Pro-X Honda 250R Cylinder Kits

    The Honda 250R engine by nature of its longevity and popularity has benefited from the addition of aftermarket cylinder kits that can boost the once 250cc engine to nearly 400cc's.  The Pro-X cylinder kits with its modern 10 port layout and a wide selection of bore sizes make for potent engine combinations for every type riding conceivable. 

    Pro-X cylinder kits with varied bore sizes and stroke combinations come in several popular sizes- 330, 350, 370, & 390.  We've omitted the 310cc kit from our engine line.  The cost difference between a 310 and a 330 in minimal however the power output potential of the 330 kit is much greater.  The new style 330 cylinder kits do not require case boring as they once did.

    Due to such a varied assortment of combinations listed is some general guidelines and some of the components we like to use.

Pipes:

    The larger bore sizes of these motors presents a problem with the pipe design.  The larger bore sizes create a greater exhaust volume that most pipes have troubling dealing with effectively to prevent extreme exhaust gas temperatures.  The pipe body diameter, and most importantly the stinger outlet diameter are crucial for ensuring proper EGTs.  There are several excellent big bore pipes available on the market that suit a wide range of riding needs.  We have used the ESR TRX-5 Centermount on most of our all around motors.  We like to use the FTZ Fat In-Frame drag pipe for the top-end motors.  The Curtis Sparks big bore pipes are also an excellent choice. We've begun testing on an all new pipe that has its application talken from a Rotax 800cc twin.  So far that testing has been superb!

Intake System:

    Again the increased bore size of this motor requires special attention to ensuring it gets the air that it needs.  Larger carb diameters ranging from 38mm to 42mm are standard.  The reed cage is a choke point.  Often the reed cage is nothing more than a 250cc reed cage stuffed into the cylinder.  We've tested the ESR Series 2000 reed cage and have found it works well in hillshooting and drag racing applications.  The V-Force reed cage with a CR250 intake boot work very well with most other engine configurations.

Crankshaft:

    Patriot Racing cannot stress enough that a quality crankshaft is the heart and foundation of any high output motor.  We have found that the stock crankshaft is hard to beat.  While there are more economical choices for the lower output motors.  We choose to use only Honda OEM crankshafts.  In some of our stroker motors we opt to use a 132mm long rod.  The increased rod length works to offset the increased side-thrust from the increase stroked.  This increases the reliability and longevity of our motors.  Crankcase trenching is often not required up to a 4mm stroke increase as the rod can be dressed and polished to clear the cases. 

Ignition Timing:

    Too much ignition advance in any motor is a bad thing.  In a big bore motor its compounded!  A careful balance must be struck with the target RPM, compression ratio, and octane fuel used to ensure the motors lives.  Detonation is often instant and its results are catastrophic.  In some of the stroker set-ups retarding the timing is often better.

Cylinder Porting:

    As mentioned the Pro-X cylinder feature a modern 10 port layout.  However the cylinder porting must be addressed and careful, well planned, and tested changes must be performed.  In the stroker motors, this is really where experience comes into play even more.  The cylinder porting in these big motors is what sets them apart.  We've got a great deal of experience in crafting these motors for all applications from MX to drag racing- along the way we have learned what works and what does not.

Pricing varies considerably. Please call with your needs!

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