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  1. #1

    66v x 2 = 4 cylinder?

    Hi everyone

    I had an idea recently. I was thinking that it would be possible to make a 4 cylinder out of 2 chopped 3 cylinder engines.

    basically since the cylinders are all separate you need not worry about the cylinders, or heads. the only big hurdles would be the engine cases and the crankshaft. since the cranks are all just pressed together from parts, its a lego's solution. take it apart, retime it to a good 4 cylinder crank firing order,and re assemble all the parts to make a 4 cylinder crank.

    the cases could be made by a cut after the second cylinder on one set of cases then machined clean, along with a similar cut on the remaning set of cases AFTER the second cylinder. simple machine them clean, and bolt them together for some welding. you could even stagger the cuts, make the top and bottom cases different so the loads are more evenly distributed.

    the last part is the exhaust and intake, which is suddenly easier, a simple side draft setup intake manifold, and the exhaust could be made simple with a manifold designed to utilize the factory exhaust pipe and whatnot.

    if 155/3=51.6ish then 4*51.6=206 hp.. add in the normal speed tricks and you could REALLY have some power at a weight much lighter then a 4 cylinder.

    ignition is really a non issue since simply 2 800 ignitions could be used, but reality would be alot cheaper if an aftermarket 4 channel ignition were to be used.


  2. #2
    Paul2005GPR's Avatar
    Join Date
    Oct 2009
    Northern Illinois
    would you use two 800 exhaust systems for the exhaust?

  3. #3
    Quote Originally Posted by Paul2005GPR View Post
    would you use two 800 exhaust systems for the exhaust?
    I could but that would likely take up alot of space. Id rather just make a new manifold or modify the 3 cylinder manifold to make it a 4 cylinder unit. I would maintain the rest of the 3 cylinder exhaust system. in effect you CAN utilize the 3 cylinder exhaust as it is single wave tuning, not a harmonic tuning. (atleast thats what the expert of 2 stroke pipe software wizard has told me)

  4. #4
    PolarisNut's Avatar
    Join Date
    Dec 2006
    Lower Michigan
    Too much trouble for a theoretical 200hp, when you can get that with a big bore 1450 3 cyl motor. You won't get a 4 cylinder 2 stroke to run well on a single pipe, especially one designed for a 3 cylinder 1200cc engine...If you ran 2 twin cylinder single pipes, you'd get a significant amount more power (basically double what the 800 66e motor makes ~240hp). The only 4 cylinder 2 stroke I've ever seen (other than an outboard), was the Yamaha VMax 4 snowmobile. It was basically designed as 2 twin cylinder engines, running two pipes.

  5. #5
    AWA Member 32DegH2O's Avatar
    Join Date
    Aug 2006
    Minneapolis, Mn.
    Randy at Watcon did this to 2 Polaris triple cylinder engines. The tough part of course is making the cases. You keep the back of the eninge at the same location as stock that way there is nothing you have to change with the driveline. Obviously this pushes the engine forward so you make yourself a custom gas tank which is much easier to do than fabricating new driveline components.

  6. #6
    Spark timing will be a drama as the stator is set up for 3

  7. #7

    Join Date
    Oct 2009
    I have a buddy that does these conversions on snowmobiles. He has bolted 2 670 rotax motors together. He is in the process right now of adding a 4th cylinder to a thunder cat 3 cyl. Sounds harder than it is. You Need $ to do the project or a bunch of spare parts.

  8. #8
    txgp1300r's Avatar
    Join Date
    Apr 2006
    Dallas , Texas
    .....even if you had 1000 H.P. in your ski , you still are funneling it through the pump at 155 would be cool to have a giant tunnel so you could use a 14 inch boat prop like a mercury tempest or trophy....there is a member here who put a mercury v-6 in a ski , not sure how it ran,but im sure it sounded wicked.

  9. #9
    Fat Man, Little Boat Region8Ultra250X's Avatar
    Join Date
    Jun 2007
    zapata did this before on one of his GP ski's.... it was two 951 motors sandwiched together.

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