30 degree valves

[dirk489]

Hi all,

I have an old Italian motor bike with 30° valves.
I always wondered why they did this(The Alfas have them as well)
Is there any advantage? Or is it an adaptation for quick setting the valve/seat combination?
Thanks,
Dirk/Antwerp

 

[BCjohnny]

Predominantly improved low lift valve airflow.

30 deg valve/seat angles are often used on lower speed engines (such as diesels) though not exclusively, with moderate cam events, where the superior low lift flow (over a 45* seat) can improve torque.

I don't know of any quicker seating benefits , that I assume you're alluding to.

"It's not always a case of learning more, but often of forgetting less"

 

[franzh]

Many domestic US engines used 30 degree seats on the intake and 45 degree seats on the exhaust. Cylinder combustion pressure has a different amount of sealing force on different degree valves as well. There is more force on a 45 degree seat than a 30 degree seat.

Franz

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[dirk489]

Thanks guys!
As I have to renew the seats and valves anyway,I think to revert to 45 °
Dirk

 

[TrackRat]

The lower 30 degree angle also gives reduced valve face wear in many applications.

 

[andyv8]

If valve seat wear was a problem in development, then changing 45deg seats to 30deg seats would increase the sealing area without having to change the inserts/head....