Starting unusual build..

[fasteddie313]

I have these pieces...








And I'm going to jam them in here...



80 Porsche 931 turbo with K-jetronic convering to KE-jetronic with microsquirt control..

I don't have any questions yet but I probably will.. You have been warned..

[R100RT]

Good direction, the more K-Jetronic that is retired, the better in my opinion. (some of my most painful troubleshooting moments took place trying to recesitate a non co-operative VW with K-Jetronic components that seemed to have a direct connection to our bank account access )

[fasteddie313]

K-Jet has been good to me all the way up to 1Bar/15psi of boost..

Need more boost, need more fuel and finer control..

[elaw]

Keep in mind if you increase boost beyond a certain point, you'll need to increase the CIS line pressure.

As you probably know the CIS setup is a little weird in that the fuel distributor regulates *flow*, not pressure... the pressure in the system is constant. The injector tips have valves that are spring-loaded shut and the fuel pressure opens them. The rub is that intake manifold pressure is on the other side of those valves so it's opposing the fuel pressure. With stock boost the fuel pressure is enough higher than manifold pressure that the valves can open, but if you increase boost you can hit a point where they won't at which point your engine suddenly goes lean...

[fasteddie313]

Good point.. The differential pressure between the outside and inside of the injector is going to decrease as the boost increases..

This new fuel distributor does not have an integrated system pressure regulator, rather it is a seperate component. iirc it is set at 80 psi but from previous experimentation I know I can easily get 100-120 psi out of my fuel pumps but I don't know at how much volume.. If I need to I can run double pumps..

I can test flow volume @ system pressure @ airplate position @ DPR internal diaphragm differential pressure and see if I get a system pressure drop off at high volume flow.. I was told this distributor will supply 700hp worth of fuel (not that I'll need that much, maybe half)

But I don't have a handy way to test injector flow with boost pressure on the other side of it, maybe I can make something... Hmm...

I have a portable air tank, maybe I can put an injector in it on an air line, spray in it for 30 sec at 0 psi atmosphere, weight the fuel, then spray in it for 30 sec with 20psi behind it in the tank, weigh the sprayed fuel, and compare the results/weight differences..

Could do it in 5-10 psi incriments and make a chart..

I did a similar test on my OEM k-jet and recorded 300hp worth of fuel at max airplate and max lambda differential pressure but that was at atmosphere behind the injector..

To be honest this isn't something I've thought much about previously, you have me down a whole nother rabbit hole..

What are your predictions with 20-25psi behind the injectors?

Good to know there are some guys here that know something about CIS.. I hope I'm not completely on my own as I've never done a standalone before..

[elaw]

Oh man, it's tough to say as my experience with this is very limited and on a slightly different system.

If you want a number as a "jumping-off point", you can look at line pressure and injector opening pressure for the system... the "headroom" (allowable boost) in theory would be the difference between the two. For example if line pressure is 80 PSI and opening pressure is 60 PSI, you could have problems above 20 PSI boost. The problem with that approach being that the line pressure and particularly the injector opening pressure aren't likely to be exactly what the book says.

My one data point is from a 1980 Saab 900 running K- (not KE-) Jetronic - it started having problems around 25 PSI of boost. Luckily in that case it was a simple matter of pulling the cap off the line pressure regulator and adding another shim* to the stack under the spring.

Arbitrarily changing the line pressure can affect fueling across the operating range, but luckily your setup will be able to compensate for that!

* "Shim" = washer found in the parts bin.

[fasteddie313]

I was running 100psi system pressure with the shim method on my k-jet..

Here is my build thread for this stage of my car project.. with more pics and rambling..
http://924board.org/viewtopic.php?t=42444&highlight=

Here is my IC and intake plumbing install im working with..
http://924board.org/viewtopic.php?t=412 ... sc&start=0

My turbo is a compressor off of a 951 on my 931 bearing housing and hot side that I built myself..

Here are some general car pics..
http://www.924board.org/viewtopic.php?t ... 2c643199e2

I'm pretty DIY mechanical and fab but no so much circuit boards and electronics like you guys are here..

[Paul_VR6]

Its easier to use k jet and use the lambda valve for more fuel. 50% duty to start and up/down to adjust. I did that on my cis Rabbit back in the dark ages and it worked well.

Agreed though you will probably need want at least an 044 fuel pump.

*edit I vaguely remember the stock turbo cars having a vac/boost reference control pressure regulator to combat the differential pressure issue across the injector noted above

[fasteddie313]

Its easier to use k jet and use the lambda valve for more fuel. 50% duty to start and up/down to adjust. I did that on my cis Rabbit back in the dark ages and it worked well.

Way easier, but I want more fuel than my K-Jet will put out at 100% frequency valve duty cycle.. Hence the V8 KE-Jet..
Put it this way, I turned everything up to 11 on my k-jet and want more fuel..

*edit I vaguely remember the stock turbo cars having a vac/boost reference control pressure regulator to combat the differential pressure issue across the injector noted above

Yes, my OEM K-Jet has boost enrichment on the control pressure regulator, but that just regulates the airplate's resistance to deflection, not the actual pressure behind the injectors.. And was designed for like 8psi of boost..