Tell me about this fuel system

[Sagaris]

On these old M10 and M12 race engines it looks like they use the equivalent of a diesel injection pump. The fuel injectors are fed straight off the pump. Wouldnt that imply that the fuel flow rate is linear with RPM? which doesn't seem right at all for an engine. How do these things work and what are they called?

[DaveSmed]

It's linear with RPM crossed with throttle angle. The setup is tuned with a replaceable orifice similar to jetting a carb.

[der affe]

Mechanical CIS. Looks similar to the system Porsche used on the early FI cars except the ones in he pic are slide type throttle bodies.

I have it on my 914-6, it is simple and works pretty well, but is a pain to tune and does not like drastic outside temp changes or extremely hot weather and tends to idle very high in the summer.

[nando]

yeah, mechanical injection. Yuck. It was better than carbs back in the day, but compared to modern EFI, it's junk.

[Rigmaster]

yeah, mechanical injection. Yuck. It was better than carbs back in the day, but compared to modern EFI, it's junk.

True.

But looking at those 2 engines still gives me a tingle in my pantalones..........


;)

[nando]

the engines are cool, yes. Now imagine how much better they'd be with EFI. :D

[LJ851]

kugelfischer mechanical fuel injection. That is not CIS and when properly set up and functioning works very well. Early 911's used this system as well. If you have ever driven a 2002 Tii you would not call this system junk. There is a 3 dimensional cam in the pump , tuning is done by altering cam shape and timing and is a bit of a black art these days. The slide throttles shown would not have very good street manners, though.

[nando]

I didn't say it doesn't work. but tuning (trial/error) with a set of different shaped cams? or tuning with 3D fuel & spark maps in real time? hmmmm..

even the Motronic 1.0 system that came on the early E30s is lightyears beyond that stuff.

[LJ851]

I didnt say it was easier to tune, nor did i mention the ignition system. Fuel is injected at over 200 psi and properly set up is an excellent fuel system with killer throttle response and good fuel mileage.

[nando]

that's just it though.. "properly setup"

mechanical systems like that are difficult to tune properly and ultra-finicky. If they were truely better, they'd still be in use today.

[der affe]

kugelfischer mechanical fuel injection. That is not CIS and when properly set up and functioning works very well. Early 911's used this system as well. If you have ever driven a 2002 Tii you would not call this system junk. There is a 3 dimensional cam in the pump , tuning is done by altering cam shape and timing and is a bit of a black art these days. The slide throttles shown would not have very good street manners, though.

Well we have always called it MECHANICAL CIS (mechanical constant injection system).

Comming from someone who actually owns a car with it (914-6) it does work well WHEN it is turned and all the stars align on a perfect spring day. It is finicky to tune, and he trial and error mehod is a pain. It also does not have any way to cope with outside air temp changes other than retuning. I don't know about the BMW system, but the drive gear on the Porsche pump is made of magnesium and wears the cogs out ($500 replacement cost).

It's neat for the nostalgia, but there is so much better out there now.

[bimmerteck]

If you have always called Kugelfischer MFI "mechanical CIS" you've been wrong. There are very distinct differences in operational theory between the two. Lack of training about all the variations of Bosch's different varied systems is part of what makes it so hard to find a good running example today.

your 914-6 uses d-jetronic that is not what is pictured above. Jetronic is speed density style injection.(edit, my mentor has corrected me, your 914 could have used carbs, MFI, d-jet, depending on how/when it was ordered, either way MFI and CIS are still based on completely different theorys of injection.)

the motor pictured above are direct mechanical injection and are a very close cousin to an diesel injection pump. They are race style injection systems which have poor metering for partial throttle but make great power at full throttle. Early 911s used this system as did Porsche race cars but they were very expensive to maintain and fell out of favor quickly for street use.

[der affe]

I should clairfy, the motor in my 914-6 is from a 1971 european 911s. It is the mechanically injected multi throttle bodied 190 hp 2.4 lt. engine. Not the carbed 2.0 that as standard on the 914-6 nor the standard d jet on the 4 cyl. models.

[bimmerteck]

I should clairfy, the motor in my 914-6 is from a 1971 european 911s. It is the mechanically injected multi throttle bodied 190 hp 2.4 lt. engine. Not the carbed 2.0 that as standard on the 914-6 nor the standard d jet on the 4 cyl. models.

Nice! I have a '72 911t w2.7 lt. that was blessed from the factory with the mechanical fuel injection as well. . . which is why I have begun learning all about it from a local friendly retired Porsche tech who likes good beer. :)

[der affe]

If I did it again I would do a 3.2 c-2 motor and be done with it. Turn the key, boom, working a/c and everything.