.:Custom CIS Tuning & Theory Questions

[jrcook320]

To the K-jet experts:

I have a few questions about a few k-jet enrichment methods and the theory behind the inner workings of the fuel distributor and was wondering what your thoughts are. As you may know, I’m running a Volvo 240 turbo FD on a Porsche 924 80mm downdraft AFM. The Volvo unit is commonly said to support up to 220 hp in stock form. Last summer my car dyno’d in 100 deg heat with little air flow over the intercooler at 188 hp at the wheels at 7 psi which was boost creeping up to ~10-11 psi above 5500 rpm. At 15% power loss this translates to around 220 bhp. I adjusted my wastegate properly and I now hit 11-12 lbs at 3k. That in combination with and I would guess I’m making more like 230, maybe even approaching 240hp on a cool day (this guess is from lb/min calculations based on ambient air temps and improved intercooler efficiency). I currently lean out above 6k rpm and would like to increase my fueling capacity to allow me to pull to at least 6500 and if I can pull to 7k it would be even better. So far I've just been living with it by short shifting.

The first thing I will buy this spring will be a wide band setup, and I expect it to reveal some shortcomings in my current tune. I still have much to learn about squeezing the max out of this system. I’ve heard rumors of Volvo guys pushing up to 300 hp with k-jet, but I think that is with piggyback micro fuelers, etc, which I would rather stay away from unless absolutely necessary. I think I can squeese 250 hp out of my current system with no additional injectors or systems.

Currently my system pressure is shimmed up to about 85 psi compared to 75psi stock and I’m running a 911 turbo fuel pump which is supposed to be good for up to 450 hp (overkill, I know, but it’s genuine Bosch cost less than a stock pump).

I know that raising system pressure ultimately increases the maximum flow through the FD and thus the injectors at WOT, at least until you reach the point of maximum sensor plate travel. But I’m wondering how that affects FD diaphragm position and fuel flow at lower loads.

Ben Watson states in his book that when the plunger rod is completely down, the pressure in the upper chamber is 1.5 psi lower than the pressure in the lower chamber. This is enough to close the injector ports in the upper chamber, but as soon as the plunger rod lifts, pressure equalizes and fuel can begin to flow. In my mind, only a 1.5 psi difference at rest is hard to believe, and I’m not sure I believe the chamber pressures are completely equalized at low plunger travel. The plunger is still restricting fuel flow, therefore there has to be a pressure drop across it until you reach maximum upward travel, correct? I would think this pressure drop would be a linear relationship to plunger position until upper and lower chamber pressures are equal at max travel.

With higher system pressure, I would assume the pressure drop across the plunger rod would remain at about the same ratio, so diaphragm position closing off the injector ports shouldn’t change much, right? Are the springs that push the diaphragm away from the injector port adjustable? If so I’m wondering if increasing the tension on them slightly could allow for more maximum fuel flow, or is that risky business? If I had a spare FD I would tear into it to answer some of my questions but I threw it away prematurely.

I’m also guessing that it is appropriate to raise control pressure a certain amount to compensate for higher system pressures. This would help to account for increased fuel flow for a given sensor plate position, and it will ultimately raise the point at where you reach maximum sensor plate travel.

Another method of enrichment I’ve seen is the frequency valve. I have seen a few guys plumb in an additional valve to bypass the stock valve. They trigger this valve to run at 100 % duty cycle at a certain rpm or boost pressure to enrich the mixture.

I find it a little counter intuitive that lowering pressure in lower the chamber can enrichen the mixture except that you can have higher pressure in the upper chamber than in the lower chamber, thus opening the injector ports further and increasing fuel flow. I would think the effects of this can only last for a split second as upper chamber pressure would quickly drop as well. Or is the lower half of the FD plumed in such a way that the center of the FD always sees system pressure, and the lower chambers feed from there and are bled by the frequency valve? Or am I correct in my thinking that the lambda system can’t maintain a richer mixture be bleeding off lower chamber pressure?

I need to just pick up a junk FD and tear it apart to figure some of this stuff out on my own, but any info or advice anyone can give me would be appreciated.

[TheNeek]

The plunger is still restricting fuel flow, therefore there has to be a pressure drop across it until you reach maximum upward travel, correct? I would think this pressure drop would be a linear relationship to plunger position until upper and lower chamber pressures are equal at max travel.

Theoretically this is true. A small opening still creates pressure. But if the difference in pressure is 1.5PSI like was mentioned it only takes a VERY small opening to equalize these pressures. Does it state in your book how this 1.5PSI is maintained? That might give you some insight into how Bosch designed the units to function at idle and off idle performance.

With higher system pressure, I would assume the pressure drop across the plunger rod would remain at about the same ratio, so diaphragm position closing off the injector ports shouldn’t change much, right?

I agree with your logic here.

Are the springs that push the diaphragm away from the injector port adjustable?

I don't belive so, but springs can be replaced. McMaster has more springs with more freelengths and lb/in ratings than you can shake a stick at.

If so I’m wondering if increasing the tension on them slightly could allow for more maximum fuel flow, or is that risky business?

It's no more risky than running lean up top.

You're going further into K-Jet then I've ever seen. I know there are guys that sware by it. Some VW guys go from pulsed injection to K-Jet. Not sure why, but they do.

Back to work.

[BoostedE21]

Another method of enrichment I’ve seen is the frequency valve. I have seen a few guys plumb in an additional valve to bypass the stock valve. They trigger this valve to run at 100 % duty cycle at a certain rpm or boost pressure to enrich the mixture.

This is what i did with mine. I had two extra injectors that would come on at different boost levels. One would come on at 4-5 PSI the other at around 12-13 PSI or max PSI. The seconded one was there for testing and never took it out and TBH, it was hardly used. The first injector i used all the time, any time i wanted to boost it, i would flip a switch to engage the switch and then at 4-5 psi it would kick in.

You I could easily tell the def when we installed the first injector, it had such a big difference and made the car run that much smoother.

[jrcook320]

I'm not talking about additional injectors, I'm talking about an additional frequency valve which would allow the FD to flow more fuel to the existing mechanical injectors.

The ONLY way I would consider an additional injector is if I could tune it to increase it's pulse width based on rpm or boost or both. A flat rate on-off injector blowing it's load regardless of those factors is out of the question and far more crude than stock k-jet enrichment means (ie boost sensing WUR).

[Layne]

You probably don't want to give up on the volvo dist yet, but you might consider going to a 6 or even 8 cyl one and plugging the unused ports. Then get some really big injectors. If you want to toy around with springs, you can send me one and I'll tell you what the rate is. Then you can order up-rated ones from McMaster or whatever. You can probably do that yourself, but thought I'd offer since I've done it before.

[jrcook320]

That's basically what the volvo 240 FD is, its a 6 cyl unit with 2 ports never machined. I don't think I'll get any more fuel flow unless I can use the additional ports, which means a v8 dizzy would be the way to go. Here's mine:


I've thought about swapping to a dizzy off of a MB 450 SEL 6.9. It had a 6.9L SOHC v8 making 286 hp 405 ft-lbs tq.

Here's a pic of one installed a 4 cyl turbo audi:




the problem would be plumbing 4 additional injectors. I thought of using a 2.0l manifold on a 1.8 head to use both sets of ports, but I don't want to use that manifold.

[TheNeek]

What about a combination of the V8 Dizzy and larger fuel injectors (I use the word lightly)? Plumb the 8 lines back into 4 and use 4 of the biggest K-Jet fuel injectors you can find. The flow through the dizzy wouldn't be your problem then, it would be finding K-Jet injectors big enough. Making custom injectors would be easier than making a manifold.

[jrcook320]

The largest injectors I know of are the MB 6.9 injectors. I have heard of some rally cars plumbing 2 fuel lines into 1 injector. it's worth trying if I ever find a 6.9 FD and AFM for a decent price...

The problem is the rarety of these parts. There weren't many sold in the US.

[BoostedE21]

The largest injectors I know of are the MB 6.9 injectors. I have heard of some rally cars plumbing 2 fuel lines into 1 injector. it's worth trying if I ever find a 6.9 FD and AFM for a decent price...

The problem is the rarety of these parts. There weren't many sold in the US.

Oh got ya, i miss read what you wrote and thought you were talking about adding an additional injector.

As for the fuel injectors, FD and AFM, if you want, i can have my dad looking to those as he works on new and old MB. FYI i used the 6.9 injectors, i dont think ill need them anymore since im changing my setup. If u need anything, ill try and see if i can locate any.

[jrcook320]

Cool, thanks. I may be interested in some MB stuff down the road someday.

I'd be interested in your injectors now though, let me know how much you want for them.

[Layne]

I don't see the use in tee-ing two outlets into one injector. If you block one port, more fuel is forced out the other ports, therefore achieving the same effect. The limits then are the lines and of course the injectors. If you consider dual injectors a viable option maybe you could use the 318i manifold and just make some plugs to convert the efi injector holes down to CIS size. That would certainly be easier than re-doing all your piping to accomodate the early e21 manifold. You might even be able to use two different popping pressures so that only one set is active at idle.

[TheNeek]

I don't see the use in tee-ing two outlets into one injector. If you block one port, more fuel is forced out the other ports, therefore achieving the same effect.

I guess that's true. Each port and line has limitations based on cross sectional area though. So with the same control pressure it might only flow as much as a normal 4 cylinder unit if you block off 4 of the ports.

[BoostedE21]

Cool, thanks. I may be interested in some MB stuff down the road someday.

I'd be interested in your injectors now though, let me know how much you want for them.

Sure thing, let me check where they are at. I think i got them new and they only have like 5-8k miles (if that) on the injectors). I will let you know.

[jrcook320]

I would think blocking 4 ports would disrupt the relationship between sensor plate travel and fuel flow. For a given CFM, regardless of # of cylinders or displacement, the sensor plate will lift a certain amount. On an 8 cyl. FD, it will be calibrated to flow a corresponding amount of fuel out of 8 ports, I would think blocking 4 of them would cut the fuel mixture in half. I'm not sure how you would would tune that type of a setup, though I know the group A volvo's did exactly that (see photos below). One thing to consider is that even at only half capacity the MB unit was supplying 3.45L making 143 hp. With the old addage that CIS can fuel up to double the stock hp, you could theoretically fuel up to 286 hp (or more due to the larger sensor plate) with only 4 ports at stock system pressure.

I don't think that blocking 4 ports would increase the capacity of the remaining 4 ports. System pressure wouldn't increase and thus lower chamber and upper chamber pressures would remain the same. Assuming that, the diaphragm pressure regulators at each injector port would restrict available fuel flow to the 4 remaining ports due to the relationship between upper and lower chamber pressure along with the spring pressure. I could be wrong on that train of thought.

Also consider that CIS injectors are not the bottle neck on flow rate (in a stock system, anyway), the FD is. With a v8 FD feeding 4 injectors, it would be possible to push more through each injector. This approach was done on the porsche 924 gts which made 270 hp.

Porsche 924gts

I do like the idea of an m10 L-jet manifold modified for CIS injectors. I also agree that it would be ideal to use all 8 injectors rather than a T.

[JDB]

I would think that 2 injectors rather than doing a tee would be the way to go.
I have never tried a tee so I am not quite sure what the result would be, but I would think volume change not presure.

As far as putting a kjet injector in a Ljet hole, I am doing that on my 323 using a 325i manifold. Just a slight modification to the 80+ injector seal and I have not had any issues with it.

Life will change in a big way once you have a wide band O-2 sensor. And I am using data loging as then you can go look at RPM and A/F ratio.
You will never remember the # and how can you see the meter when you are flogging the car?? This made tuning the kjet ALOT easyer and for the mods in this thread a requirement.

I found that a lower primary presure with a lower control presure ended up working best for me, but I am not running forced induction, I feel my issue is getting the sensor plate pulled open fast enough. With high primary presure in resisted the sensor plate from coming up and I am running a 535i throttle plate, in a 325i housing, to give more airflow at higher rpm, but that kills velocity at low rpm
So we all have different combinations and therefore what is working for me won't work for a (even modifyed) 323 with a 200 head, I run a 885 head.

And with forced induction it of course all changes again, With 8 injectors, I think you will be doing alot of the opposite kind of tuning from what you have been....trying to go lean!!!

Jeff

[jrcook320]

well my goal is to stick with my current fuel distributor and squeeze as much fuel out of it as possible. We kinda got off on a tangent talking about MB 6.9 and porsche 928 Fd's.

I think I'm realistically pushing around 230-240 right now, but I think I can eek out 250 with additional tuning and larger MB injectors which will allow higher system pressure.

I think I will need higher control pressures to limit sensor plate travel so I can flow more air before it maxes out. I'm hoping that higher system pressures will push more fuel through the system to keep things rich enough.

With my boost sensing WUR I haven't noticed a problem with the mixture enrichening under boost. It seems that it swings rich as soon as the boost builds. When I get the wide band installed it will tell the true story, I'm sure I'll learn much more about what's going on.

depending on what I find out I'll be tempted to either try an auxillary injector (with a rising rate pulse proportional to rpm), or find an L-jet manifold and v8 FD.

Speaking of which, Jeff, I found this on ebay today:
911 turbo fuel system

[autox320]

Hmm. Thinking back to the turbo car Fred acquired a ways back. The guy that built it said it ran laps around the porches on track in its day. No doubt it was old school, but even today the principal was the same. It was 2.0L cis gigantic rayjay turbo the size of a small basketball. Had the cold start injector come on via pressure switch under high boost in conjunction with another switch plumbed in for water/alcohol injection. Had dash lights for the low level of water injection and another for extreme lean fuel conditions so the driver knew to get out of the throttle. WUR was adjustable I think, it's been awhile.

Beyond the thinking of increasing the standard cis configuration, an extra injector is the only way I see getting more out of it.

My suggestion is this:
http://www.sdsefi.com/eic.html

[JDB]

Wow, That 930 turbo fuel system is a rare find, This dude must have had a shop. He has some very hard to find Porsche items, and a Porsche Kjet fuel dist. that M20 folks have been talking about wanting.

Josh,
I see how different our approche to tunning our cis has to be, You want to keep your sensor plate from maxing out, and then going lean, Forced induction
I want the damm thing open, without going to rich! naturally aspirated.

Have you played with springs tention in the WUR at all?
Jeff

[jrcook320]

I have not messed with secondary (vacuum/boost) spring tension yet. I’ll have to drill a hole in the brass plug to gain access to the allen screw. I’ve made both my warm control pressure and cold control pressure externally adjustable.

With as good as the car runs I haven’t felt that my measuring tools have been accurate enough for me to mess with that yet. I intend to get more in depth with the wide band. I do need to figure out a way to data log rpm vs. afr, not sure how to capture that yet without spending more cash on a logger.

How big is your sensor plate? I could probably benifit from going with a larger setup, that porsche 930 setup is said to be good for 450 hp, which would be about 300 if I blocked 2 ports off. It basically looks identical to the MB v8 FD and afm with 2 ports unmachined.

[Layne]

JR, I found something interesting in some papers about k-jet that I copied a long time ago from some service manual. Something called the "Throttle Actuated Regulator". I quote:
"In addition to the standard WUR, 1973-74 Porsche 911 models utilize a throttle-actualted regulator to further correct air/fuel ratio. The throttle-actualted regulator consists of a cam (mounted on the throttle shaft) which acts on a spring loaded diaphram valve. As the throttle (cam) position changes, the diaphram valve varies the amount of fuel returned to the fuel tank. The greater the amount of fuel returned to the fuel tank, the lower the control pressure."
I also found part numbers for the pressure regulator shims on realoem (listed under 'carburator' where no one can find them). With these you should be able to get them at the dealership (maybe).
http://www.realoem.com/bmw/showparts...24&hg=13&fg=05

[jrcook320]

interesting info. thanks layne.

I wonder if the early turbo 911's used a vacuum port WUR or if it was a standard WUR from the days before they had the vacuum/boost enrich WUR's??

[jrcook320]

Atilla, any word on those injectors? I want to get into the realm of 90+ psi system pressure this spring.

[jjgbmw323]

Atilla, any word on those injectors? I want to get into the realm of 90+ psi system pressure this spring.

What HP are you going to be pushing? Are you going to upgrade the turbo?