2.4T converting MFI to CIS

[Greyn57]

Hello from down under. Been a while since I posted on here. I have a 72 2.4T MFI motor fitted in my Type 34 Karmann Ghia. I want to convert the MFI to CIS in the interests of better cold starting and fuel economy. But I also dont want to make any major changes to the heads / cams / motor so I can swap the MFI back on if I want to do some drag racing etc.

So my question is, I understand that I will need the CIS fuel pump and manifolds in addition to the CIS injection gear. Can I use the 2.4T MFI heads/cams with the CIS injection? Will plugging up the holes for the MFI injectors with the correct threaded plugs be ok?

Advice appreciated please. Also understand that I will drop some HP.

Thanks for your help

[Rick V]

I am sure someone will chime in here with more detailed info but in order to run CIS you will also need to change out the pistons to the ones used in the CIS engines. I don't know if the MFI engines are the same as the CIS ones. Just a thought.
Sweet car, do you have any more pics to share?

[Greyn57]

Thanks for the compliments. More info and pics here ==>> Type 34 Karman Ghia with 2.4 MFI Motor

[911st]

This can be done in car with care. You have to plug the MFI holes and grind reliefs into the intake ports to fit the raised CIS injectors. The prime reason for the differed pistons is emissions and motor will work fine with out.

Note that if a CIS fuel head is not stored correctly it will need to be rebuilt our you are very likely to have problems.

Having said that, would suggest it would be easier to just sell the motor and buy a 2.7 or better yet a 3.0 motor w CIS complete.

2.4 T motors may have interest to those that want to build RS or RSR replicas as it has a great crank and the full MFI set up.

Could send the pump out for service and get your system back into spec. so the system you have works better.

[Rick V]

Thanks for the link, very sweet car.

[daepp]

I don't know anything about fuel economy with CIS, but cold-start is great with MFI. Was the hand throttle installed along with the conversion to the 911 engine? I believe it to be essential to the cold start process.

Also, I have heard that the MFI doesn't like changes to air flow - non-stock air cleaner or muffler. Do you have the original air cleaner? Just a thought.

Beautiful car by the way! It's very impressive!!!

[BK911]

It will probably cost you more for the conversion than you will save with the fuel economy. Spend the money on some steelies and hub caps for the ultimate sleeper look.

And I agree with David, I've never had an issue cold starting an MFI engine. (I haven't always lived in FL)

[jwernquist]

I agree too, I would keep the MFI , you will miss it if you converted. Dont get me wrong I Like CIS now that I know how it works, but I still like MFI Better. Keep the MFI You will be happy you did.

JW

[RWebb]

that is about the worst thing you can do to a Porsche engine

think it thru carefully -- fix your mfi

if you must get rid of it, sell - for a lot - to someone who appreciates it and go with an efi system - not the hydraulic cis

[911pcars]

There's a difference in the fuel mileage numbers between MFI and CIS. Not sure keeping the system intact is as much of a requirement in a converted Karmann Ghia. A mileage step between would be carbs.

Sherwood

[BoxsterGT]

Convert it to EFI, its far better than CIS, and less money than buying new CIS components.
Len

[Greyn57]

Thanks for the input everyone, some great advice here. I did a search and found a post that showed the differences in the heads between CIS and MFI, so I would need to do head work to run the CIS. (reliefs in the inlet ports for the injector)
So I think I will stick with the MFI. Economy wise I am getting about 20 miles per gallon (13ltrs per 100klms) and the pump and injectors are in great condition and throttle bodies were rebuilt last year so no issues with the condition of the system. Cold start valve is missing and hand throttle was never fitted, so starting its a case of crank and crank till it catches and then warm it up a bit before driving off.
Probably better getting these bits fixed up and keep the MFI.
You are right about missing it, the MFI certainly gives you a good kick in the pants when you floor it!!

[daepp]

Do yourself a favor and figure out how to reproduce the hand throttle feature of the early MFI cars. I suspect you'll be happy that you did!

AFAIK, on the 72 and 73 cars it's fairly straightforward. On the earlier cars I think it provided raw fuel to the throttle bodies (a potential fire hazard) but I think in 72 it got somewhat safer.

Ther eare so many that understand MFI better than I do - sear fo "earlySman" or "Ulimate MFI".

[Schwarzeritter]

I would recommend you go with a EFI system, its a more direct simplistic system.
They seriously dont cost that much and you'll over-all improve all around fuel economy, performance, reliability.

I have owned vehicles with CIS, and its cool and fun initally until it starts too age.
Where with the EFI system you can really get a really nice tune.
I have done this too a few BMW's, Ferrari 308GTSi, various 911's the way too go is EFI.
Carb's and MFI are cool for period tuning. Ofcourse like with all things there are acceptions.
But absolutly I will argue it with anyone that its not cost effective too go from MFI too CIS.
The other Pluss is that you can have a wide choice over the timming.

[Schwarzeritter]

P.S. Your Ghia is ( very cool )~