CIS Guru Question

[MBEngineering]

HI Jim Williams
the info for you.











give me a shout if it is not good to read as it is getting late hear and the camera will not hold steady

regards mike

[Pkaaso]

Very Cool Jim. I am interested in your drawings. Please post what you come up with.

My 81' U.S. is a xxx.149

What I need is the xxx.070 This may richen up the top end.

WANT TO BUY: Air Flow Meter xxx.070

Thanks,
Paul

[Pkaaso]

By the way, the other CIS I dug up in the "garage 'O' parts" is also the xxx.149 ARG!!!

[MBEngineering]

HI Paul
is any of this lot any good for you,












regards mike

[Jim Williams]

Paul,

I'm not sure this sketch will help, but here it is. Measuring the insides of the housings with the relatively un-sophisticated tools that I had on hand when I did this, points out that the internal configurations are more subtle that they appear to the naked eye. The eye can spot a discontinuity in the venturi wall easier than it can be consistently measured, or drawn on a small scale sheet of graph paper.



The most obvious difference is the diameters of the sensor plates. I'm sure the CIS engineers had good reason for choosing the slopes of the interior walls of the venturi, but with no more precision that I have been able to draw them here, the effects on the mixture at various air flow rates aren't readily apparent.

Mike,

Thanks for your photos. The ones with the translations will help out.

[1982911SCTarga]

Great stuff.

I'm sure the CIS engineers had good reason for choosing the slopes of the interior walls of the venturi, but with no more precision that I have been able to draw them here, the effects on the mixture at various air flow rates aren't readily apparent.

Jim, when you say "CIS engineers," are you referring to Bosch personnel? How did they do CIS development for so many manufacturers? Did Bosch dispatch engineers to each company's development and factory floors? Or, did manufacturers send Bosch each engine type for CIS development? Sorry in advance if this takes the thread off track, but I'm curious to what degree each manufacturer had a say in their individual company's CIS (Ferrari, VW, Mercedes-Benz, Delorean, etc.).

Brian

[Pkaaso]

1982911SCTarga,

Not off track at all. Great question! Like to know the answer myself.

Jim,

Thanks! The drawings are excellent. I knew about the plate size difference, but I didn't know about the verturi shape changes. Real curious as to why the changes and what results where obtained.

Paul

[Pkaaso]

Now coming from someone who is still on the incline part of the learning curve with the CIS system. I am going to make educated guess that the larger the plate the more the same amount of air flow will lift the Fuel Distributor plunger and allow more fuel per air ratio.

The shape of the venturi should also add/subtract from the pressure transferred to the plate.

Paul

[Jim Williams]

Paul,

I thought I had posted this thought on this thread, but it must have been another CIS thread. Anyway, your thought just adds credence to my same conclusion. The step-up in plate size (to 80 mm) was with the 3.0 of the SC. A question that comes to mind, though, is why the Carrera 3.0 still used the smaller plate (76 mm).

Another thought is that the fuel distributor needs to be paired with the right air flow sensor to get the desired result for fuel delivery for each displacement engine. (Yes, and cam, and compression ratio maybe, as well.)

[Pkaaso]

My thoughts exactly. The 77' 3.0 was a very strong running stock motor. Why the smaller plate and shaped venturi is a mystery.

I have found that what Gunter had suggested a
while back was, "why don't you get a complete 78-79 CIS system and be done with it."

Well, hind sight 20/20 I guess.

From what I can tell the AFM I should have for my set up is the xxx.070.

Paul

[MBEngineering]

HI Paul
some info for you to ponder over;






regards mike

[Gunter]

Good stuff, Mike.
Thanks for your efforts on this issue.

[Pkaaso]

Mike, actually this puts and end to the pondering. That answers my question perfectly.

+1 for Gunter, I appreciate this. A great contribution.

Thanks,
Paul

[450knotOffice]

Interesting stuff.

Paul, are you out of the shop already? I saw no life there today or a few days ago.

[Pkaaso]

Hey Scott,

Nope, busy as hell. Just closed for the holiday. Back on Monday.

Thanks,
Paul

[Pkaaso]

Scott,
I do have an AFM meter on the way. And I think I figured out my hot start fuel pressure problem.

Paul

[450knotOffice]

Excellent!

[Pkaaso]

I finally got the .070 metering plate installed on my engine. and all I can say is.........

WOW like a MOFO... It did make a very noticable difference on the entire power band. Added great throttle response off idle, added nice smooth (increased) power to the mid and top end. It pulls real nice upto about 7,000 and seems to want to go futher.

Next, I need to run it on the dyno and see if I still have the lean condition up top. I'm almost sure that it will show a nice mix up there by the way it's running now.

Thanks for all the input and help,
Paul

[450knotOffice]

Very good Paul. Thanks for the drive, btw!

[Jay Laifman]

As Jim certainly knows, I've been having a terrible headache getting my 73.5 to run right again. To my great surprise, in the middle of it all, I found that I had the 006 FD (from a 75-77 car), not the correct stock one - and I've owned the car since it was last driven in 1978 with 40,000 miles on it.

EDIT: Ah, I think I found it. The sensor plate housing for an 006 FD should be the 004 housing. Now the questions are (1) how different is the 004 sensor plate metering than what the stock 73.5 would have - which doesn't appear to be listed, and (2) what do I actually have on the car.

EDIT 2: FWIW, I did find on the PET that the sensor plate housing is listed as the "mixture control unit" and it is Porsche number 911.110.915.00 for the 1973.5 CIS 911. So it is definitely different. The question is still how different the 1974-1977 sensor plate housing is from the 73.5 one. Maybe it is inconsequential.


I guess another question would be if the throttle bodies are dependant on these parts too.

Thanks!