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Thread: Anyone try a Parallel-Twin engine in FSAE?

  1. #11
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    TALKING TWINS.
    ===============
    A quick comment on terminology. Parallel-twins, aka In-Line-twins, I-2s, L-2s, etc., come in two main varieties.

    1. The "parallel" parallel-twin, which has both its pistons moving up or down together, and 360-360 degree firing intervals. So sometimes called an "even-fire" parallel-twin. This type has a primary "shake unbalance" equal to twice that of its single cylinders.

    2. The "anti-parallel" parallel-twin, which has its two pistons moving in opposite directions (ie. as one is going up, the other is coming down), and 180-540 degree firing intervals making an "odd-fire" parallel-twin. This type has its two cylinders' primary "shakes" cancel out, but they still add up to a primary "couple unbalance".

    Anyway, for clarity of communication it would be good to always refer to the different engines mentioned above as "360-degree I-2", or "odd-fire L-2", etc. So the AMG engine is a 360-L-2, while I think the Yamaha Genesis is a 180-L-2, and the Rotax ACE is also 180-L-2 (ie. "odd fire" according to MCoach).

    FWIW (and as mentioned by MCoach) given NA+restrictor+plenum, it should be easier to get consistent air-filling of the two cylinders of an even-fire(360)-twin than the odd-fire(180)-twin. On the other hand, it is easier to completely eliminate the primary unbalances of the odd-fire 180-L-2s, because only one balance-shaft is required, whereas two are needed for the 360s, same as with a single. However, both types of twin have exactly the same second+-order unbalances. In fact, the second-order unbalance of the twins is significantly more than that of a same capacity single, because the two smaller pistons (+ pins, etc.) are heavier than one bigger piston.

    Z

  2. #12
    MCoach, thank you for refreshing my memory, yes the Genesis is odd-fire. The second year the engine was ran a dual-plenum setup was used (don't ask about the first year....) and it apparently worked well enough to get hp on the dyno.

    Z, the Genesis is an "I-2" if I'm using your definition correctly, the pistons are side-by-side in the block.

  3. #13
    Quote Originally Posted by Z View Post
    FWIW (and as mentioned by MCoach) given NA+restrictor+plenum, it should be easier to get consistent air-filling of the two cylinders of an even-fire(360)-twin than the odd-fire(180)-twin. On the other hand, it is easier to completely eliminate the primary unbalances of the odd-fire 180-L-2s, because only one balance-shaft is required, whereas two are needed for the 360s, same as with a single. However, both types of twin have exactly the same second+-order unbalances. In fact, the second-order unbalance of the twins is significantly more than that of a same capacity single, because the two smaller pistons (+ pins, etc.) are heavier than one bigger piston.

    Z
    If you rev a single fast enough, above what speed does "pumping through the restrictor", or running a single stop being a detriment? Interestingly, pairing single cylinder, two cylinder, and maybe 3 (haven't had experience with those) cylinder engines with turbochargers has similar issues and it just becomes a non-intuitive process without a little math. All the traditional simplified calculations assume constant flow through all of the components, which is a laughable nonreality with these engines. Think a GT06 will be good enough for a single? Think again! Boost creep to the moon! And other adventures will small, interesting motors...


    Z, the ACE 600 actually did away with the balance shafts and just lives with the inherent shake that occurs. I mean, this is a rec(kless)reational personal vehicle. Why does a little shake matter? This isn't some perfectly balanced, drive your sweet, ol' grammy to the store vehicle!
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  4. #14
    Quote Originally Posted by MCoach View Post
    Think a GT06 will be good enough for a single? Think again! Boost creep to the moon!
    I know its not your primary point, but that problem is a really easy problem to solve with a whole host of approaches.

    I would really like to see modern 2-stroke motors like the BRP E-Tec engines allowed.
    Jay Swift
    Combustion Powertrain
    Global Formula Racing 2013-2014

  5. #15
    Of the engines proposed, it would seem the Kawasaki 650 twin would be the best choice. They are about $750-1000 USD on eBay, and have been developed for flat track racing to around 100 hp (unrestricted). Additionally, a twin vs. a single will reduced the instantaneous torque spikes through the drivetrain, and may increase traction at the tire contact patch.
    Brian Dondlinger
    New Publication: Vehicular Engine Design, 2nd ed. on Amazon and Springer.com

  6. #16
    How short some memories are!

    The Wattard engine, designed and developed by a Univeristy of Melbourne team led by William, now Dr. William, Attard was a 430 cc parallel twin. William wrote a number of SAE papers on this engine back 8-10 years ago.

    To the best of my recollection, there have only been four engines specifically designed for FSAE and FS competitions. The Western Washington Viking V-8 back in 2003, the Mahle 3-cylinder used by a handful of teams (not very successfully), the recent UAS Graz/AMG deigned 2-cylinder engine, and the Wattard engine.

  7. #17
    Quote Originally Posted by Michael Royce View Post
    How short some memories are!

    The Wattard engine, designed and developed by a Univeristy of Melbourne team led by William, now Dr. William...
    Not completely forgotten! Aluminum crankshaft, gasket-less cylinder head and exhaust plenums? We have read all of the papers .
    Jay Swift
    Combustion Powertrain
    Global Formula Racing 2013-2014

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