CIS to MFI conversion on a 75

[RetroSC]

Looking into possibly swapping my CIS 2.7 in my 75 for a MFI 2.7. Few questions for an MFI novice..

1. Can I do this without the MFI fuel console and just use the existing CIS pump, regulated down to 10PSI, and will it start ok when cold without the cold start enrichment circuit that's fed off this console?

2. I see MFI needs a few electrical extra's, most notably the RPM transducer that goes on the engine compartment electrical console. Do I need a whole new console from an MFI car?

3. How confident would one be to acquire an MFI engine that's lowish miles, but sitting 15-20 years, even if properly pickled. Do the pumps tolerate this well?

[rowingone]

Yes you need cold start enrichment but you can just do this with a manual switch for prime. I would buy the correct fuel pump and filter for MFI. The rpm transducer is not necessary as it is only there to reduce fuel dump on deacceleration so many run without this feature. If and its a big if . . the engine was stored and put away properly should be ok but any engine sitting that long is a crap shoot. I would not pay a big premium for this engine over CIS since it is not original to the car, it may not add much value.

[nickelplated5s]

Yes, it can be done. Look on PP Marketplace. There's some MFI parts there that might be for sale. It will be a spendy swap but I love mine. Better question is your states smog rules. It's one reason Porsche went to CIS. Secondly a local shop that can work on them. They generally don't like owners touching them to much.

[RetroSC]

Thanks all! Yes, not having a shop around here to help me sort things is a bit of a concern. I've done carbs, but MFi would be a learning experience. No smog here in Kansas, so all good there.

Still.. sort of a bucket list item for me. Will continue to research.

[nickelplated5s]

Get the Rice paper here or on Early9's. Mine's going into a dyno shop this spring. Best guess is some bushing replacement, idle is off with air screws correct. Yours will need some pump work for the 2.7. There is a PP member in Bend, OR who might help but don't know him. MFI will cost you some MPG but you will like it.

[tobluforu]

It would be a ton of work and cash. Don't forget, you will need to have the heads worked on. Pumps are calibrated, for the most part, to the cams. So, you will need those as well. If you want to dive into that rabbit hole, sell the cis, buy a mfi car, or just the motor.

[RetroSC]

Sorry, should've been more clear on this. It's a complete 2.7 MFI motor that was already sorted and running, albeit 15+ years ago it sounds. Still, I'm on the fence about it since it's not 100% bolt in and go ready..

Originally Posted by tobluforu

It would be a ton of work and cash. Don't forget, you will need to have the heads worked on. Pumps are calibrated, for the most part, to the cams. So, you will need those as well. If you want to dive into that rabbit hole, sell the cis, buy a mfi car, or just the motor.

[stownsen914]

If you don’t mind spending the money, it’s certainly possible to find a good MFI motor, or refurbish/rebuild one. MFI pumps can be finicky, so knowledge to tune one is important. There are rebuilding services for the MFI pumps to make them good as new for $$$.

You do want the MFI stand, or replicate its function. Probably easier to just get one. Re: the fuel pump, I’d argue it’s acceptable to use the CIS one since MFI has a return line. Pumps designed for high pressure operation are perfectly happy operating in a lower pressure system as long as it’s not choked, like in a deadhead carb setup with no return line.

[nickelplated5s]

Do some research and call around to MFI shops. They will know who might have a setup. Best guess is around 20K. Think about carbs. Someone here had a Weber setup last year that should work for you.

[Jonny042]

The MFI filter console serves the purpose of de-aerating the fuel and also provides fuel pressure regulation.

The CIS tank has a swirl pot, so if you can regulate the pressure down to 10 or 12psi you can probably make it work.

If you have a line on a motor with a good setup that mimics the 2.7RS setup, with the correct cams, MFI pump with the 2.7RS space cam, stacks, throttle bodies, etc. it could be a good setup. That's a lot of "if"s.

Again, IF it's a properly built 2.7 MFI motor it would be a blast.

I built an entire car around a 3.0 conversion to a 3.2SS MFI. Not for the faint of heart:



https://forums.pelicanparts.com/porsche-911-technical-forum/979976-project-heavy-metal-all-steel-classic-remastered.html

[r lane]

I have a 2.7 MFI car. Started as a 2.4. Installed a 2.7 kit, cut the heads to raise it to 9.5 CR, 2.7 RS space cam, 4.5 S engine cams and I

[r lane]

I have a 2.7 MFI car. Started as a 1972 2.4. Installed a 2.7 kit, cut the heads to raise it to 9.5 CR, 2.7 RS space cam, 4.5 S engine cams and I think it has a MFI fuel pump. Drive it regularly, a blast both bottom and top end. I race a MFI 911 that uses a SC fuel pump. As stated, the fuel return valve on the MFI console handles it. Neither car has the transducer. Maybe it's my fundimental Christian upbringing requiring that I routinely punish myself, but honestly except for a few hiccups they have been incredibly reliable. I have an EFI 965 which I love, but it has produced more issues. Go for it. Bob

[r lane]

A couple of details I should have added. Went from original MFI to Webbers then back to its current iteration MFI with S stacks. stainless lashcaps for the tensionsers to accommodate chain slack. Bob

[RetroSC]

Appreciate all the good info and feedback! Looks like I've got some thinking to do..