The origin of engine braking?

I wondered i could pick the brains of the more knowledgable folk around here. See, I dont understand how engine braking comes about, why four-strokes have alot and why 2-strokes dont have alot (almost none). I understand that 4-strokes DO have engine braking, and that generally the bigger the pistons the more engine braking you have. I dont actualy understand though why a 650cc IL4 has less engine braking than a 650cc V-twin and so on so forth

let the discussion begin...

Being consdierably less than knowledgable, I'll reply

Simple and probably completely wrong explanation. 4 cylinders means each cylinder stroke moves whirly round sprockety thing 1/4 revolution. 2 cylinders means each stroke moves it 1/2 revolution. To move 1/2 revolution takes more power than 1/4, so when the power input is lowered, it has a greater effect.

SOunds good and logical anyway

i see, i get that

[Viney]

Magic and acts of god, or gods, or nymphs

[flymo]

We did this subject recently I think. The conclusion from memory came down to the energy required to simply turn the working parts of the engine, mostly friction etc.

Initially I thought that the level of compression of the engine would influence the engine braking effect but it turns out not to be the case, although this is also influenced by the engine configuration.

Originally Posted by flymo

We did this subject recently I think. The conclusion from memory came down to the energy required to simply turn the working parts of the engine, mostly friction etc.

Initially I thought that the level of compression of the engine would influence the engine braking effect but it turns out not to be the case, although this is also influenced by the engine configuration.

i thought compression was responsible for the engine braking, but it conflicted with my understanding that 2-strokes have little engine braking force

[Mr Speirs]

Wikipedia it. Its is vastly more complicated than size of pistons. All to do with heat dissipation, exhaust flow etc.

Originally Posted by Mr Speirs

Wikipedia it. Its is vastly more complicated than size of pistons. All to do with heat dissipation, exhaust flow etc.

(that gets rid of the point of discussion...in the past, threads like this have spawned pages of glorious technical talk)

[tigersaw]

bump start a 2 stroke - easy peasy.
bump start a IL4 - possible
bump start a V2 - jolly tricky

[the_lone_wolf]

Originally Posted by tigersaw

bump start a 2 stroke - easy peasy.
bump start a IL4 - possible
bump start a V2 - jolly tricky

Bump start a ~600cc single with slipper clutch and no electric start...



F*ck it, go home....