Norton actually has new motorcycles in the USA

NorTriDuc said:

100% what Eddie says.

Velocity is more important than big flow numbers.
A port can flow big CFM by being huge, but if it’s too big for the engine and RPM range, velocity drops, equals weak torque, lazy response, poor fuel control.

Sometimes depending on port shape, you’ll raise the port floor to straighten the port to increase velocity

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Fast Eddie said:

Tony,

As you have both heads off, it would really be ideal to get them on a flow bench to see both the flow and velocity numbers. The shrouding (as you refer to it) ‘may’ be a deliberate move to make the throat smaller in order to increase charge velocity.

Getting a good balance between velocity and flow is the tuners art. We all know flow is important, but at anything other than WOT velocity can be as, if not more, important.

High velocity increases cylinder filling by creating a ‘supercharger’ effect caused by the inertia of the charge in the port forcing in more charge for a longer time after the piston has stopped ‘sucking’.

In simple terms, the bigger the port: the higher the flow and the lower the velocity. A smaller port will have higher velocity and less flow.

Basically the flow needs to support the engines needs, whilst doing so with the highest velocity.

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TonyA said:

Thanks for taking the time to write this. I really think I am on to something good here.

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