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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269

I do not think we can combine approaches. To do the Vac-loss enrichment with an extended HP car we would have to fix the over rich issue in some other manner than using the rpm delay clamp. This takes us back to curing the metering plate stalling issue or just tuning around it with the WUR.

When we did the first of what bacame the HF head we found it went way to rich everywhere but near the end of the rpm range. With my suggestion we tryed running it without any lowering of the CP on boost. It looked like a near perfect AFR's and it even extended our fueling some up top. But again, the metering plate would start to stall and we would not get all the increase we needed nor that was available. That is when I came up with using an rpm clamp to delay enrichment. With this, the vac sensing is not viable.

Just a side note, Volvo makes a "delay-pill" that goes into the vac line to the WUR that might be somthing to look at as an easyer way to delay on boost enrichment. I do not know anything other than it exists.

One could use an Andial fueler but delay it with the rpm switch combined with the vac sensing WUR. This would give one two stages of control pressure lowering. The first with vac-loss at the WUR and the second lowering of CP under boost and later in the rpm range.

I do not think any of these add one's are required if we can match the fuel head to the WUR settings, and fix the metering cone so we do not get stalling after about 300hp worth if air flow or so.

Years ago when we were doing this, some were finding good low end response improvement with the Rice Fueler that was vac sensing. It provided both vac-loss enriching off idle and combined this with a lower on boost CP for more fuel on boost. Back then there was not the HF head to exadurate the issue. However, it was hit or miss depending on how the motor was set up. For many the early lowering of CP let the turbo spool up faster. For some, it might go fat earlyer. Just depended on the set up.

Because of this and my experance with agressively lowering the CP with my own electronic WUR I know there is a performance gain to be had.


You are on the right track. It would probably be easer to add volume to the top of the plate (see picture in post 108). Another thought is to reset the fuel head to flow say 15% more fuel (HF) and then maybe bend up the end of the metering plate. If one hit the sweet spot, the metering plate might advance 15% slower at first as more air is escaping around it to offset the added richness coming from the HF head but then the bent lip would stay further up in the cone so it would not stall as soon. If the factory did it it would just re-profile the cone and come up with a matching WUR that has the right control pressures.
Old 10-19-2009, 04:46 PM
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