MFI Pump - Open Heart Surgery - Page 14

356RS · 356RS's Garage

Quote:

Originally Posted by jeffc280sl

Can you clarify a point for me. The depth of the solenoid pin is adjustable and i agree it does lift the stylus off the space cam. Have you tested the pump with the solenoid energized to confirm fuel is 100% shut off? It seems more appropriate to have a minimal (idle level) amount of fuel present during this condition. An extreme case would be coasting down a long rocky mountain road. The ignition system is still firing but there is zero fuel in your senario. Just doesn't sound right to me.

It's an easy test. With your MFI engine at idle or whatever RPM you want, put 12 volts to the solenoid and see what happens.

Edit: PS. If the engine doesn't stop, your solenoid is out of adjustment.

jeffc280sl · 03-31-2010, 03:16 PM

You're right! One day I'll put mine back on and give it a try.

luckydynes · 04-01-2010, 07:55 AM

Quote:

Originally Posted by 911st

If I may, a lot of us have wondered about something like this. Probably not a solenoid but a stepper motor with the right controller could work.

If doing that one might just remove the space cam and use the steeper motor to determine the rack's position. Might be easier than trying to reprogram over the programing of the existing space cam.

The new D-WUR that is being used for the 930 turbo's has most of the bassic atribuites including a steeper motor controler than might be adaptable witout to much issue. One could even add 02 correction if so motivated.

My day job is designing and building robotics with servos and steppers. This would be cool to do and I've even thought about doing this on CIS cars to get rid of the barn door .. the D-WUR is neat. There a lot of cars out there that would benefit from a fully electronically controlled CIS "head" and there would be power gains ... but back to MFI.

I would still like map one of the space cams "as they are" and modify it in a particular area and look at what it did to the a/f ratio. I'm about to put my car back together and did not tear into the pump. I don't think there's anything to be gained taking it apart right now. I really want to look at what my a/f ratios are doing and make a decision from there.

I'm not sure if it's smart to add electronics to MFI when stand alone EFI can be had pretty inexpensively but I've done some really dumb things in my life ... "for testing"

. I was going to swap this car over to EFI when I bought it but the MFI has grown on me and I was also surprised how many guys said they could not get the throttle response with EFI. Seems to me if the injectors are in the right place AND you retain the throttle bodies you would be able to have the same throttle response with EFI. You don't have to build a map based on manifold pressure ... your map can be based on throttle position and RPM just like the MFI is ... I think the single throttle body is what kills the throttle response on the basic EFI conversions ... just a thought.

I don't mind fabbing up some bits if someone wants to play with some electronic controls.

cheers,

Sean

luckydynes · 04-01-2010, 08:10 AM

Are the levers on the throttle bodies stainless ... specifically the "main" lever that pivots on a shaft on the driver's side throttle body assembly? They seem like it 'cause no rust but they are very magnetic (not a common property of stainless). One of the pivot balls is loose. I was thinking about just TIG'g it if it's stainless ... probably the best solution even if it's not eh? When I first bought this car one of them came loose somewhere else and I didn't want to take it all apart so I just drilled and tapped the ball and screwed it on.

Thanks,

Sean

kenikh · 04-01-2010, 08:14 AM

I agree. I don't see the EFI ITB guys complaining about throttle response. I also agreethat keeping the space cam is a good idea, but do like the idea of dynamically altering trim via an electronic rack actuator. EFI is great, but MFI is cool in an old car and the immediacy of piston actuated fuel pulses seems superior in terms of quality to electronic actuation of and EFI injector.

jeffc280sl · 04-01-2010, 09:32 AM

Might not be able to control 100% of it, but it could definitely control a major part of fuel trim. The thermostat control side of the balance lever will provide a greater range of fuel control than the Bar cell end.

My experience on the MB version indicates the baro cell would be a better place to install an actuator. This is where Kenik mounted his device. The reason is the baro lever inside the pump is designed to lean or enrich the mixture at all rpm ranges.

There may be enough adjustment room on the thermo lever but I think the baro lever is a better place to put your efforts. The baro lever is very sensative and I think it has a more direct relationship with the rack. The thermostat also acts on the rack but it is via a slightly diagonal lever action. While designing the actuator you could also give it a more accurate and modern altimiter profile.

356RS · 356RS's Garage

Quote:

Originally Posted by jeffc280sl

My experience on the MB version indicates the baro cell would be a better place to install an actuator. This is where Kenik mounted his device. The reason is the baro lever inside the pump is designed to lean or enrich the mixture at all rpm ranges.

Your right. The baro cell would give you a better range, both rich to lean adjustments.

kenikh · 04-01-2010, 11:16 AM

OK, cool - I was wondering why this seemed to conflict with the factory's selection of the baro cell on the 935 unit.

911st · 04-01-2010, 04:30 PM

It would be interesting to use a solenoid or such to richen the motor for on boost instead of how the factory did it with a big pressure pot.

Me, I would try to stay with the old tec as that is part of what makes MFI cool to me.

Flieger · Flieger's Garage

The solenoid would need a signal from somewhere so there would still be some drilling/tapping into the pressurized intake manifold. There would not be much simplification there.

911st · 05:14 PM

Could it just be 12v, a Hobbs switch, and the solenoid and presto, you have boost enrichment?

911st · 05:22 PM

Flieger,

You are a math guy, can you figure out how much TQ this would support at about 13/1 AFR?

Anyone?

Quote:

Originally Posted by 356RS

I have installed 2.4 plungers/cylinders in an early 2 liter pump and can get close to 70ml per 1000 strokes at WOT @ 3500 pump RPM.

Mark,

What is the fuel delivery spec to support 210hp on a 2.7RS or any other peak TQ or HP for any pump?

Flieger · Flieger's Garage

Well, it depends since the torque is determined by the impulse on the piston acting around the swing of the crankshaft. The force is not constant, neither is the lever arm. BMEP would be needed, and the timing to determine the "negative torque". The 13/1 AFR is not the stoichiometric optimal so the burn speed is not just for gasoline vapor expolding/burning in air. There will be extra fuel left over so just using the amount of work the fuel can do is out. The amount of air is needed. Air is not all oxygen...

Too many variables for me. I will have to think about a way to simplify things.

911st · 04-01-2010, 09:23 PM

I would think one could make some reasonable assumptions to get into the ball park but thanks for the consideration.

Maybe we can use a stock MFI motor's WOT fuel delivery at TQ and or HP peak as a point of reference and interpolate how much TQ can be supported.

philippeF · 04-02-2010, 02:57 AM

Quote:

Originally Posted by 911st

Flieger,

You are a math guy, can you figure out how much TQ this would support at about 13/1 AFR?

Anyone?

Mark,

What is the fuel delivery spec to support 210hp on a 2.7RS or any other peak TQ or HP for any pump?

Hello Flieger

it is around 55-60 at WOT for a 2.7RS stock engine,

911st · 04-02-2010, 07:51 AM

Quote:

Originally Posted by 356RS

...I have installed 2.4 plungers/cylinders in an early 2 liter pump and can get close to 70ml per 1000 strokes at WOT @ 3500 pump RPM.

Quote:

Originally Posted by philippeF

...it is around 55-60 at WOT for a 2.7RS stock engine,

If these two data points are correct then the limit of an MFI pump is going to be about 250hp. If a high rpm cam is installed that moves HP peak up from 6500 to 7500 rpm at the same TQ that could be up to about 290hp.

The most Porsche ever pulled from one of its street MFI pumps was about 230hp from there RS pump I believe.

Seems low or need larger plungers for higher HP motors. I guess am thinking they would support in the mid 300's at a modest peak TQ RPM level without issue.

911st · 04-02-2010, 07:55 AM

Mark,

Was that delivery with the stylist fully advanced say without any space cam installed and with the rack adjusted so the plungers would reach close to 100%?

Thx

philippeF · 04-02-2010, 08:58 AM

Not sure that Mark said 70mL was the max delivery... I don't think I'll tell you what is the value i can achieve on my bench if
Mark does'nt answer before
Philippe

dicklague · dicklague's Garage

Is the stylus and stylist the same thing?

356RS · 356RS's Garage

Keith, The factory spec for the 019 "2.7RS" pump at max throttle (80 degrees) is 57.0 to 58.5ml per 1000 strokes @ 3000 pump RPM. The 2.8RSR spec at max throttle and 3500 pump RPM is 67.0 to 68.5ml per 1000 strokes. I'm working on a customers 013 pump for a 2.8 SS engine and the first test of the pump is getting 62.3ml @ 3500 pump RPM / 80 degree throttle. Just found out yesterday the Dyno test shows we need more fuel at 3500 to 4000 pump RPM.
I have produced 70ml on a 2.0S pump with later 2.4 plungers/cylinders installed.
Dick, Stylus and stylist are the same. Misspelled maybe but I referring to the "tip of the lever riding on the space cam"