Works engines now benefit from 5-axis CNC Porting.

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The inlet and exhaust port shapes are two of the key variables that affect air flow through, and therefore power produced by a high speed internal combustion engine. Small changes in the cross sectional area of the ports produce changes in gas velocity that can greatly effect volumetric efficiency.

All production engines use straight-forward sand cast port shapes and therefore the surface of the ports can only be controlled to a tolerance of around +/- 1.0mm. In racing engines, the cast shape is traditionally improved by hand using pneumatic or electric die-grinders. These were the tools wielded by the famous Manx tuners like Beart, Lacey and Lancefield. Great skill is required to produce a good port shape, but even the most experienced operator is only going to achieve a shape that is repeatable to within perhaps +/- 0.5mm at best.

It is well known that the introduction of computer-controlled CNC machines has improved production tolerances enormously. But CNC porting has only very recently become a reality. This is because engine ports are, a) a very complex non-geometric shape and b) very difficult to access with conventional milling cutters. First in Formula 1 and MotoGP and now in some of the other high-end formulae, a process has been developed that has finally allowed CNC machines to take the inaccuracy out of porting. The combination of 5 axes, running simultaneously, together with a high speed spindle (15,000 rpm) and carbide 'lollypop' cutters is now producing ports that are accurate to within +/-0.05mm.

In an exclusive arrangement, Works Racing Motor Cycles Ltd has teamed up with the staff at Denis Welch Motorsport to produce the world,s first fully finished CNC ported heads for Manx Nortons.
The process used was as follows:

  • Choose the best performing, traditionally ported head.
  • Use a 5 axis coordinate measuring machine (CMM) to measure the ports in this head.
  • Produce point cloud CAD models of the ports.
  • Design new shapes that are nominally the same but remove the errors by blending in CAD
  • Develop cutter paths to machine these new optimised ports.
  • Start production of heads featuring fully machined ports.
More details can be found at

The results are stunning - the heads come off the machine fully finished and require no hand fettling. The match between the ports and the valve seats is seamless, and because Works engines have always had CNC machined combustion chambers, the match with the chamber is also spot on. Importantly, every head is identical, making performance development in other areas much more precise.

For customers, this work delivers one thing: MORE POWER. And as anyone who has ever raced a Manx Norton will tell you, that is always a good thing.