What's the limiting factor on squeezing more fuel flow out of CIS systems?
 

Read frequently you guys state the max fuel CIS can flow for a given hp ceiling and have always wondered what exactly is limiting this.

Please explain.

With EFI, you can (up to a point of diminishing returns I assume) simply add additional fuel pressure and easily supplement the fuel needed with smaller injectors. So it would be the same case with mechanical as they operate similarly. Playing devils advocate with myself, I understand fuel pressure dictates all range of operation, so I assume that is the reason you don't just "jack up the fuel pressure?"

Am I on track? :)

Hydraulic control pressure pushing down on the top on the top of the metering piston in the fuel head against the force of the air flow meter linkage pushing up on the bottom of it is the main limiting factor against more fuel going to the injectors with CIS.
Lower control pressure alot and you can make a lot more power with CIS if you open up the intake manifold holes, injector blocks, and intake ports and then raise boost so you get enough air going in with the extra fuel.

Want to experiment with lowering the control pressure a whole bunch to get a richer mixture to go with way more boost?
With the motor and everything fully warmed up to operating temperature just unplug the 12 volt supply plug on the WUR/CPR.

Then drive for 15 to 20 minutes and watch your AFR gauge gradually go richer and and your onboard control pressure gauge drop from around 60psi down to 40 psi if you have one. At that point the motor will be getting more fuel than it can deal with, but if you had enough boost and intake air flow the motor would make more power.
Try it. All you gotta do is open the engine lid, unplug the 12volt plug on the WUR, and go back to driving. Then plug it back in and it goes back to the way it was in a few minutes.

You could make it adjustable from inside the car with a wire wound potentiometer tapped into the 12 volt supply wire going to the WUR.
Let the cold start aux air valve keep getting 12 volts all the time so the idle speed doesn't go up at the same time.

Hmmm, not certain if you meant to say diminishing returns or demolishing returns, Tip, as either could, at times anyway, be applicable ...SmileWavy

Geez, what the hell was I writing?! :p

I'm EFI, just curious.

The limiting factor is the factory settings. Change those and CIS can support twice the power it was designed for.

Hugh? I'd like to understand that more.

JFairman,

I've been planning on adding a potentiometer to the WUR circuit for some time now. Could you please give us additional details on which potentiometer you used in your setup?

Thanks for any info you can provide!

Could it be possible to use 964 dimmer switch.. it's a porsche part and it can be wired up to the dash for a stock look... I might just do that

Why would you want that action to be manual? It needs to remain automatic and consistent. If the fuel head is adjusted for the flow needed and the WUR is then adjusted to match that flow spec all is good.

It wouldn't be completely manual. More so having the ability to tune/adjust:

- Length of time it takes the WUR to change from cold to warm pressures. Sometimes I'd like my WUR to not warm up as quickly as it does.

- Ability to richen warm AFR on the fly. This could be convenient when the outside temperatures are changing.

If these things are not happening your WUR is likely worn out. Compensation for temp changes is part of normal function. Ambient temp under the hood has some affect on pressure control.

With all due respect, I actually think you are cutting this a bit too short.

A stock car is rarely ever absolutely optimized, it is within a safe range at stock performance level. However, we tend to take this a little further. Furthermore, today's AFR gauges allows us to see in real-time if the AFR is not completely optimum. I can see a difference between a cool morning, and a hot 2pm. A pot-meter may allow us to slightly lower WCP lower AFRs on cools mornings etc.

At least in principal, is seems interesting to pursue, if sticking with CIS.

Optimizing I understand but sometimes the persuit of perfection can create hypersensitivity. If your car runs just fine but then you install a guage that tells you the AFR is 0.1 point off, your car still runs fine. Different strokes but I'd prefer to spend what precious little time I have with my car driving, not fiddling with gizmos. Now get you're car back on the road and enjoy it's foibles, you've obviously got toooo much time on your hands, ha! ;)

I don't know anything about the 964 dimmer switch or how much wattage it can take or how it would handle the heat being used like this.
I suggest a wire wound potentiometer that can handle some heat. Resistance creates heat so a wire wound potentiometer like a passive 8 ohm L pad for speakers that can handle 100 watts RMS or more controlling a woofer speaker level from the back of a speaker cabinet.

I really wouldn't want anyone to try using a cheap carbon trace potentiometer or other low wattage unit that could overheat quickly and become a big problem. I don't think speaker fader potentiometers made for cars would be able to handle the continuous 12 to 13.5 volt current for an application like this safely. You need something with some wattage headroom that won't get real hot.

A good quality wire wound potentiometer that can handle some wattage could be mounted on a metal bracket under the dash behind the knee pad so it's out of sight but still accessible from the drivers position.

Good wire wound potentiometers have the resistance wire wrapped around a ceramic ring inside a metal case that can handle the heat without melting or burning so they are safe for something like this. I wouldn't try a cheap one made of plastic.

The limits of CIS can be summarized by stating that system response is not linear across the range of engine speeds/loads. If you have the ideal AFR at 3000 rpm, for example, CIS will lean a full 1% or more by 6000 rpm for the reason that Fairman stated.
What is required is way to lower boost control pressure incrementally as rpm increases. Thierry25 developed a way to accomplish this but it's not the cleanest solution from a component standpoint.
The problem with using the bimetallic strip to accomplish this is the response time will be poor.

JFairman,
Thanks for the info on the potentiometers. I was thinking about this yesterday and starting wondering if a PWM (pulse width modulation) controller may also be a good answer:

MXA066 PWM DC Motor Speed Controller

12 Volt Speed Controller | Qkits

911nut,
I agree with what you're saying and I'm hoping the FrankenCIS project will accomplish this. In the mean time this WUR mod seems to allow a general pressure change that under certain circumstances would be helpful. Especially if it doesn't cost much and is easy to install/remove.

if you are talking about changing the voltage to the WUR to change the mixture, you will not get the response needed to make it worth while.
do this. get the engine good and hot. with gauges attached, unplug the power to the WUR and see how long it takes for it cool down on a hot engine to effect pressures.
i have left the power off the WUR before. i could not drive it much past what the normal warm up time was. i dont think i was a half mile down the road before i was connecting it back up.

listen to what rarlyl8 is trying to tell you in a nice way.

If we stopped short of trying something new, nothing would evolve. Your data seems to support your argument that this is not worth trying. However, as long as non of us are encouraging anything dangerous or otherwise destructive, there is no reason not to fiddle and have fun. The way I see it, that is what this community is about. Sometimes the experts can dispel suggestions off the bat, sometimes not. And sometimes they are even proved wrong. :)

Worst case, during this discussion, though it in itself does not lead anywhere, it educates the partakers.

T77911S . This would not work like an on and off switch, the WUR would work as designed, and by adjusting the voltage it would not work instantly because of the engine bay temps.....ideally you would have your WCP set to the high end of you WUR settings , something like 3.85 bar, at 12 volts or so, 12 + volts would be the starting point on the adjustable voltage reg and by lowering the voltage it drop the WCP much like doing it manually but from the comfort of your cockpit. But you can only lower the WCP which would make you car run richer... Just saying I'm gonna try it and get back to you all,

It seems reasonable that the only way you're going to get a perfect AFR curve out of CIS is to attach the changes in active control pressure to a targeted AFR reading. Adjustable cockpit knobs on the fly are not going to accomplish that goal in a practical way. Hell I can't even keep my eyes on the boost gage when the hammer is down. You're going to need something active automatic and adaptable. I guess that is what the electronic WUR guys are trying to do. At some point it's like putting a laser site on a sawed off shotgun.

I would not be looking for on the automatic adjustment ,or adjustment on the fly, which can be done , I think it would be great when I'm on the track for 30 to 40 minutes at time.....on a race weekend, but the point being is by controlling the voltage to control our WCP value with a knob is a much easier than having to stopping the car and adjusting the WUR, and the GREAT part is the would no modification needed to our WUR's . Much like people suggest using vacuum restrictor on the vacuum side of the WUR to control the onset boost , so that WUR doesn't go to full rich at a lower RPM, I really think this would work,

There's a guy over in the 911 tech forum that mounted a fuel pressure regulator between his seats and he uses that to adjust system pressure on the fly. While that's a more in depth install the results are probably more controllable/instantaneous too. I'm trying to find the post now.

Just another option...

Here it is - don gilbert is the Pelican with this setup:
http://forums.pelicanparts.com/porsche-911-technical-forum/545766-cis-experts-these-wur-re-calibration-steps-correct.html#post5383256

first pic is my reg. next few are of dailing in afr instanly. afr gage on top control press on the bottom. car come alive on the dyno at 49lbs of warm press (217 rwhp and counting) this cannot be achieved with the factory wur setting. They make a electronic one, but very expensive and lots of fiddling. this settup cost around 100 bucks and gives real flexibility on the afr. i can dail in for milage (28+ at 58 lbs) or performance.

http://forums.pelicanparts.com/uploa...1275497453.jpg

http://forums.pelicanparts.com/uploa...1275497510.jpg

http://forums.pelicanparts.com/uploa...1275497561.jpg

http://forums.pelicanparts.com/uploa...1275497598.jpg

Yes! Let's all run 75psi of gasoline into the passenger compartment. What could go wrong?

Mount it to the engine side of the firewall, and just have the knob inside the cabin?!

Great Idea ! love it

Here's a good thread on how far the factory went with a 934. Notice the lack of a WUR, and the addition of a simple pressure regulator. It had to be tuned for each day.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/665600-information-about-934-cis-injection-2.html

Let's face it, the CIS system is just a fluid valve system and could be 're-engineered' for 1000 HP or more, depending on how extreme you wanted to 're-engineer'....:)

lmao


Of course, you do have about half that running through the tunnel fuel line.

For you horsepower junkies here is a picture of something we are working on right now. On the right is a 930 barrel showing the metering slits. On the left is a 934 barrel showing the metering slits. The slits on the 934 are over twice as wide as those of the 930. We plan to modify the 930 slits to 934 spec then pull that sizing down as needed for street manners.


http://forums.pelicanparts.com/uploa...1411089073.jpg

Tapered metering slits that get wider toward the top might work if done right. Is Larry at CIS Flowtech doing this metering slit modification?

Larry and I are working on it together. My friends in the aerospace industry have equipment with the accuracy needed to do the job correctly. The 930 slit is the width of a human hair. This mod is intended for use in race cars but juuuust might find it's way to the street on a well built engine. ;)

The slitz
 

We have done this already - with the help of a German university, what we found out is that the slits are just a part of the story and it was the simple one, later it gets a little more complicated.

However you are right - CIS can do much more: on a 8,5 : 1, 3,4 L 934 we see 720 hp using a modern cam profile..

And still it is not running lean - so the limit is not CIS !

Best reg.

Dirk

Very good; Modern electronics aside, I cannot imagine after 30+ years that there is much left that has not been modified by someone.

Is it within the boundaries Of this thread for you guys, Brian, and Jim etc., to explain how the barrels, be it 930 or 934, work?

The pictures Brian supplied would serve an explanation well.

I'm actually suprised that after 35 years were still trying reverse engineer this. Those guys were super smart. Or technology changed and most engineers dont look at that direction when thinking of car fueling. Either way the Bosch system in pretty cool.

Cis
 

Yes 100 % right - it is such a beautyful peace of engineering !

Just love it....

I think the reason why we can still improve upon CIS is because it is a system within systems. Earlier on there were probably other limiting factors; maybe the turbocharger couldn't keep up or the charge became too hot causing detonation or burned valves etc. my point is bits and pieces within this sustem are affected by new technology allowing for constant improvement of an otherwise well engineered entity.
Makes sense...?

Yes - so right, we where working on this system for a long time now starting with Golf 1 1,6 and 1,8 then Golf 2 / 16 V Group A race cars. Playing around with the first 930 we got our hands on a complete 934 CIS system and wow this time put it on the car generating 580 to 620 hp the lambda curve was as perfect as I could be - absolutely flat 0,84 through the whole rpm on full load.

There we knew it is all about understanding the complexity and cooperation of the single Bosch components - then CIS is a pleasure to work with.

Producing the high end fuel heads is quite a task and expensive so it is for puristic freaks and race application where you are forced to use the homologated technology.

Best reg.

Dirk

The things we do (we meaning myself and the folks I work with) to "improve" CIS involve tweaking what exists to work outside the factory specs on engines that perform outside factory specs. The machine work that will be done to the 930 metering slits will mimic those of the 934. Things like that are just an expansion on the platform. Any modern EFI is more efficient than archaic mechanical fuel injection but MFI/CIS still has a place with the old school guys.
Jim W and I put together some information specific to 930 CIS and posted it on the CIS Primer on my website. We plan to add a lot more and include the power mods as well.