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Thread: Suzuki GT750 EFI Special

  1. #46
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    Quote Originally Posted by Flettner View Post
    My Kawasaki, cant remember, I may have already post a picture of this.
    Flettner hid two injectors in the back wall of of the "C" port duct that fire directly across the top of the flywheel's. He used two fired together to get the volume for E85. But it could have been one larger one or the two could be staged injection. Lots of possibilities for the Suzuki 750.

  2. #47
    I've got a new lower case coming for the weekend.

    In my head I am envisioning squirting up between the crank lobes, right up the middle of each chamber.

    Other than the benefit of not hitting a hot transfer wall to help mixing it should be in a good place as far as timing goes in that I can start injecting as early as transfer close right round to BDC (and beyond a bit if needed).

    Will post pics when the casings arrive.....

  3. #48
    Ok now I am confused.

    I am running a bosch ignition trigger module to feed my coils. The output of the speeduino feeds the trigger then the trigger feeds the coils.

    My original CDI coils wont work because their primary coil is just a single connector, the other side of the coil being grounded through the case.

    This is no good because the trigger needs to see a coil with 12v on one side and the trigger on the other which switches the earth.

    The Speduino on the input then goes high and on the low pulse edge fires the trigger. All good so far.....but....

    I bought what I thought was the right 2 wire primary coil (yamaha YZ) but the input resistance is 0.6 ohms (I know that's not the true impedance of the coil but I cant measure that ).

    Long story short is all I am doing is blowing fuses now. My coil resistance must be too low? What resistance coils should I try to use on a set up like this and does anyone have any coil recommendations?

  4. #49
    I worked out the coil I had bought was for a CDI ignition, hence the low resistance.

    I tried a simple test last night replacing the coils with high watt resistors to see the trigger firing but there is clearly an issue with the trigger now.

    If I understand the trigger cct it is basically a FET and either a low or a high on the input forces the output low (shorting one end of the coil).

    Initially I tried connecting the crank signal pulse and that didnt drive the ignition module then I resulted to just applying voltage to the input which should trigger the out put when its loaded (connected to the coil/coil simulator resistor). That didnt work either so I must have fried the trigger I guess.

    EDIT: Worked it out. It is VERY easy to wire the module backwards. ...and that's exactly what I did. The upside is I have now mad a good module test system....

    Basically to test the trigger using a simulated coil, all you need is an 8 ohm (20 wattt or more) resistor which at 12v will draws about 1.5 amps (well inside the limit of the module). Connect one side to 12v and the other side to one output channel on the igniter. Now either connect the ignition channel from Speeduino to the same input channel on the igniter and either using a crank signal or speedysim's TPS control to generate a crank signel, fire it up and away it goes. Remember to ground the centre pin on the 5 pin (input side) of the module. To 'show' it is firing I also wired a LED and 540 ohm resistor across the 8ohm resistor so that I can see the fire.

    The module prefers a 5v drive from speeduino and gives a much better square wave on the output of the trigger, the 12v option pulse doesnt pull low enough and the signal is a bit rounded on the trigger output which will affect the coil drive.

    You can actually test it without Speeduino attached and just make and break (momentary) a 5v level to the trigger input

    Ironically the original 3-4 ohm coils for the factory bike are probably OK but obviously not high performance

  5. #50
    and here's one I made earlier!!

    Click image for larger version. 

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  6. #51
    I've been looking at the injector positions.

    The X's marks the points where ideally I would put injectors so that they fire right up the middle of each cylinder.

    Click image for larger version. 

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    This would angle my injectors up at about 45 degrees and although they would be squirting towards the inlets, as I have reed valves I dont see a problem.

    Problem is the middle cylinder, X cant be in that place because of the water jacket, so it will be slightly to one side. The little red circles mark the injector positions
    Click image for larger version. 

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    Good news is the case looks thick enough to take a screw in, O ringed boss (not much room for welding one).

    This means the fuel rail (which will obviously have to be custom should sit between the exhausts and the casing. Maybe!!

    EDIT. Or, crazy thought? The oil feed SRIS valve positions (green circles) could be used as an inject point and I could make new SRIS ports which might be neater. One SRIS feed is a bit under a crank lobe though......

    Click image for larger version. 

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    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #52
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    Quote Originally Posted by Kettlekev View Post
    I've been looking at the injector positions. The X's marks the points where ideally I would put injectors so that they fire right up the middle of each cylinder.

    Click image for larger version. 

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    Hi Kettlekev. I am excited by the ideas, they look good but I do have to point out that I have not done this myself so you are leading the way here.

    Because a real sucky pipe will make more power when there is more crank case volume to draw from. On my engines I have turned the inside face of the crank wheels back to the big end thrust washer surfaces to increase crankcase volume and skimmed an extra mm or so from the outside face and flywheel wheel rim to reduce hydra-static drag. If needs be you could maybe skim a bit of to un shroud the injectors.

  8. #53
    The GT cranks are heavy but that helps the drive/feel.

    I could lighten them but will probably look at that as a next step as there is a fair bit of space in there.

    My only worry was the flow out of the injector getting inhibited but I guess as long as it all end up in the crank case somewhere and doesnt focus over one transfer then it should mix?

    Looking more at the SRIS inject point option (green circles) the problem I see with that is the injection would flow horizontally first for about 50mm then vertical into the casing. Not only would that add some time but in might pool fluid in the track so that may not be as good as 'direct' injection near-vertically?

  9. #54
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    .
    I think squirting the injected fuel up a narrow passage way will be an issue as the misted fuel will wet out on the walls of the passage.

    If I was putting injectors in the bottom of the crankcase I would aim them so the injected stream of fuel impinged on the underside of the piston crown. That way you get good evaporation and piston crown cooling. At high speed and engine load the injector would be squirting for nearly a full crank cycle so plenty of time for the fuel stream to reach the piston and cool it. (piston cooling was the main reason I wanted to try crankcase injection.)

    The only issue I see with this is that the injection stream will wash the bigend, maybe not a problem if you are squirting pre mix like I do but might be an issue with raw fuel.

    Click image for larger version. 

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    When I welded in the injector bungs I could only get to half the area needed. After they were securely tacked into place I sealed all around the bung with Devcon F. But any good metal glue would do.

  10. #55
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    I'm on my phone having chocolate fudge (very nice) so pictures hard to see, but I'd want to avoid bearing wash as TZ says but also the spray will cone out and wet the crank surfaces i would think.

    Can you not move them near the front angled a bit up so they are nearer transfer bases and at the top of the crank?

    There was an RZ350 on RD/RZ500 forum using R6 parts i recall. Into the throttle is looking more attractive if you have compromised positions. Peak power revs must be pretty low.

    Disclaimer; I know jackshit about injection.
    Don't you look at my accountant.
    He's the only one I've got.

  11. #56
    As you say raw fuel and bearing wash could be a bit of an issue potentially.

    The 2 stroke oil inject point is on the inlet, post reeds (piston side) so kinda drops onto the conrod bottom bearings and if I am squirting up past them the other way it may be OK. For a good portion of the cycle the injector wont be obscured by the conrod (except the middle one is a bit of a challenge) because I want to stop injecting around BDC if possible.

    Maybe I should try a more direct spray pattern but then I would reduce atomisation I guess.

    Pro's and cons. Think I might just have to try it and hope I dont de-oil the bearing to much.

    Still thinking......

  12. #57
    OK, looking at the casings again....new plan.

    To help with the oil mixing I am going to inject at the back of the crank chamber near the inlets and again straight up. It will mean loosing some casing ribs and some tricky welding but I think its dooable.

    Click image for larger version. 

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    The yellow circles mark the spots.

    Hopefully the raw fuel wash will be minimized

  13. #58
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    Oil injection. Heck hadn't considered that properly. Do KTM mix first then injection both?

    I wouldn't want to pass air over an oil dribble and hope it combines with the crank mixture to lubricate everything. I'd want the oil to be in direct path of the petrol spray which is how it occurs with carbs.

    Are you sure you don't want to inject into throttle bodies?

    What if you oil injected into the spray tube? Nah too much chance of blocking an injector with such a small volume and high pressure with 2 distinctly different viscocities and no mixing agitator.

    My T125 has pressure feed to the crank, but you still need to mix gas with oil to do the bores.

    Unless I misunderstood I think you need a revision.
    Don't you look at my accountant.
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  14. #59
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    Quote Originally Posted by F5 Dave View Post
    Oil injection. Heck hadn't considered that properly. Do KTM mix first then injection both?

    I wouldn't want to pass air over an oil dribble and hope it combines with the crank mixture to lubricate everything. I'd want the oil to be in direct path of the petrol spray which is how it occurs with carbs.

    Are you sure you don't want to inject into throttle bodies?

    What if you oil injected into the spray tube? Nah too much chance of blocking an injector with such a small volume and high pressure with 2 distinctly different viscocities and no mixing agitator.

    My T125 has pressure feed to the crank, but you still need to mix gas with oil to do the bores.

    Unless I misunderstood I think you need a revision.
    Most of the KTM patents they quote relate to the oil injection, i cant recall if the patents are Keihin or Mikuni though.
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




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  15. #60
    Where I am planning will mean air and oil will come in together then will mix with fuel close to the inlet track, although the oil squirt might need to be a bit more directional now which is tricky......Will have to look at that.

    If I put fuel back in the throttle bodies, I will likely loose efficiency although it would oil mix very well.

    I guess that why they call it experimenting....Downside would be a seized crank though!!

    EDIT. I just reread what I posted and it is B******S......The SRIS system has 2 oiling methods. The pressurised feed from the pump is fed direct to the crank bearings and small ends. The remaining oil that doesn't stick falls into the casing and is pushed out via one way valves to appear again in the inlet ports. This then mixes with the fuel and lines the cylinder walls. SO the second part if my concern but I think there will be enough petrol wash to pick up the inlet oil and spread it around. I guess the temperature gauge and the blue smoke (or lack there of) will tell me!!

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