Middle Year and CIS Flogging

[cowtown]

Originally posted by CamB
At least the cars are light - it makes the hp go a long way. My '75S is pretty quick.

I agree here - my '75S with SSIs is quicker off the line than my '88 Carrera (or at least it was, until the 2.7 came out of the car last weekend). Not just seat of the pants - repeated GTECHs confirm this. The Carrera has about 500pounds on the '75 because I've stripped out the '75, but still...CIS can't be all bad, if the application is appropriate.

Also, like another poster said, the idea that everything is mechanical is attractive, just because everything else has so much electronic stuff in it. I'm a gadget lover, but sometimes a minimalist approach is just cool.

[chuckw951]

I don't mind the CIS bashing. Keeps the prices of used CIS parts low. I've seen whole systems for $300.

Some day when I have the dough maybe I'll convert to an exotic EFI system or something, but I don't know if the bang for the buck is there.

Chuck

[Randy Webb]

Yes, PAG went with it because of emissions and fuel economy considerations (remember the two gas crises? Today is nothing compared to that). And, yes, DIS works -- but WHY did you buy a Porsche? You have to answer that first, to see if you want to keep the CIS (or spend a bunch of $$ to improve on it). By, 1984 Bosche had EFI ready and PAG moved to that for the Carrera. The EFI systems are marvelous in their ability to optimize power, economy, and emissions -- not to mention the low maintenance. But I like carbs for that raw, early car feel and response. And the '73 which has a CIS 2.7L in it now, will be getting carbs (and 0.5 more liters of displacement).

[Randy Webb]

"the idea that everything is mechanical is attractive" Uh, one more thing -- the idea may be attractive, but it is incorrect. CIS uses hydaulics (air vacuum) so call it that to avoid confusion with mechanical fuel injection which PAG used on the '73 S and RS, for example. That's true MFI, and CIS is not.

For a great intro to how it works, there is a yellow booklet that Bosch used to put out.

[cowtown]

I've got the yellow Bosch book, thanks.

IMO you're being a bit pedantic. No one in the thread appears confused about the difference between CIS and MFI.

Colin

[wckrause]

CIS is great -- if you want an obsolete economy car FI system

While CIS was used on some economy cars (VW's, and others), it was also used on top of the line Mercedes, Ferraris, Rolls Royce, BMW's and others. It WAS state of the art in FI during its time. The fact that many of these cars are still running with their original CIS components says a lot about the reliablity of the system.

[CamB]

I agree here - my '75S with SSIs is quicker off the line than my '88 Carrera (or at least it was, until the 2.7 came out of the car last weekend). Not just seat of the pants - repeated GTECHs confirm this. The Carrera has about 500pounds on the '75 because I've stripped out the '75, but still...CIS can't be all bad, if the application is appropriate.

I read this and remembered how the car was noticeably quicker again when I took the interior (including passenger seat!) out

I have a RoW 911S - Porsche quote 175hp and 175 ft/lb

In '72/73, the T (with MFI) had 140hp, the E 165hp and the S 190hp. They all weigh about the same as my '75 (Porsche figures - ~1050-1080kg for all 4 cars). In comparison to the T and E, it isn't slower at all if you compare apples to apples (which would be a '74 RoW 911S, which has the 7:31 R&P transmission (my '75 has the first 8:31 R&P so is slower)).

Of course the T, E and S all sound better

(disclaimer) I have only actually driven a '72T. I'm guessing about the E and S. The '72T was slower than my '75. It sounded 10x better. My '69 with a 2.0 T engine with E cams (a whole 125hp on the dyno) is much slower than both. It also sounds 10x better than my '75.

[CamB]

Oh, but another negative to CIS I just remembered. Also applies to the exhausts Porsche used on the majority of CIS cars.

Valve adjustments. CIS = bulky. Carbs = minimal.

[john70t]

One thing the D-jettronic engines have over CIS is their response to vacuum leaks. The MAP sees only the manifold vacuum and can correct for it but the CIS is pretty vulnerable to anything after the distributor(injector orings, boot etc..).

Also the CIS needs clean water free gas all the time. The plunger in the distributor has to make a high pressure fluid seal by fit alone and slide accordingly to adjust for the WUR pressure.

The air vane in the distributor also reacts slowly to short bursts of air by having to overcome control pressure above it in order to richen the mixture, but overall it's a simple, reliable system.

Not to start another thread, but except for the #%$# platinum plugs, most of the things Bosche does very well. The company history is quite interesting. A noble man.

[Jamul74]

Part of the beauty of this BB is how a relatively innocent question can bring out a myriad of responses containing everything from "rat brain" responses to highly technical. Kudos to all! However, I will go on record as saying that there are some of us, perhaps a lot of us, that take what the Porsche engineers gave us and work with/live with the product. I have no desire to ****can the CIS and install an MFI or anything like that. I just enjoy the feel and sound of a 30 year old sports car. I accept the period shortcomings and relish the "obsoleteness" of an earlier era. In other words, I am what I have experienced. And if that is a 2.7 CIS Porsche then life ain't so bad.

ps Did I mention I blew by a new Turbo and GT2