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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Checking the condition of your injectors is always a good idea. There is also some info hear as to how to verify the fuel quantity deliver to each injector is balanced.

As you have the ability to monitor AFR's, I would shoot AFR's on boost at TQ peak and HP peak in the mid to low 11's. Many makers of Turbo car's often have there on boost AFR's set in the 10's for safety so it is ok if you dip into the 10's some at first boost and or at TQ peak. For a street car it is also ok to bump up to about 12.5/1 near red line.

CIS definitely seems to have a 'fuel curve' on modified 911's.

There is more HP if you can run in the low 12's but with CIS there is not any features to adjust for varying environmental conditions like being able to adjust fuel or ignition when there might be detonation should the motor run lean or heat soak.

You kind of have to play off on boost AFR's against idle and cruse AFR's. The hope is you can be in the 14's at light load. Many end up in the 13's in search of enough fuel to support 1 bar and to improve off idle acceleration. Pre-boost acceleration is best when AFR in near 13/1.

If you can not achieve this with the stock WUR then you might be able to use an adustable WUR to get things closer. There might still be some comprises like being a bit to fat on first boost (in the 9's) so you can access the extra fuel available up top.

The D-WUR can make a significant difference in tune-ability of your AFR's and get you up to about 1 more point of fuel in the upper RPM range where a stock WUR will often run out of fuel on a tuned motor. It can also be used to increase MPG by running in the upper 14's at idle and cruse, drop to 13/1 with acceleration from idle, and just under 12/1 on boost.

Just my opinion.
Old 03-26-2010, 05:48 PM
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