Physics of Engine Braking

[Twister]

Ok, so how does engine braking work for a normal run-of-the-mill 4 stroke combustion engine?

Theories?

Simple theory is that its the compression stroke of the engine. Problem is that after TDC (top dead center) the valves are still closed and the power stroke would give most of that power back.

So is it the heat loss of the compression stroke that leads to a net braking effect?
Hmm...

Edit: this debate sparked by http://forum.pafoa.org/lounge-108/41...ns-page-2.html

[dman]

!!!!!!!!!!-???????-Phissssst!

[Twister]

!!!!!!!!!!-???????-Phissssst!

heh.

Edit: remove brain fart comment about guns.

Ok, I am officially bored.

[P-11 shooter]

We're talking about normal engines and not Jake brakes right?


I was always under the impression it was simply the compressing of the air in the pistons while limiting the fuel. I think your torque converter on an automatic helps add some friction to the equasion as well.

[PisnNapalm]

http://en.wikipedia.org/wiki/Engine_braking

[H.E. Pennypacker]

You cut the fuel to the engine and let the compression slow the car down.

[Twister]

http://en.wikipedia.org/wiki/Engine_braking

That article needs some better sources, and they just hand wave at the mechanics of it.

[Twister]

You cut the fuel to the engine and let the compression slow the car down.

But what about the power stroke? The valves are still closed, most of that compression gets released back into the piston after TDC.

[dman]

Top-dead-center,there ,I've said it,I'm kinda a bottom-dead-center myself,what can I say???

[Twister]

Ok, another side note... how the hell how do multi-quotes of this forum work? Baffling.