeefe is offline
one of the great unwashed
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Join Date: Apr 2004
Location: Ringwood, NJ
Posts: 2,850
Although I have a different application than a typical 930....3.0 Turbo SC, with the SC CIS system, I do have both the adjustable WUR and the RPM switch. I run a substantially lower boost level than most 930's; I run a Tial with 5.8 PSI spring. My AFR curve looked pretty much like the one posted by quicksilver77 (but my peak power is about what quicksilver makes at 5000). After the first dyno runs, I spoke with Brian, and opted to get the RPM switch.

I have tuned my WUR a lot, as it is a non-standard application. I was seeing basically 10:1 AFR's on the track last fall, but that may have been due to the fact that I fried my heating elements in the WUR (Brian has since repaired it...excellent customer service!!!). I also had massive air leaks in the system. I have found that the car seems to work well with the boost threshold closer to warm control pressure. I keep my warm pressure set up around 3.2 bar, and that will allow me to have non-boosted AFR's up around 13+, and it transitions to boost a lot better. It is a lot of time and tweaking to get it close, but it can be done, mostly.

The benefit of the RPM switch is that it will delay the massive fuel dump until the RPM switch is made, owing to the non-linearity of the WUR at the onset of boost (full throttle) enrichment. The control pressure drops pretty fast at this point, like the floor on a gallows. I view this as a clever work-around to the enrichment problem. I don't believe that over enrichment at threshold can be tuned out of the WUR completely. I have mine pretty close at the moment. So, to rarlyl8's point of the RPM switch being a band-aid, it can easily be used as that if one doesn't want to invest the time in the fine tuning of the WUR. I find it gets that last bit of adjustment in mid range pretty close.

I will have the car at the track Friday, and I'm curious to see how the winter's tweaking of the WUR works out. This is pretty much the sole purpose of going for one day, to shake out the fuel system. I'm hoping to see AFR's in the mid 12's at the track
Patrick E. Keefe
78 SC
01 Boxster
Old 04-02-2008, 05:17 PM
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