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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
You can try to copy a 930 by going for the same system pressures and use a 930 WUR to control it. This will probably require you to copy the 930 fuel pump set up as noted.

I hope you will have a wide band O2 so you can monitor in real time.

If so, what I would do is set it up and get it running and see what you have.

You might just be able to set the CO adjustment fat and get close.

If that dose not do it, then start shimming for more fuel.

Shimming will change the slope of your AFR curve if you leave your WUR stock. That is if you shim it for 10% more fuel, it will give you 10% more every where. You can pull the AFR back at idle but then all points past that will start to get rich.

If you get lucky the shimming will change the slope of the AFR curve enough that you do not need to change to a WUR that has enrichment.

Supper chargers are more liner than a Turbo so you might bet lucky and be able to tune your motor by only playing with system pressure.

Here is my thinking.

If you shim it about 10 to 15% more fuel you will get that much more fuel at all points.

Thus, you can set your AFR at 14.5/1. At curse (say apx 50hp) it might then be at something like 14/1. Then at 200hp WOT be in the 12's.

Your goal being to be at about 11.5/1 at TQ peak.

The AFR curve is just that, a curve. The metering plate moves quite a bit at first with changes in air flow. Latter in the cycle because of the design of the metering area and the angle of the metering arm to the metering pin, it starts to move slower the the AFR curve starts to turn. If you are lucky you will get the richest AFR at TQ peak as that is where you are most at risk.

Timing is the other thing. At full power you might want to start at about 16 to 18 deg advance and add more in a bit at a time. Your goal is about -10 at idle, -18 on boost above 3500rpm, and -30 or so at curse.

I am not a real expert so do this at your own risk but this is what I would do.

Good luck. This is an interesting project.

Last edited by 911st; 01-20-2010 at 09:22 PM..
Old 01-20-2010, 09:19 PM
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