AFAIK the rising rate fuel pressure regulator allows more fuel to be injected as the fuel pressure to the injectors when on boost will be higher than when not on boost. It senses boost from the intake manifold.

More fuel pressure to an injector means more fuel will be sprayed when it is open.

ya I know, I thought all 930s had these

No. I think the fuel head decides what to send back to the tank although I am not sure when or how.

makes sense, but I don't know jack about cis

no CIS my friend. They don't have the same system as we do

Since I forced myself to learn jack about CIS (although I am ignorant to the inner workings of the true 930 system), they are a more stone age fuel delivery system than the EFI stuff. Fuel delivery is controlled via the WUR, or control pressure regulator, which can be thought of as a bleed. As the engine wants to get richer, ie cold, the control pressure drops, or bleeds, and basically gives the engine more fuel via the fuel head and injectors. Once warm, the n/a WUR just pretty much maintains a set control pressure. Fuel delivery volume changes solely due to the rise in the plunger from the airflow plate, which thus meters the correct dosage of fuel. The 930 WUR has a boost enrichment which allows boost to work the WUR diaphragm, and drop the control pressure, feeding the engine more fuel.

I couldn't get AFR's rich enough with a stock WUR from the SC, so I ended up getting a 930 WUR, along with an IA fuel head modification. I also have an RPM boost switch, which delays the onset of boost enrichment to a predetermined RPM, to keep from getting pig rich in the mid-range. These few CIS mods were $1000 worth, plus a load of tweaking. If you start with EFI, in my mind, it just has to be simpler.

BTW, mmn710, have we scared you off yet?
Pat

Yeh, Pat's got it. The WUR (or Control Pressure Regulator) controls the, well, uh, the control pressure. It provides warmup enrichment and boost enrichment, both of which drop the control pressure for more fuel (less resistance to the movement of the fuel head piston - and thus the flapper).

Changing the control pressure is just a big, coarse, richer/leaner adjustment over the entire range.

It's the fuel head that meters how much actually goes to the injectors, based on the position of the piston - directly connected to the CIS air flapper in the throttle body. Like an AFM that controls fuel flow directly and hydraulically without a Motronic, if you like.

The fuel head also regulates overall CIS system pressure via the regulator valve in the return circuit that goes back to the tank, but this function is unrelated to the fuel metering due to the flapper plate position.

With EFI, you don't necessarily need rising-rate FPR although it can provide extra tunability if you're a tad lean up top - the 951 guys tend to just swap out the stocker 2 bar FPR for a 3 bar item for mild to mid-range upgrades, which reduces the duty cycle on the factory injectors, or lets them avoid buying the next-step-up big-#-age injectors that make the idle really suck...

http://www.dragtimes.com/Porsche-911-Timeslip-3319.html

Very impressive for the amount of work thats done to the car.

i'm pretty sure that's the car that shoots flames on youtube.

Can you post the video of that car on youtube because i can't find it. Also if anyone has any videos of their 3.2 turbo or anyones 3.2 turbo can you post them up. I would love to see how they sound and run.