XR250R Big Bore Kit


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Honda XR250R Big Bore Kit Increases Power and Torque

An XR250R big bore kit increases power and torque, and it increases the overall performance and fun factor of the Honda XR250R.  As larger bikes like the XR400 have been introduced, some people have favored the extra power of the bigger engines, but were not so fond of the extra size and weight of the bigger bikes.  As a result, some people have opted to use an XR250R big bore kit to boost power while still retaining the more compact size and lower weight of the Honda XR250R. Kits are available that increase engine displacement to 280cc and even 320cc.  This increase in engine displacement can provide a nice increase in performance.  For additional horsepower, an aftermarket camshaft can also be used which can further increase power output.  When you are choosing a big bore kit, you might notice that certain kids have different compression ratios.  A boost in the compression ratio will result in a boost in power as long as you have a high enough octane fuel to match the higher compression ratio.  If you boost compression ratio too high on low octane pump case, then you could get detonation and blow a hole in your piston.  If you plan to run on pump gas, then you probably want to stay below a 11.0:1 compression ratio.

Honda XR250 

If you have access to high octane race gas and don't mind paying a premium for race fuel, then you can go with more compression and gain some more power.  In addition, if you can find some of the Octane Supreme 130 octane booster with real lead, then you can also mix your own high octane fuel from pump gas.  Just be sure to get the actual Octane Supreme 130 additive, because it will allow you to easily mix your fuel to 100+ octane.  Forget the overpriced octane boosters found on most auto parts store shelves.  Most of them are a joke... many of them only boosting octane by TENTHS of a point (in other words, not even 1 point).  As noted, the Octane Supreme 130 will boost your octane WHOLE POINTS and you can mix your fuel up to 110+ octane if necessary.  You should be able to order Octane Supreme 130 online.  Thankfully, a motorcycle doesn't consume as much fuel as an automobile, so mixing your fuel for higher octane is more reasonable to do in smaller quantities.  However, it really is convenient to just be able to run on premium pump gas anytime anywhere, so keep this all in mind when selecting the compression ratio of your big bore kit.          

XR250R Big Bore Kit

If you are thinking about increasing the power output of our XR250 with a big bore kit, then you might also be thinking about other ways to boost performance.  As already mentioned, an aftermarket camshaft can help unleash some extra power.  Also, removing restrictions in the intake and exhaust systems can increase air flow and potentially boost power output further.  Just keep in mind that once you start messing with the intake and exhaust, then you will make your XR250 louder.  Some people like a more aggressive sound, and some people might find it very annoying.  You have to decide what you prefer to do in those areas.  There are aftermarket exhausts for the XR250R such as the FMF Powercore 4 slip on performance muffler.  The fact that it is a slip on muffler makes installation a lot easier than replacing the entire exhaust system.  People who have tried this particular FMF exhaust have said they noticed an increase in power.  Just remember that these aftermarket exhaust are much louder than stock.  Another thing to keep in mind when contemplating an aftermarket exhaust is the fact that most of these need to be disassembled periodically and repacked with new sound absorbing material.  Depending on your perspective, this additional maintenance could be an annoyance or it could be a non-issue for you. 

Honda XR250R FMF Powercore 4   

Another way that XR250R owners have tried to increase exhaust flow is just by removing the baffle in the stock muffler.  This can be done for free.  Some people have reported a noticeable increase in performance (and of course in noise).  Whether or not the extra noise is worth the small increase in performance is for you to decide.  No matter what you do with your exhaust, you are not going to gain a huge amount of power on your XR250R.  Remember, this is not a 2 stroke engine we are talking about here.  On 2 stroke engines, it is possible to get much bigger power gains with a different exhaust.  This is not as true with a 4 stroke engine.  All that to say, just be realistic in your expectations about what is to be gained with an exhaust change.  Speaking of being realistic... it's a well known idea to remove exhaust headers from the XR250R engine and grind down the weld protrusions that are inside the header pipe.  Most people that have gone to the trouble of doing this have noticed NO difference in power.  So, save yourself the time and hassles and don't bother with this modification unless you are bored and have some time to burn.  In addition to the exhaust modifications, some people also remove the plastic snorkel from the top of the stock air box under the seat.  This should increase the airflow into the stock air box.  It will also most likely increase noise.  You might be surprised at how much engine noise can come through the intake side of an engine.  Even so, this modification will not increase noise as much as messing with the exhaust.  The stock air filter element can also be replaced by a UNI filter.  When making changes to the airflow dynamics through your engine, then you will probably also need to be prepared to re-jet the carburetor to get the proper air/fuel ratio to match your modifications. 

In conclusion, the Honda XR250R is well known for it's solid reliability and good overall performance.  If you are one of those people that likes the size and weight of the Honda XR250R, but want some additional "get up and go", then you might want to consider getting an XR250R big bore kit.