Buell XB9/12s/r/x

By Enthusiasts for Enthusiasts

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The XB Engine's are already quite highly tuned compared to the "standard" sportster engines they are based on. The XB9 is the engine to have if you want to build a bike with hp and higher revs, whilst the 12 is the better engine for torque and all out grunt! So if you're starting with a good engine, it won't be easy to get any cheap gains? Or will it?

These pages currently concentrate on bolt on style mods, which can be completed by a competent mechanic with reasonable tools. They do not include any mods inside the engine, but may do so in future, with assistance from other members of the forum.

There are 3 main elements to tuning an engine, Getting the fuel in, Making it go bang! Then getting it out again! All of these can be improved from standard as we are not constrained by environmental and noise emissions regulations in the way the factory are.

Airbox Mods

Snorkel Removal - The earlier XB's (Pre 06) have the inlet routed in through the left frame beam. Inside this is a rubber snorkel, which can be removed to provide greater airflow into the airbox. This is a standard mod as recommended by the Buell race kit and best of all...... it's free!

9 to 12 Airbox Mod - The early XB9 airbox had a flat top, whilst the XB12 has a vortex in the top to guide air into the throttle body. Replacing the early XB9 inner airbox lid with the one from the 12, has been known to provide performance improvements.

Hole Saw Mods - Possibly one of the best cheap/free mods you can perform. This has now been replicated by the factory on the newer 2006 and 2007 XB's. Greater airflow into the engine will generally give greater hp figures, but can result in a slight drop in torque at low rpm.This is from the official Buell Technical Forum, showing the additional holes in the 07 airboxes.


Ultimate Airbox - This takes the "Hole Saw mods" to the ultimate level! The entire inner airbox is replaced by a lid on top of the airbox only. Retaining the vortex, but providing maximum airflow into the throttle body. This mod will give 2bhp in high rpm on a standard engine, but may result in a small loss in torque at low rpm.

If you want to retain your standard airbox without modifications, but have the benefit of maximum airflow into the filter, this is the way to proceed.

If your standard airbox is not important to you, it is easy to make your own, or achieve similare results, using generous application of the holesaw mods!

Re-Route Breathers - This is an ongoing solution to the problem of pressure build up in the crankcases causing oil in the breather pipes. The standard Buell design routes this back into the airbox and back through the engine. As these vapours will not burn, they result in reduced power. This has been proven in the US to be worth 2-4hp! Not a bad result for another potentially very low cost project.

The current breathers come up into the airbox base. They need to be pulled down, then joined together with a 3/8" T Piece. Then run a single 3/8" hose to a suitable container to catch the fluid in. This container can be a billet catch can, or any suitable container. This will need to be emptied every 500-1000 miles or so, therefore should be accessible. Ideally, the hose should flow downwards at all times, but have a t piece fitted somewhere, with a breather located above. This will allow the crankcase to breath as designed and should be tee'd in and routed high enough to ensure the pipe does not fill to this point.

There will now be 2 holes in the airbox, where the breathers used to enter. These need to be blocked, usually with rubber gromits. If you use sealant, ensure it is oxygen sensor friendly (non silicon)


Standard XB exhaust silencers are made from mild steel, and prone to rust, whilst the headers are made from stainless and tend to be long lasting.

Many owners choose to replace the standard exhausts with something more free flowing, allowing the engine to breathe better. The choice is then between a slip on silencer or a full system. Full systems tend to produce more power, but do take a lot more time to fit (2-3 hrs first time.)

Replacing the standard exhaust on a 12, will mean that you either leave the redundant exhaust valve inside the airbox, or fit an exhaust valve eliminator to prevent the engine management warning light coming on. An example circuit diagram for an exhaust eliminator is shown below, or buy one from Trojan.

An alternative option is to run the race ECM which does not expect the exhaust valve.

Slip on silencers

Standard silencer - The Standard Buell silencers differ between the 9 and 12 models, in that the 12 has an exhaust valve controlled by the ECM, whereas the 9 does not.

Modded Standard - A Tubbs Special! This involves a bit of cutting and welding on the standard can, to retain the standard look, whilst letting the gases flow.

Buell Race - Unlike the popular race pipe for the tube framed Buells, the XB Race pipe does not have a great reputation. Renowned for noise not performance.

Remus Revolution - A popular silencer, with removable baffles for street or track use

Hot Performance Aero Corse Reverso Road Exhaust - Silencer only road version of the front exit exhaust as used on the Adrenalin Moto race bike.


Full Systems

The full systems are capable of providing better power characteristics than the slip ons using standard headers. One drawback is the time required in fitting them. It is also avoided by some, as the engine needs to be rotated to gain access to the rear cylinder studs. This is not as difficult as it sounds. It does take some time, 2-3hrs first time for the whole job, just over an hour if you've done it before. If you are a competent mechanic and have access to normal maintenance tools, this task is easily achievable in an evening.

Micron Serpent -  A full system with all the backing of Micron's flow testing technologies. Serpent headers as used on the Petronas MotoGP race bikes provide the maximum possible flow. The only question is some people love the look of the headers, others hate it. (I have one and think the technology is so in line with the Buell, they look wrong, but are so right,  they belong on a Buell!) Recently rated as the best pipe on the market by an American Dyno Shootout, yet the same price as most slip on silencers.

Hot Performance Aero Corse Reverso Race Exhaust - Front exit pipe (gases exit in front of and below right foot) as used by Adrenalin Moto on their race XB.

Ti-Force - A full titanium system, possibly the ultimate look, but not cheap and has been known to blow apart on US race bikes.


Fuel Injection / Ignition

Whatever mods you do to your fuel injected Buell, you will need to ensure that you run the bike in closed loop mode to allow the ECM to reset its AFV value. This will richen or weaken the mixture across the board, to ensure the ECM is generally mapped to accomodate the modifications.

Standard ECM / XB9/XB12 - The standard ECM on the Buell DDFI systems is an excellent product, which copes very well with providing the correct fuelling across a range of environments. It has a self learning ability, whereby it can optimise the fuelling for the airflow through the engine. This process is called closed loop operation and causes the ECM to adjust an AFV (Air Fuel Value) to compensate the mixture across the board. It will not optimize the fuelling for all throttle/rpm combinations, but will provide a percentage increase/decrease against the standard map. Care needs to be taken when tuning a Buell, as it can be perfect on the dyno, but the ECM can then adjust the AFV value, causing the map to be incorrect at higher rpm.

XB9 White Wire Mod - On the XB9, there is a white wire, which can be disconnected and results in a noticeable improvement in performance.

It is possible to either cut the white wire (bad idea) or remove the connector from the plug (better) For these connectors, you want the equivalent of a "pick tool". The connectors latch into the blocks by a little clip mechanism. Once you've separated the two halves of the block, there is a "Secondary Locking Wedge" that is a sort of cover over the female part of the connector. You have to prise that off before you can depress the terminal latch and remove the connector.

The white wire is on the grey deutche connector between the black/white and the pink/yellow wires, the second one in from the centre in the front row. This white wire goes to the vehicle speed sensor. This wire is related to the dip in performance to pass noise emissions tests, hence removing it on a 9 should improve performance. On a 12, there are questions as to the results.

Buell Race ECM - The Buell Race ECM, was originally rated as the best upgrade to sort out the fuelling when other performance mods were fitted. It retains the self learning ability of the standard ECM, with improved fuel and ignition maps for free flowing systems. Another handy feature is that it does not expect an exhaust valve on a 12, therefore prevents the warning light if the valve is removed.

Power Commander - Dynojet withdrew their Power Commander for Buells, allegedly due to difficulty in sourcing required components. A number of members have experienced problems with Power Commanders on Buells, therefore they are not recommended.

TFI Techlusion - This is a piggyback style system, plugged into the standard wiring loom and provides the ability to add fuel at 3 points in the rpm/tps map. It provides a function similar to jetting on a carb, but is limited by the ability to add fuel only. This system can be used to provide a safe setup with performance exhaust and airbox mods fitted, but will not deliver the best performance.

RapidBike - This system is similar to the Power commander, in that it is another piggy back controller, but there has been somewhat more success with this. Adrenalin Moto have used one on their XB race bike throughout 2006 with no problems. Both fuel and Ignition maps can be remapped using this equipment.

Direct Link - This is a slightly different kind of solution. It is a software product, supplied with a serial cable and dongle, which allows you to read and modify the factory tables in the standard ECM. You have full access to the fuel and ignition maps for the front and rear cylinders independently. You can also modify the acceleration and deceleration tables to add or remove fuel as required. Once you have finished reprogramming the ECM, you disconnect the cables and the bike appears to be totally standard.

Additional features of the Direct Link software is that you have the ability to read and reset both the AFV value and TPS values. These are critical to ensuring effective tuning on a Buell and for this reason alone, I strongly recommend the Direct Link software.

One last feature available with Direct Link is that it includes a data logging function. This allows the tuner to check the fuel maps out on the road in real world conditions. The disadvantage is that you have to ride with a laptop in rucksack or tank bag to take advantage of this!


Clutch products - There are a couple of products which reduce the pressure required at the lever, by replacing or extending the lever mechanism inside the clutch. Simple to fit, get great reviews, but I've never tried one personally.

Drive Belts - A popular subject amongst Buell owners and also other bikers looking at the Buell. So how long do they last? How do you adjust them etc, being normal questions? The answer is that they were originally given a service life of 15,000 miles on XB's up to 2003. The 04 and 05 models had a service life of 25,000 miles, whilst the 06 onwards models have a lifetime warrantee on the belt. Never needs adjusting, never needs lubing, just needs checking for damage every so often.

Q: Can I fit a lifetime 06 onwards belt to my 04 or 05 XB? A: Yes, it is a direct replacement and can be fitted in less than half an hour.

Q: Can I fit a lifetime 06 onwards belt to my 03 or earlier XB? A: Yes, but you need to purchase new front and rear pulleys, speak to your dealer or Buell specialist for advice.

I had visible damage to my belt, which I pointed out at the nearest dealer. A new belt was immediately offered and fitted free of charge under warranty. The 04 belt was replaced with an 06 belt as a standard procedure. I didn't even buy the bike from them! Now that's great service!

Free Spirits Drive Belt Tensioner - This tensioner prevents the Buell drive belt from being over tensioned, when the suspension is on full travel (eg, whilst performing stoppies). It also allows the belt to move out, should gravel be caught between the belt and pulleys, also potentially reducing the risk of broken belts. These are popular items, often fitted by knowledgeable Buell enthusiasts, but it is difficult to prove the actual value of them with statistics.

XB Home Page XB Models Handling Performance Other Popular Mods Known Problems Links