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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Advanced CIS Turbo Tuning Discussion Thread. Ultimate?

I though I would start a new thread on this as some of us have hijacked the “Digital WUR” thread ( Digital WUR ) and have been disscusing some great ideas that should have some huge potental.

I am hoping others will be interested in discussing advanced tuning concepts and existing best practiced as it relates to getting the most out of a CIS 930.


Porsche seems to have designed the 930 fuel systems to work very well to just over 300hp. Past this the fuel metering system starts to stall with further increases in air flow that come with higher boost, bigger displacement, and increase in VE found with bigger cams, ports, inter-cooler, headers, mufflers…

With our demand to flow more air the AFR’s can become exaggerated and go lean before the end of the WOT operating range when the metering plate.

Current Fueling Strategies:

Fueling strategies have been developed so more fuel can be derived to support higher air flows and HP. An added fuel injector is one. This is not seen as a good solution by most experts that belive that it can creat uneven fueling to different cylinders.

Lowering the control pressure using an Andial Fueler or with a readjusted WUR that has lower on boost control pressure are valid strategys. However, this tends to over exadurate the enrichment cycle to much at first.

The latest approach is to run a fuel head that is adjusted to deliver more fuel than spec like the IA head. This delivers an increased percentage of fuel at all points of operation from start to stall. As such it requires significant manipulation of boost CP including delay of enrichment with an RPM boost clamp to try to overcome said limitation. Using the new digital WUR is a potentially a very good fit with this but still leaves some fuel delivery on the table by not curing the metering plate stall issue.


I believe that by curing the issue with the metering plate stalling we can get more fuel deliver from our existing heads close to equal to that of the EA head.

If done correctly it can greatly free up the true for a high flow fuel head (IA) and gain even more increased hp potential.

Reconfiguring the WUR can allow us to take advantage of these two concepts to potentially obtain near ideal AFRs at idle through curse. Allow for a near ideal on boost through redline AFR curve. Allow for reduced restriction from the metering plate upon first acceleration so it acts like an acceleration pump to increase AFR’s to a near ideal TQ setting almost immediately.


By correcting the metering plate stalling, modifying the delivery rate of the fuel head, and modifying the way the WUR functions and fine tuning it, we can access higher HP levels safely, get increased throttle response, and do so without any external manipulation. This can be accomplished in an near OEM way.

A note:

I feel strongly this is a valid opportunity after spending countless hours studying CIS, trading hundreds of posts on Turbo boards about five years ago with other turbo nutts including some of the current top tuners, and even paying a CIS expert to help me develop my thoughts. Drawing on what I learned, another turbo nut sourced the first fuel head rebuilt to flow more fuel after my conversation with the builder. He was sourcing his parts and coatings throut IA and that was the start of the IA head. We quickly discovered issues with to much fuel. Playing with WUR tamed the to rich boost cycle but wemlost our extra fuel. I suggested dropping the boost CP back down and using an MSD rpm switch to drive a solenoid and delay enrichment. Now many are using this system I see with solid success.

I chose a different direction for my 3.3 C2T and assembled my own electronic programmable WUR using the Andial-Fueler plumping and a spec built controller so I could tune my control pressure at each rpm by load point. I spent hour’s monitoring my car AFR’s, manifold pressure, and RPM with a Motec wide band’s wires taped to the out side of my car and my lap top. I then had the WOT dialed on on a dyno. It ended up transforming my car with ideal AFR's and increased throttle response. The new Digital WUR will accomplish very much the same results.

I am not really an expert nor a professional. I make mistakes but I do love how CIS works and hope my interest will be of value to others that love these wonderful cars.

Discussion is welcomed for the greater good.

More to come.
Old 03-06-2009, 09:50 AM
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