Converting MFI to work with a larger displacement engine???

[82SC]

well I may be buying a tub with an engine that comes with MFI...can I take this unit off and install it on a 3.5L hotrod SC engine?

what is involved in converting the MFI?
I am assuming different space cams??

my MFI knowledge so any explainations should be written at the fifth grade level....

and what costs are we looking at??

thanks

MJ

[Rot 911]

Anything is possible with the MFI if you have enough money. Gus at Pacific is the guru that can probably answer your question. Hell, John Walker probably can too. But for what it would cost, why not just go with a Motronic injection system? You can sell the MFI to cover most of the cost.

[Paul Thomas]

I have MFI on my 3.5 and i can tell you it isn't cheap to make it work. The problem is getting enough air to the motor. Your choices are get a set of high butterflies ($4000-6000) or get creative. I chose the latter. I took a set of 69 S magnesium manifolds and bored the crap out of them. 49mm at the top and 43mm at the bottom. Then i bolted a set of vintage carrera six velocity stacks on top so it looks correct. Likewise i had Matt at Eurometrix rebuild and bore my throttle bodies. Matt had to make new throttle plates and bore the opening to match up. Then you have to get the space cam right for that much motor. Gus at Pacific or Hans at H&R in New York are both good.

There are much cheaper ways to go but i like MFI and it makes my car look period correct when you open the hood. (except for the twinplug crankfire ignition.

Paul

[82SC]

give me details of your car!!!!

I think I am headed right down your alley....or you are welcome to email me and I can send oyu my phone number...

I was planning on SC case
3.2L crank
3.2L heads
100mm 9.8:1 Mahles
2 plug
MFI/Carbs
RS/S cams...

let me know

[emcon5]

For the money you would spend on that, have you considered just getting a 3.6?

Tom

[82SC]

ahhhh the good old 3.6L debate...

maybe I should get a 3.6L sell off all the intake crap...slap on some PMO's

eh...I guess it is something to think about...but there is something about building your own engine...

my 3.5L and a 3.6L transplant will probably be about the same price...the 3.5L may actually be a little cheaper...

both would be hard to do...we'll see...

MJ

[jkeyzer]

Oh man, I bet just the sound of a 3.2 MFI would kick some serious a$$. And yes, it looks cool just standing still with those air intakes...

It's going to cost you some big bucks. Figure well over $1000 for a TB rebuild and modifications once you get a decent pair, then a pump rebuild and space cam change from Gus.

[724doorE]

Damn Paul! Give us a sound bit. MFI is the *****!

If you want raw violence mfi is the way. Do you have the specs of your space cam?

Hey making that cam is not out of the realm of possibility for the average guy with a nice lathe, cylidrical grinder, and high temp ovens. Keep mine in the basement..... well maybe at work.

Actually, I am considering building a slide valve setup for my 2.5 project. Any experience with slidevalves?


Dennis H.

72 911E

[Paul Thomas]

A friend of mine, that did the work on my manifolds, has a 2.5 with slidevalves. He says it makes close to 300hp, he had it in his 906 but couldn't keep the skinny vintage tires from breaking loose.

Slidevalve is really cool but a decent set will set you back around $9000. I checked into that with Jerry Woods before we decide to bore the 69's

jkeyzer is right though, i have over $2000 in just my intake alone. I wish i could give more details of the innards of the motor but i bought it whole and made some external mods which i would be happy to discuss if you want to email me. The PO made some concessions towards practicallity to make it streetable. He was willing to give up power for heat, and wasn't creative enough to come up with a better intake solution than RS plastic intakes.

I wish i were technically gifted enough to get a sound bite. If anyone can give me an idea other than dragging my cpu into the garage please let me know and i'll be happy to post it.

Paul

[campbellcj]

Can't you also mate up the Bosch MFI pump with aftermarket TB's, i.e. TWM? Then you can get just about any size you want (I know they make at least up to 50's). Of course that ain't cheap either, and I think most people who spring for the TWM's go for a full programmable EFI setup.

I'm dreaming of that myself, but in reality I'll probably end up with Webers or PMO's on my next car. I'm no engineer and doubtful that I'll be able to afford to have a pro rig up a killer MFI or EFI rig.

[Paul Thomas]

if it loads, here is a pic of a motor with MFI and TWM manifolds. I looked into it briefly, but from what i understand form the owner of this motor was that the big deal was the linkage since the rod to the pump has to be a certain length and in a certain spot in relation to the pump.

[beepbeep]

Why oh why...?

MFI isn't gods gift to fuel injection...it might be better than CIS but it's still mechanical wide-assed way of determining amount of fuel to be injected.

Go out and buy Motoronic , or Haltech or Autronic or SDS or whatever...sell MFI to somebody who really needs it and save yourself from hassle and frustration.

geez...it's 21:st century for gods sake.

[jkeyzer]

Isn't MFI's greatest strength the operating pressure, which is on the order of 200 psi? Are there any EFI systems that can match this?

[beepbeep]

Well, it probably is , but i don't see any obvious benefits of running extraordinary fuel pressures besides arguably better fuel-atomization if paired with right injector nozzle, boosting efficiency in modern EFI-engines...which isn't the issue anyway. You might little better throttle-responce, but that's probably placebo.

It's cumbersome, it's mechanical, it's inexact, it's untunable...if it was that good we would use it in modern cars.

If trying to bring the car to original shape, fine...if trying to extract as much power as possible: EFI is the key...

[Paul Thomas]

I can't think of something that i would like more than twice as much wiring and a bunch of electronic crap under the deck lid of my 911.

MFI is, in a word, pure. It sounds great, performs extrememly well and it is EXTREMELY tuneable and easy to understand. I dont like the idea of having to plug a friggin laptop into my car to figure out what is going on if it isn't running right. Have you read about the problems associated with having a lighter flywheel on a 993? Check out B.A.'s column in this months Excellence.

Also, an uncluttered engine bay is a beautiful thing, i like the newer cars too but damn, you open the hood and where is the motor? Oh! It's under all of this plastic i have to remove to change the plugs.

No thanks.

[Matt Holcomb]

Originally posted by jkeyzer
Isn't MFI's greatest strength the operating pressure, which is on the order of 200 psi? Are there any EFI systems that can match this?

Jeff,

It's actually 250psi!


Beepbeep,

It sounds to me like you've never driven an MFI-injected 911.

Those that have know that there is no substitute!

MFIWDP! We've just witnessed a birth!


Matt Holcomb
1974 911 Carrera 2.7 Euro
1975 Mercedes-Benz 280SE
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
Pelican Gallery Profile

[82SC]

hahaha

yes there may be many a rational explaination why EFI is better or motronic is better...but I like my cars that are void of electronics and more car then computer...

I think P-thomas said it best...

I am going to look into this further...my interest has been perked!!!

MJ

[724doorE]

Matt,

I'm there MFIWDP.

Yea sounds like he never drove a real porsche ( as pwd72s would describe it).


I suspect it is easier to tune than six webers on a v-12 Ferrari... and no one would put efi on that!

This mfi issue is one of those-- you either get it or you don't--- deals. There is a real reason that we die hards cling to mfi!

No, I think the only thing I'd plug into my 911 is Kurt's G-tec.


Dennis H.

72 911E