Page 1 of 3 123 LastLast
Results 1 to 10 of 21

Thread: MFI self build pump setup and tuning

  1. #1

    Question on MFI tuning on own build MFI test bench

    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
    Attached Images Attached Images     
    Last edited by BartdeBruijn; 01-21-2023 at 02:14 AM.

  2. #2
    Impressive set up well done wish that I could help you but will be watching this thread

    Thanks, Rick

  3. #3
    That is a really nice setup! The inverter/variable speed drive is the same one I used on mine. I'm pleased to see another DIYer taking the initiative to build a test setup.

    To answer your first question about the adjustment I would move on to the next tests and start playing with the other adjustments, since the part load settings are off they will need to be set with the part load screws. Ignore the "RACK" note in the book. Yes it will affect those adjustments too but you'll have to fiddle with the part load settings to get it dialled. By the looks of it you are not far off.

    The calibration fluid viscosity should not affect the tests appreciably. The pump is a positive displacement device and will deliver the same amount of fuel (or fluid) regardless the viscosity (within reason of course).

    Last but not least, I notice you haven't replaced the thermostat with a "test" screw (that I can see) but you must have done something to accomplish this or you would be getting fuel delivery far in excess of the specifications.

    Enjoy!

  4. #4
    Hereby video of working test setup!

    https://youtu.be/o7XkqSn0jDk

  5. #5
    Quote Originally Posted by BartdeBruijn View Post
    Hereby video of working test setup!

    https://youtu.be/o7XkqSn0jDk
    I like the way you used the fuel cut-off solenoid to stop delivery before the test. If I had to build another test bench I'd look into using a much smaller electric motor and drive setup, I went with a fairly big motor so I could accelerate to the test speed in a short time.

  6. #6
    That's an impressive set up for what may be a one time use? I can't tell, is there oil in the pump sump? don't see any evidence of oil in the clear return tube.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  7. #7
    Wow, very impressive to DIY a test bench like this!
    1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
    Early 911S Registry Member #425

  8. #8
    Part 2

    @Jonny
    So understanding you correctly I should focus more on the tests B and tests C
    Test B is full load on different rpm ranges all controlled by the rack head screw, right!?
    Confusing part is that reading on the different forums I understood/read the following:

    1)Rack head (overall adjustment) - internal adjustment
    2) Caspule - centre screw - idle adjustment/CO
    3) Capsule - 2 x black screws 450-1000rpm (pump rpm)
    4) Capsule - 2 x white screws >1000rpm (pump rpm)

    Reading the Bosch data sheet the full load conditions with different RPM’s ranges (Test B) all need to be adjusted by the rack screw….. So can I conclude that full load conditions do ‘overrule’ the table where all rev ranges are controlled by the capsule screws?

    In test C, there is during the whole test range only for 3 (below) situations where how the adjustments need to be done
    400 rpm —> idle screws
    800 rpm —> black screws
    2000 rpm —> white screws.

    All the load conditions between these three conditions have nothing mentioned where/how to adjust, does this mean this means that the earlier mentioned rev ranges and dedicated screws are valid here too? Will give that a try ;-)

    Thanks for your insight on the viscosity, I agree that it is displacement/volume controlled. Maybe will try fuel one day going outside to be sure but for now I agree fully with your assumption.

    Yeah, I made already a test screw to replace the thermostat and will mount that one of the coming days.

    Using the solenoid to start the measurement after the pump is up to speed I saw somewhere on the internet and gave me the chance to speed up the pump slowly(programmable).

    @ Ed
    Yep, probably one time use….For me it is hobby to understand hoe things do work and the fun of doing it yourself ;-)
    I filled the pump to a certain level. So it is splash lubrication and doing it like this I can adjust the capsule without draining the oil every time.

    @ All
    Thank you all for the kind reply’s!
    Last edited by BartdeBruijn; 01-22-2023 at 07:45 AM.

  9. #9
    Hi Bart, sorry for the slow reply!

    I suppose you might have figured this out by now, it's easiest to remember how the fuel delivery works as plotted out on a graph - the main rack screw moves the delivery curve up and down the Y axis, and the part load screws change the shape of the curve (mostly minor, and mostly at the bottom 3rd of the curve).

    To more specifically answer the question, the full load 3000RPM test results wouldn't be changed much, if at all, by the capsule screw settings. If you change all of them from one end of the setting to the other you would probably find a small change in the full load/RPM which you would then have to correct with the main rack adjustment, then go back and forth a few times to reach your final settings.

    The amount of adjustment available to you on the part load screws is fairly small - they really are there to adjust for manufacturing tolerances and to make sure the pump is tuned to the fuel curve that's been machined into the space cam. So don't get discouraged by the lack of responsiveness with the part load screws when making adjustments. In particular, if the stylus is resting on some spots of the space cam (as it is not particularly smooth) you might find making a screw adjustment will change fuel delivery in the opposite direction than you expected!

    Also, it's possible for the Black screws and Idle screws to interact, such that if you screw in the black screws too far that spring will take over too soon and limit the effectiveness of the idle screw adjustment.

    Keep playing with it until you get it and most importantly, understand it for yourself - you've come so far with this you may as well get to the point where you could write your own book about the system! You aren't far off!

    Quote Originally Posted by BartdeBruijn View Post
    Part 2

    @Jonny
    So understanding you correctly I should focus more on the tests B and tests C
    Test B is full load on different rpm ranges all controlled by the rack head screw, right!?
    Confusing part is that reading on the different forums I understood/read the following:

    1)Rack head (overall adjustment) - internal adjustment
    2) Caspule - centre screw - idle adjustment/CO
    3) Capsule - 2 x black screws 450-1000rpm (pump rpm)
    4) Capsule - 2 x white screws >1000rpm (pump rpm)

    Reading the Bosch data sheet the full load conditions with different RPM’s ranges (Test B) all need to be adjusted by the rack screw….. So can I conclude that full load conditions do ‘overrule’ the table where all rev ranges are controlled by the capsule screws?

    In test C, there is during the whole test range only for 3 (below) situations where how the adjustments need to be done
    400 rpm —> idle screws
    800 rpm —> black screws
    2000 rpm —> white screws.

    All the load conditions between these three conditions have nothing mentioned where/how to adjust, does this mean this means that the earlier mentioned rev ranges and dedicated screws are valid here too? Will give that a try ;-)

    Thanks for your insight on the viscosity, I agree that it is displacement/volume controlled. Maybe will try fuel one day going outside to be sure but for now I agree fully with your assumption.

    Yeah, I made already a test screw to replace the thermostat and will mount that one of the coming days.

    Using the solenoid to start the measurement after the pump is up to speed I saw somewhere on the internet and gave me the chance to speed up the pump slowly(programmable).

    @ Ed
    Yep, probably one time use….For me it is hobby to understand hoe things do work and the fun of doing it yourself ;-)
    I filled the pump to a certain level. So it is splash lubrication and doing it like this I can adjust the capsule without draining the oil every time.

    @ All
    Thank you all for the kind reply’s!

  10. #10

    Bosch data

    Just to add - I think the "Bosch Data" in the book has been transposed and interpreted to some degree in the book - there is a lot of duplication in the sheet, for instance the conditions in test (A) are revisited in test (C). It's not particularly well presented or explained. And at a glance it appears more complicated than it is.

    Since you had your pump completely apart the fuel delivery settings for the individual cylinders would need to be set with the adjusting collars so they are not only even, but have the specified fuel delivery at, say, 7.00mm rack movement. Once that is accomplished you can ignore test A and go onto test C, really, and only do the 3 tests that are shaded/highlighted and add a max throttle 3000RPM test and be done!

    So here's a summary -

    1. Spin the pump at 2000RPM/Full throttle and adjust the main rack screw so that you are getting 7.00mm travel. Set all your cylinders to pump 47-48.5 ml/1000. Get them as even as possible as this is your only chance to set the individual cylinder "trim".

    2. Do four tests:

    400RPM/Closed throttle (adjust the idle screw)
    800RPM/8.3 deg throttle (adjust the black screws)
    2000RPM/29.5 degree throttle (adjust the white screws)
    3000RPM/Full throttle (adjust the main rack)

    3. Repeat the tests in step two until the settings are correct.

    It's not actually necessary to do full timed volumetric tests for each test, the dial indicator on the main rack can be used to get a relative measurement as soon as the pump is up to speed and this can be a help to get in the ballpark by looking at the rack movement instead of going through a full volumetric test.

    Looking at the Bosch Data for the 2.4S it looks like there's some issue with the co-relation between the rack movement specs and delivery rates so take anything on those spec sheets with a grain of salt!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Message Board Disclaimer and Terms of Use
This is a public forum. Messages posted here can be viewed by the public. The Early 911S Registry is not responsible for messages posted in its online forums, and any message will express the views of the author and not the Early 911S Registry. Use of online forums shall constitute the agreement of the user not to post anything of religious or political content, false and defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, or otherwise to violate the law and the further agreement of the user to be solely responsible for and hold the Early 911S Registry harmless in the event of any claim based on their message. Any viewer who finds a message objectionable should contact us immediately by email. The Early 911S Registry has the ability to remove objectionable messages and we will make every effort to do so, within a reasonable time frame, if we determine that removal is necessary.