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 anything on a stock engine (unless you needed to replace your WUR anyway), 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.

I know about the limitations of CIS, and I am not talking 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. But 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.

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

Peter Zimmermann

Warm Up Regulators adapt to changing temperatures, which allow a proper mixture through the warm up cycle by changing as necessary the pressure on top of the fuel distributor. I'm not aware of anyone's aftermarket product having that capability.
Pete

art

I saw a site where someone was saying they were going to introduce a 'digital' WUR. I don't remember where, but it was one of the well known tuners if I recall.

Also, it would not be hard to disable the bimetal spring and put in an adjustable control on these. It would not even be that hard to retain the warmup capability and put in a screw to push the spring away to create a richer mixture. My problem with this is that it richens it everywhere, not just in some rpm range where you might need it. This is fine for a displacement or CR increase where the engine wants more fuel in all cases.

psalt

Tom,

If you have an 82 SC, it already has an adjustable fuel pressure regulator built into the lambda feedback system. The frequency valve is essentially a pulse type injector in the pressure loop of the lower chamber of the fuel distributor. It is pulsed by the ECU under the seat based on the 02 sensor along with a few default settings. All you would need to do is plug this injector into a programmable injector controller to have control over the entire fuel curve. Why don't people do this ? Because the CIS lamdba is fine for a stock or mildly modified engine, but the twisted intake path and air flow sensor design are no good for a high performance engine, and the system lacks the supply capacity for more than around 6 psi boost. You are trying to answer a question that does not exist.

Paul

Peter Zimmermann

Tom: CIS engines are mild by design. Healthy intake manifold vacuum, that the CIS requires in order to operate, must be created by mild cam timing, hence a mild engine. That's why when people switch to carbs they also go to something on the order of MFI S cams. The best gains that can be had on a CIS engine are SSI heat exchangers, or headers, coupled to an efficient muffler that satisfies your local tracks's db requirement. The CIS engine has no electronic detonation protection, but also loses performance when set too rich, so its setup has to be carefully planned & logged. It's a great engine for Club Racing, but don't expect to gain an unfair advantage over competitors. Yes, you can balance your internals to a knat's eyelash, make sure that your engine is fitted with Nikasil, not Alusil, piston/cylinders, make sure that your valves/seats are perfect and that your cams are timed within .001 mm of each other. Everything else is suspension and driving.
Pete

emcon5

How important is this? I had a CIS tester on my car this morning, and the control pressure went from the cold to the hot spec in under a minute as the heating element on the bimetal strip got power. Granted, it wasn't cold outside, about 55º F, but it made the transition very quickly. After that point, the Warm control pressure is constant as long as the engine is running, except for some systems that have Vacuum enrichment.

I saw that as well, and while it is interesting , it is much more involved than what I am suggesting. That is exactly what I am talking about, like a 9.8:1 short stroke 3.2 with 964 cams and SSIs. Also for a rece car, that primarily lives in a specific RPM range, you adjust the control pressure so it is where you want it where the engine's primarly operating range, and let the rest of the RPM range live with whatever it gets. For a race car, you can probably tolerate some hard starting and low RPM ill manners if it helps you out in your peak power range.

The Lamda system reverts to open loop at full throttle, running the frequency valve at a fixed duty cycle. In Open loop operation, the engine is limited to the whatever the fuel distributor is able to deliver at the current control pressure. If your engine needs more fuel due to a displacement/compression/cam change, lowering the control pressure slightly should richen the mixture across the board. Again, well beyond the scope of what I am suggesting. I am talking about replacing the Warmup Regulator with a simple mechanical fuel pressure regulator, available for under $100, not a complex electronic engine management system. Once the engine is hot, that is all the CIS WUR is anyway.The twisted intake path doesn't help, but frankly I think the single plenum is more of a restriction of power due to limited cam choices. Who said anything about boost? Again, I am well aware of the limitations of CIS. For some people, removing CIS is not an option, for a variety of reasons, like class rules for a race car, (Not Porsche specific, but SCCA Production limited prep rules, lots of cars out there with variations of CIS) or smog rules for a street car (California, or any other state with a visual inspection). But 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.

Any other thoughts?

Tom

psalt

Tom,

The system goes open loop at 15% throttle and the default setting is around 50% duty cycle, giving you plenty of adjustment for the whole fuel curve. I mentioned 6 psi boost because it is beyond the modifications you are talking about, and the stock CIS can supply the proper mixture. A fixed pressure regulator in place of the WUR will just give you an engine that runs like a pig until it is fully warmed up, with a fuel curve that is only correct at one point.

art

Keep in mind that for relatively small engine changes, the airflow measurement of the CIS will handle it fine. Lowering control pressure just fools the airflap into thinking there is more airflow, so you are limited to the range of the system anyway, but I think these have reasonable headroom. There are guys who specialize in CIS for performance bug applications that really have done cool things. CIS is a really nice system and there is lots of room for inspired r&d.