Intake valve Mach Index calculator

[Unkl Ian]

Don't use commas when inputing rpm.

[atvporterguy]

I played around with the caculator. That number, the mach index, what is it and why is it important. Is that the velocity that you should shoot for? What ever the speed of sound is for that climate at which the machine will be run, or the climate of inside the port? And if it is will it provide a wide board power band?

[Unkl Ian]

My understanding is that as the speed of air in a port approaches the speed of sound,it becomes more turbulant and creates a restriction.Some refer to this as "sonic choke".

.55 Mach seems to be a popular limit on a flow bench.
Anything higher is thought to create sonic choke in a running engine.

If I'm wrong about this,hopefully someone will correct me.

[atvporterguy]

I am in no way an expert, but i like to aurgue both sides of things to get the most out of things, so please dont take this as an attack. More of a way to get more ideas out.

If the speed is higher and the pressure drop is the same and not climing. Wouldnt that mean that there is more flow?

[Unkl Ian]

I always figured "The more velocity,the better" for a given flow.But it seems that is not an absolute truth.

I think the point is that there IS such a thing as too much velocity,which can show up as a loss of HP in a running engine.

If you check the archives on
and this has been covered by people much more knowledgable than I will ever be.