MFI on a 964

[Clay Perrine]

I have a 2.4 T motor right now, and love the MFI. I would like to keep in in the new motor that I am building, but I need some expert advise.

I have a 1991 3.6 motor I would like to put MFI on. It is possible, but will an S pump and S stacks flow enough to work correctly? If so, how big of displacement and cam can I use with the MFI??

[YTNUKLR]

You will need adapters for the throttle bodies. 964 has 3 studs, 911 has 2. Someone makes them, or you could make your own (talk to a machinist)

You will need the pump re-calibrated and rebuilt. I don't think 911S pump is enough, I imagine you might need an RSR pump space cam or someone who is handy reshaping the standard space cam.

You will also probably need to start with '69-71 throttle bodies and machine them out to match the ports. I have a set of '69E throttle bodies that would work for this.

EFI would probably work better, technically speaking, and be more precisely adaptable. However, perhaps not cheaper, once you get done tuning it.

[Bobboloo]

It'll run with S stacks but really they are too restrictive. The ports are 36mm on S stacks and T bodies. Your 91' 3.6 has 41.5 mm intake ports. Ideally that's what you should shoot for. Unfortunently 2.4T stacks aren't big enough to modify. Any of the magnesium stacks will do but the 2.2 stacks E or S are the best choice. Both would need boring and have throttle plates replaced with larger ones so you might as well save your money and get a set of 2.2E stacks and T-bodies. 2.0 liter E or S is also an option but 2.2E would be my choice.

You could go with a more aggressive cam than the 964 but how much power do you really need?

Here's a link to Paul Thomas' car when he just got it painted back in 2002. He built a 3.5 MFI motor on a 3.0 case and used 69'S stacks as his starting point. He bored the ports out to 43mm (993 port size). You should send him an email and get his input.

Car back from the paint shop


P.S. Paul eventually went with EFI and ITB's.

[kenikh]

I am certain a '69S pump would have enough fuel to feed a hot 3.6. With the right tuning a 2.4T pump was made to work on very, very hot 3 liter. A '69S pump, per Gus words, can feed enough fuel for any NA 911 motor. Look up Jeff Higgins Ultimate MFI thread on the "how-tos" of tuning MFI.

Your biggest issue will the stacks and TBs. I know it isn't vintage, but going EFI would most likely be cheaper and give you the throttle response you want. But if you want true vintage, go MFI.

[304065]

Who am I to discourage anyone's intellectual curiosity, but for the difficulties and expense of adapting MFI to a 3,6 you would REALLY have to get a bang out of a vintage-appearing system.

By the time you source a pump and have it rebuilt and get a good set of stacks and have them bored you're probably over the $4k range, and that doesnt include the MFI adapters from Len Cummings at Autosport Engineering (BoxsterGT here on Pelican). Then you have to tune the sucker and get a vintage twin-plug distributor, all for less control, less flexibility and probably less power than a modern EFI system (perhaps even what came on the 964).

The hot ticket is the 993 RSR setup with ITBs and a resonance plenum intake, a certain engine builder, tuner, aviator and all-round righteous hombre from the Rose City is the Resident Expert thereupon. . .

Don't get me wrong I LOVE MFI but for a BIG motor . . .

[Clay Perrine]

I am considering this as I already have the 2.2S mag stacks and the throttle bodies. I also have the 69S pump. The distributor I can get, and I can have the stacks opened to the 41.5mm.

I like the idea of making a vintage fuel system work on this engine. I like both the look of the 12 wire distributor cap and the MFI pump plumbing.

It would certainly be unique in a 914 /6.

Oh.. and I am going to 105mm nickies and JE pistons to make it a 4.0L , plus GE100 cams. Because you can never have enough horsepower.

Thanks everyone. Y'all answered my question.

[356RS]

Clay, Please keep us posted on your 4.0L project.

[jpnovak]

Cool project.

I wonder if 41.5mm ports and intake will flow enough air for a 4.0L at the rpm required with a GE100 cam.

[BURN-BROS]

Originally Posted by Clay Perrine

I am considering this as I already have the 2.2S mag stacks and the throttle bodies. I also have the 69S pump. The distributor I can get, and I can have the stacks opened to the 41.5mm.

I like the idea of making a vintage fuel system work on this engine. I like both the look of the 12 wire distributor cap and the MFI pump plumbing.

It would certainly be unique in a 914 /6.

Oh.. and I am going to 105mm nickies and JE pistons to make it a 4.0L , plus GE100 cams. Because you can never have enough horsepower.

Thanks everyone. Y'all answered my question.

Hi Clay,

I am doing a similar setup for a 3.5 .

You have the right stacks and throttle bodies but they will need to be bored to handle the 4.0 liter displacement and aggressive cam. The throttles can easily handle a 44mm butterfly and a 42mm intake opening. Stacks can be bored to 52mm on top and 44 to 45mm on the bottom. the 69 pump will definitely handle a 3.6, not sure of the 4.0 but my guess is yes.

Good luck!!!!!

edit; 41.5 is way too small for a ge100 cam either go bigger or use something smaller than a ge 80.

[Clay Perrine]

Originally Posted by BURN-BROS

Hi Clay,

I am doing a similar setup for a 3.5 .

You have the right stacks and throttle bodies but they will need to be bored to handle the 4.0 liter displacement and aggressive cam. The throttles can easily handle a 44mm butterfly and a 42mm intake opening. Stacks can be bored to 52mm on top and 44 to 45mm on the bottom. the 69 pump will definitely handle a 3.6, not sure of the 4.0 but my guess is yes.

Good luck!!!!!

edit; 41.5 is way too small for a ge100 cam either go bigger or use something smaller than a ge 80.

I have to have the heads done for the injectors anyway, so I can enlarge the intake ports. But how big do I go?

[BURN-BROS]

Originally Posted by Clay Perrine

I have to have the heads done for the injectors anyway, so I can enlarge the intake ports. But how big do I go?

Clay, You misunderstood.

Your intake ports at 41.5 are not bad, it is the throttle plates and the stacks that have to be enlarged further for what you plan to do.

Just for reference, valve size for the 993 3.8 RSR is 51.5/43.5 Intake port is 47mm. Keep in mind that this is a race motor but it should establish the upper limit of port/valve selection.

The 3.8 RS has the same dimensions as the RSR with a smaller intake port (45mm?)

993 has a IIRC has a 49mm intake valve with a 43mm intake port.

With this in mind I would take your throttle bodies out to at least 43mm if you can. Again, there is enough there to bore to 42mm without any issues and I am positive you can go more.

So
52.5 upper stack matched to 52.5mm air horns
44 or 45mm lower stack
44 or 45mm throttle plates
43mm lower throttles ports to match 43mm intake ports

a cam choice of or in between dc 80 and dc100 depending on what rods you will use for those heavyish 105mm pistons.

[Clay Perrine]

Ok. .I get it. When I do the head work, open the ports to 43mm and drill them for the MFI injectors.

Get the stacks and throttle bodies bored to the specs listed above.

A GE100 cam shouldn't be a problem. I am using the R&R Rro Billet 4340 Chromoly Steel Connecting Rods that LN Engineering sells. I figure that they are already tested with the Nickies and the JE pistons.

Now to get a hold of Henry to get the throttle bodies, stacks and pump done up.

Anyone know where to get the adapters to put the throttle bodies on the 3.6 heads?


If anyone is interested, this is not going in a 911, it is going in my 73 914/6 conversion. It already has a 2.4 T motor with MFI, and I just love the throttle response and the SOUND of the MFI at full song......EFI, even with ITB's, just doesn't have the feel of the MFI.

This is gonna be FUN!!!!

[HKZ Bob]

Originally Posted by Bobboloo

It'll run with S stacks but really they are too restrictive. The ports are 36mm on S stacks and T bodies. Your 91' 3.6 has 41.5 mm intake ports. Ideally that's what you should shoot for. Unfortunently 2.4T stacks aren't big enough to modify. Any of the magnesium stacks will do but the 2.2 stacks E or S are the best choice. Both would need boring and have throttle plates replaced with larger ones so you might as well save your money and get a set of 2.2E stacks and T-bodies. 2.0 liter E or S is also an option but 2.2E would be my choice.

You could go with a more aggressive cam than the 964 but how much power do you really need?

Here's a link to Paul Thomas' car when he just got it painted back in 2002. He built a 3.5 MFI motor on a 3.0 case and used 69'S stacks as his starting point. He bored the ports out to 43mm (993 port size). You should send him an email and get his input.

Car back from the paint shop - Page 2 - Pelican Parts Technical BBS


P.S. Paul eventually went with EFI and ITB's.

Hi paul how did you managed the interference with the MFI

BR
Bob