XB9 primary in a XB12

[Laroucheyves]

You'll get roughly 350-400rpm more at highway speed which is 120kph for me (75mph). It makes me want to shift into a 6th gear but I never seem to get it! :p lol Its not so bad though.

[Laroucheyves]

Here's a link to a step by step. Its not perfect but consider it as a good guideline to get your job done. Primary swap Helped me at least with the major steps although I did a few extra things in the process like locktighting and a few others.

[Laroucheyves]

It says on the discussion if you read the entire post:

the RPM at a given speed and in a given gear should be increased by a ratio of 12/11 based on the drive sprocket diameters. Currently I get 3000 RPM in fifth gear at about 63 mph. With this change I'd get 12/11 X 3000 = 3273 RPM at the same speed in the same gear.

I think its a bit more but whatever... its a good guesstimate 'cause its not exactly 12/11.

[Loki]

So you have more pull (tourqe feeling) in the lower gears? Easier to wheelie? Our bikes have never been speed bikes so thats ok but if i can get more pull out of lower speeds that would be awesome. Would it be better to get just a 9 engine or is the 12/9 parts make a great combo? How much would this cost and where would i get the parts?

[Laroucheyves]

You get more torque in every gear actually! A 9 engine would make your bike WAY less powerful!

IMHO, the max power you can pull out of a buell (xbr/xbs models obviously) without putting a turbo which is a little overboard is a 12 engine with 9 primary, a good aftermarket exhaust, high airflow filter and all the little mods like ngk plugs, breather re-route etc. all combined with a corresponding race ECM. Plenty of different race maps out there that you can mod yourself with ECM SPY without buying a RACE ECM. Check out the DIY section for details on how to do the entire ECM mod thing.