1973.5 911T to MFI project

[Martysentme]

I have a 73 911T with a 2.4L 7R case and originally CIS. It needs a full rebuild. I will be replacing the pistons/cylinders, heat exchangers regardless of the build. If I had access to an MFI setup, complete with the full set of parts can the existing case be used? If yes, would it require modification?

The case I have is part no 901.101.101.7R and 901.101.102.7R.

Also, what are thoughts on modifying to 2.7L. I like the idea of extra power and building a motor closer to the iconic 73 Carerra.

[30westrob]

Yes, your engine can be modified to accept MFI. The bottom end requires no modification if you stay with 2.4 L. Rob

[nickelplated5s]

You would like it and I think there is most of a 2.4 setup available here or PP. Here's your conundrum. Mine is getting shipped today or tomorrow from the west coast to the east. Presumed turn around time is two months but I doubt it. In retrospect I should have done this in the fall so as not to miss my dry summer.

[E Sully]

You would want different cylinder heads and cams.

[targa72e]

The 2.4 CIS heads are unique. These engines had the CIS injectors mounting in the cylinder heads vs manifolds on later engines. The intake ports are also very small. That said they can be used. You can remove the injector bungs in the head and then tap them for threads and screw in plugs to block them off. Alternatively you could have them welded up. Then you can machine for MFI injectors. You will want to bore the ports out to match the larger 2.7 port size. You will also want to change out the pistons so you can use once that match the MFI cams you will want to run. So a little work but not impossible. The thread below show dyno results from a couple engines I built. The last used 2.4 CIS heads.

https://forums.pelicanparts.com/porsche-911-technical-forum/1151593-dyno-summary-testing-early-2-4l-2-5l.html

john

[Martysentme]

Thanks all. I will miss this summer and next summer as well. Currently, this car is a shell.

targa72e - great method/data from the motor builds. Impressive.

[nickelplated5s]

Pretty shell. If you want to got MFI here's my advice and why. A) sourcing parts can be difficult. B) My pump is off getting shipped to the East coast. Supposedly a 2 month turn around. Throttle bodies the same to Bend, OR. I think the two month time quote is optimistic. As far as I know only 93K on them but they are from a 69. Mine ran/runs fine but just thought it was time.

You will love it but expect pops on decel. You can also expect about 12MPG when you are on it. Perhaps 20MPG loafing around.

[stownsen914]

As the CIS injectors are in the heads, I would think you'd put the MFI injector (which also screw into the heads) in the same spot. You'll probably have to modify the heads to have the accommodate the threaded MFI injectors.

[Martysentme]

When I bought this project car, the original CIS heads were not so great. I was told that another set of heads would be included. Turns out that the 'additional' set of heads belong to a 2L with 901.104.305.02. I'll clean them up and make sure they are in good shape before trading them for 2.4 or 2.7 MFI heads.

I had heard of inserting a plug in CIS heads as a mod for moving over to MFI. More to learn...

[stownsen914]

I googled and found what appear to be 73.5 CIS heads. The injectors appear to be in the same location where MFI injectors go, in the head near the intake port. I’d look into rescuing those holes for MFI injectors.

In case you wind up using some other heads, note that carb heads and later CIS heads don’t have the injector port, but the heads can be drilled and tapped.

[skinnerd]

Performance will be better with MFI. Fuel economy will be worse. Expect the engine to run eye watering rich. Just the nature of the beast. I’ve had both MFI and CIS. Prefer the CIS for daily driving. MFI is a way cooler looking “Motorsport” like setup for the engine bay.

[Martysentme]

Looking forward to the performance aspect (and motorsport vibe). Efficiency? That went by the wayside long ago. This project is my undoing with respect to efficiency. I spent the better part of a week learning to hammer and dolly. It was all worth it. The perfect sound of a 'tink' when the metal moves just like you wanted and slowly becomes smooth to the touch...good stuff.

It is good to know that there are options available for different head setups.

[E Sully]

As long as you're willing to spend the money, it can be a great ride. One of the first things if you want to do it right would be to split the case, see if it needs a line hone or more serious work for the crankshaft bearings.
It should have the appropriate timecerts and case-savers to reinforce the soft magnesium. It would also be advisable to do the oil bypass modification and get a later oil pump.
Going to 2.7 would require a little bit of work to increase clearance for the slightly larger cylinders. With a good set of heads and the right camshafts it would give a good horsepower boost.
You will also want to get a front oil cooler setup. The stock engine oil cooler is marginal and won't do enough if you bring up the power. I installed a later SC oil cooler setup.
I would recommend getting in touch with Henry Schmidt https://forums.pelicanparts.com/members/21558.html
He has many years of experience bulding Porsche motors. I have been keeping my late model '73.5 CIS mostly original. The numbers matching curse stops me from doing much, aside from putting in an '86 3.2 Motronic engine for a few years. That only required a few easily reversible modifications. I do miss that engine, but my stock 2.4l is still a lot of fun.

[Martysentme]

The case is split. The bearings are worn past the copper. It needs time certs, line hone etc. Oil bypass is on the list. I too suffer from the numbers matching curse. I'll probably keep the 2.4L for that reason.

[stownsen914]

MFI is a bit of an anachronism, and got a bad rap from some as it has some complexities and many just don’t know how to set it up. It can be done by a knowledgeable shop, or with some diligence if DYI.

[r lane]

I have a 72 that has been MFI'd for 30 years. Didn't have to deal with the CIS heads, but you should be able to come up with a set of heads that will work. I used a MAHLE set of 2.7 P&Cs. I cut the heads to get the compression to 9.5-1.0. Put a 2.7 RS space cam in the pump. What a blast to drive that car, never tire of getting in it and the way that engine feels. I used a 2.7 case as I didn't want to cut my 2.4. May not be the direction you would want to go, but a great package if you do. Bob

[cmcfaul]

Will need the MFI cam with the gear on it for the MFI belt to the pump and the heat exchanger with the hot air connecter for the MFI thermostat.

Also, highly recommend a O2 sensor attached to the exhaust to run an AFR meter.

Chris
73 911 E