Replacing CIS '77' Carrera
 

I have a RS spec 'Euro'' Carrera with CIS. I had a chance to ride in a 3.0 SC with throttle body injection, 10/1 pistons, and an aggressive cam grind. The car absolutlely peeled my eyelids back. At $8 grand plus my old CIS and my twin plug set up I have to admit it is tempting. The same mechanic that built my engine would do the install. What factors should I be taking into consideration or other power options I have not considered?
Thanks,
Bob

:)

CIS requires mild cams and special domed/dished pistons for proper combustion.

Changing to TBI allows a change to more agressive cams & fully domed pistons which produces the new found power.

Why must you give up your dual ignition?

The twin plug setup should make it run better & allow lower octane (less costly) gas to be used.

What will you use for ignition if the dual plug is removed?

How reliable will this system be? How many systems like this have been built? Does it run well in cold weather? Will it run well in hot weather?

What is the cost breakdown, parts & labor?

Are you getting a top-end rebuild as well?

$8,000 for all of the above doesn't seem too high with today's prices.

Len

:)

What's the TBI out of?

Joe

I think you will find that any sys. that allows higher CR, better cams will roll your eyes back.......its not just your CIS that's slow, its the big picture here. I would get a real education to make a choice b4 I spent money on carbs, there are many other choices beyond caveman stuff that will roll your eyes back and be much more fun and adjustable

Bob,
Nice too have a faster car. Is smog testing a problem where you live?
Selling a non-smog car can be a problem.
My 2.7 '76 is heavily modified for the track.
Makes it a tough sell. Impossible for the street in a smog county or state.

And also if you need to get rid of your double plug sys..can I buy it ?? (but truly it will make your engine more efficient.)

In Massachusetts a car over 25 years does not need a smog inspection. So selling is not a problem; I'm not selling it so that's not a problem either. My car was built for the track (COA) hence it has all the goodies that will make it run fast and be reliable. At 4 grand it comes on cam and revs to 7 grand in the blink of an eye due to lightened reciprocating mass. For the moment I will spend the year exploring the limits with what I have, and save any major upgrades such as TBI for the winter.
Thanks,
Bob

Joe,
I actually don't know, but I did a Google on 'TBI Porsche' and found a number of systems offered.
Bob

I understand the advantages to twin plugging and if I do decide to go with the TBI, I would sell it.
Bob

Bob,
I'm glad to hear 25 year old cars are exempt from smog inspection in Massachusetts. Makes all the fun stuff simpler.
Here in New Mexico, we have two counties with smog inspection. Not where I live though.
I just replaced my 8:31 915 transaxle with a '72 7:31 transaxle. Big difference in acceleration. I use my '76 on a 1.66 mile, 14 turn road course here in Albuquerque. I'm still learning how to best use the new gearing. I expect to lower my 1:38/7 lap times to 1:35/6.
Z06 Corvettes are doing 1:30/2 here.
This is great for this track. It does increase rpm's at freeway speeds from the low 3,000's to the high 3,000's. Also drops the max speed to just over 125mph.
I kept my original 915, 8:31 as a spare.
Only down side is the earlier trans uses a mechanical speedo drive.
With this change your '77 will at least stay with Carrera's.

Interesting are you running a four or five speed tranny?
Thanks,
Bob

Bob,
The transaxle is a 5 speed 915, from a '72 911.
They are getting harder to find because of the demand from racers.
A good ring and pinion set can be found for $500. The labor to install the R/P into an existing trans can run $500 or more. The set up done properly requires special tooling that some mechanics don't have.
From what I have read, it isn't a job for us home mechanics.

Doug,
Since I have a LSD, a 8.3 ring and pinion and occasionally need to hit Autobahn speeds. Prudence would indicated money is better spent elseware. It's pretty cold up here, I suspect the transaxle oil is the viscosity of taffy. That would explain my more horsepower is better mind set. In truth I doubt if I ever could push my car near it's limits, not in my lifetime anyways; but I'm having fun trying.
Best to you,
Bob