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Thread: Suzuki GT750 EFI Special

  1. #31
    Cheers,

    I totally get all that and thanks for confirming.

    What I was trying to do with the excel which allowed for rpm, TPC position and fuel volume was to estimate where the end inject point needed to be based on how long it took to get the fuel load in at each RPM.

    I can see its easy enough to do with trial and error but was just trying to add a bit of calculation to understand a start point.

    If you are at all interested I can email the excel sometime?

    Anyways, bits are at the machine shop. All good fun and I think I have found space in the barrels to squeeze the injectors in....

  2. #32
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    The Neil Hintz story and the birth of Two Stroke TPI injection that KTM later copied.

    https://www.drd.co.nz/2-stroke-tpi-c...yGjmrXAhLNFCxM

  3. #33
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    Quote Originally Posted by Kettlekev View Post
    What I was trying to do with the excel which allowed for rpm, TPC position and fuel volume was to estimate where the end inject point needed to be based on how long it took to get the fuel load in at each RPM.
    The amount of air/fuel transferred to the cylinder is roughly the volume contained in the Transfer ducts. The crankcase transfer cutouts are also part of the transfer duct. Very little extra if any comes from the crankcase proper on each individual cycle.

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    By finishing injection at BDC or shortly after. Pretty much that transfer duct's worth of air/fuel mixture that is drawn into the cylinder will be at the correct air/fuel ratio.

    I would be very interested in your spread sheet. I will PM you my email address.

  4. #34
    Quick update.

    Managed to work out how to kid Speeduino how it can be a 3 cylinder, 2 stroke controller...

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    Signals look good on the scope (ignore the required fuel and mix ratio for now, corrected already).

    I've found what looks like a good injector outfit who have helped with characteristics definition....https://www.fiveomotorsport.com/keih...husaberg-zx10/

    I have made an auto calculating spreadsheet to calculate injector end inject times which hopefully works.

    So crank wheel is back from the machine shop next week then its run the new ignition with carbs on the dyno to get a baseline, strip barrels and work out where I can squeeze injectors and a fuel rail and a MAP sensor in....

    All good fun...

  5. #35
    Managed to get a knackered set of barrels to play with, and I think my injectors will fit into the base of the transfers.....

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    Just gotta make some fancy ports and a fuel rail but its looks like it will be neat enough

  6. #36
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    It is looking good. I can see how the injectors will fire across the rearward transfers but how are you going to place the other injectors for the forward transfers?

  7. #37
    I was kinda hoping I wouldnt need 2 injectors per cylinder but I guess from your post you are advising I do. Thinking about it makes sense to get better mixing.

    What if one injector were more angled down into the crank, do you think that would work. If not I need 6 injectors in pairs I guess......

  8. #38
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    I have tried one injector on one side. It did not work, I got rough running with a sort of hit and miss detonation. My guess is that the air/fuel ratio was not consistent.

    6 injectors fired in pairs, an injector firing across the base of each transfer on a triple is the go.

    KTM run an injector both sides but at low fuel demand they fire them alternately. I expect they get away with it because there will be wet fuel still evaporating of the duct walls on the alternate side to the firing injector and that balances up the air/fuel ratio a bit.

  9. #39
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    This is my staged injection air cooled cylinder. The outer injectors fired across the base of the transfers and impacted on the far side of the transfer duct. Any wet fuel that made it that far was then evaporated of the hot metal. Evaporated the fuel and kept the transfer duct cooler. This arrangement worked well.

    Click image for larger version. 

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    Could you place just one injector in the middle that fires up under the piston. The injector could be in the front or back or even the underside of the crankcase between the crank wheels. I remember Suzuki twins of the GT750 era had drain plugs in the bottom of the crank cases. Maybe the 750 has them too. They could be modified for an injector. Worth a thought.

  10. #40
    Under the crank would definitely work. I can make space there.

    I still maybe be able to squeeze 6 in but the fuel rail will be a challenge and it wont look too pretty.

    I'm sure I can machine features under the crank. Good idea!

    If its a no go I will look at double injectors on the barrels. Hopefully the speeduino has enough current capacity for dual injectors.

  11. #41
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    Disclaimer, I have not done this myself but have thought about it and would like too.

    If you are firing directly up from the bottom of the crankcase between the crank wheels you should only need one injector per cylinder until you run into the rule of thumb engine performance > 10kRPM/10Bar point where staged injection could become necessary.

    The ideal is one injector big enough that it can deliver the max amount of fuel required in the smallest amount of time available at high RPM and small enough that at idle/low RPM it does not drown the engine with its dribble when its opening in the dead time zone.

    Injector sizing is a balance. When using just one injector, think smallest injector possible.

  12. #42
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    Quote Originally Posted by TZ350 View Post
    .
    It is looking good. I can see how the injectors will fire across the rearward transfers but how are you going to place the other injectors for the forward transfers?
    Quote Originally Posted by Kettlekev View Post
    I was kinda hoping I wouldnt need 2 injectors per cylinder but I guess from your post you are advising I do. Thinking about it makes sense to get better mixing.

    What if one injector were more angled down into the crank, do you think that would work. If not I need 6 injectors in pairs I guess......
    Quote Originally Posted by TZ350 View Post
    .
    I have tried one injector on one side. It did not work, I got rough running with a sort of hit and miss detonation. My guess is that the air/fuel ratio was not consistent.

    6 injectors fired in pairs, an injector firing across the base of each transfer on a triple is the go.

    KTM run an injector both sides but at low fuel demand they fire them alternately. I expect they get away with it because there will be wet fuel still evaporating of the duct walls on the alternate side to the firing injector and that balances up the air/fuel ratio a bit.
    I can't remember the rule of thumb, but modern engines have something like 3x the cylinder volume stored mostly in the transfers.

  13. #43
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    Click image for larger version. 

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    It might not be that hard. If the crankcase plugs were adapted for a injector. Some crankcase nuts could be replaced with pedestal nuts that also act as mounting points for a conventional style fuel rail. You will no doubt have to make the fuel rail and nuts to suit.

  14. #44
    I am liking this idea more. I have a suspended engine so no frame getting in the way and I can work around the exhausts I think.
    Time to buy a knackered lower casing and have a tinker me thinks.....

    I honestly think there isn't one component on the bike I haven't modified now.....

  15. #45
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    My Kawasaki, cant remember, I may have already post a picture of this.
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