Dyno tuning a SC.

[autobonrun]

http://www.dynoperformance.com/article_details.php?ID=15

This article touts the advantages of dyno tuning a 993 engine. Does the same principle apply for the SC? The article talks about optimizing the tuning at different RPM points. I assume for an SC with the CIS and no computer, this would mean selecting a single point on the curve and optimizing that. Does anyone know how they would adjust timing at multiple points on the 993's curve? I assume this is through the 993's computer.

Lastly, and I think this is what JW has been saying, the car should be leaned out to the appropriate CO level. I interpret this to mean that I should have the same octane gas in my car at the time of the tuneup as I plan to run in the car. If I tune the car with 91 octane, it will run well with 91 but not well with 87. If I have it tuned with 87 in the car, it will run well with 87 but with less power, and adding 91 does nothing. Do I have this correct?

[dd74]

I don't know about leaning the mixture out. I can say dyno tuning was reccomended to me for my SC engine. I was told it should squeeze out a few more horsepower.

[Vipergrün]

With an SC you'd want to do the dyno with a unit that has knock sensor capabilities. You can then advance the timing and adjust the mixture and verify your getting the 35 degrees max advance and 3.5 CO without getting detonation. If you are getting some, just back off the advance. I'd suspect that's how they are squeezing out the additional power. I run my SC near these figures and always use 91 octane and sometimes mix in a few gallons of 100 if it's really hot or I'll be driving at elevation.

[Superman]

JW does not lean them out. He richens them. I believe that factory spec is something like 0.8% CO. John sets them at 3.5% CO.

John sets ignition timing at 35 degrees full advance. Just like any other engine, they run best with as much advance as possible, without causing detonation.

Higher octane gasoline resists detonation better. It does not act differently in any other way. Does not make more power. It just resists detonation.

If you set your car's CO to 3.5%, set timing to 35 degrees full advance, and run reasonbly high octane gas, then I would expect minimal improvement from dyno tuning. Unless you want to fool with the sensor plate positioning.

[dd74]

The sensor plate allows for air intake, correct? How does one adjust it?

Thanks.

[911nut]

The sensor plate rises or falls depending on airflow through the sensor plate body. The mixture screw is what adjusts the sensor plate height at idle.
Once the idle mixture is set, the control pressure or incoming fuel pressure would have to be changed to deal with mixture at certain throttle positions.
A dyno would be a tool to discover how the mixture varies with engine speed.

[wckrause]

The mixture screw is what adjusts the sensor plate height at idle.

That's not correct. The mixture screw adjusts the position of the fuel plunger within the fuel distributor relative to the position of the sensor plate, it does not adjust the sensor plate height. The only way to adjust the sensor plate height is by adjusting control pressure, and that should be set according to the specs on the WUR. The only other adjustment of the sensor plate is it's resting position.