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     Tomd |
Hi, Of course I can't leave well enough alone, I find the stock gearing just a little too tall for me. Does anyone know if the smaller crank gear and shorter chain from the 9 engine will bolt on the 12? If my math is correct, that would get me about a 10% lower primary ratio. Since I keep it under the century mark in my old age, I figure I'm not going to miss much on the top and the wheelies around town will be even easier. :-) Oh, second question, Has anyone tried a lightweight crank gear? If you have, let me know what you think of it. How is the idle? Response? Let-off? Tom | ||||||||||||||||||||||||||||||||||||||||||
| Diablobrian |
you should be able to swap the entire primary drive without any problems. I have heard of people doing this in both directions for different reasons. I would be leary of swapping the crank due to balance issues (I could be wrong, feel free to correct me on this) the 12 rods are heavier, I believe, than the 9 rods. I don't know how much difference there is in piston weight. I have it on VERY good authority that you would do well by putting 9 (domed) pistons in place of your 12 (flat top pistons) Cheap way to increase your compression ratio. | ||||||||||||||||||||||||||||||||||||||||||
| Blake |
You mean the primary drive "sprocket" right? | ||||||||||||||||||||||||||||||||||||||||||
| Blake |
Diablo, I don't know who's authority you find so very good, but you cannot simply throw a set of XB9 version domed pistons into an XB12 and expect the engine to run well or reliably. The compression ratio would be more than just a little increased. Giving that kind of advice so freely and without any qualification is a good way to blow up someone's engine, yeah it would be cheap too. If you don't know yourself the details of this kind of work, please don't advise others that they would do well to do such a thing. | ||||||||||||||||||||||||||||||||||||||||||
| Diablobrian |
Henry Duga is my source. I figure Buell race support doesnt routinely give bad advice on engine upgrades. I did state that compression would be increased, and I figure that someone that has done enough research to know the primary drive ratios are different between the bike has a little bit of mechanical knowlege, or they wouldn't be attempting this intensive of mods. know what i mean? However, (mea culpa inbound) it is late and I am tired. I should have thrown in a warning about blowing the motor if done wrong and needing to run high octane fuel to avoid putting Gaping holes in the pistons when the motor starts pinging and detonating. 12 intake and injectors may also be required. YRMV  (Message edited by diablobrian on August 26, 2005) (Message edited by diablobrian on August 26, 2005) | ||||||||||||||||||||||||||||||||||||||||||
| Screamer |
Diablobrian, 9 pistons can be used in a 12, but it can't be run on pump gas. Cams with huge overlap are also recommended, which also requires fuel delivery which typically is beyond what the stock ecm or race ecm can provide. | ||||||||||||||||||||||||||||||||||||||||||
| Diablobrian |
Yeah screamer, so noted in my revision. The cams are required for top end hp however It didn't look to me like he was looking for monster top end hp, and it would appear Tomd is also trying to work within a budget or he'd just send the motor off to ...insert your favorite Buell/H-D specialty shop's name here... I could be way off base in my assumptions (yeah, I know never assume)  Or I could be off in my own little world. Insomnia does that to you. | ||||||||||||||||||||||||||||||||||||||||||
| Tomd |
Hi all, I'm trying to figure out if I can do a simple swap of the primary chain and the front primary sprocket to lower my overall ratios across the board. There was a lightweight primary front sprocket listed on one of the sponsors sites, I was just wondering if anyone here has tried one and if they have, did it make a difference or not. I don't want to split the cases and change the crank or pop the top end off and swap pistons so it will have a 14-1 CR and I have to run Sunoco 117 race gas. If this was a Sportster, I would just pop a countershaft pulley on from an 883, adjust the belt and ride. Since the XB's have a fixed belt tension, I'm pretty much locked into a primary change unless I want to start making components. Tom | ||||||||||||||||||||||||||||||||||||||||||
| Racerx1 |
I run all my bikes (1200's) with XB9 pistons. you get about 12.7:1 compression ratio without cutting the heads or cylinders. I run stock cams on my XB9/12 roadrace bike with the XB12 race ECM and run 100 octane unleaded with no detonation issues (fan is removed as well). I do run all aluminum cylinders however. My drag bike is a tuber with an XB top end and aluminum cylinders with XB9 pistons, and stock 'B' cams. I run it on 91 octane pump gas without detonation, but its always pretty cold when it runs...wouldn't necessarily recomend it for the street. The big thing you have to watch is piston to head contact between the intake pocket ridge of the piston on the front cylinder and the exhaust pocket ridge on the rear (the piston rocks forward at TDC so those are the tight areas. Very minimal clearance there, especially when using a multi layer laminate style gasket. I have seen contact in this area with a 0.040" MLS gasket, but never with the stock head gasket. I clayed it and its pretty tight, and thats on an uncut head. I now clearance the edge of the combustion chamber 'bathtub' by 0.030" and haven't seen an issue. Please note I'm not talking about the squish/Quench area, as there is plenty (too much) clearance there. | ||||||||||||||||||||||||||||||||||||||||||
| Dana P. |
Blake one thing...Wes doesn't run a programable Ecm.He runs the 12 ecm.And the race Module in his drag bike.But Race fuel is key.You'll have to run it. | ||||||||||||||||||||||||||||||||||||||||||
| Blake |
Thanks for the clarification Wes! 
(Message edited by blake on August 26, 2005) | ||||||||||||||||||||||||||||||||||||||||||
| Blake |
"He runs the 12 ecm and the race module"  May I assume you are saying that Wes runs the XB12 OEM Race ECM? What cams and what engine is he running? | ||||||||||||||||||||||||||||||||||||||||||
| Blake |
Never mind, I see the man himself set us all straight. Thanks Wes. Also note that my table above appears to be incorrect as it was based upon an apparently incorrect assumption that the squish face of the XB9 and XB12 pistons were co-planar and equidistanct from the wrist pin axis. Bad assumption. Or maybe some bad math?  Had an old spreadsheet that I modified to calculate the above, here it is..
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| Dana P. |
Blake reread Wes's post above again.He runs the 12 race ecm in his road race bike and the race module in his drag bike.Both run the 9 pistons he run's the stock I believe X1 cams that are B cams.Now is that better? | ||||||||||||||||||||||||||||||||||||||||||
| Fullpower |
to expand on the other portion of the original question: yes you can run the xb9 primary drive sprocket and chain pair with in the xb12 for. the net result will be 10 % more rear wheel torque at any rpm and in each gear. speedometer will still read true. wheelies will be easier, even to the point of being difficult to avoid. | ||||||||||||||||||||||||||||||||||||||||||
| Blake |
Thanks Dean. I agree that the best approach is to run the entire front & rear sprocket and chain. Partial reconfig will likely require a custom chain length. I don't know how easy or difficult that might be to obtain/accomplish for the primary chain. | ||||||||||||||||||||||||||||||||||||||||||
| Wyckedflesh |
As Dean pointed out, switching to the 9 primary sprocket and chain will give you 10% lower gearing, which means you will also run into 10% less top end speed. If you go with the lightened primary gear, keep in mind that you will hit redline faster as the rotating mass of the engine is lower. | ||||||||||||||||||||||||||||||||||||||||||
| Fullpower |
the primary sprocket AND chain are a direct swap from the 9 to the 12, when swapped as a combination. the only other part you need is some red loctite and a primary gasket. the diference is 4 teeth on the drive (engine) sprocket. the reduction in the gear ratio is exactly 1-(34/38)= 10.5%= 2nd gear roll on wheelies at 2000 rpm. be careful. one very nice thing about the primary gearing change is that it will not affect the speedo accuracy. | ||||||||||||||||||||||||||||||||||||||||||
| Opto |
Sounds like an interesting mod for those who don't need to exceed 120 mph, but want to get there quicker? Does anyone know if the XB9 clutch springs will fit the XB12 to get a lighter action on the clutch lever (for my partner) or is that just asking for trouble? | ||||||||||||||||||||||||||||||||||||||||||
| Dbird29 |
Opto, Put the Formula + tranny fluid in and you can use the even lighter springs from the '06 models. At least that's what we found out at the BRAG event in CO. DBird | ||||||||||||||||||||||||||||||||||||||||||
| Opto |
Thanks for that David, the 2004 Lightning parts catalogue I have doesn't show springs as such, just a big plate called a "SPRING, clutch" p/n 37929-04 for a 12 and 37893-02 for a 9. | ||||||||||||||||||||||||||||||||||||||||||
| Tim |
It is just one "spring" plate. | ||||||||||||||||||||||||||||||||||||||||||
| Cdrlmr |
I am glad to hear the 9 and 12 primaries can be swapped. I do most of my riding on the Interstate at around 80mph. I have a XB9S and wanted to lower the engine RPM while cruising at these speeds. It looks like I will have to get ahold of Daves to get some prices on sprocket and chain to do the swap. |
Chamber Volumes and CR