Porsche Newbie Question: What is a CIS?

[9fourteen]

I see CIS in posts from time to time when talking about sixes. What exactly is a CIS? Which engines and years was it produced. What is the advantages/disadvantages?

Thanks. Sorry for my ignorance. I'm still learning.

[chrisreale]

Continuous injection system. Thats all I know

[Bleyseng]

ContinuousInjectionSystem used on Rabbits,Jettas, Dashers in the 70's and early 80's. Kjet is the other name
Geoff

[Potter]

Potter (Jackass) in Dayton...........gimme an e-mail sometime and we can connect. It is lonely here being the only sap in these here local Ohio parts with a "that some kinda TR7 or some rice burner you done got there?" car. I know Dave Barber is somewhere in Ohio........but not near me. Good to hear another voice from so close!

[Zeke]

CIS was introduced on the 911 in the US starting on the '74 2.7 and all models were designated as "S," and continued on the 3.0 "SC" in '78. CIS was replaced by the electronic injection in '85 on the 3.2 engine when the 911 became the Carrera.

[sammyg2]

CIS was first sold on a 911 in 1973 1/2, i thought it was a 2.4 but I'm not sure. Anyway, they discontinued it in 1984 when they changed from the SC to the Carrera.
CIs or Bosch K-jetronic was also used on BMWs and Mercedes cars, it basically uses a large aluminium plate that gets moved by the intake air. The more intake air flow, the more the plate moves. The plate is linked to a valve mechanism in a fuel distributor. As the plate moves and the valve is actualted it canges the fuel pressure in the fuel distributor and sends more fuel pressure to the injectors.
The injectors are basically spring loaded nozzles that squirt fuel any time the fuel pressure is above 3.5 bar (IIRC). The more fuel pressure to the injectors, the more fuel that gets injected.
The injectors are not timed to the intake stroke and are not electronically controlled. The only electronics in the system is the fuel pump (duh) the warm up regulator, cold start valve, thermo time switch, AAV, and on the later systems an O2 sensor loop.
It is genius in simplicity and reliability, but it does give up a little bit in performance when compared to more modern fuel injection or large multi-throated carburetors due to the restriction of the sensor plate.

[Dave at Pelican Parts]

Sammy's got it right: 1973.5 911T was the first CIS-equipped car in the world. All US-spec 911s used CIS from 74-83, be they plain 911, 911S, 911 Carrera, or even 911 Turbo. (The Turbos used CIS all the way up until, I think, the 993 Twin Turbo. Hmm, I'm not completely certain about the 3.6 964-based turbo, but I am sure about the 3.3 one.)

Also used in VWs for years and years.

CIS cannot tolerate very wild cams, which also liimts its performance potential.

Trivia time--the 1974 1.8L 914 was the very first production car in the world to use Bosch L-jetronic FI. This is the FI system that most modern FI systems are based on.

--DD

[9fourteen]

Thanks for all your replies. Now, my first car I ever owned was a 1988 VW Fox. I believe it was K-Jet Injection. So, more or less it was the same CIS found on the Porsches?

[sammyg2]

Yup, same thing, except on the VW the fuel distributor only had 4 lines coming from it

Porsche used CIS on the 924 and some of the 928's also, dunno about the 944.