We are building a 75 conversion with a freshly rebuilt stock 69S 2.0. I have a set of 914-6 webers that were just rebuilt (jewelry), and the fellow that sold the motor has offered up the injection for it.

I really wanted the sound and stock look of carbs, but my friend said that the injection provides close to 40hp for this motor, and sounds better than carbs??

Any thoughts?

Seems to me it's down to your preference: originality vs convenience (post install/tuning) and drivability in varied conditions.

Cis or Mfi

Assuming MFI I would try to go for it. That again assumes that it is in good working condition. If not in good condition then you have to be willing to work and or spend to get it right, which can be a project

The carbs are a more straightforward tune. All of the setup is a pretty well known formula for carbs.

The MFI just adds a bit to the “cool” factor. Sound should be the same, maybe slightly better for MFI. I would be very skeptical of the 40hp claim. Well tuned carbs should not be very far behind MFI in the HP department, if at all.

Either way I am a big fan of the small bore, narrow body hot rods.

I agree - would try to keep the MFI if at all possible/affordable. In addition to the extra coolness factor, its throttle response and drivability beats carbs. Someday I may actually try to convert my car over, and it already has MFI compatible cams as a start.

MFI is expensive to buy and expensive to build

But oh so cool!

MFI certainly does have a cool factor and will make the motor worth a lot more with that injection on it. It will have crisper throttle response and an interesting sound.
I don't see anywhere near 40 hp increase though.
Costs a lot more to buy and set up and tougher to adjust unless you know someone very comfortable with it.
As I remember it was not easy to get at the adjustments on the pump when in a 914 because it is backwards. I saw people cut through the firewall to get the adjustment tools through.

Then again.. Dealerships in the 70's weren't pulling MFI off engines and replacing it with carbs for no reason..

My mechanic had a bunch of twin plug MFI engines running around the Boston Area
back in the 80's and 90's...

MFI for sure, carbs are a little loud right behind your head for any extended driving.

I had MFI installed on one of the engines in my -6 conversion. Pretty straight forward to get working from fuel system standpoint. The pump just wants to see fuel pressure at a constant 14psi.
Two problems with MFI in a 914 are that there are no provisions for getting heat to the thermostat and the standard -6 sheet metal will not fit.
I used a wide band O2 system to tune the MFI and had it working very well. I had to eliminate the thermostat as it did not function properly without heat ducting. When everything was tuned well for hot running the car would not start when cold. I did not have the auxiliary cold start injection installed. I ended up making a mechanical adjuster in place of the thermostat to start the car when cold.
There are other solutions to make this mechanical with a cable to the passenger compartment for cold start enrichment.

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For the sheet metal It needed to be modified to accommodate the pump drive. I had to use a 911 and 914 pieces spliced together to get it to work.
The airbox was also a little tight on clearance so I removed the torsion bars for more clearance but this could of been do to engine mount positioning.

john

The factory hp rating was I believe 10hp between the 68s with carbs and the 69s with MFI

But the 69 heads also have bigger valves than the 68
So that could of been a part of the difference

I believe the MFI had bigger cams and more compression ratio. You also drive the pump off the rear of the left hand cam.

Jett, mine is a 2.2 E with S pistons, Mod-solex cams and 40 PMOs. I love the power, the look and sound all the way to 7 grand.Click to view attachment

If nothing else secure the MFI
It is expensive to rebuild but when done it is utterly dependable and magic.
The sound is the same as carbs.
I dream of MFI on a 3.2 short stroke in my GT replica
I do have a 69 S that luckily still has its MFI but needs a restoration.

The engine is so much more valuable with the correct mfi.

MFI -- if you've got the coin, and can find someone to set it up properly that is the way to go.

I'm not sure if my numbers are right but I've heard that MFI rebuilds and modification can push $8k - 10k?

Didn't @ClayPerrine used to have a 2.4 MFI? Would be great source of info.

MFI, apparently the motors matching unit.

Thanks everyone! Fortunately the MFI is not took expensive and we have folks to rebuild and tune. I’ll try to buy the unit

Great looking car!

Sounds like you will get the MFI. The tools to tune a MFI (of carbs ) are so much better today than even 20 years ago. Using a wide band O2 system you can dial in the mixture very well. There is also a lot more documentation on how to go outside the factory tuning if displacement or cams do not exactly match factory.

john

MFI all day. My '69 911S was one of my favorite rides, that motor was incredible

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I had (and still have) a 2.4ST motor with MFI on it. I ran it my six conversion for years.

MFI runs great, and sounds tremendous. But unless you have someone to either teach you how to set it up and tune it, or you can pay someone to do it, then it is a bear to keep running correctly.

The thermostat on the MFI pump can be setup to work with heat exchangers. I was lucky, I got a set of 916 heat exchangers for mine. but it is simple enough to add the proper pipe to feed hot air to the pump. As for the engine tin, It is not hard to modify it to work with MFI. The only piece you have to modify is the right rear where the pump drive is located. I cut the tin and built a cover out of the 911 cover that worked great.

The cold start system is very primitive. It is nicknamed "the firestarter" for good reason. I never hooked it up. So starting the car on really cold mornings was a real process. I kept starting fluid in the car, and I had K&N watershield air cleaners. I would spray a shot of starting fluid under the air cleaners and try to start it. It would cough, sputter, spit and run on 4 cylinders, gradually adding cylinders as it warmed up. Oh.. and a hand throttle is an absolute must when running MFI. You have to use it to hold the throttle open while it warms up. About 10 minutes of letting it warm before trying to drive it.

But once it was up and running, it was a blast to drive. Phenomenal throttle response, and the sound would raise the hair on the back of your neck up. It sounds like the 917 in the movie Le Mans at full song.

I have a 69 911S MFI pump, and I considered putting MFI on the 4.0L motor. But I wanted a car that I could turn the key and drive, so EFI won out. I do miss the MFI sound and throttle response.


There is a video of my car with MFI out on Youtube if you want to hear it. It was wet that day, so I couldn't really open it up. Too much wheel spin.


https://www.youtube.com/watch?v=UHzPt2H5h0Q

My previous 914-6 had a built 2.8L with RS spec MFI. Yes, it was difficult to cleanly start cold. It was fitted with a manual enrichment switch on the dash; "ignition on, hold cold start switch for a count of 8 with full throttle then engine crank to start". It was easy to flood and often idled badly or stalled when cold. The MFI pump is also a potential source of oil leaks.

Never ran the engine with carbs, so I can't say for sure about improved warm engine performance other than the throttle response was pretty sharp. Was it worth it, not really. Well set up Webers will do most cars quite well.

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Beautiful car! I have onky watched a video of the motor rev’ing and was shocked at the acceleration.

sounded great! Thanks for sharing!

My mechanic is a legend race motor builder and tuner, but he does talk of retirement.

Thanks. We have the carbs as backup