New Mini Moto / Pocket Bike Cylinder Barrel / Head Design for Maximum Performance

This post is going to be a sneak preview of a new cylinder head design I'm working on for 39/49cc  aircooled engines typically used in Pocket Bikes.

An initial design parameter of this design is full backwards compatibility with existing engine cases and engine internals, as such, I've stayed with a fairly conventional appearing external shape.
Ultimately these heads will be available paired with the billet engine cases which are in the works, but for the near future, the barrels and a custom cylinder head with a selection of compression dome inserts will be available.

The following images are WIP CAD models. There's revisions being done and lots of flow modelling at various piston positions (every 10 degrees of crank rotation.).

Cylinder Barrel Without Fins

You can see from these images that the cooling fins haven't been modeled yet. They're going to be positioned and their density determined by thermodynamic modelling in an effort to gain some level of control over the conditions in the combustion chamber.


Of note is the round exhaust port which has been shaped and sized to match up seamlessly to the best race pipes for these heads. This alone makes a significant difference in the amount of flow the heads will sustain.

Exhaust Port View

The interior or the exhaust port has been carefully shaped, and although the bottom 10% or so isn't really visible in this view because of the port floor contour, the overall shape can be seen.

The ceiling of the port has been raised 2.25 mm from stock on the 39CC variant, and 2.85 mm from stock on the 49CC version when compared to standard 'High Performance Heads'. Also, much work has been done refining the shape of the port transition and ensuring that flow is optimised  from the very moment the port is opened, through the piston being all the way to BDC.

Thought has been given too towards the air/fuel charge being pulse returned from the exhaust pipe with the floor of the port being shaped to direct this flow precisely where it's most desirable for the custom shape of the combustion chamber.

Quarter View Into The Top Of The Barrel

Lastly, using very carefully shaped and flow tuned contours for all the ports has yielded great results. The ports all have semi-angular domed 'ceilings' with multiple internal angles which direct the incoming air/fuel charge precisely yielding a very desirable swirl which works in careful conjunction with the small returning air/fuel charge from the pipe.

When I have achieved precisely what I intend to with this modelling, I shall post some video of the flow modelling during the compression phase of the engine operation but suffice to say for now that this barrel / head combo is going to make more power, more reliably, and allow for a wider range of tuning options whilst offering a complete intake charge burn than anything else on the market available for the air-cooled engines.

Lastly, provision has been made during the design of these heads for a 6mm thick thermal insulating layer between the base of the barrel and the engine cases. This should serve to not only allow the bearings to run cooler and longer, but to keep the air/fuel charge cooler and denser as it enters the combustion chamber for further improved power.

These heads will NOT need to be ported, smoothed or modded in any way to offer outstanding performance. In all actuality, these heads are tuned to the point that any modifications will likely be detrimental to performance.

More info to follow shortly.