converting CIS to carbs

[bossladys 911]

Novice interested in how to convert a 77 2.7 that I will use to replace my 73 MFI 2.4 that is locked up. I am not sure how or if its possible to make the CIS work or would it be easier to convert to the 40 series carbs I have. I have both complete engines but understand the cams and heads are different. Your sage advice is greatly appreciated.

[2.7RACER]

Welcome to the board.
This is a loaded question.
What is a "locked up 2.4"?
What kind of condition is the 2.7 in?
You know the 2.7 with CIS is a lower HP motor than the MFI 2.4.
Just replacing the CIS with carbs will not increase performance.
To get more out of the 2.7 you are looking at carbs, manifolds and linkage, $2,000. Cams, "S" or others $500, pistons, $1,000.
Plus whatever else is needed to get the 2.7 up and running.
This of course doesn't include any labor.
'73 911 with original motor and MFI is worth significantly more than the same car with ANY other engine.
I would seriously look into fixing the 2.4 and keeping it original. You could get your investment back at sale time.
Hey, I run a 2.7 because it's what I have. If it blew up I'd put in a 3.6, but I'm talking about a '76, low value.
'74's and older, especially with MFI are going up in value.
Don't screw up a future Classic.

[azasadny]

Doug,
My "future classic" is kicking my butt and has been all summer! I have a 2.7L CIS engine and I'm seriously considering putting Zenith carbs on it to get rid of my CIS. I'm not thinking about performance, I'm thinking about reliability. Tinkering and futzing around with the mysterious CIS is giving me brain damage and I can't take it any more. I need a car that I can drive in the summer without spending every other day under the hood or under the car. Are carbs more reliable?

[2.7RACER]

Art,
The MFI equipped Porsches are all worth keeping original. They will be amongst the most valuable because of the power, throttle response and relative rarity.
The '74's in my view are valuable because in many if not all states they are exempt from smog inspection.
With all due respect any 2.7 CIS will not find itself in the same class as a MFI car.
I switched my '76 from CIS to Carbs along with 9.5 JE pistons and a Solex cam for added performance.
Since I use the car mainly for the track, smog was not an issue. It won't pass smog as it is.
I'm curious as to why your CIS has been such a problem.
I'm sure you are tired of hearing how reliable it is.
My experience with CIS was positive as far as reliabilty goes. I just wanted more power.
Switching to Carbs has been a learning process, particularly since I live at 5,000 feet. Most of the standard jet settings just don't work here.
If you feel like it, tell us about your adventures this summer.
I've got a shed full of CIS parts.

[bossladys 911]

The 2.4 only rotates 1/2 a turn by hand then stops I found the 2.7 locally witha fresh rebuild and the suggested conversions,new studs,carrera tensioner kit etc. I know the MFI is stronger but $$$ are my limitation. The gentleman I purchased the 2.7 from showed up in a beautiful guard red 77' but his didnt want to start after our visit. That was the beginning of my not having "warm fuzzies" about the CIS. Also a major concern was making the system work with my current wiring. There doesnt seem to be much difference between the two so maybe I can make it work.

I live outside Indy and found the 73 in Ohio as a true barnyard baby. It was stripped to bare metal on half of the body so surface rust was an issue. It is now ready to paint thanks to a lot of Eastwood/PPG products and my time invested. I bought it to restore for my wife hence the log-in name. I may try to swap the 2.7 to pay for the 2.4 rebuild if I can find a willing Porshefile. I understand the originality issue and power but since it is for her thats not such an issue.It's the look that counts. I could keep the 2.4 in the garage and possibly secure the resale value that way. Thanks for all your current and future help.

[dd74]

If the 2.7 is a 2.7S engine, you might have the same hp. amount with webers as the stock 2.4. The stock 2.7S had a half-point higher compression than the normal 2.7 (8.5 vs. 8.0), which was the difference between 150 and 175 hp. Retrofitting Webers and recurving the disto can possibly get you 10 more hp. You might be able to do some "while you're in there" work to gain a little more, but overall, you should be right about where the 2.4 is, and have better throtle response and an overall lighter engine - it all adds up - and potentially be equal with a 2.4. Also, because this is for your wife, maybe you should think about driveability. The 2.4's power doesn't come on to very late in the revs, while the 2.7 has more torque. So that might be a consideration for her if she drives around town.

With that said, though, I wouldn't get rid of the 2.4. Hopefully there's a way to have both the 2.7 and 2.4.

[bossladys 911]

Thanks dd74. I plan on keeping the 2.4 in case I do sell the car in the future. I have a set of what I believe are called 40 series carbs. I understand there are sources that supply carbs linkage and special adapters to plug injector ports in the 2.7 CIS heads to convert to carbs. The 2.7 is built and ready to install. I may look at getting manifolds and tops to use the carbs and add them before I install in the car. I can probably have the adapters made.
I am not sure about any wiring differences in my harness compared to what the CIS requires. That system seems to be more of a mechanical setup as opposed to an electric injection. Any info on what would be needed to even try the CIS in the MFI chassis is appreciated. How can I tell if the 2.7 is an S type?

[dd74]

Bosslady - I sent you a personal message.