The cylinder head

No matter what anyone says, the head is the heart of the engine and this is where the power is developed.  This has to be right in a racing motor; if this is set up wrong the engine will never perform, and therefore the engine will have little potential. 

The existing head is skimmed to remove the taper on the squish band, and to increase the compression ratio.  The top of the plug recess is also cut to reduce the threaded length of the plughole to allow the OS R5 plug to better fit the combustion chamber space.  The edge of the combustion chamber is radiused to allow better gas flow across the squish band and into the combustion chamber.   If this cylinder head is placed on an otherwise standard OS 25FX the rotational times on 60ft 014” lines will go from 17/7 to 16-16.1/7.

Crankshaft

The crankshaft is lightened and the crank gas flowed.  The inlet passage on the crankshaft is polished, the inlet port opened up and radiused carefully to relieve operational stresses.  The area behind the crankpin is carefully radiused also to help reduce rotational weight.  The whole lot is then carefully polished to reduce stresses, and it also looks very cosmetically pretty.

Piston and liner

The piston and liner fit is tested to ensure that the system has a good fit. If the piston liner fit is too loose the piston is refitted to make sure the right amount of nip is present.  The piston crown is radiused, and the sides of the piston scalloped to lighten it and also to provide better gas transfer during operation.  The liner timing is left the same; however, the liner ports are gas flowed to ease the flow through to the combustion chamber during transfer. 

Con rod and back plate

The con rod is lightened to reduce the all-up rotational weight of the system. This must be carried out carefully, as removing too much metal can result in catastrophic failure during operation!  We have not broken a con rod yet, included our modified rods, where 30% of the weight is reduced, but hey! we still have time ...

The back plate is also gas flowed. We swap out the existing back plate for a custom made one with much better gas flow characteristics.  We would need to put metal back on the existing FX backplate to make it fit better, so a custom-designed one is the only way to go.

Fuel intake

We use either a Rothwell B T/R venturi set up, screwed into a pressed in delrin inserted into the crankcase intake casting, or a custom-made control line venturi, also made from delrin, and bored to the correct intake size for these engines.