MFI self build pump setup and tuning

[BartdeBruijn]

Hi!
After finishing the full restoration of my ‘69 911T she is performing beautifuly ! Now a few years later I decided to build a more powerful engine and keep the matching number engine as it is.
Slowly I am collecting parts for this new engine. It should run with this fantastic MFI. I have restored the whole MFI setup. Bored throttle bodies removing the wear and added one size bigger valves. After that I restored the whole MFI pump, great piece of mechanical engineering.
With a lot of information from the forum
Jonny042 - Project heavy metal
Jeffc280sl - Open heart surgery
356RS [Mark Jung]
And many others!
I managed to restore the pump and build my calibration setup. Bringing it to Eisenbrand Renn & Motorsport is easy but only half the fun, right!?

So that as a short introduction, I ran into some issues that I do not really know how to resolve.
1)
In picture one [Bosch datasheet], rack movement at pre adjustment, I managed to get the following vallues for the rack.
Angle rpm rack
Max - 2000 - 7.02 (should be 7.00)
0 - 400 - 4.46 (should be 4.45)
8.3 - 800 - 4.25 (should be 4.25)
29.5 - 2000 - 4.73 (should be 4.75)

Now when I move forward to the next set of tests the Full load vallues,
Angle rpm rack
Max - 700 - 7.00 (should be 6.25)
Max - 900 - 6.83 (should be 6.75)
Max - 2000 - 7.01 (should be 7.00)
Max - 3000 - - - - (should be 7.3)

The full load vallues should be corrected via the rack head screw[as per Bosch data sheet], right?
Question 1: If so, I will alter also the value(s) obtained in the first table as the first line adjustment is through the rack head screw and that is the one I have to use to correct the second table. So feels like chasing my tail!

For now I am using a diesel calibration fluid that is odorless and not flammable (like petrol or white spirit) Only thing is that diesel (like) fluids have a slight higher viscosity.
Question 2: Does anyone has an idea on the effect of this difference on the quantities I am measuring/adjusting now?

Thanks a lot,
Bart

[BartdeBruijn]

Hereby a video of the working test setup!

https://youtu.be/o7XkqSn0jDk

[rudedude]

Nice setup! I wish I could help you but it’s over my head. I would like to see what my pumps would do as I’m certain after 50 some years they could use some fine tuning.

[stownsen914]

I plan on doing similar in the next couple years. I’ll be following along!

[r lane]

I have built a setup as yours. Yours much more clinical appearing than mine. To quote a friend who stopped in for a viewing, ''looks like a collaboration between Juels Verne and Buckwheat''. I am focusing on race pumps primarily, so am not worried too much about any thing under 4500 rpm. Looking at your chart, the only piece that appears significantly out of range is Max/700. I assume you have checked the delivery amounts, and that is what I would want to see. You are going to have to spend a bunch of hours doing repeats and adjustments with detailed notes. Eventually you will have your reward, but it is not just monkey see monkey do. A lot of understanding will need developing. Have fun and good luck. Bob

[BartdeBruijn]

@rudedude
Yeah, I guess they do run out of tune after 50 years….. mine was all over the place wen I sent it to Eisenbrandt in Germany. That is when I decide the pull the whole pump apart and do it all myself….Big fun and getting closer. New engine build will follow after this!

@Stownsen914
When I am done, as I probably will not start a business on this you could be interested in my setup ;-) By the way there are very interesting threads already on this topic. Going way more deep than mine, even that I just started.

@Bob
Thanks for your comments, the last line is where it is about, Have fun!
Cheers,
Bart

P.s. Will be continued probably this weekend and will be posted!

[356RS]

I hope the data sheet I sent you will help out.

[Jonny042]

Originally Posted by 356RS

I hope the data sheet I sent you will help out.

Mark,

I don't see how the flow rate at rack movement of the 8.3 degree/800 RPM test can have rack movement of 4.25mm gives a 14.0-15.0ml flow rate, yet the 0 degree/400 RPM test has a rack movement of 4.45mm and the lower flow rate of 13.5-14.5?

There has to have been some error in that sheet originally from Bosch? As long as you ignore the rack movement for those tests and tune for flow rate (which is the only sensible thing to do) it doesn't really matter... but curious nonetheless.

[356RS]

Jonny, You're right about some error's on the data sheet. I sent Bart a 2.4S original data sheet yesterday. As for ignoring rack movement measurements on some pumps you are correct. Reason for this is because there are a lot of pumps out there that have been rebuilt, re-calibrated, etc; etc; and when the rebuilder adjusts the equal flow rates by loosening the plunger rack gear collars then that can change the real rack movement measurements while you are adjusting for equal flow rates. It's more important to have the correct flow rates than rack movement measurements on some of these old pumps.

[BartdeBruijn]

Gents,

Thanks again as that is exactly what I am going to do, measuring flow rates also suggested by Jonny at my thread at early911s!

Cheers,
Bart

[Jonny042]

Originally Posted by 356RS

Jonny, You're right about some error's on the data sheet. I sent Bart a 2.4S original data sheet yesterday. As for ignoring rack movement measurements on some pumps you are correct. Reason for this is because there are a lot of pumps out there that have been rebuilt, re-calibrated, etc; etc; and when the rebuilder adjusts the equal flow rates by loosening the plunger rack gear collars then that can change the real rack movement measurements while you are adjusting for equal flow rates. It's more important to have the correct flow rates than rack movement measurements on some of these old pumps.

OK I'm glad it's not just me that couldn't make sense of that!

As for measuring flow instead of rack movement that makes total sense, at least once you are in the ballpark.

[BartdeBruijn]

Part 3

Finally found some time this weekend to work on my pump.

Taking Jonny’a advise I started with
2000 rpm full throttle position
After some tweeking the clamps/collars on the main rack the results were:

Rack movement 7.02 mm.
Cylinder 1 2 3 4 5 6
CC. 48.5 48.5 48.5 48 48.5 48.5 [47 -48.5]
So check, that one is ok!

Now moving on to the next 4 tests
400 rpm; 0 load; run time 2:30
Cylinder 1 2 3 4 5 6
CC. 14 13.5 13.5 14 14.5 14 [13.5 - 14.5]
OK too!

800 rpm; 8.3 load; run time 1:15
Cylinder 1 2 3 4 5 6
CC. 15 14.5 14.5 15 15 15 [14 - 15]
OK too!

2000 rpm; 29.5 load; run time 30
Cylinder 1 2 3 4 5 6
CC. 25 24 24.5 24 24.5 24.5 [24 - 25]
OK too!


3000 rpm; full load; run time 0:20
Cylinder 1 2 3 4 5 6
CC. 54 54 54.5 54.5 55 55 [48.5 - 50]
NOK. I had to turn the rack 10 clicks CW (Less rack travel) but seem s to react slowly and only moved +/- 3CC by 10 clicks. I can go further of course to get to the 48.5 - 50 range, however I was afraid that I ruined the earlier settings…..
I did a check after this 3000 rpm full load exercise by redo the 2000rpm and 29.5 load. this resulted not in the earlier tuned 24.5 ‘ish CC but in 20’ish. This sounds logic as I turned the rack to achieve the 3000 rpm and full load volumes…..
So I am running in circles somehow!

I was pretty happy till the last bit. Is this me not understanding the system or drill!?
Thanks,
Bart

[356RS]

Bart, You have all the Low to Mid settings about perfect so why are you adjusting the main rack for the 3000 WOT. Adjusting the main rack now will alter all the other settings. You should be adjusting the White head screws on the spring capsule for the 2000 to 3500 adjustment. Back out CCW the White heads 1/2 turn each and see if that lowers the numbers.

[BartdeBruijn]

Hi Mark,
I received the advice to use the rack for 3000 rpm and full load. I am a novice enjoying the learning curve!
Iread read somewhere (maybe from you) that each spring will generate a part of the total spring curve and the stiffness can be adjusted separately, however the whole curve can be shifted over the y-axes by using the rack……
So going back where I was before adjusting the rack at 3000 and 29.5. Checking earlier quantities again and than use the white screws?
So both 2000/29.5 & 3000/full should be adjusted through the white screws (stiffest spring)?
Issue I see that if I get 2000/29.5 ok through the white screws and 3000/full is not ok, by making 3000 ok I will alter the 2000 condition or do I miss something?
I wrote to Jonny on early911s. Not handy choice from me to be on both forums….
Thanks in advance,
Cheers,
Bart

[356RS]

Bart, First off, the only Bosch data sheets the state 3000 rpm @ 29.5 is for the 2.7RS. I thought you had a 2.4 S. For a 2.4S, the White head screws will get the main rack set for 7.00mm @ 2000 rpm and 7.30mm at 3000 rpm or as close as you can get. Then check the flows for 47 to 48.5 mL/1000 @ 2000 rpm and 52 to 54 mL/1000 @ 3000 rpm both at WOT. A little richer will be better because of todays gasoline specs. Remember these data sheets were made for real gasoline octane in the early 70's not like todays. Buy the way, you are really close to perfect specs on your testing. Great job Bart.

[Jonny042]

Sorry to be late to the party, Bart. It wasn't clear that you made adjustments between the tests.

Yes, as Mark says you'll have to bounce back and forth a bit between the main rack and part load screws to get everything dialed in. It would be good to double check that your test screw has fully seated the warm-up linkage in the "hot" position as this could cause issues, and also double check the other measurements ("f" and "c") to make sure they are in the ballpark.

There are other adjustments you can make but let's see if we can get you there without getting into those!

[Jonny042]

PS - Subscribed to the thread

[BartdeBruijn]

Hi Mark & Jonny,

Yeah sorry for confusion….
@Mark: yep it is 2.4S spec and it was a typo the 3000 rpm and 29.5. Should have been 3000 rpm and full load. Also the CC numbers for the 3000 rpm full load check where wrong should be 52-54 CC.

@Jonny: yes I put the test screw in place in stead of thermostat. (Will buy eventually the lever type from Henry@Supertec). I choose a value in the given range that I have full bottoming out. Will measure the c-value to be sure.

Will do the measurements again when I can focus as I hate it when typos and misinterpretation of al your info happens. As said, I am close but not there yet……

So my test plan for the weekend will be:

Rpm Load Rack CC Adjustment Action
(1) 2000 Full 7.0 47-48.5 Rack Get rack displ, equal and correct quantities

(2). 400. 0. 4.45. 13.5-14.5. Idle.
800. 8.3. 4.25. 14 -15. Black
2000. 29.5. 4.75. 24-25. White
3000. Full. 7.3. 52-54. Rack

So is this test scheme correct?
(As both 2000/full/7.0 and 3000/full/7.3 are to be controlled by the rack? If so they are dependent and if one is correct, automatically the other has to be correct too….right!.)
Could you say looking at the Bosch test sheet, all full load conditions are corrected by the rack screw and all other load situations are by the ‘capsule screws’?

Will start fresh on Saturday and see what that will bring ;-)
Thanks again,
Bart

p.s. this 3000 rpm stuff is impressive. If you see the technical effort, all mechanical, of the MFI compared to a Weber carb where some simple physics will do the job. That is what MFI so much fun and I am really curious on the driving experience and throttle response!

[356RS]

Bart,
That test screw in place of the thermostat is you "f" setting basically. So next would be the ""c" setting with correct shims under the Barometric cell, .8mm is what your adjusting for.
As far as the spring capsule screws, the white pair adjustments are for 2000 rpm to 3000 rpm 80 degrees throttle. The main rack is NOT for adjusting the 3000 rpm full throttle. The main rack affects all the settings from Idle to WOT.

[Jonny042]

Keep at it, Bart! You're on the right track. You are best to study what's in front of you and come to your own conclusion about what's going to work, and why. Not saying that to be discouraging, rather the opposite - once you fully understand it you'll have that as your own.

The white screws AND the main rack will both affect the 3000RPM full throttle settings. The settings interact and intersect to some degree so making blanket statements about what screw is for what test result is asking for trouble IMO.

Don't forget that you can correlate rack movement to fuel delivery - if you keep an eye on rack movement you can make a change to an adjustment and instantly see the result without going through a full volumetric test each time. This one tip can save you quite a bit of time and frustration.

Also, I don't know if it's just me but at first I would get confused about which way to turn the screws and/or main rack adjuster to add or subtract fuel. I always try to think of the main rack like a tap, and you are turning it CCW to open it and add more fuel. The lower screws are the opposite and the phrase "Lower > Left > Lean" is a good memory aid.