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  1. #1

    Coffman SuperJet 650 pipe on a 700?

    I am replacing my 633 SuperJet engine with a 701.

    Years ago Coffmans told me that the 650 pipe was for the 650 only, not the 700.

    But I have asked around and everyone I talk to says that it will work fine. In fact I see pipes being sold used as "Coffman 650/700 SuperJet pipe".

    Also I know that the Riva 650 pipe and the 700 pipe were the exact same pipe. Not that that has anything to do with a Coffman pipe but its interesting.

    I'm wondering if anyone here has any experience with these pipe and can let me know?


  2. #2

    Join Date
    Jul 2008
    Orange County, NY
    2 strokes require that the pipe be sized according to the engine size but I don't think a increase of what amounts to less than 10% will make a big difference. Ideally you'd want a pipe designed for a 700 but I'm sure the 650 one will be close enough. If you were going from a 500 to a 750 then it might be a bit of a problem and limit your power.


  3. #3

    Join Date
    Aug 2006
    They are only offering one manifold now days to save costs, but the 701 manifold(the part that is different from 650 to 701) has larger ports, and larger bolt holes in the flange that bolts to the cylinder. You can use the 701 one on the smaller cylinders, but the ports don't match so well (701 is wider) but it does seal, and run ok.
    In your case, you can drill your 650 manifold to the larger 701 bolt size, and port the manifold a little bit to make the port match better, but don't go too far or you won't get a good seal. I would use the Yamaha 650 exhaust gaskets, they are stronger and have that sticky seal stuff on them which will be better to ensure the water jackets seal. Also, you might have to find a couple of "Raider" exhaust manifold bolts, these have a flange washer built in, and also have a smaller than normal hex head. ITs a real tight fit on a couple of those bolts since you are going to the larger 701 cyl bolts. I beleive Factory pipe offers these special bolts, as well as Yamaha and maybe Coffman. Call them, they will know what you are talking about. Oh yeah, and if Coffmans pipe is simular to Factory, you will need one special Longer (3-4" or something like that) bolt in that 701 bigger size for that one corner bolt that goes thru the pipe too.

    PS SJ's are the bomb with bigger engines!!

  4. #4
    Great, thanks guys for all the advice. I got a lot more info about this here in 1 day than waiting on the pwctoday guys for almost a week. The info you just gave me would have taken me weeks to work through on my own. I know I would never have summoned the courage to fire up the drill.

    > They are only offering one manifold now days to save costs ....

    Which one are they offering, the 650 or the 701? I'm hoping its the 701, since it sounds from your description as though it would bolt right on to my new motor with no drilling.

    And by 'they', do you mean Coffman's? I am very surprised that they still carry these old items.

  5. #5
    I just realized I have posted this in the wrong section, this forum is for GPR and XLT only - sorry about that.

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