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  1. #1
    fastkaz's Avatar
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    Flat to Pistons & Oem

    what is the differenece between flat top pistons and oem pistons? and what do you have to do to run flat pistons..just installed them? are any doms needed to run it to get all of the power out of it? runin a gp1200r jetted carbs


  2. #2

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    Flat top pistons are just that - they have flat tops. You need flat top piston domes (in an aftermarket head) to run them. The cylinders also need to be decked and resleeved. They're normally used in a superstock/race gas set up although you could get someone to cut lower compression domes from blanks to be able to run 93 octane. In other words, you can't just swap your pistons to be able to use them...

    PM me if you're still interested in going that route though - I have the pistons and cylinders and domes for sale for less than 1/2 the price of new ones but they only have about 10 hours on them. Race gas is too damn expensive here in Japan.

    enjoy,

    Ray

  3. #3
    Duke's Avatar
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    Ski will run but not very well. The cylinders have to be decked to get proper squish and proper domes need to be cut to desired CC. Not exactly a straight easy swap.

    Don't know why the cylinders would have to be sleeved though, didn't used to be required.

  4. #4

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    Mine are Riva/Farthing ported cylinders. If I'm not mistaken, they deck on the bottom, not the top and the sleeves need to be pulled to do that. Then they resleeve so that you can bore them out as needed.

    I suppose you can deck the top but I'm not sure how that will affect the porting. Wouldn't you have to pull the nikasil sleeves out for the decking either way? At that point, it makes sense to resleeve them - at least to me anyways...

    But I confess to not running flat tops on stock cylinders so I might be speaking out my ass here...

  5. #5
    Duke's Avatar
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    Quote Originally Posted by RayinJapan View Post
    Mine are Riva/Farthing ported cylinders. If I'm not mistaken, they deck on the bottom, not the top and the sleeves need to be pulled to do that. Then they resleeve so that you can bore them out as needed.

    I suppose you can deck the top but I'm not sure how that will affect the porting. Wouldn't you have to pull the nikasil sleeves out for the decking either way? At that point, it makes sense to resleeve them - at least to me anyways...

    But I confess to not running flat tops on stock cylinders so I might be speaking out my ass here...
    On an OEM cylinder there aren't any sleeves. A good machine shop can remove the needed material from the top or bottom without pulling anything. The problem with taking it off the bottom is you alter the port timing by dropping them down, cutting the top changes nothing.

    Nikasil coated cylinders are actually stronger and less likely to score then cast iron sleeves. If this were to be a rec ski I would definately go with the nick.

    Depending on what head you have now, there is a possibility of getting recessed domes designed for the FT pistons and not have to do anything to the cylinder. I think ADA will make these or at least they used to.

    Not trying to discredit you Ray, this is just what I remember from helping Bo Dupriest.

  6. #6

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    You can't discredit me any more than I do that myself Duke. It's been 4 years since I last pulled an OEM cylinder so it's very possible that I'm very wrong. I thought for sure the nikasil was a "sleeve" though albiet a very thin one that can't be bored out if you sieze it...

    All things considered, I'm not sure going through the hassle simply to run flat tops on pump gas in a stock cylinder is worth the trouble. I'd be interested in knowing if anyone has done it and how it has worked for them...

  7. #7
    cheatin' piston popper addicted's Avatar
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    just out of curiosity, what is the advantage of flat tops compard to domed pistons?

  8. #8
    Duke's Avatar
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    Quote Originally Posted by addicted View Post
    just out of curiosity, what is the advantage of flat tops compard to domed pistons?
    Duh, they make more power.

    JK, for whatever reason wether it be flame travel or increased speed of fuel delivery out of the transfers they seem to make more torque. I watched Bo go to a set of flat tops and not even have the right head on it yet and the 0 to 70 dropped noticably. At that time he was taking OEM pistons and having the domes recut to a 2 or 3 degree top, can't remember.

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