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  1. #1
    cmherrera's Avatar
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    How to turn my 1200 into a 1390?

    I’m starting on a new project on a GPR I just picked up. It came with a Riva motor that has been sleeved. The case and crank are shot so I’m starting new. What will I have to do to make this a 1390 monster? It has factory triples, MSD total loss, Novi 48, Riva heads & magnum pump.


  2. #2
    2000 GPRXP 4tec shooter98xpl's Avatar
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    Send your cylinders off to get bored out and renicked. I used Millenium for that, they did an awesome job on my cylinder. Then order you some pistons, I think Group K is the only one that sells the 1390 pistons, but I maybe wrong.
    Are you going to go ported? If so, you have Tim Judge or Lowell Horning that can port those cylinders for you. They probably rework the heads to fit the 1390.
    Crankworks did a great job on repairing my crank and the pricing was not bad at all, in fact, a lot cheaper than I thought it would cost me. Or if that cranks pretty bad, I know Dan @ waterworx (he posted a thread up in the FOR SALE section) has hot rod cranks for sale for around $550 or so, no core needed, and for another $30/40 he can have it trued and welded.
    From what I hear not a cheap job to get done. I would shop around for getting your cylinders bored out and renicked, price everything out and then go from there. Good luck with this project, i hear the 1390 triple pipers are well in the 85+++ mph range. Buy you a helmet and a neck brace, hahahaha.
    SHOOTER

  3. #3
    WATER WOODY's Avatar
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    A sleeved 1200 right? Not sure but i believe they bored the cylinders out too much for the sleeves to take them out and go Nicasil.Probably have to get new jugs.IM NOT 100% sure though.Someone will chime in.

    Lowell or TJ for boring/porting
    T&W crank (protec/crankworks)use yours as a core if possible
    cut oem head 150-160 psi
    different timing curve
    there are used cases floating around GreenHulk
    repitch on prop
    pump tunnel reinforcment
    DO NOT use an 800 grate till Jerry comes out with the SS ones!

    Thats some of the things

  4. #4
    cmherrera's Avatar
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    Click image for larger version. 

Name:	Cylinder 1.jpg 
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Name:	cylinder 2.jpg 
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ID:	48914

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    Here are the pictures of the Riva cylinder.

  5. #5
    Duke's Avatar
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    I think the sleeved cylinders can be bored to 87mm. Definately can't renick them tho, once sleeved it stays sleeved. The step in the top of the cylinder for the sleeve to stop on is huge.

    Give TJ or Lowell a call. They look like TJ's port design.

  6. #6
    cmherrera's Avatar
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    So to get 1390cc out of a 1200cc, you must bore out to 87mm?

  7. #7
    mrbtd's Avatar
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    Quote Originally Posted by cmherrera View Post
    So to get 1390cc out of a 1200cc, you must bore out to 87mm?
    Yep

  8. #8

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    Cool

    I think you should go with 1200 setup just redo,you have tripples,big novi's and other goody's ,get with jim's OR island for handling package
    what you have now sounds like s/s ski to make into rec. ski
    will take some tuning and change overall (will still be killer ski)

    later cd

  9. #9
    Duke's Avatar
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    Also you can't just bore and go, cylinders will have to be reported by a quality portsmith.

  10. #10
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    does any one have a# for lowell or tj
    or know how to get a hold of them
    thanks mike

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