CIS vs DME

[Wil Ferch]

Many of you know me .. or know of me .... and I have posted here a number of times. I learn a lot and likewise I hope I'm offering advice that can be of use to other people, too, when I feel I can comment on that topic. This is a great community of like-minded people.

Today's question is a bit uncomfortable for me, as it sounds rather "newbie". I have had considerable experience with the 84-89 DME cars and feel very comfortable with them . I am momentarily "between Porsches" and am back window shopping...itself a nice experience. But I digress.....

I've broadened my search to include the 78-83 SC range of cars with their CIS injection. Frankly... that aspect spooks me. Familiarity, it is said, breeds contempt but it also breeds comfort and I am not at all familiar with CIS. Reports span the spectrum of this being an unnecessarily complicated and delicate system to get right and fiddle with...others say "ya gotta learn and understand and then all is OK".

Opening up this thread to hear the pros/cons of this topic. Maybe get it down to the issue of..."once it's tuned right, can I set-and-forget it like DME?

[psalt]

Wil,

The final version of CIS lambda on the 81-83 911SC works very well. The engine can be tuned to provided good mpg and WOT performance by someone who knows the system. However, it is a bit like steam heating systems, the people who know are called the "dead mens society". It has more flaws and needs more expertise to get the best out of it than DME.

The bottom line is that CIS is inferior because of the expensive and NLA components that handle fuel and the changes in fuel chemistry over the past 30 years. If you find a car with a new FD, WUR, and Accumulator, injectors and sleeves, the CIS should be good for another 30 years.

[T77911S]

i like it, but it is what you know that makes you he most comfortable.

cis is not that hard to understand or work on. the problem is, it is getting very old and you can drop some $$ getting it into shape. at the minimum, i would count on replacing ALL rubber/ seals that are related to the CIS. that is how i would look at it if iwas looking at another CIS car.

i prefer the pre 80 CIS. mainly due to reliability. the ONLY thing fuel related that will cause me to break down is a fuel pump/relay. usually with CIS, it will start to run bad before it stops running at all. there is nothing electrical that runs my injection system.

[Vincent Hill]

I "Had" a 1976 and the MAIN Reason I bought the 1982 SC I have is because I Knew what I was getting into and understood it! Plus it is also very similar to the 1982 BMW 320I I have. "For ME", it is very easy to adjust and work on. A Lot of the parts fit all years. The only one in the group you mentioned that I would be careful of is the 1978. I think that is the year they expirmented with a lot larger sized Inlet runner so if you need anything for that year, the parts can be more expensive and harder to find.

Once I had my 1976 set up, we drove it for close to 10 years before my wife (The fast cars are really all hers because I ride the Motorcycles) wrecked it at over 130 MPH going through her favorite turn. The car had just under 400,000 miles

There is also a Bosch Fuel Injection Book I have that really explains the Warm UP Regulator adjusting and a few other things. I am trying to avoid the 1984 and later!

[Wil Ferch]

Hmmm ..... although Spendy ... maybe PMO's or rebuilt Webers become an option to consider?

[db_cooper]

I grew up with CIS and don't think its a big deal. Pretty reliable and simple. Components can be pricey, they always were. Get a good set of CIS gauges and some tech data, your good to go.

Our modern fuels would be the big concern. Ethanol and the many "O" rings and seals in CIS may not be the best combination. If I go the CIS route with my next Porsche, I would keep a bottle of Marvels Mystery Oil around to mix with the fuel. (I use it with my 3.2 also)

DME is very simple, as you know. CIS is thermo-hydroylic, you just need the right tools.

[Wil Ferch]

It's beginning to get clearer in my head now.....

1.) requirement to read, study, learn, textbook stuff, Bosch manual, etc and
2.) start (again) buying specialist tools, gauges, etc..... all for an "old" system that is out-of-print

For me at least,.....this might be the push to keep me with DME and the 84-89 cars. Or find a 3.0L with Webers and PMO's. YMMV.

[Wil Ferch]

Follow up....

I think concurrent threads like this one just put the nail in the coffin for me, I'm getting too old to futz around with stuff that seems more "chore" than "joy"-->

Warm start problem on 911 SC (1978)

[T77911S]

when you read more about CIS, you will find that it is a pretty cool system. but then i have been doing some reading on carbs, pretty cool stuff too. i have found that webers might be prone and/or sensetive to air leaks than CIS. most cis leaks are just easily replaced rubber, with a weber, its more of send it off and have it machined.

carbs sound AWESOME!

[Vincent Hill]

The 2 main things you need to deal with CIS are a LONG 3 MM Allen wrench and a Fuel Pressure Guage with some adapters. Using some old parts I made the line for the Warm Up Regulator, Main Fuel Pressure that I could actually ride around with and in line injector adapter. I think I spent at Harbor Freight about $5.00 for a set of Long Allens and at a SPeed Shop about $50 for the pressure guage and I am still waiting for the time I cannot find the part I need NEW from the dealer or on this web site.

As far as the Reading is concerned, I do not know many people that work on any car that has memorized the Specs on everything. I use the service Manual and Bosch manual (WHich is less than 1/4 inch thick with a lot of Pictures) as a reference Guide more than Not Known Knowledge.

Saying all of this I also want to say that FIRST, I would look for the years you mentioned and go Older vs newer. The older the Porsche the more Back Yard or Home Garage friendly they are. Take a New Turbo Porsche with 7 Oil Pumps. How in the Hell0 does anyone work on them? Even at the dealer I go to they take the engine out and put in a new one and SHip the broken one out to a special Porsche repair place.

BTW, the prices charged by Pelican are very close to what I can get from the dealer with the parts person Discount and in some cases Pelican was cheaper.

[BernieP]

I have an 80 Euro SC that I have used as a daily driver for 9 years including Pittsburgh winters
and have have never had a problem with my CIS. Passes PA smog without a cat. YMMV.

Bernie

[RWebb]

carbs have poor cold start & driveability -- but...!

I would not say CIS is complicated; it will cause you grief with Ethanol if they ever go much higher.

EFI is where it's at for modern systems AND you already know it. How hard can it be to find an '84 in NY?

[Wil Ferch]

it's not a question of finding an 84 in NY.....I'm simply expanding my base and price range since the car will likely be modded and you hate to start off with "too nice" ( and too expensive) a car...although frankly the pickens are indeed mighty slim for either nice SC's or 3.2's in the Buffalo area I'm in....WAY across this state. Most people immediately think NYC when we say NY state.

My search is nationwide and I have also given myself a long time frame for the search...as the "hunt" is part of the fun.

[psalt]

Wil,

Cars are cheap right now and probably falling another 20-30% along with other assets. My advice would be to focus on a g-50 Carrera if you are interested in future mods.

[boyt911sc]

Originally Posted by Wil Ferch

Many of you know me .. or know of me .... and I have posted here a number of times. I learn a lot and likewise I hope I'm offering advice that can be of use to other people, too, when I feel I can comment on that topic. This is a great community of like-minded people.

Today's question is a bit uncomfortable for me, as it sounds rather "newbie". I have had considerable experience with the 84-89 DME cars and feel very comfortable with them . I am momentarily "between Porsches" and am back window shopping...itself a nice experience. But I digress.....

I've broadened my search to include the 78-83 SC range of cars with their CIS injection. Frankly... that aspect spooks me. Familiarity, it is said, breeds contempt but it also breeds comfort and I am not at all familiar with CIS. Reports span the spectrum of this being an unnecessarily complicated and delicate system to get right and fiddle with...others say "ya gotta learn and understand and then all is OK".

Opening up this thread to hear the pros/cons of this topic. Maybe get it down to the issue of..."once it's tuned right, can I set-and-forget it like DME?

Will,

I enjoy CIS troubleshooting and it is fun for me. Between CIS and the DME cars, the later model cars are far more modern and efficient than the CIS cars. Although I intent to keep my two (2) SC's as long as could, the DME engines are far better than my CIS cars.

A few months ago, I had an opportunity to work on a 3.2 Carrera in my garage and was totally impressed and amazed about the DME technology. The change from CIS (partial electronic) to DME (electronic) is a giant step towards modern EFI system.

But people who don't understand how the system works blame CIS to be troublesome and difficult to maintain. That is true for people who don't know and understand it. Who could blame them for their ignorance!!!!

DME technology regardless in Porsche or in any German cars are far superior than the CIS!!!!! It's no brainer. It is far much better. Now to answer your question, you can have an SC car that's dependable and reliable like a Honda Civic. This is my actual experience after owning these cars.

Tony

[longhornchris04]

CIS when its working is good...
When it isn't working, its fairly easy to diagnose... but parts are starting to get expensive.
Once all the parts are working, there are only a few things to adjust, and its fairly easy to do 'on the fly,' hell I did it on the side of the road because it doesn't adapt well to 7000ft altitude changes (but the mountain roads sure were fun).

Of course DME is better, as is having a bit more displacement. The question is the cost differential between what's available, and what (if anything) you do to the car.

While I'm happy with CIS for now, I do plan on going to Carbs... but the I'm not looking for a daily driver and carbs look so damned cool.

[BernieP]

Hey Walt, if your looking for an SC to mod you can buy my 1980 Euro SC for $5,000 and have plenty left over for mods.

Bernie P

[Wil Ferch]

Another thread on CIS finicky-ness....seasonal changes--->
It's that time of the year AGAIN! (CIS)

[brads911sc]

Love my PMO ITB's with Megasquirt EFI. Runs smooth through the powerband. No issues. cold / warm up could be an issue in Buffalo... Dont forget to recurve the dizzy if you buy a SC...