Improving MFI with electronics ?

[michel richard]

There, I have'nt even gotten my MFI installed that I'm already dreaming about improving it.

Does anyone have input on how complicated / difficult / impossible it would be to implement the following:

A small mechanical device that would fit in place of the thermostat, electronically controlled with a Head temp sensor, a lambda sensor, and a very simple analog (or digital?) computer.

The idea being that the thermostat, which is controlled by the heat exchanger is already configured to impact mixture by moving a rack inside the injection pump. If the same rack can be moved in response to both a head temp sensor and a lambda sensor, the whole system might be made more efficient. A microswitch might also be used to send the system to full rich under wide open throttle.

How complicated might it be to find the mechanical device, what type might it be (electrical motor driven ? magnetic field control ? pneumatic ?) and how complicated to design and solder a computer together.

The sensors are readily available.

The idea would be to improve mixture control while keeping the great throttle response.

I'll do a little research on my own, of course, but I know next to nothing about electrical and electronic engineering.

Not sure how realistic this is, but it might be interesting to think about.

Michel

[BRAINIAC]

I had this same idea years back. It's a very good idea and I think it's do-able. A closed loop/feedback mixture compensation on MFI! Cool! You would need a very precise jack-screw type servo motor to push in and out where the T-stat goes because VERY little movement here equals a big mixture change.

The trouble with MFI is that it has no load sensing capabilities. It only knows throttle position and RPM. (Well, temperature and barometric pressure compensation too.) If you set them up clean running, they go way too lean under load. You lose the transitional performance. (driveability) The feedback system would allow you to set it rich and let the feedback system lean it out under normal driving. Better mileage, cleaner plugs, longer engine life, and still great throttle response and power.

I hope someone figures something out. My MFI set-up is sitting in a box in my garage just waiting for me.

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[Roland Kunz]

Hello

A fast stepmotor or a good selenoid can do it. The electronics ? Mabe a Twintec or HJS add on unit ?

Grüsse

[Natchamp]

Sounds like an interesting idea and would be great.

You would definitely have latency issues with both head temp and O2 for determining load but it still might be a great improvement to having absolutely no load adjustments.

The hard part is the controller. It would have to be able to receive the appropriate input signals format, be adjustable, and output to potentially different signal formats.

Have you looked at any of the cheaper engine management systems? It might be a good method for just the controller aspect. You might be surprised.


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Mark
The Beast
mark@hargett.com

[Early_S_Man]

There are small linear stepper motors that would work fine in place of the warmup thermostat ... I have a couple with 1" range and 0.001" resolution, and another model in the same line offers 0.5" total range and 0.0005" resolution!!! The other MFI pump adjustments could be electronically controlled as well with gear reduction rotary steppers!

I envision interactive control by the driver with position display for making dash adjustments and displays for the O2 sensor, Head Temp sensing with aircraft thermocouple probes and gauges, and EGT as well ... kind of like Mark Donohue's BIG POWER KNOB on the dash of the 917-30!

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 07-27-2001).]

[Oldporsche]

I like the ideas expressed here that would definitely help the MFI. I have always liked the simplicity of the MFI and the fact that it will produce the power of which this engine is capable. OOOh the sound of it!

If the lack of a heater warm up box on the heat exchanger or something like that preventing you from proceeding on your project, I would like to make this suggestion.

Many years ago I was treated to a ride in a 911S that had undergone an RS conversion. It had been done by the Penske organization. In looking the work over I saw that they had installed a "T" handle cable control just above the tunnel opening in front of the back seats. This "T" handle control moved the rack on the FI pump for cold starting. In other words it made a "manual choke" out of the unit. This thing worked very well.

That sucker flew too!

Good luck,
David Duffield