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Thread: Suzuki GT750 EFI Special

  1. #1

    Suzuki GT750 EFI Special

    I am new to the forum so bear with me on posting issues.

    Over two years ago, having just restored an old GT750, I decided it might be fun to take one of those bikes and push the design as far as I could.

    Two years down the line and pending paint and final EFI work I have this.....

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    I wanted a suspended and tucked engine so started with a VFR 800 frame and designed new suspension/engine mounts to graft in the SS swing arm.

    I hated the front radiator on the GT so found a nice underseat Benelli Tornado option which meant adding the Benelli subframe and fans.

    Front end is Suzuki GSXR 750.

    Clocks are suzuki Bandit ....and there are various other bits from around 13 bikes now.

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    The main bike is Arduino powered (including the clocks) and includes;
    RFID ignition lock
    GPS
    Digital speedo and tacho
    Electric water pump and fan management
    Proximity sensor alarm
    SD card logging
    Real time clock

    The engine mods are broadly speaking;

    Ported near to TR750 specs
    Reed valves
    Dry clutch
    Close ratio gear box
    Custom exhausts
    Replaceable (tuneable) squish heads
    Zero deck O ring head

    For its first dyno run I have carbs fitted but have started an EFI project with a speeduino.

    I have also managed to get a set of Triumph Tiger throttle bodies working with fly by wire throttles so plan to use them in the EFI.

    I've got to the point with the speeduino where the basic ignition is kinda working except the spark modes I can find dont allow me to run 3 independent ignition channels which is my first hurdle.

    I've done lots of reading especially on TZ350 excellent thread here (and still have lots to read) and am just getting into the fuel planning for the EFI. I believe the summary of what I have read includes;

    1. Although my engine is relatively low revving (8.5k peak power), throttle body injectors probably wont work so I need transfer port injecting
    2. The Kettle has two ports so do I need one injector per port? I assume so?
    3. Best position is probably to squirt under the piston
    4. For smooth running I may need to consider TZ350's pseudo MAP approach, so a MAP sensor in one cylinder under the inlet reed is probably best?
    5. From a injection timing perspective, is it better to start injecting on the down stroke or wait until BDC and then inject until the transfer closes to get best mixing?
    6. I probably need an injector flow of around 300cc
    7. Given my rev range I shouldnt need staged injectors (small/large) although bottom end response might benefit from it.
    8. With my Spark and VE tables on my Alpha N system, keep the steps leading to peak power fairly short

    As I get into the injector choice/setups I am sure there will be more observations/questions, the first one that springs to mind is how much fuel am I trying to inject at each squirt and what calculates it?

    I will post some more detail of the build thus far and the EFI work as it goes on.....Hope this helps...

  2. #2
    Join Date
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    Welcome to the crazy zone.

    Nice work you've done there.

  3. #3
    Join Date
    18th May 2007 - 20:23
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    Hi Kettlekev. Looks a very interesting project. I am impressed with the quality of your work.
    .
    Quote Originally Posted by Kettlekev View Post
    From a injection timing perspective, is it better to start injecting on the down stroke or wait until BDC and then inject until the transfer closes to get best mixing?
    Think in terms of where to end the injection cycle. Setting the "Ending" somewhere between BDC bottom dead center and TPC transfer port closing seems to work best.

    The engine will run smother and smother as the time (measured in crankshaft degrees of rotation) increases to the point where the injection cycle covers the time the transfer ports are open. Use the smallest injector possible to get the longest injection cycle that will fit inside the maximum RPM time limit. The injection cycle could eventually stretch out to nearly 360 deg of crankshaft rotation at say 9k RPM. An injection cycle includes opening, injecting, closing.

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    These are two injectors in a 350cc Kawasaki singles crankcase "C" port wall. They are fired together as one logical injector. This injector position worked very well in the big single.

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    The drill indicates the firing position of my transfer port injection in the air cooled 125. This combined with under piston injection for staged injection also worked very well for a high revving 125. And is my favorite but hard to replicate on a water cooled cylinder.

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    This is my "B" port and "C" port under piston injection on a water cooled cylinder.

    The "C" has the small injector and the "B",s are fired together as one big logical injector for staged injection.

    KTM's does their staged injection by alternating the "B"s and then firing them both together when they need a bigger logical injector.

    This works because there is always some residual fuel floating around in the crankcase. It seems that it takes something like 6 to 10 crank cycles to completely flush the crankcase. So injecting just maintains a working average of air/fuel ratio in the crankcase.

    Personally, for the GT750 engine I would use a single injector a cylinder and look to copy the 350cc Kawasaki or fit the injector in the reed block between the reeds and crankcase.

  4. #4
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    Cool bike.......
    I just boiled the kettle
    It reminds me of a modern silk/scott
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  5. #5
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    13th June 2010 - 17:47
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    Very nice work indeed.

    Does your engine still have the oil draining crosslinkage between the crankchambers ?

    I'd be tempted to block that off on the grounds that it could produce conflicting or unreliable signals on your sensors.
    It may not of course. I'm not qualified to judge. But that feature is I believe unique to those engines.

  6. #6
    Thanks for the feedback guys...

    So I guess throttle body injection even with reeds just isnt going to get the mixing right even though I am lower revving but squirting just the other side of the reeds and still into the inlet port might work (if I am understanding TZ350's post)?

    I have a spare barrel so will start looking at places to inject. I think there may be some space to do it more like the Kawa 350 so will post some photos later. I will also try to squeeze a MAP sensor feed in to one cylinder just in case I need it. I guess the sensor can be remote (end of tube)?

    My current issue is with Speeduino/Tuner studio in that there are settings that allow the injectors to fire in sequence (1,2,3) at 120 degree intervals but the spark options (for crank only sensing) either pair the ignition circuits (1&3, 2&4) or put them all on cylinder 1, so I cant get 1,2,3 in sequence. I need to get this one sorted first.

    Yes I am still running the SRIS oil scavenging system and the mechanical pump, it is way better than premix and I dont think it will mess with any sensing but we will see.

    I clearly need to get my head around some injector volume/timing maths but will do that in another post......

  7. #7
    Having played with Tunerstudio/Speeduino settings a bit I think this is the only way to fool it to be a multi (3) cylinder 2 stroke?

    Any thoughts anyone?

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  8. #8
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    Quote Originally Posted by Kettlekev View Post
    Having played with Tunerstudio/Speeduino settings a bit I think this is the only way to fool it to be a multi (3) cylinder 2 stroke?

    Any thoughts anyone?

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    I have only worked with single cylinders but 6 cylinders and wasted spark looks good for (a single trigger and) 120 deg firing order for a 3 cylinder two stroke.

  9. #9
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    .

    If you do decide to try to work with crankcase pressure as a pseudo MAP reading.

    For a crankcase pressure sensor you could use the same type (2.5 bar MPX4250) pressure sensor that the Speeduino uses.

    I use a 2.5 bar sensor left over from my Ecotrons days.

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ID:	348223 Mount with a short tube 2 to 3 cm long. Angle it down so that it drains.

    My sensor puts out a reading every ms for 1 ms. I expect the MPX is the same. You will probably get a reading like this.

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  10. #10
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    Quote Originally Posted by Kettlekev View Post
    So I guess throttle body injection even with reeds just isnt going to get the mixing right even though I am lower revving but squirting just the other side of the reeds and still into the inlet port might work (if I am understanding TZ350's post)?
    Yes ......

  11. #11
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    Dont waste your time and money with TBI.
    If want to introduce the fuel at the TB, use a carburetor

  12. #12
    Thanks guys. Port injection it is then.

    I will hack my development barrels and post some images.

    I am trying to get my head around fuel load/injection timing now and will post a spread sheet later.

    BTW does anyone know a link to a Keihin injector spec sheet website? I cant see anything on line. I have some GG12 (pink dot) injectors and would love to know the specs.

  13. #13
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    Quote Originally Posted by Kettlekev View Post
    Thanks guys. Port injection it is then.

    I will hack my development barrels and post some images.

    I am trying to get my head around fuel load/injection timing now and will post a spread sheet later.

    BTW does anyone know a link to a Keihin injector spec sheet website? I cant see anything on line. I have some GG12 (pink dot) injectors and would love to know the specs.
    https://www.injectorrx.com/fuel-inje...uel-injectors/

    gg12 is showing up much? any other numbers?
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  14. #14
    Thanks, I did see that one but I think it is for a different injector type. Mine come from a Tiger 1200 and the only number on it is GG12. Will keep digging.

    Just for fun I have been trying to understand injector maths....I am sure there is a simpler way to do this and I am probably missing something major but with the end goal to define when to stop injection at the various rev numbers, I came up with a auto calculating excel sheet. I cant seem to attach it? but here is a screen shot.

    Caveats are;
    1. I dont have definitive injector specs yet
    2. I am not sure of the required fuel number (see comment)

    Anyway I am sure someone will correct or it may actually be a useful exercise??

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    If anyone is interested I can email it unless there is another way to attach?

  15. #15
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    https://injector-rehab.com/knowledge-base/flow-rates/

    *Disclaimer about Keihin numbers. These numbers do not represent a Part Number, but yet a manufacture date and batch codes. There is no way to tell the flow rate of a Keihin injector by the number alone!
    email these guys with a few pics of your bike and i am sure they can help they have most others listed.
    http://www.factorypro.com/about/indexabout.html
    the other option is just measure them yourself.




    or just get someone to test them..
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

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