EFI with MFI Stacks??

[1972_911T]

Has anyone ever succesfully managed to find a way to mount an EFI injector in a MFI stack? Would it be possible to weld some sort of injector boss in the stack's above the throttle's would this cause any running issues with the injector mounted above the throttle?

Steve

[beepbeep]

There are many (race) cars running injectors above throttle. Only thing that might be affected is emissionss as atomization might sufferon part throttle.

I believe that top-mounted injectors running high fuel pressure and shooting directly into stacks are the very best hi-power solution. Especially when teamed with slide-throttles.

[jmz]

I have a buddy that ran a 2.7 RS Spec w/ MFI stacks and motec. It was pretty trick. I can't remember how they did the injectors but I think they may have just tapped the thottle bodies and put injectors in.

The funny thing is that the car passed the scrutineers at the CVAR races a few times without questioning the motec. It looked nice and stock.

[gestalt1]

i've wondered if the injector blocks made for turbo motors could be sandwiched between the head and throttle bodies. you would still need to add a tps and map sensor somehow.

[304065]

Why use 30 year old proprietary Porsche MFI stuff when you could use brand-new throttle bodies? Sure it's possible, but most MFI TBs need to be reworked, the throttle plates wear a groove in the magnesium.

[lateapex911]

Steve, i just finished reading your sig. thread over lunch. Wow. you have built that car three times over! Cheers to your dedication! If you are married, it's remarkable that your wife hasn't divorced you. LOL. It looks like one of THOSE projects. Love the color, and the T bar covers are pretty neat.

There has been much discussion on the EFI/MFI thing here. A search will yield three or so threads I had them saved on my laptop until a burgler entered my house and nicked it, so I can't give you links.

I had considered doing it myself, as i loved the MFI look, but the EFi drivability. Each solution though, as I recall, had its drawbacks. Putting the injectors above the throttle plates will yield crappy running when cold and at low revs, etc.

I nearly decided to go with a kit made my Motomotions (Souk from there posts here) which included ITBs, a Megasquirt EFI controller, and the necessary bits, but I decided the time aspect to get it running right would overwhelm me, so I went with PMOs.

Still I think you could do a cool MFI look EFI system, but it will be a lot of work. (Looks like you're ok with that, though!)

[Steve@Rennsport]

Originally Posted by beepbeep

There are many (race) cars running injectors above throttle. Only thing that might be affected is emissionss as atomization might sufferon part throttle.

I believe that top-mounted injectors running high fuel pressure and shooting directly into stacks are the very best hi-power solution. Especially when teamed with slide-throttles.

Hi Goran:

Having raced a 3.0RSR with slide throttles, we tried both injector positions (stacks and heads) both on the dyno and in the car.

We measured no power differerences between injector positions but a major flat spot was noted when the injectors were positioned in the stacks above the slides. This was due to fuel pooling on the top of the slides that made the engine hesitate when you opened the throttles.

One can use slide throttles for an EFI installation but I would mount them between the slides and the heads.

[beepbeep]

Originally Posted by Steve @ Rennsport Systems

Hi Goran:

Having raced a 3.0RSR with slide throttles, we tried both injector positions (stacks and heads) both on the dyno and in the car.

We measured no power differerences between injector positions but a major flat spot was noted when the injectors were positioned in the stacks above the slides. This was due to fuel pooling on the top of the slides that made the engine hesitate when you opened the throttles.

One can use slide throttles for an EFI installation but I would mount them between the slides and the heads.

Hello Steve!

Well, there must be something good with top-mounted injectors as F1 cars are running them. My guess is that top-installation allows engine designers to use smooth intake passages w/o any notches for injector installation. I guess such approach is somewhat overdone for a street car so you are probably right. But it still puzzels me why certain manufacturers still opted to do top mounts? I believe injector spray shaping and distance is issue as well.

Interesting videos:





Pics:

Modern Toyota:


Old race BMW with Kugelfischer?


Old Beemer (Kugelfischer?)


Pooling?


Beemer seems to have quite nice responce despite having it's slides "washed":




Regards,
Goran

[Steve@Rennsport]

LOL,..EFI affords very precise fuel mapping and the ability to cut off all fueling when the throttles are closed, regardless of RPM. MFI, on the other hand is pretty crude in that regard.

I think that can cure the big stumble,...