MFI Pump - Open Heart Surgery - Page 5

Jeff Higgins · 02-28-2008, 01:24 PM

John, I've replaced the warm-up thermostat with a device pretty much as you describe. It is actually a screw that I can back out for starting, then screw in (full lean) once it's warmed up a bit.

Yup, that 7,000 rpm is as close to "full load" as I can achieve on a public road. It's in third gear. That still has me looking nervously about for any traffic cops...

I had the same thought about moving the center of the range up a point and a half to two points. I do have some room to move up, while remaining safe from detonation. Maybe if the next plan doesn't work, that is what I will do.

The "next plan" stems from going back through this thread and looking at the various diagrams and such. I'm starting to think I have been barking up the wrong tree. I may very well be totally screwed up and leading everyone astray right along with me. I just had one of those "aha!" moments that bears some more thought. And driving and adjusting...

I'm thinking of those white screws. I'm thinking of the weight of the spring they bear against, and how much heavier it is than the idle and mid range springs. I'm thinking of the Mercedes diagram posted on page one of this thread. It refers to those white screws as "top speed". There was another diagram, or instruction manual page, that cautioned against messing with them because they would "alter the entire operating rang of the pump" or some such verbage. Finally, I keep thinking of the real name for that main rack adjustment - the "part load" screw. So I think I may be using the wrong screws to fatten up the top end.

Here is tonight's plan: Return the part load screw to its original position and run the two white screws back in to their original position. Then, from there, start adjusting those two white screws towards rich, and see what that does to the top end. If my hunch is correct, I may be able to clean up that idle and mid range while fattening up the high end. I think I have erroneously been using the part load screw to richen up the top, and with it, overwhelming the available adjustment on the governor screws. I'll try it and report back.

jcge · 02-28-2008, 01:25 PM

The fixed pin in place of thermostat that John Cramer has described is used on the RSR pumps. (ableit it enters the pump from the top, as opposed to the governor cover)
Regards
John

michel richard · 02-28-2008, 01:30 PM

Does anyone have a closeup picture of a space cam ?

jcge · 02-28-2008, 01:34 PM

jcge · 02-28-2008, 01:45 PM

(C) B Buschen

Jeff Higgins · 02-28-2008, 05:56 PM

Well then... I guess you can all forget about my earlier assumptions concerning the roles of the various adjustment screws on the governor assembly. Today was a major epiphany; the white screws are, in fact the "top speed" adjustment as labelled in the Mercedes manual.

I reset all of the adjustments to "nominal" today and started over. This time, I adjusted the white screws towards "rich". This had a significant impact on the A/F over 4,000 rpm all the way up to 7,000 rpm. Even more important, it did not affect the low end and mid range as the part load adjustment had. They were both back to exceedingly rich, as I knew they would be.

This time, rather than try to adjust that out with the part load screw, I used the two black governor screws. Viola'; the low end and mid range were leaned considerably without affecting the high rpm range. Now we are making progress...

To make a long story short, I now have full throttle running from 12.5:1 to 14.2:1 across the entire rev range from 2,000 rpm to 7,000 rpm. Part throttle cruise is about 12.5:1 to 13:1. Idle is about 13.5:1. I couldn't be happier. I may yet tweak it some more, now that I have a clear understanding of what the adjustments really do, but I could certainly live with it like this.

Yes, Virginia, it turns out a dead stock "T" pump can run a hot 3.0 liter; there is enough adjustment. I just had to play with them and understand what they do. And, in the end, the only really significant adjustment from the stock "T" settings is on those white screws. They are right at the limit of their range on the rich end now, but that's fine. Everything else wound up pretty close to nominal for a "T". Maybe if I had started with an "S" or an "RS" pump I would have had some adjustment left over, but hey, there was just enough in that "T" pump. Good enough for me.

So, in a nutshell: White screws to adjust high rpm full throttle delivery. Black screws to adjust low to mid range full throttle delivery. Part load (main rack) to adjust, well - part load at all rpm's. The center idle screw for - wait for this - idle. It all makes sense now. It is all predictable and repeatable. "X" number of clicks on the white screws affect the high end A/F ratio by "Y", and so on for the black screws and the idle screw. The role of the "part load" is what clouded the matter for me. I had been shown to, and always used it as a "high speed" adjustment. It most decidedly is not.

So, mystery solved. I hope my trials and tribulations can help some one else get through this. Adapting a given pump to a different application than intended need not involve the expense of a space cam change. Combinations outside of the accepted norms for MFI are indeed possible. Maybe not all of them, but taking a 2.4 liter "T" pump and making it run well on a hot-rod 3.0 liter has to be about as radical of a change in displacement and cams as most would be likely to try. So grab those LM1's and go to work...

jcge · 02-28-2008, 06:14 PM

Glad to hear you're happy with your results Jeff - I'm sure may people on the forum have learned plenty from your exploits in MFI

Thanks for sharing the nuts and bolts details (or should that be screws...)

Regards
John

Jim727 · 02-28-2008, 06:42 PM

Excellent!

I'll be right up - trunk should hold about enough beer to get my 2.0S pump singing on my 2.2E .....

This would be great documentation to include in the "Ultimate MFI" thread.

Drago · Drago's Garage

Quote:

Originally Posted by john_cramer

...although to really get it loaded you would need to be at the maximum vehicle velocity in fifth, not easy to do)

Have you ridden with this man? It’s not only easy, but repeatable.

304065 · 02-29-2008, 10:29 AM

Quote:

Originally Posted by Drago

Have you ridden with this man? It’s not only easy, but repeatable.

Hmm, perhaps the gentleman has access to Ehra-Lessien? A track that is absolutely flat and 9km (5.59 miles) long, you can't see one end from the other due to the curvature of the earth.

Public roads scare the crap out of me, I prefer to do my testing on the race track. Obviously there is no public road in the USA where top speed could be reached without fear of imprisonment for a long time indeed.

With an "O" third and a 24.2" tire diameter and a 7:31, 7000 rpm gets you 123 mph, just about running out of revs before the Bus Stop at Watkins Glen.

That is the great thing about the LM-1, you can set it up to log while you concentrate on the road and then read everything back in the paddoc.

Drago · Drago's Garage

Quote:

Originally Posted by john_cramer

Hmm, perhaps the gentleman has access to Ehra-Lessien? A track that is absolutely flat and 9km (5.59 miles) long, you can't see one end from the other due to the curvature of the earth.

Public roads scare the crap out of me, I prefer to do my testing on the race track. Obviously there is no public road in the USA where top speed could be reached without fear of imprisonment for a long time indeed.

With an "O" third and a 24.2" tire diameter and a 7:31, 7000 rpm gets you 123 mph, just about running out of revs before the Bus Stop at Watkins Glen.

That is the great thing about the LM-1, you can set it up to log while you concentrate on the road and then read everything back in the paddoc.

Nope, sorry. We only speed on public roads here...preferably in school zones.

Jeff Higgins · 02-29-2008, 08:46 PM

Well, it looks like this project is just about a wrap. I played with it a bit more tonight, and was able to narrow the range of A/F variation just a wee bit (like by about half a point). I think it is about as good as it is going to get. Next step will be to dyno the little beast and she what she can pull. I have an appointment next Wednesday. I'll report back when I have some numbers.

And don't believe a word Drago says about me.

kenikh · 03-01-2008, 12:26 AM

Super cool, Jeff. Now we need to try rebuilding one...and I have a perfect candidate. Bulding a pump dyno can't be that hard, either.

FWIW, I never hear anyone mention a local MFI guy:

http://www.wesingram.com/nonalfa.htm

Anybody ever met him?

Jandrews · 03-01-2008, 09:02 AM

Best-MFI-Post-Ever!!!! Period!

Jeff,....thanks for braving the uncharted waters beyond the previously generally accepted limitations of MFI part-load and idle circuits!!!!

JA

speedingbullitt · 03-01-2008, 02:12 PM

Great work guys!!

'71 911E Coupe · 03-01-2008, 06:31 PM

Quote:

Originally Posted by Jeff Higgins

John, I've replaced the warm-up thermostat with a device pretty much as you describe. It is actually a screw that I can back out for starting, then screw in (full lean) once it's warmed up a bit.

Jeff, great to hear you got the car running right. I'm planning on messing a little bit around with those screws behind that cover soon! I can't press the adjustment screw in to meet with the idle screw for some reason, so I have to take this cover off anyways and see what's up.

My engine is drinking a lot of fuel right now, the level in the tank goes down quickly, so I know I most of the adjustemnts are set too rich.

My question is, could you provide some info with how you made the screw for in place of the thermostat? I am considering doing this as well. Did you have to make threads inside the pump? (Maybe this is one reason my engine runs too rich, I cleaned my thermostat and everything but I think the screw is a better idea)

Thanks!

724doorE · 03-01-2008, 08:42 PM

Great thread This would probably help me with my stock E pump, 2.7RS pistons/cylinders and DC 40 cams... I love it! Thanks!

kenikh · 03-01-2008, 10:28 PM

FWIW, this thread is worth its weigt in gold. I was worried that my '69S pump might have problems with my upcoming 2.3L motor. Now I know that just isn't the case. Jeff, can't wait to pick your brain...

Jeff Higgins · 03-02-2008, 06:36 AM

Kenik, your 2.3 with the '69S pump seems like it should be a piece of cake after my '72T to 3.0 stretch. I think it would be fun to apply what I learned from this to another, far different, application. When you get that thing up and running, we'll have to hook up the LM1 and go for a drive. I'll be happy to show you exactly what I did on mine. I'm sure it will respond similarly to the same adjustments.

Anthony, my thermostat replacement screw is almost embarassing in its crudeness. It is meant to be temporary, just to get the thing running while I tackle more difficult issues. All I did was find a screw that was small enough in diameter to go through the hole in the pump, and long enough to reach the lever. Then I took the spacer that goes between the thermostat and the pump, and used it to capture a nut between it and the pump. The nut was ground down on its flats just enough to fit the big counterbored recess common to the hole in the pump body, so it bottoms out in that. I used a couple of washers as shims between the nut and the spacer, so when the spacer is tightened down it presses the nut firmly down in the bore, to keep it from rotating. Eventually I'll get some one to braze a nut onto the spacer, which is what most guys do.

kenikh · 03-02-2008, 12:38 PM

Thanks, Jeff. Can't wait!