Morris Minor Owners Club

RogerRust wrote: Sadly I went back and checked, it is in fact atmosheric pressure that charges the chamber.

But but but - that's nonsense. Without the partial vacuum created by the piston falling, air pressure would do nothing. Bizarre

Maybe instead of causing a partial vacuum the piston going down just creates more space, so the pressure fills it?

The air wouldn't enter the cylinder unless the pressure inside was lower than that outside - a pressure differential caused by the movement of the piston. The piston movement sucks the air in by causing a partial vacuum.

Blmey - I was right
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I reckon the correct answer is atmospheric pressure. I think the clue is in the question. It refers to "a normally aspirated" engine.

Yes, the piston is creating a partial vacuum when it moves down, so it is "sucking", but the question is what causes the fuel/air mixture to go into the cylinder to fill that partial vacuum.

In a normally aspirated engine, it is atmospheric pressure.

In a turbocharged engine, it would be the pressure created by the turbo charger.

If the answer was the piston "sucking", then turbo charging would have no effect, as the "suck" would be identical. i.e. the piston moves the same distance and so creates the same amount of "suck" in a turbo charged engine as it does in a normally aspirated one.

It is the "push" at the open end that makes the difference.

So was I when answering the quiz, but since I have questioned it. Sorry to labour the point, but if the pressure is in fact lowered by the piston going down, does that constitute 'suction' or just allowing the outside pressure to be pushed in?
You just got there first Ax!

Isn't that pretty much the definition of 'sucking'? "Draw into the mouth by contracting the muscles of the lip and mouth to create a partial vacuum" is what this 'puter's dictionary says.
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what does it say about 'push'?

"Exert force on someone or something... in order to move (it) away from oneself or the otigin of the force"
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Thanks, these brain cells now need a rest!

Much more my kind of mind exercising - all this physics gets a bit much
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That wasn't the only question that was badly worded either...

I've always been led to believe that the fresh charge is drawn into the cylinder for serveral reasons:

a) the partial vacuum caused by the piston moving downwards.
b) the slight sucking action caused by the exhaust valve remaining open and the exhaust gases travelling down the pipe (creating a vacuum behind them)
c) the momentum of air flowing through the inlet manifold (creating a positive 'over atmospheric' pressure in the inlet manifold)

82. I reckon the pulleys did it for me, never could get my head round them or gears (and there were a fair few geary questions too!).

I always end up comparing things to the gears on a push bike. Well, it works for me
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aupickup wrote:is that all i got 99%
and i can do the times crossword

I can do the Times crossword... it goes something like "my name is Reginald Iolanthe Perrin....." lol

alainmoran wrote:I've always been led to believe that the fresh charge is drawn into the cylinder for serveral reasons:

a) the partial vacuum caused by the piston moving downwards.
b) the slight sucking action caused by the exhaust valve remaining open and the exhaust gases travelling down the pipe (creating a vacuum behind them)
c) the momentum of air flowing through the inlet manifold (creating a positive 'over atmospheric' pressure in the inlet manifold)

B and c will be minimal (if anything) compared to the huge changes in volume and hence vacuum caused by the piston on the down stroke when the inlet valve is open.

Bugger, 76 %

sucking and pushing are non-technical terms...
A gas will move if there is a pressure differential.

78% only