Just a thought... - Engine Valves

[squishio]

Why are they always round?

Randomly popped into my head that you could probably get more surface area covered therefore a bigger port covered if the valves were square or maybe semi-circular.

https://www.srcf.ucam.org/~mmp26/images/rebuild/head-valves.jpg



somthing like this...

https://www.rdphoto.co.uk/mg2/pictures/valves.jpg


is it because the air flows better past round shapes as opposed to square pointy things?
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[NSR Mick]

A round hole is easier to seal than a square one.
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[Paulington]

I'd assume it'd be to do with:

1) Better air flow, more uniform and less turbulent.
2) More uniform pressure, if you had a non-uniform valve there'd be more pressure on certain parts/points of it due to being an odd shape.

Probably wrong but we shall see when other people post!
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[27cows]

Honda gave oval pistons a whirl...maybe they should try oval valves too

[The Artist]

Same reason pistons are not square.

Too much pressure at the corners which is why circles are perfect as they spread the pressure all the way around.

If you want more air/fuel in your engine then that is what a turbocharger is for

[iooi]

There is also the heat matter.

Round the heat is evenly spread.

Make it like your drawing and you will find that the corners get a lot hotter and will burn more. Leading to a very poor seal after a while.

Also the head does need to be able to disipate heat, in your example there is very little left to do that.

Never mind that there is the matter of you have blocked out the spark pulg hole
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[prawny1]

not to forget that valves can spin under normal use

are we looking at a 1.0l corsa head?

[Pete.]

[ZRX61]

[squishio]

[squishio]

just posed this question to my dad and his reasoning was as Geri said wast machining.

Valves used to be turned on a lathe. Are they still?

I would be quite surprised if they still are as the waste material and machining involved would be pretty high in relation to the quantities of engines (cars, bikes mowers etc) being produced.
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Current - Hornet 600, Transalp 650, X140 Pit, GPZ400R
Past - SY125, GT250, GT650, CX400, CBF600, Bandit 600, SL1000, GT250

[Ariel Badger]

Even if you could machine them well enough to get them to seat ( tolerances of a couple of micron) you could never lap them back in.
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[prawny1]

I have always fancied the idea of cylindrical valves (basicly a tube with a hole going thru the side) with oil fed ball bearings either end that fit in the head like a cam shaft only you wouldnt need as many bearings with it having no side loading,

The way I figured it you could maybe use the graphite (think thats what they are) seals that are used in mazda rotary engines to ensure no compression loss and some sort of close fitting scrapper to stop carbon build up on the valves and maybe even reed valves on the inlet to prevent back firing,

They would have no/very high rev ceiling could be made to have variable timing, reduce internal power losses and give unempeeded gas flow into and out off the cylinder further increasing power and efficiency.

[ms51ves3]

[G]

In a lot of case a smaller diameter can mean more gasses flowed.

Prawny; are you aware of 'rotary valves'?
Seems to be around what you're describing. There's a variety of different designs, not sure any have had amazing sucess, except perhaps the MZs, which I've got a feeling use them, though don't know of the history
Here's some: https://www.dself.dsl.pipex.com/MUSEUM/POWER/unusualICeng/rotaryvalveIC/rotaryvalveIC.htm

Rotary valves courtesy of google images

[prawny1]

double post oops

[prawny1]

[prawny1]

[chris-red]

[prawny1]

1L 12v corsa is a three cylinder engine,

[G]

[chris-red]

Learn something new everyday!
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[ms51ves3]

[Pete.]

[Ariel Badger]

I once owned this rotary valve head. It was built in 1946 by New Imperial of Birmingham and never went into production.
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