CIS, Adjustable Fuel Pressure Regulator instead of WUR?

[emcon5]

Doing some thinking on ways to hot rod a CIS engine, and perusing the Summit Racing catalog. The warm control pressure is within the range of a number of adjustable fuel pressure regulators. Something like this Holley universal which is good for 35-65 psi. Most CIS warm pressures are in the 45-55 PSI range depending on model.

As I understand it, adjusting the control pressure would allow you to tweak the mixture more than the system is designed for by lowering the warm control pressure below the stock range. This woudn't do much on a stock engine, but for a larger displacement/hotter cam, it may allow more fuel than the Warm-up regulator will allow. Of course you would need to tune it on a dyno, with a pressure gauge attached.

The only down side I can see is the lack of cold-start enrichment the WUR provides, but for a race car, this wouldn't be much of an issue, especially with a properly functioning cold start injector. You would probably also need to do some fabrication to get the fuel lines to work, but this wouldn't be difficult for a competant hydraulic shop.

Any reason this wouldn't work? Thoughts, concerns, ideas?

Tom

[kstylianos]

Tom,

I like the way you think

Thats about all I can offer.........

[beepbeep]

Frankly, I see this as flogging the dead horse. Problem with CIS isn't fueling. They usually flow enough fuel @ WOT. It's the flapper that's the culprit.

I wouldn't expect big gains by tweaking AFR. Frankly, paying dyno time to tweak a hopeless FI system so it would have little richer AFR is a waste of money.

When it works correctly, CIS will do the best of it's (limited) posibilities. Flapper cone is stepped in a way that allows it to run slightly rich @ WOT.

You can attach LM1 with simulated lambda output into lambda brain modulating frequency valve doing dyno pulls configuring stuff but it's a giant solution to non-existing problem.

Happy tweaking.

[Porsche_monkey]

Can't the same thing be achieved by modifying your Porsche pressure regulator? You could change the springs and do the same thing.

[MotoSook]

Why not just make the WUR adjustable? Like Goran said, fuel delivery is not an issue. If you really need more fuel it cna be done.

If you really must have a simplified CIS. Get rid of all the internal air bypass (AAR and AAV), get an appropriate back pressure regulator to replace the WUR, get rid of the CSV, then have fun tinkering. If you want to take it a step further, get vacuum assisted regulator and make a manual air valve, both controllable from the cockpit. hit a switch and lower the control pressure then pull on the valve cable to open the air by pass.....

....I don't know if it's worth it, but there ain't nuthin worng with tinker!

[emcon5]

I know about the limitations of CIS, and I never said anything about big gains. For some people, removing CIS is not an option, for a variety of reasons, like class rules for a race car, or smog rules for a street car.

All I am saying is if you build a hot rod CIS engine, and find it is too lean, this seems like a viable and fairly inexpensive option that may work to richen it up enough to run safely.

It is also a lot less expensive than a new (or even used) stock WUR, if you need to replace one.

As to making the WUR adjustable, the adjustment most people make only effects cold control pressure. Once the bimetal strip is hot, it is no longer in contact with the springs, and has no effect on hot pressures. John Walker posted a thread on an internal adjustment screw for the warm pressures, but I don't know what ever happened with it, or if all WURs have the screw, I don't remember seeing one in mine. The other method of trimming the metal rod inside the WUR seems like a hack job, with a high posability of screwing things up.

Aside from the cold start issues I have mentioned, is there any other reason why you couldn't/shouldn't replace a WUR with an adjustable fuel pressure regulator?

Tom