MFI Pump - Open Heart Surgery - Page 11

356RS · 356RS's Garage

Keith, If you think about it, the main reason for the spring capsule is to set the stylus in the proper path on the space for each different model space cams for the different engines. The spring capsule wasn't designed to adjust richer or leaner conditions, it's just for set-up for the different space cams. The real way to tailor you fuel requirements is to shape the space cam for your torque path. When customers want an MFI pump recalibrated for a specific highly modified engine, I ask for a dyno sheet to see where the AFR problems are then reshape their space cam for that application. There is some minor spring adjusting afterwords just to help guide the stylus down the new path. It's very time consuming but pays off in the end.

911st · 03-28-2010, 05:07 PM

Quote:

Originally Posted by 911st

...The spring tensions can not add any extended fuel delivery capacity or range per say. They just let you advance to a higher delivery part of the space cam faster or slower...

Agreed, we are on the same page!

luckydynes · 03-28-2010, 05:20 PM

Quote:

Originally Posted by 911st

We need someone that can translate or program our space cam needs on a 3d mill of some type.

We could even cut out the map area out of the space cam so the map section could just be milled and replaced.

Dam this is exciting stuff!

I'd be interested in contributing some time to this when someone's ready.

Does this profile see a lot of load? ... could we use some kind of epoxy to experiment with different profiles? If it's loaded they can be welded and built up and I like the idea mentioned above of milling out the section and "replacing" it ... be cool to make this an interchangeable piece for different maps but I'm not real familiar with this part yet.

cheers

luckydynes · 03-28-2010, 05:26 PM

How are the space cams clocked and locked to the shaft they are mounted on?

jeffc280sl · 03-28-2010, 05:32 PM

Maybe Jay Leno will let you use his 3D scanning tool. This is as cool as the space cam.

NextEngine's 3D Scanner - Extras - Jay Leno's Garage

jeffc280sl · 03-28-2010, 05:46 PM

Here is a sketch showing the basics of the mfi pump.

As you step on the gas pedal the throttle linkage rotates the space cam clockwise up to about 90degrees. The space cam moves forwards and backwards on the main shaft and is controlled by engine rpms which effect the flyweights. As rpms increase the flyweights move the space cam to the rear. Precisly at what rpm range this occurs is a function of the spring tension on the flyweights as adjusted by the white and black screws.

luckydynes · 03-28-2010, 06:06 PM

Thanks ... it's sinking in ... just one of 'em.

If someone wants to send me a part I'll map it out ... I don't have areason to take my pump apart yet

.

cheers

luckydynes · 03-28-2010, 06:19 PM

I'm having trouble visualizing the need for the peaks and valleys along the length of the the cam. They are obvoiusly there for a reason ... just not making sense in terms of transition of engine control ... that would be causing more rich or more lean as you progressively move across the cam's profile ... but I guess there is perhaps more than one engine parameter at play and it's maybe compensating for some kind of resonance or something ... that is a very very precise piece I would expect. ... more precise than I envisioned at first.

luckydynes · 03-28-2010, 06:26 PM

Quote:

Originally Posted by 356RS

Keith explains the space cams function very well. I have used the black marking pen method on a space cam before and documented throttle positions at every 10 degrees to 80 degree full throttle and rpm's at every 500 up to 3500 pump rpm. Below is a crud photo of this. The lower right corner of the space cam is the starting point. Up is RPM and to the left is throttle.

I've not seen the need for these peaks and valleys when I've mapped EFI engines with an LM-1 just based on AFR on the tail pipe but I might be picturing this completely wrong or my EFI maps needed much more work?

jeffc280sl · 03-28-2010, 06:56 PM

The space cam is a very precise and complicated device. Here is an example of what it tries to do. Your crusing along at 3k rpms. For this example let's say the throttle position asks the stylus to read the profile at 45 degrees CW rotation of the space cam. Your cruising nicely so lets say the stylus is reading a middle spot on the space cam as determined by flyweights. Remember the space cam can rotate CW and CCW90 degrees based on throttle position and move forwards and backwards based on rpms and flyweights. This example has the stylus reading somewhere in the middle.

Mash the accelerator and the space cam rotates to a full CW position. The engine is under a large load and rpms are starting to pickup. The space cam now has to provide a different afr profile to the mfi. As you stay at WOT and rpms increase afr is again changed because the stylus is reading a different profile on the space cam as it moves rearward.

Think of every combination of engine load and rpms and you can begine to imagine what sort of afr map/program the stylus it is trying to deliver to the pump.

luckydynes · 03-28-2010, 07:26 PM

Quote:

Originally Posted by jeffc280sl

The space cam is a very precise and complicated device. Here is an example of what it tries to do. Your crusing along at 3k rpms. For this example let's say the throttle position asks the stylus to read the profile at 45 degrees CW rotation of the space cam. Your cruising nicely so lets say the stylus is reading a middle spot on the space cam as determined by flyweights. Remember the space cam can rotate CW and CCW90 degrees based on throttle position and move forwards and backwards based on rpms and flyweights. This example has the stylus reading somewhere in the middle.

Mash the accelerator and the space cam rotates to a full CW position. The engine is under a large load and rpms are starting to pickup. The space cam now has to provide a different afr profile to the mfi. As you stay at WOT and rpms increase afr is again changed because the stylus is reading a different profile on the space cam as it moves rearward.

Think of every combination of engine load and rpms and you can begine to imagine what sort of afr map/program the stylus it is trying to deliver to the pump.

Yes it is. I think from reading some posts those ridges act as a kind of a detent on the system ... not the smooth piece I was thinking that a map is.

cheers

356RS · 356RS's Garage

luckydynes, The space cam does not have much of a load on it at all. Epoxy would be fine for an experiment. Remember, adding height or ridges to the space cam will pull back the main rack for a leaner mixture, valleys will make a rich mixture. The stylus only has about a 2.5mm to 4mm movement from idle to full throttle depending on which space cam, T E s or RS. The main lever assembly almost doubles that stylus movement.
jeffc280sl, Great example of the space cams job.

911st · 08:34 PM

I do not know if I would consider the programing of MFI complicated in nature. It is more like getting comfortable with the medium we are working with.

Compared to programing EFI it could be easier.

MFI is not that accurate by its nature as it is purely a 'reference system' and dose not measure or compensate for variations in air flow, temp, or much of anything else once warmed up. It will be rich, lean, or right on at any given moment. If we get a perfect 13.2 AFR from 4-7000rpm at WOT on a given day it will not be that on a hotter or colder day. If the air filter is dirty and less air is taken in than expected, it will go rich...

It is just RPM by Throttle Position (TP) as it relates to expected TQ at said points.

One should be able to make up a starter map out the box using a basic understanding of changes in VE for a motor depending on its size, cam timing, peak VE expected, and some other basics. Someone that knows what they are doing could calculate most points for a motor just like EFI companies can generate a start up map for a fresh build.

Then we could carve a test map. Then data log said map in the real world so we could make correction and then produce a final map.

If you have seen a used space cam, maybe about 50% of it seems to be tracked by the stylist and used much so we really just need to get that part right.

If we get the steady state points right, and the WOT points right the rest should come together with out to much issue.

A third year mechanical engineering student that loves cars could probably set up a program pretty easily to compute the map based on basic motor expectations that would then output this to a mill to carve said maps.

Just a thought.

Maybe MFI's time is coming back. Still, it will never be as accurate or efficient as a good EFI system.

Flieger · Flieger's Garage

To some degree, the barometric compensator is good enough and you do not need the temperature sensor. Since warm air will be less dense, the pressure should be less?

jeffc280sl · 03-29-2010, 06:58 AM

Flieger,

I believe your are correct about the barometric compensator.

Epoxy models maybe okay, I would be concerned about matrching the space cams mass. Something to consider.

The MFI is not efficient that's for sure. With a hand held O2 meter you can watch afr bounce all over the place while driving. One thing I know Bosch was concerned with is afr while coasting. When the throttle is on its stop and the engine is still producing rpms during a downhill coast you can watch the afr meter go lean. Vacuum timing adjustments are also crude by todays systems.

luckydynes · 03-29-2010, 07:30 AM

Quote:

Originally Posted by 356RS

luckydynes, The space cam does not have much of a load on it at all. Epoxy would be fine for an experiment. Remember, adding height or ridges to the space cam will pull back the main rack for a leaner mixture, valleys will make a rich mixture. The stylus only has about a 2.5mm to 4mm movement from idle to full throttle depending on which space cam, T E s or RS. The main lever assembly almost doubles that stylus movement.
jeffc280sl, Great example of the space cams job.

Interesting .. so as the stylus "climbing" up the space cam it is actually leaning the mixture ... I see that when I've mapped EFI engines after the tq peak but I'm still not sure why you would want to go lean in places as you are climbing in engine rpm before the tq peak? Could be in an area of the cam map that rarely get's touched and/or fuel economy?

Now I'm really looking forward to getting my car back together and seeing what is really coming out the tail pipe.

Like 911st said ... I think MFI's time is coming back. I like the programmability of EFI but am now appreciating the (cough) simplicity of the MFI.

No need for expoxy now I kinda understand what's going on ... I thought that would be necessary if they were attached to an expensive drive shaft or something. I think we can just make it out of metal and even weld onto it if we take too much material off ... I would just put some index locations on it so I can grab it in exactly the same spot again if we wanted to re-machine one.

To do this I would map one for which I had documented a/f ratios ... then duplicate it with a mod in some place if it is a rare part or just modify the sample. I would hope from the documented a/f ratios there would be an area on the cam that we would want to concentrate on. Getting an engineer to map out a VE table would work but I'm not convinced that the cam is just a VE table yet ... I just get the feeling those ridges create some kind of mechanical hysterisis under certain conditions. The ridges maybe where the stylus rarely rides ... throttle closed/deceleration? ... don't think that's the case from other posts though.

Just some thoughts.

cheers

jeffc280sl · 08:29 AM

Here is another pic of a space cam. There is a reference hole on the side for the throttle linkage ball to mate with.

Only 90 dedgrees of the space cam is etched. The mid right side front of the space cam is the idle position.

911st · 03-29-2010, 08:30 AM

I love this picture.

For fun lets think of this as a fueling map.

The left side axis from top to bottom is RPM.

The bottom axis from left to right is TP (Throttle Position).

At idle the cell in the lower left cell determines the fuel. If it takes 10hp to maintain idle that is about 70#TQ.

Going to WOT the active cells skip quickly accrost the bottom of the chart to the 100% throtle section. The cells at the far right starting from the bottom and progressing to the top as RPM advances. Thus, if you have a representive or calculated WOT TQ curve you can map this section pretty easyly from 1000rpm to red line.

Steady state cruse would mostly be the cells progressing on the diagonal from the lower left hand idle rpm cell to the top right hand cell which would be the cars top speed.

Just off the cruse line will be acceleration cells. If the TP is advanced a small amount out of the steady state line, fuel might be increased say 10% to take us from the 14's to the low 13's to promote acceleration.

Get the WOT and the steady state sections right and the other stuff might fall in to line.

Quote:

Originally Posted by 356RS

luckydynes · 03-29-2010, 08:41 AM

Quote:

Originally Posted by jeffc280sl

Here is another pic of a space cam. There is a reference hole on the side for the throttle linkage ball to mate with.

Only 90 dedgrees of the space cam is etched. The mid right side front of the space cam is the idle position.

Is the cam actually on a bearing in this pic? Looks like multiple pieces. Other pic's it looked solid. I.d. is seeing a lot of relative velocity to the shaft yes?

911st · 03-29-2010, 08:52 AM

Sorry for the quality but here is your basic RPM by Throttle Position map.