Port shape

[superbike]

Here we have to different styles of port.

Say both ports have the same size valve ,same valve angles and same entry position.

If we took our green port and deepend the bowl pocket to something like the blue port do we have any ideas what may happen.

I would say the blue port would flow better due to flow being distributed onto the valve more equally.

[Guy Croft]

Nope, the green one will flow more because it has a more acute angle between valve stem and port axis.

If you 'bowl out' the green port the air won't even 'see' the mod.

GC

[superbike]

Nope, the green one will flow more because it has a more acute angle between valve stem and port axis.

If you 'bowl out' the green port the air won't even 'see' the mod.

GC

Interesting ! What about at the lower lifts ?

[Guy Croft]

Same, Chris, the short side radius and generous radius at port roof opposite it as shown in the blue sketch is a necessary 'evil' on a head with shallow (or nil) downdraft.

On a sidedraft port or one with shallow downdraft you can sometimes alter it (to make it a bigger rad) and gain higher lift flow but often that is at the expense of lower lift flow. The net gain in power usually makes the trade off worth the while.

On a well-downdrafted port the incoming air is far better distributed around the valve diameter, you don't have much of an SSR there and you don't need one.

GC