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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
The heart of our problem with getting enough fuel to support increased HP is the stock CIS metering system is designed to stall at an air flow rate equal to the expected maximum HP.

That is, if the motor is designed to make 300hp at 5500rpm the metering arm will advance down the cone until it gets to the targeted max HP air flow. Then the cone configuration is designed to start spilling air so the metering plate stalls at that point.

Otherwise the motor would continue to get more fuel with increased air flow that comes with more rpms past HP peak. The motor would not be able to use that extra air flow as efficiencies are falling off quickly.

When we modify a motor it flows a lot more air, the metering plate stalls at the 300hp mark, and we keep asking for air and go lean.

Understanding this is central to getting a near ideal AFR curve with a motor making more HP.

As a bandage we try lowering control pressure on boost (at the WUR or as the Andial fueler did) which dose move the stall point a bit, however, then lets the metering plate advance further than we need it to in the early stages of boost and we end up with a big fat spot on first boost.

Then we have to add another bandage so we put on an RPM clamp that delays enrichment or have to develop a programable WUR.

For someone that is skilled, it should be possible to put a CIS metering unit on a flow bench and by re-profiling the metering cone or adding volume to the top of the metering plate (see my wedge drawing earlier in this thread) we should be able to move the stall point to equal the expected air flow need to support our peak HP goal before it stalls. We would then also get proper AFR's.

We do not have much issue with getting more fuel to support HP up to 500fwhp, we just do not control it very well.

I trully belive we do not need excessive reduction in on boost control pressure, bost clamps, or D-WUR to achive our goals.
Old 09-21-2009, 10:48 AM
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