Paul,

    I think everyone can agree that the rotary conversion needs a
    cost-effective fuel system that does not involve spending thousands of
    dollars.

    When we start with a stock Mazda engine we have an immediate problem
    with cowl clearance with the bulky intake manifold. This can be solved
    two ways -- either fabricating a new low-profile manifold, or cutting
    peripheral ports into the housing and adding a couple of tubes onto
    which we can mount two motorcycle carbs.

    If we don't want carbs, two runners can easily be made that loop over
    the top of the engine. Similarly for the carbs, the velocity stacks can
    loop over the top.

    I think the p-port is a very attractive option in this regard, in terms
    of time and effort -- compared to fabricating an intake manifold with
    four to six runners. Plus you get a good shot of extra power in the
    bargain.

    Now that we have air, a lot of options have been suggested for fuel --
    everything from your slide throttle carb, to EFI, to mechanical
    injection, to motorcycle carbs, to the picaxe with mass flow sensor (and
    I'm probably leaving out a few others).

    You have complained about the high cost of the motorcycle carbs. The
    Mikuni HSRs can be bought new on ebay for $370 apiece. That's less than
    $750 for the two. The Keihin CV 51s go for about $450 apiece.

    Is that too much? How much does an aftermarket ECU cost? More than that.
    Even the smallest Ellison costs $825 -- you would need two.

    Now what about your ultimate DIY ideas -- the slide carb and the picaxe
    computer. The slide carb sounds like a fine idea, but this is hardly a
    proven carburetor. It has never even run on an engine, we don't even
    know if it is going to leak fuel, much less how well it will actually
    meter fuel.

    Yes, with a fuel injection system, using the slide throttle just for air
    is fine. But as a carb, this is a long-term development project at best.
    Are you really saving anything if you spend many hours tinkering with
    this and getting it to work.

    And what about the picaxe? This uses the mass air sensor to meter fuel.
    What happens if the sensor fails? Your engine stops, that's what
    happens. At least with the mega squirt and Tracy's box they are not
    wholly dependent on a single sensor. And this too is something that's
    going to require a lot of hours to develop, write the code, build the
    box with connections etc.

    Neither of these options is even remotely realistic for the average
    amateur airplane builder who simply wants a reasonably-priced engine
    that is going to run dependably from the get go.

    Even a megasquirt or an aftermarket ECU is not ideal, in my opinion
    because it relies on the electrical system for getting fuel to the
    engine. This may be fine for your car, but it is not great for a flying
    machine.

    I think you would be doing the whole rotary community a great service if
    you concentrated your efforts on building and testing a p-port engine
    with motorcycle carbs and a flywheel magneto. This would be a true
    aircraft engine using proven, simple technology -- and people would then
    have a viable option to a Lycoming, which is mostly what they want.


    Regards,

    Gordon.

    Nice summary. A couple of corrections. You don't need a mass air
    flow sensor
    with the PICAXE as you can use the same solid state manifold
    pressure sensor Tracy
    uses. The PICAXE is so cheap ten can be bought for the price of
    Tracy's system.
    However it requires a bit of computer expertise to use them. Same
    goes for
    the Megasquirt but it is a bit more overkill and a lot more
    expensive than
    the PICAXE.

    I am not really serious about the dual carb system using the slide
    throttle and needle
    valves. It would require a total redesign and much R&D. On that we
    agree.

    Changing Doc's oblong slide for a round hole slide with the ramp system
    is my leading choice. That was the very first idea way back when.
    That combined
    with some sort of adjustable fuel pressure regulator is super simple
    and no
    functionally different than dual Mikuni 48 mm. It uses regulated low
    pressure
    instead of vacuum to inject the fuel. I will probably test it on the
    RX8 p-port
    engine.

    Forget smaller carbs. If you are going to go to the trouble of
    building a p-port why
    shoot your self in the foot by going to smaller carbs to save a few
    bucks. I don't
    recommend any carb shy of 48 mm as you will take a big HP hit. See
    the enclosed
    dyno chart for both the Power Sport p-port engine with 1 3/4 inch
    dia. 28 inch long
    runners and the ACRE p-port engine using the 2 inch dia. 28 inch
    long runners.

    Carbs also have the drawback of having to devise a way of leaning them.

    The Mikuni 48 mm is also not easy to tune with several jets that
    must be adjusted
    in size. In fact most carbs are over kill as far as the accuracy of the
    mixture over a wide range of conditions that are not found in
    aircraft use.
    One example is the accelerator pump. Aircraft engines do not accelerate
    at the same rate as car engines due to the rotational inertia of the
    prop.
    Aircraft engines spend the vast majority of the time at WOT with one
    load.
    Starting mixture enrichment can be accommodated by increase the fuel
    pressure.

    BTW turn the engine over with the starter BEFORE turning
    on the electric fuel pump or the engine will flood.

    With Teflon O-rings the round hole slide with the ramp system will seal
    perfectly however sealing perfectly may not be needed as the only
    way for
    leaking fuel to get out is into the engine. No different than the
    slide throttle
    with electronic fuel injection. Same situation.

    Paul Lamar ...No rotor no motor.

Paul,
Thinking about your slide Throttle, I was wondering if you looked at the
Revmaster ( Revflow Injector Carb) revamped Posa design as is the Aero carb.
The Revmaster uses slide technology with fuel metering by way of needle into
a seat, the needle goes through the slide, the seat is at the bottom. The
needle can be remotely adjusted for mixture or fuel cut off via Vernier
control. The slide is directly controlled by a toothed wheel , with cable to
vernier slide. Very simple and could be easily incorporated into the your
slide throttle. Might be worth looking at.
George ( down under)

Send me a scale dwg.