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Buell Motorcycle Forum » XBoard » Buell XBoard Archives » Archive through April 20, 2007 » Benefits of using an XB12 header pipe on a 9? « Previous Next »

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Tintin74
Posted on Tuesday, April 17, 2007 - 06:12 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I got my 05 XB9R used and it has a dent in the pipe header tubes. (Actually I saw several other XB with similar flaw but no other damage and I wonder how it got there).

There is a trend in the european Buellists to replace the XB9 header pipe by the wider XB12.

So before deciding to replace it ($200 parts & another $200 work) I'd like to raise the issue:

Anybody can comment on the benefits/drawbacks of this setting?
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Glitch
Posted on Tuesday, April 17, 2007 - 06:23 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I wouldn't do it unless I had some way of adjusting the ECM, like Direct Link.
What you're thinking of doing is going to alter the exhaust flow, by opening it up quite a bit.
I'm not saying you'll be screwing the pooch if you do it without adjusting for the extra flow capacity, but if it were me I wouldn't take the chance.
If you have a free flowing muffler, and an open air box, I definitely wouldn't go in that direction without being able to adjust for a lean condition.
Now, that being said, if you're going to run the original stock muffler and air box, your risk would go down quite a bit.
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Buellinachinashop
Posted on Tuesday, April 17, 2007 - 07:58 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Glitch hit it. My buddy wants to do this to my 9 and said exactly what he did. If you increase air flow, the ecm needs to be played with. I have the race ecm in mine, so he thought I'd be good without the tinkering as long as I didn't add an airbox cover with the grate on the front or holes in it like you see on some new carbon fiber after market covers.

(Message edited by BuellinaChinashop on April 17, 2007)
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Trojan
Posted on Wednesday, April 18, 2007 - 03:11 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Unless you ae planning on doing some moe tuning work on your bike in future then you won't gain any advantage running the 12 headers on your 9. In fact you may even lose some performance.

If you plan on doing some engine tuning as well (more than just an airbox & muffler) then go for it : )
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07xb12scg
Posted on Wednesday, April 18, 2007 - 01:56 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

It seems like this mod, even with proper adjustment, will kill your top end, but possibly give more low end grunt in theory anyway.
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Buellinachinashop
Posted on Wednesday, April 18, 2007 - 01:58 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

He'd probably have to port the heads as well.
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Xbeau12s
Posted on Wednesday, April 18, 2007 - 02:07 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

You could attach a 12 to that header you know. j/k but the same goes for all applications even on cars/trucks. If you go with an exhaust that is too big you will get too much backflow and can possibly damage something internal. I learned the hard way on an old VW GTI which I bought with 2.5" exhaust that someone welded in place. Went back to original size of 1-1/4 and Vroom, back in biz
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Strato9r
Posted on Wednesday, April 18, 2007 - 09:28 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I'll second, third and fourth everything already said. One of the most common mistakes made when choosing exhaust headers for either cars, or motorcycles, is to choose pipes that are too big for the engine displacement or intended torque curve. The common "proper" thinking states that there must be a certain amount of "back pressure" for a system to work properly. This is more or less correct, but, as stated on another thread, addressing the usefulness of those "anti- reversion cones", the critical factor actually lies in the exhaust gas velocity.
As exhaust gas leaves the combustion chamber, any restriction in it's flow path will increase the amount of power required to push the spent gasses from the engine. That would seem to make increasing the diameter of the header tube a good idea. The reality of the situation is actually quite contrary to this idea, however. If the tube is too large, the speed of the mixture as it passes into the port is the same, but as it enters the tube, the increase in diameter, and subsequently, volume, causes the mixture to expand, and in so doing, lose velocity. Bernoulli's Law states that, "As speed increases, pressure decreases", and this loss of velocity effectively increases the amount of power required to evacuate the exhaust gasses, as the high speed gas just slams into the slow moving, higher pressure lump in front of it. This is the phenomenon that increases the primary backflow that those cones and other gizmos are supposed to help prevent.
Assuming that the header tube is properly sized, the length of the tube, collector design and muffler all have their own effect. Generally speaking, a longer tube will favor power output at lower engine speeds, and shorter tubes, higher speeds. You may have seen primary header tubes on racing engines that are stepped; the diameter of the pipe increases as it gets further away from the engine. this is primarily done to keep the gasses at a constant speed as they loose thermal energy.
Ideally, the primary header tube should be proper length so that as the last of the spent charge passes into the collector, it leaves negative pressure in it's wake so that the next charge is actually "pulled" into the pipe, reducing the amount of power required to evacuate the cylinder, an effect known as "scavenging".
Aaaaaaaannnnnyway, the 12's pipe MIGHT work on a 9, IF the engine speed could be increased to the point where the actual pipe diameter could be warranted. Problem with that, is the length of the pipe would not be correct to match the engine's torque curve.
But, for some, I guess it's a visual thing. I once knew a guy that put a Kerker header onto a Kawasaki Z1-R, and after having the carbs re-jetted, that freakin' thing was a monster. A week later, he had the stock pipe back on it, for the simple reason that "The tubes were bigger".
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