So why is my 4-Stroke outboard quiet???

[MrFish]

This is kind of funny..... This morning my mother came over for brunch and I was proudly showing off the new Yamaha 4-Stroke hanging off my boat. I was telling her the usual virtues we all spout (fuel efficency, no stink, low idle speed). When I got to the point of saying I enjoyed the reduced amount of engine noice she said, "Why's that".

Any of you mechanical types have an answer that I could explain to a curious seventy-two year old mom?

[1pump]

A 2-stroke has a compression stroke on every revolution, so it's going to be noisier. AND, (I don't want to get too technical) most 2-strokes are dependent on a supersonic exhaust pulse to aid in scavenging. (Ever wonder why the pipe on a 2-stroke bike is shaped weird?)
In addition, 2-strokes have an extremely high air intake velocity, and outboards don't use any silencers. That's actually the main source of noise with an outboard.

[ampersat]

ya know, i've always wondered how 2 stroke engines work. well now i know, thanks to howstuffworks.com. here's the link to their explanation of a 2 stroke engine
http://www.howstuffworks.com/two-stroke.htm

the reason 2 strokes are louder than 4 strokes is because they don't have valves like a 4 stroke. when the exhaust gas is released, it's still expanding from the explosion at the top of the stroke and is still under a great deal of pressure. in a 4 stroke engine, the exhaust gas isn't released by the valve until the bottom of the stroke so it's under less pressure.

[drhall99]

Four strokes use Stealth Squirrels. They also have all black fur and wear sunglasses.

[ 07-13-2003, 08:41 PM: Message edited by: drhall99 ]

[fishinfool]

DRHall99 that was way to funny!! :laugh: :laugh: :laugh: :laugh:

[drhall99]

Now if I could just learn to spell - blakc? Time to go back to school

[MrFish]

Ah, Mom will be relieved to get the information. She suspected it was squirrels with dark glasses all along.

Thanks Ampersat, I checked out the web site and it was just what I needed.

MrFish

[Lepper]

Originally posted by drhall99:
Four strokes use Stealth Squirrels. They also have all black fur and wear sunglasses. <font size="2" face="verdana,arial,helvetica">I thought it was the new stealth mice. Making it possible for the smaller motors..