Ultimate 3.0l CIS to MFI conversion thread

[kiwiokie]

The 1974 Carrera RS 3.0 had a 3.0l engine with MFI which by all accounts was a sweet combination. Since there were only 55 of these machines built I suspect that over the years people must have attempted to emulate this engine by starting with a ROW 76/77 Carrera 3.0 or SC 3.0 and converting the CIS to MFI. The purpose of this thread is to store the cumulative wisdom (or folly ) of those that have attempted a conversion from CIS to MFI on a 3.0l engine.

This is not a thread to argue the merits of MFI vs CIS vs EFI vs carbs. There is plenty of information out there on current EFI conversions and much advice on carbs.

Just interested in hearing the experiences of those that have done this conversion and what they had to do to make it work. For instance:
- Will MFI work adequately with the stock CIS pistons?
- What 3.0 parts did you change? Pistons? Heads? Cams?
- From what model did you source the MFI parts?
- What space cam are you using in the MFI pump?
- What gotcha’s are out there?
- Perhaps most importantly, now you have done it would you recommend someone else attempt it?

Here are some pics to get this thread started.

[Flieger]

Talk to Jeff Higgins.

CIS pistons will not have the clearance for E, S, 906, RSR, etc. cams.

[Flieger]

MFI Pump - Open Heart Surgery

MFI Barometric Cell

[Jeff Higgins]

I think MFI will certainly work with stock CIS pistons, and the cam limitations imposed by those pistons, but it certainly will not take full advantage of the conversion. MFI, like carbs, opens up the selection of cams beyond those which are CIS compatible. I believe that in order to realize its full potential, any switch from CIS to MFI should be accompanied by a piston and cam change.

With that in mind, I used JE 10.5:1 compression pistons and a custom cam grind from John Dougherty, which he calls his "GT2/102" grind. If you look at the cam spec chart on his site, you will find a "GT2" grind on 112 degree lobe centers. All he did was narrow the centers to 102 degrees. The only other engine modifications were to open up the intake ports to 38mm and to twin plug it. Starting with an early large port 3.0 as a base would negate the need for the port work.

My MFI system consists of 2.4 "S" throttle bodies and stacks, along with a 2.4 "T" pump with the "T" space cam. The 36mm throttles and stacks are enough to feed a moderate rpm (up to 7,000 rpm) street motor, but if you want it to spin up higher, it will need bigger throttles, stacks, ports, and cams. Not to mention some lower end improvements (mine has stock SC rods with ARP bolts). Think Carillo or Pauter rods if you want to spin a 3.0 much higher.

There are a lot of little details that differ from a CIS motor to an MFI motor. Some of the little pieces are optional, depending on how you would like to supply oil for the MFI pump - its own isolated, self contained supply or recirculating engine oil supply. Some of the "gotcha" details:

Fuel pump is different.

Scallop in the intake port for the CIS injector needs to be welded over.

Hole for MFI injector needs to be drilled and tapped into intake port.

Breather cover needs oil return line from MFI pump if recirculating supply is used.

There is an oil feed line (to the MFI pump) that goes underneath the oil pressure sender where it screws into the top of the case that is unique to MFI. This is only used for the recirculating oil option.

There is an rpm sensor that reads from the distributor that activates a fuel shutoff solenoid on the MFI pump during trailing throttle. Most of us take this system off, and live with a bit of popping and banging on the decel. If you want it to work, you need this sensor.

Four bearing cams are larger in diameter than three bearing, so the original MFI drive seal on the front of the left cam will not fit. Use a seal from a turbo oil pump drive or get a custom made seal from Supertec.

The tin is different on that left front corner because of the MFI drive.

The tin between the upper and lower valve covers on the left side is different; the MFI tin has a steel tube through it that is used to hook up the hoses to the warm-up solenoid on the pump, and a heat take-off tube unique to MFI on the left heat exchanger. Many of us eliminate this system as well, replacing the solenoid with a screw or with one of Supertec's cable actuating systems.

The left heat exchanger needs that warm-up take-off tube if you want to run the stock warm-up solenoid.

MFI needs a floor throttle to keep it running before it gets warmed up. CIS cars don't have this. The car will run without one, but it really is a lot nicer to have as it's warming up. Without a floor throttle, you will need to keep it running yourself, with your right foot, while it warms up.

There is a thermal time switch that activates a bypass solenoid on top of the fuel filter console to prime the motor when cold. Many of us eliminate this thermal time switch and simply wire a momentary contact pushbutton switch mounted in the dash to give us direct control over when and how much the motor gets primed.

Speaking of the fuel filter console, it is unique to MFI. The CIS one won't work.

That's it off the top of my head. Like so many things, "the devil is in the details". None of the MFI unique stuff is particularly hard to find or expensive, but it will slow things down if you find out too late you need it. Best to gather up all of the odds and ends before you even start. I hope my list helps with that.

Would I do it again? Would I recommend it to others? Hell yeah - the difference is truly astonishing. The throttle response, the sound, the added power, and the cool factor definitely made it all worthwhile for me.

[sc_rufctr]

Thanks Jeff... Just when I was happy with the way my SC has been running you post something like this...

[Flieger]

I might have to disagree about the MFI stuff being hard to find and expensive. I can think of a few pieces that are...

[kiwiokie]

Here is a 3.0 MFI engine that giovanni86 is building for his '74 Carrera 3.0 RS clone:
74 rs 3.0 -clone-

Details are:
SC case
Mahle high compression pistons and cylinders
SC heads
3.0 RSR camshafts
MFI from a 2.4
throttle bodies modified (bored out?) to '74 Grp 4 specs

Interestingly engines built like this are granted FIA approval as RS 3.0 equivalent.

[kiwiokie]

Jeff, thanks for the details on your engine. I have watched your track video and it sounds fantastic. Did you keep the SC distributor? If so did it need to be recurved?

[Jeff Higgins]

I started with an SC distributor that I had re-curved by Barry Hershon. It was set up for full advance to come in at 2,500 rpm, so it was effectively running full advance all the time, only retarding to help it idle. That was the first iteration of the motor, when it was single plugged. I'm now running twin plugs, lit by an Electromotive crank fired ignition. Five degrees initial advance and 25 total.

Flieger, I've admittedly been out of touch on current prices for MFI gear - I squirreled away a bunch of it before everyone wanted it again. What pieces are getting expensive? I still think a guy can piece a setup together for far less than the cost of PMO's or any of the newer EFI systems. Granted, more expensive than Webbers, but not much. Or am I woefully out of touch (as usual...)?

[Wilhelm]

The MFI injection pumps are rather expensive. And the fuel pumps. Expensive for my budget anyway ! But from my experience MFI is worth it.

[Flieger]

The electric fuel pumps are $500 plus unless you have a core.

RPM transducers seem to be harder to find.

The injection pumps in goo condition fetch a pretty penny.

Good throttle bodies are worth a lot, as well.

Most of the used stuff is out of spec, so the good stuff is getting harder and harder to find. And the guys who can tune or rebuild them are getting fewer and fewer, it seems.

[j911brick]

Originally Posted by Flieger

The electric fuel pumps are $500 plus unless you have a core.

I think I paid $500 to have a pump rebuilt a couple years ago. At least at the time new ones were NLA. But you can use an aftermarket pump at a fraction of the price.

[giovanni86]

thanks to Jeff Higgins

[giovanni86]

home-made conversion

YouTube - porsche rs 3000 e luca palermo

[Flieger]

Originally Posted by j911brick

I think I paid $500 to have a pump rebuilt a couple years ago. At least at the time new ones were NLA. But you can use an aftermarket pump at a fraction of the price.

I have yet to see an aftermarket pump that has the correct flow characterisics. Most with adequate (higher) pressure do not have the mass flow capabilities for MFI at high rpm.

The $600 new ones from Porsche are made in China, so I would rather go with a rebuilt German Bosch unit.

[onboost]

Nice thread,,,

I remember a guy here in the mid-Atlantic area who was playing with MFI on 3.0 Ltr motors way back in the mid 90s. Yes, when the parts were more reasonable and there was more of the stuff floating around.

[Jeff Higgins]

I think Zim's still rebuilds the fuel pumps for something like $300-$400.

It's actually not all that hard to do yourself. I started a thread on how to do it a year or two ago when we needed one for my youngest son's 912 to 911 conversion. If it needs brushes and to have the commutator turned, any auto electric place can do that. If it leaks, replacing the o-rings isn't all that hard.

[Flieger]

The problem was the brushes had worn down through the commutator into the shaft.

The little trooper kept on going until the bitter end. You have to love that German craftsmanship. They certainly do not make them like they used to.

If you have a rebuildable core, it is not so bad, but if you are converting to MFI or your core is not rebuildable, then it gets more expensive.

[Jeff Higgins]

I wonder - could the MFI specific pump housing end be grafted onto a carb or CIS fuel pump? Or could the armature from a carb or CIS pump be used to replace one in an MFI pump? Do the electric motors run at different rpm's, or are they physically different sizes, or anything like that that would preclude making such a "frankenpump"?

[YTNUKLR]

The standard CIS fuel pumps are adequate, set to 14psi with a PMO fuel pressure regulator.

Or you could use a few of the Bosch aftermarket pumps, the "044 Motorsport" pump comes to mind...I think it is <$200

Mark Jung tested some of the cheap pumps that say they work for MFI, and they did not have enough flow (although high enough pressure for low flow)