9 replies to this topic

[Jammy]

Why is one square and the t'other round?

My guess would be that its either something to do with ease of casting, or airflow speed.

[Bungle]

its so stupid people don't get them mixed up

[Jammy]

*cough*

[Bungle]

[Big_Adam]

Helps with flow as the exhaust gases are bias to the corners. So the left most port is bias to the top left corner.

I think.

[Bungle]

so if they were hexagonal shaped it would flow better because there were more corners

[Big_Adam]

Ok, why do no one seem to grind them round then?

[Bungle]

the exhaust manifold is square and would not fit

[Ethel]

I reckon Bungle could be on to something...

Either that or the space available between 2 pushrod holes and the flat top and bottom faces of the head just happens to be square so the biggest port you can fit in will be square too.

That just leaves figuring out why the inlets are round....

Carbs are round and circles have less perimeter in relation to volume - as an observation

[Sprocket]

Inlet ports are round because 'air' in a square duct naturaly travels mainly down the middle avoiding the corners, kind of a laminar flow sort of thing. This would cause problems with the fuel seperating out of the charge in these corners. having a round port on the inlet reduces this by keeping the flow similar across the port area.

Square ports on the exhaust wont really matter as much as the exhaust gasses while still expanding, are being pushed out.