New generation Norton head (theoretical)

acotrel said:

I was interested in the comment that somebody bought a FA head then enlarged the inlet ports in an attempt to get more power. I did that sort of thing when I was a kid, but learned better.

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Jim Comstock is still doing that to FA and RH10 heads with very good results.

This is my head.

comnoz said:

So now that I identified a problem with my prior velocity readings and corrected them -here is the flow tests with the 1.5mm oversize intake and a little work in the valve guide and bowl area.

Nice improvement for a steetbike running a .400 lift cam.

Flow

Velocity

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Does what is achieved on a flow bench correlate with what actually happens in an inlet tract when a motor is running ? If you think bigger inlet ports are an improvement, then perhaps bigger diameter exhaust pipes might also be better ? When a Commando motor is running at 6000 RPM what is happening in both the inlet ports and exhaust system is sonic - normal flow changes under those conditions. If you assume a flow bench give meaningful results, you might be very wrong. Even with an excellent dyno, you might not see improvements in torque - which is more important than top end power.
A friend of mine was a Senior Research Scientist on the trans-sonic wind tunnel at our Aeronautical Research Labs in Victoria, He showed me what happens when conditions are sonic. You get the unexpected.

acotrel said:

If you assume a flow bench give meaningful results, you might be very wrong.

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If you know a flow bench gives meaningful results, you are 100% correct.

Perhaps this will shed some light on the topic for you Al.

Below are before and after graphs, one for velocity and one for flow.

The dyno difference was 9bhp...