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Readyxb
Posted on Thursday, July 27, 2017 - 08:51 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

One of my current projects is to replace the pistons in my XB12R with those from an XB9. There are several threads discussing the reason, which is to get a nice bump in compression. But I haven't seen documentation on the difference in piston weight, so I thought I'd add that for the community.

A stock XB12 piston with wrist pin, retainers, and rings weighs approx. 466g. This is one of the pistons from the bike.



A stock XB9 piston with wrist pin, retainers, and rings weighs approx. 474g. I weighed a second new XB9 piston assembly and it was within 1g of the first.



A difference of 8g is not as big as I was expecting. That's the same weight as one 25 and 10 coin together. But, I'd like to bring the weight down a bit to more closely match the XB12 piston weight as I imagine that the rotating assembly is somewhat balanced (or close to it) from the factory.

There's really not a lot of extra material to safely work with for weight reduction. In this picture, it may look like the right-hand side of the skirt is thicker than the left, but it's really isn't; just the lighting of the photo.



Current state of affairs:
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Sagehawk
Posted on Thursday, July 27, 2017 - 10:05 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

find a way to measure the piston crown thickness. more material on 9 piston , reason for more compression. the reverse dome area on 12 piston is lower compression but probably more detonation resistant. wrist pin to top of piston would be a way of determining a distance. will 12 head take the 9 piston?
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Phelan
Posted on Thursday, July 27, 2017 - 10:26 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

The xb9 and XB12 pistons I have measured within .003" for crown height (obviously not the same dome height).
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Portero72
Posted on Friday, July 28, 2017 - 08:08 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Curious as to what year and model bike you are working with, as well as how you are going to tune it.
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Readyxb
Posted on Friday, July 28, 2017 - 07:33 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)


quote:

will 12 head take the 9 piston?



It has been done. Here are a few threads talking about this "upgrade":
1. XB9 pistons in XB12 motor......why?
2. XB12 Motor write-up thoughts (long and not 100% complete yet)

Per the first link, Erik Buell Racing mentioned the piston swap as an 'inexpensive' power upgrade:

quote:

XB9 pistons bolt right in with no other changes, and they increase the compression ratio. You really must run premium fuel, and a good race map, but it is a very inexpensive power upgrade without the risk of higher RPM's which are the kiss of death to 1200's.


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Readyxb
Posted on Friday, July 28, 2017 - 08:09 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)


quote:

Curious as to what year and model bike you are working with, as well as how you are going to tune it.



2008 XB12R. I will retune the fueling as I have done in the past, with two o2 sensors in the front and rear header and lots of datalogging. Ignition timing is a different animal, and I'll leave that alone at least initially.

My other projects for this bike are to pick up the 2010 model year functional changes. I already have dual o2 headers, but I'll also get (eventually):
- P0130.7AA fuel pump
- P0268.7AA fuel rail
- P0221.1AM fuel pressure sensor (discontinued0
- M0854.7AA right-side 'mini-scoop'
- H0110.1AMCZT black ZTL2 caliper assembly
- H2531.1AM front brake line
- H0507.1AMD master cylinder
- Y0401.7AC LED taillight w/ Y0514.7AA license plate light
- Y0526.7AA and Y0527.7AA diamond-shaped turn signals w/ clear lenses (I've heard these referred to as LED, but they appear to have standard colored bulbs)
- 2010 wire harness that will have to be adapted from either a Ulysses or Lightning model because the 2010 Firebolt wiring harness has been discontinued. I've already modified a DDFI3 harness for dual 02 and dual MAP/Baro (with only 1 in use), but it has wear from lots of experimentation.

There was some Mfg update to the P0278.4A8A head temperature sensor, but I'm not sure what was changed. Anybody know?
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Readyxb
Posted on Friday, July 28, 2017 - 08:57 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)


quote:

the reverse dome area on 12 piston is lower compression but probably more detonation resistant



Sagehawk - I'm curious what you meant by 'reverse dome'?
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Phelan
Posted on Friday, July 28, 2017 - 10:39 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I'm guessing he saw the dome on the 12 piston and mistook it for a reverse dome because of the angle of the photo.
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Ducbsa
Posted on Saturday, July 29, 2017 - 05:47 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I assumed he meant the underside of the crown.
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Sagehawk
Posted on Sunday, July 30, 2017 - 06:54 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

My bad. This left hand thing and married to a artist as well , sometimes I take what I see first and interpret it. The way it is pictured , I thought I saw a reverse dome there. After looking at it, it's not. Sigh!I've never had my heads off of my 12 , so I have just Deen pictures. The are so many different configurations in the motor world that anything could be possible. I've tagged performance engineering on facebook, and they showed a cylinder that was questioned about a larger bore for the bike. But that would take out the fire ring in said cylinder. Haven't heard the word fire ring in years. 78 Husky 390 2 stroke I had I guess would qualify for that.
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Portero72
Posted on Saturday, August 12, 2017 - 09:21 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Updates or it never happened!
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Phelan
Posted on Saturday, August 12, 2017 - 10:28 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I've put XB9 pistons in several bikes, though usually I shave about .050" off the domes and round the edges to avoid hotspots, as well as flatten the eyebrows on the valve pockets. Most commonly I put these and re-timed XB cams in XL1200 Sportsters for a hefty compression and cam bump. Even with stock heads, these bikes make nearly 100 RWHP in this setup with proper intake, exhaust, and tune.
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