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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Originally Posted by WinRice View Post

...I have the small white Porsche spec book for 78-81 SC and Turbo and it has every spec you could think of, except that.

It does show the minimum fuel system flow rates:

SC - 1000cc / 30 sec
Turbo - 1500cc / 30 sec
Great info! Same for the fuel pump flow / amp.

So that would be

SC - ---2000 cc/min, and
Turbo -3000cc/min

In the real world we know the turbo suports up to about 400hp at one bar using only a reduced control pressure.

I have alwas believed that the metering plate stalls even with a control pressure of under 2 bar and that there is more fuel to be had. I learnd of this potental from a conversation with Lee Rice of the Rice Fueler. He said he had a 930 at full tilt on a dyno and was able to push the plate down even further and flood the motor even though the control pressure was already lowered to the max.

This seems to be supported even using Daves higher fuel rate of 642cc/100hp. That would indicate a 440hp potential.

Thus, the stock SC looks like it has enought fuel to support 312- 400hp (500cc to 642cc/ min per 100hp).


So what would I do.

The cheapest way to get more fuel out of a CIS motor is to shim the fuel head. However, that can effect AFR's at points other than max HP.

The next and most taken rout is to lower Control Pressure. One can use a 930 WUR but it will probably still need to be adjusted to fit the air flow / metering of the SC system.

I would probably play with the SC WUR and mod it so with vac goes away, the CP is lower so it functions like a 75-77 3.0 Turbo WUR.

There is the option of using an Anidal fueler or a frequency valve to bled off control pressure or get a D-WUR for the ultimate in CIS AFR tuning.

If a combination of those two do not work I would then look at the head. One could try to source a good used 930 unit but I would probably just send it to Larry at CISFLOWTECH to have it rebuilt and calibrated for more fuel. He did the very first HF FD at my request about 7 years ago and later all the HF fuel heads for IA. He can also rebuild and reset you WUR to 3.0 Turbo or any other settings you might want.

This way one would have a known fresh FD and one that will do what it needs to.

Last edited by 911st; 01-25-2010 at 07:40 AM..
Old 01-24-2010, 10:55 AM
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