Oversized valves

[TobyB]

Can somebody explain the benefit of having oversized valves in a M20 head?

Bigger valves are not an immediate solution to any of the flow 'problems' with the stock M20.
Or most BMW engines, honestly.

They flow pretty well compared to most stuff out there, generally speaking.

t

[apostate]

Ok, let me put it this way: how come a bigger valve is better for actual flow compared to a smaller valve?
Unless you have such a huge port that you cannot close with a nominal valve, what's the use of an oversized one?
Has anybody done such HUGE ports that cannot be closed with a nominal valve?

[jeffnhiscars]

Someone running oversized valves will not have an untouched head.

I think the question referred to the cam comment

[apostate]

Someone running oversized valves will not have an untouched head.

Then the next questions come: how much of a porting is needed to run oversized valves?

And isn't it always a good idea to keep the valves as small as possible compared to the ports?

[SkiFree]

Someone running oversized valves will not have an untouched head.

[apostate]

And how is that, given the head is untouched?

[badwella]

Increases cross sectional area for volumetric gas flow in and out of the combustion chamber. Essentially makes it easier to breathe.

Increasing valve duration will increase the volume of gas flow into the combustion chamber as well.

[apostate]

Hi guys,

Can somebody explain the benefit of having oversized valves in a M20 head?

Thanks. Cheers.