Pelican Parts Forums - Could someone educate me on CIS systems please?

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- - Could someone educate me on CIS systems please? (http://forums.pelicanparts.com/porsche-911-technical-forum/988402-could-someone-educate-me-cis-systems-please.html)

Fred Cook, I had a device on my 85 vw GTI track car that if I can remember correctly
had a wiring harness that would read my tach output and another connection inline with the "fifth injector" (cold start) to turn it on at an adjustable RPM for the same purposes you mentioned.

I think it was something like Accutune or something to that effect. I had it mounted in the glovebox and it had a dial for adjustments.

Terry

Quote:

Originally Posted by '76 911S 3.0 (Post 9938232)

This PLUS the flapper door air flow meter for fuel pressure control. A hot cam results in very unstable/low manifold vacuum and causes the door to oscillate and makes the fueling very unstable, particularly at idle.

I am curious of how much of an effect that actually is. I had a Rabbit GTI race car with CIS and a cam considerably hotter than SC (243º/240º @ .050" 110ºLC for mine vs 228º/218º @ .050" 113ºLC for the SC), the idle was a little lumpy, but made good power and driveablilty was fine. A buddy had one even hotter, (250º/252º @ .050" 109ºLC), idle was a little worse than mine, but still seemed to work fine. On edit: For comparison, a MFI S Cam is 263/235º @ .050" 98ºLC.

Who knows, maybe a 4 cylinder is more tolerant of reversion than a 6.

It is more of an academic curiosity, not advocating anyone try it. I wonder if there was a race class where cams were free but induction must remain stock, how far people would be willing to take it.

Quote:

Originally Posted by fred cook (Post 9938272)

When I built my 3.0 into a 3.3SS, I decided to keep the CIS and see how much performance I could get out of it. However, what I built was a Frankencis system using a 1978 large port airbox and hardware from a 1980 system. I plumbed it to be as much like the 1973 1/2 system as possible with the addition of the AAV.

Makes sense to dump the "bells and whistles" in the build. But I'm surprised you kept the AAV.

Quote:

Much to my surprise and relief, the system runs great! It took some tweaking here and there but now it starts easily even after sitting for a couple of weeks, idles well and pulls like a freight train up to 7500 rpms where I have the ignition interrupt set. I added a little trick by adding a contact switch on the throttle linkage so that the cold start valve is activated at full throttle (only).

Cool stuff using the CSV for enrichment ! Are you also saying the engine is started without the CSV ?

Quote:

This drops the A/F ratio from about 14.5 down to the low 13s to help prevent burning a valve and giving it a bit more fuel on the top end. The cold start valve has its own little distribution box that makes sure each cylinder gets some extra fuel.

The distribution box is not the factory spider you are referring to ?

Quote:

The only changes I make now are in the spring and fall when the weather changes. So, are all CIS systems trouble free? No. Can they be made to be reliable? Yes. And, there is a lot more performance potential than most people give credit for!

Certainly, there's the tinkering fun aspect to it.

Quote:

Originally Posted by pmax (Post 9938591)

Makes sense to dump the "bells and whistles" in the build. But I'm surprised you kept the AAV.

Cool stuff using the CSV for enrichment ! Are you also saying the engine is started without the CSV ?

The distribution box is not the factory spider you are referring to ?

Certainly, there's the tinkering fun aspect to it.

I kept the AAV so that I would not have to create a choke.

The CSV does work when starting the engine.

Yes, I used the stock aluminum distribution box and runners that are built into the air box.

The seasonal changes amount to just adjusting the fuel mixture slightly and adjusting the air correction screw. I have an a/f meter permanently installed in the car so the tuning aspect is quite easy. Just for the record, this engine is running 964 cams and Mahle pistons at 10.8:1 compression.

Quote:

Originally Posted by fred cook (Post 9938931)

The seasonal changes amount to just adjusting the fuel mixture slightly and adjusting the air correction screw. I have an a/f meter permanently installed in the car so the tuning aspect is quite easy. Just for the record, this engine is running 964 cams and Mahle pistons at 10.8:1 compression.

So why is this necessary? CIS should compensate for air density and temp on its own.

It should, but..............

Quote:

Originally Posted by emcon5 (Post 9939047)

So why is this necessary? CIS should compensate for air density and temp on its own.

It should compensate, but........ normally, it is just a small "tweak" to keep it running just right! Actually, I could probably just leave it alone, but where's the fun in that?

Quote:

Originally Posted by fred cook (Post 9938931)

I kept the AAV so that I would not have to create a choke.

Yes, makes sense.

I had the wrong impression that you were referring to the pancake like appendages.

CIS Primer from Jim's Basement Workshop as someone else has already mentioned.
911 CIS Primer - Introduction

Porsche Factory Manual
https://www.manualslib.com/manual/1101788/Porsche-911.html

Bosch K-Jetronic Workshop Manual
http://www.type17.ch/downloads/Injection/Bosch%20-%20K-Jet%20-%20Workshop%20Manual.pdf

Bosch K-Jetronic Technical Instruction
https://www.slideshare.net/guestceff35/bosch-k-jetronic-fuel-injection-manual

I printed all that I could for when the world goes back to analog. These and the Bentley manual are my keys to the kingdom.

And if you can manage to stay awake through it, this is also informative.

https://www.youtube.com/watch?v=a4fJAfXYxWk

Enjoy!

Eliminate all air leaks and all stock settings snd the cis works. The turbos used it so it should be able to feed some high hp.

Quote:

Originally Posted by 47silver (Post 9954073)

Eliminate all air leaks and all stock settings snd the cis works. The turbos used it so it should be able to feed some high hp.

Take a look at the Turbo and Carrera 3.0 fuel distributor/air flow meter assembly. It is a robust monster.

I have an 81 with CIS. A guy showed me his 79 GTI CIS system. It was "cute" compared to mine - just as mine is cute compared to the 930.

Engine Builders Supply told me they had taken a 3.0 up to 4.0 and the stock CIS worked fine. Regular CIS, not the Carrera 3.0. Just one conversation though.