Porting
What iB Knows — and What We Don’t Do
Porting is a subject often associated with increasing engine output.
However, iB is not a tuning shop.
Many people expect port work to focus on extracting more power from the engine.
That field belongs to professional tuners, and we respect their expertise.
That said, there are things we must understand about porting in order to do our work correctly.
For example, there is a well-known principle in two-stroke engines:
If the exhaust port height exceeds half of the stroke, the engine will not build proper compression.
If a machinist does not understand this, it becomes impossible to respond correctly when a customer reports a problem.
We once had a case where a customer complained that the engine would not build compression.
When we measured the cylinder bore, all dimensions and finishing accuracy were correct.
The problem turned out to be the porting modification performed by the customer, which had raised the exhaust port beyond that critical limit.
Because we understood this principle, we were able to identify the real cause and resolve the issue.
What iB Does Know About Ports
One of the areas we deal with regularly is port chamfering.
The edges of ports must be treated carefully to protect piston rings.
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Horizontal edges: a relatively wide chamfer with a shallow angle that gently pushes the ring back into the groove
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Vertical edges: small and rounded edges
The exact dimensions depend on the cylinder size and port geometry, so experience and judgment are essential.
iB’s Core Port Technology
Bridged Ports and Bridge Relief
The area where iB’s expertise truly stands out is in Bridged Ports and bridge relief machining.
In a two-stroke engine, the piston is constantly pushed sideways by side force perpendicular to the crankshaft.
Ideally, the cylinder wall should support this load.
However, in two-stroke engines, large intake and exhaust ports remove a significant portion of that supporting wall.
By installing a bridge inside the port, the cylinder regains the structural support needed to handle this side force.
In that sense, this can be considered a form of “ideal porting” that solves one of the fundamental weaknesses of two-stroke cylinder design.
However, installing a bridge in the exhaust port creates another challenge: heat management.
To prevent the bridge from overheating, precise bridge relief machining is essential.
This is where iB’s core technology comes in.
We are able to machine exactly the same bridge relief geometry both before and after plating, maintaining perfect alignment with the final bore size.
Achieving this level of accuracy relative to the finished bore is an extremely rare capability — and one of the key technologies that allows iB to contribute to the world of two-stroke engines.
FAQ
Does iB offer port tuning for more power?
If customers already have port timing data or specifications, we can perform machining based on those instructions. However, iB does not take responsibility for designing power-increasing port modifications ourselves. That work belongs to professional tuners. Our role is to ensure the highest machining accuracy and durability for the cylinder itself.Why are bridged ports important in two-stroke engines?
Two-stroke cylinders often have very large intake and exhaust ports. This removes a significant portion of the cylinder wall that normally supports the piston. A bridged port restores part of that support, helping the cylinder withstand the side forces applied by the piston during operation. This can significantly improve durability and stability in high-performance two-stroke engines.What makes iB’s bridge relief machining unique?
The relief cut on a bridge must precisely match the final bore geometry after plating. iB has developed machining methods that allow us to reproduce exactly the same relief geometry before and after plating, aligned with the finished bore size. This precision is extremely difficult to achieve and is one of the core technologies behind ICBM™︎ cylinder processing.Learn More About ICBM™︎