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Thread: The XB4R build begins...

  1. #21
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    Huh, weird. 515 + 515 = 1030 so how does a 1030 kit equal a 1050? Also, an xb12 has the same bore as an xb9 but there is an obvious difference in the engine displacement. I'm just trying to understand how it's possible for different cc kits to be the same. Also the blast kit is made for the blast head which is different than the xb head which is what I'm using. The xb9 piston is done shaped, higher compression than the blast but the blast has the same bore and stroke as the xb9 but uses a flat piston which is where is loses compression but keeps the cc and also it is exactly half the cc displacement of the xb9

  2. #22
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    The stroke is longer on the 12 than the 9 and blast. You have to use bore and stroke to figure out your displacement.

  3. #23
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    Yes, I understand that exactly. That's why a 12 has more power using the same cylinder and heads as an xb9. Because it uses a longer stroke and a flat piston to keep compression high. I'm not confused by that, I'm confused about how a blast 515cc is the same as half an xb9 1050cc which is 525cc

  4. #24
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    Its in the naming. An XB9 is closer to 1000cc than it is 900cc (984cc, but you know that); they're just rounding the cc's (incorrectly, I might add).

    I know XB's have a different head design than the Blast, I'm using an XB9 top-end in my Blast.

    I was merely pointing out that between the two kits, the displacement of each cylinder is the same.

    Stock bore is 3.5" (88.9mm)
    515/1050 kit is 3.5625 (90.49mm)
    Stroke is 3.125" (79.37 mm)

    Displacement (doing the math (pi*(bore/2)^2*stroke)/1000)
    Stock Blast 492.663cc
    Stock XB9 985.326cc
    515 Blast 510.443cc
    1050 XB9 1020.886cc

    There's the real displacements of the engines.

    Going for half of a 1050 kit would be the way to go, IF you already have an XB front head; and IF the shop is willing to sell half a kit.

    FWIW - The shape of the piston/head have no bearing on the displacement of the engine/cylinder, only on compression ratio. Displacement is determined solely on bore and stroke, as in the above examples and calculations.

    Because it uses a longer stroke and a flat piston to keep compression high
    It uses a dished piston to keep compression DOWN, not high. If the 12 used the same piston as the 9, it would have an ~12:1 compression ratio. Buell gave it a dished piston to counteract the longer stroke to keep the compression ratio at a more reasonable and reliable 10:1.


    Going by Harley's retarded rounding rules, the Blast should be a 400, not a 500...or the XB9 should be an XB10.

  5. #25
    Ok this is some real engineering, I'm all over this like white on rice. More balls than most! Go for it. I realize were not talking uncharted territory here but this would make a hellified Bonneville bike! If this is lighter than a stock Blast this will be a crap ton of fun to ride.
    MORE PICS

  6. #26
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    It's essentially an engine swap on an XB9, most of the mounts already line up. A little fab is needed, but it's certainly not some amazing feat of mechanical engineering. The most difficult part will be getting the ECU to work properly without the rear cylinder, which is electrical. If you want Blast engineering, that's elsewhere.

    Not talkin' down on the swap, if I had the parts I'd do it in a heartbeat. Also a huge fan of the color choice, the only XB-R colors that should've ever been offered, imo.

    Do you have an XB-R front end, or using the Blast?

  7. #27
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    Xbr front, doing a tail swap to an s though. So far problems are the trans shaft have different teeth than the xb pulley, and there is no idler pulley mounts, no kickstand mounts, primary cover isn't exactly a direct fit. But that's just what I have so far. FedEx just called me, squidbuellies parts just arrived at my house

  8. #28
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    What are you doing with the XBR tail?

  9. #29
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    I'm swapping with a guy, but his only transportation is his bike so I have to wait till he can do the swap. Supposed to be around beginning of August I guess

  10. #30
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    For an update, still waiting on a few engine parts and just realized that I didn't order the gaskets for the cylinder and such. I tried a test fit for the frame and front end which healped me find out that I need new steering head bearings and a new front axle because it's bent. The rear shock isn't attached so the rear looks low because of that. I have the fittings needed to make my own oil lines to work with the '07 swing arm. Also attached new fittings for the oil cooler.




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