CIS question???
 

Greetings All,

How different are the CIS units from a '73.5 2.4 & mid-year 2.7? Can they be swapped either way?

Thanks for your help, Bill

they made improvements over the years to fix problems or short comings. i would try to use the 76-79 cis if i could. the runners on the 78-79 are larger and can really only be used on larger port heads, but i think the fuel dist will fit earlier air boxes. i have an 80's throttle body on my 77 so i know that will back date.
i prefer the 76-79 over the 80's lambda units for reliability. there are NO electronics or relays in the earlier cis that will keep it from running. some will say the cars run better or get better gas mileage, but i prefer the simplicity and reliability.

the best thing to do is read as much as you can find about CIS. here is a good start.

CIS Primer for the Porsche 911

The injector ports for the 73 mimic the MFI ports. The 74 were changed and remained the same for the 77,
The 74 heads will bolt on the 731/2 and permit the use of the 74 to 77 injection.
Bruce

73.5 CIS also uses a throttle position device that was abandoned in, I believe, 75 and later versions. The WUR in the 73 & 74 are also unique and not rebuildable. 76 and later CIS have an "automatic" warm up circuit that replaces the hand throttle on the 73.5 and you'd have to provide wiring for that fit--it can certainly be done. In short, if you don't care about originality, a later CIS system may be easier to maintain but regardless, some modifications must be made to a 73.5 engine for it to work.

Thank you all for the replies. Always good help here. -Bill