| Author | Message | ||
     Readyxb |
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:  | ||
| Sagehawk |
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? | ||
| Phelan |
The xb9 and XB12 pistons I have measured within .003" for crown height (obviously not the same dome height). | ||
| Portero72 |
Curious as to what year and model bike you are working with, as well as how you are going to tune it. | ||
| Readyxb |
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:
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| Readyxb |
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? | ||
| Readyxb |
Sagehawk - I'm curious what you meant by 'reverse dome'? | ||
| Phelan |
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. | ||
| Ducbsa |
I assumed he meant the underside of the crown. | ||
| Sagehawk |
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. | ||
| Portero72 |
Updates or it never happened! | ||
| Phelan |
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. |
