Why do 2 strokes have lots less engine braking than 4stroke?

[NSR125-Kid-UK]

Just something I've been wondering for a while, I've never really found out why.
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https://www.bikepics.com/members/nsrandy/96rs250/ My Bike!

"I'm either going to teach andy to get his knee down, or I'm going to get him killed. One of the two" - Teaman

[Dom_]

Because 2 strokes fire twice as often, helping to spin the engine.

I'm crap at explaining, but it's not hard if you really think about it.

[Silver]

You mean NO engine braking? I nearly bloody crashed into a roundabout when I rode my brother's old RS250!

Errr, don't know anyway, aside from the obvious "difference in engine design" answer.

[NSR125-Kid-UK]

Well there's enough engine braking on my NSR to lock the rear up shifting from second to first ?
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https://www.bikepics.com/members/nsrandy/96rs250/ My Bike!

"I'm either going to teach andy to get his knee down, or I'm going to get him killed. One of the two" - Teaman

[Silver]

That's not engine braking!

[NSR125-Kid-UK]

What is it then?
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"I'm either going to teach andy to get his knee down, or I'm going to get him killed. One of the two" - Teaman

[Frost]

One of the main reasons it because people compair them to a 4 stroke of similar power, which is typically double the capacity. and allthough it gives the same power as the two stroke, it gives more than double the engine braking.

Stroke length and compression would also play a part.

[Silver]

Briefly:

That's you changing down too early and the back wheel turning at a different speed to the engine.

Engine braking is when you back off the throttle and the bike (and cars too) slow down (fairly quickly). Two strokes keep rolling.

[NSR125-Kid-UK]

Ah okay, nope the NSR just keeps rolling.
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https://www.bikepics.com/members/nsrandy/96rs250/ My Bike!

"I'm either going to teach andy to get his knee down, or I'm going to get him killed. One of the two" - Teaman

[BLOFLY 636]

I think it is to do with the size of the cylinder and compression ratio for example a 1000cc V-Twin has a lot of engine braking because it has 2 500cc cylinders and a high compression ratio where as a small 125 or 250 has 1 or 2 125cc cylinders with a relatively smaller compression ratio
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Those bloody footpegs......they ought to do away with em!

[Ric]

lol @ no engine breaking on the 250 silver

feels well odd when its just not there!! just not right

it has something to do with the 2 stroke moving parts (ie doesnt have to move so many things in the engine) the 4stroke has weighty bits that move when the engine turns

or so i think i herd

[Dom_]

I would have thought it's mainly to do with the fact that the piston is being fired on every other stroke, which helps move the bike. Whereas on a 4t you got to have 4 strokes before each spark, so its twice as good at slowing down.

[NSR125-Kid-UK]

MEh.
All that power on a four stroke engine that goes to waste turning the cams and opening/closing valves .

I read somewhere that a huge chunk of engine power goes to running the engine, and a lot's taken out of the power before going to the rear wheel - of course, I'm sure you probably know all this, but the idea of such a wasteful inefficient engine gives me pause .
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https://www.bikepics.com/members/nsrandy/96rs250/ My Bike!

"I'm either going to teach andy to get his knee down, or I'm going to get him killed. One of the two" - Teaman

[cagiva gezzer]

No exhaust stroke, and where the exhaust stroke should be is a power stroke, wel almost.
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"because one stroke isnt enough and four strokes waste two"

[mrchips]

Riding even a 4 stroke 125 is an amazing difference from a 2 stroke as you can't coast it to the same extent ie coming up to a roundabout or something.
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Northern Irish? www.nibikers.com

[Kickstart]

Hi

A 4 stroke has a compression stroke where it is compressing the full volume of the cylinder by about 10 to 1.

With a 2 stroke a load of ports are open so it is only compressing it by 6~7 to 1.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[loply]

four stroke has 3 nice big reciprications of the piston all without any power being produced what so ever!

two stroke gets new power produced every second recprication.

dont know how much this contributes to engine braking since the throttle is closed anyway so the power strokes wont be making much power anyway.
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[kasandrich]

The four stroke may do two revolutions per power stroke (per cylinder of course), but when it does a compression stroke it is a full length compression stroke, whereas a 2 stroke has ports that are open, so only gets half a compression stroke.

Its a little more complex than that, as the 2 stroke cylinder is charged, by crankcase compression, and when the throttles shut, the charge into the crankcase is reduced, therefore when its compressed very little happens. (If you compress a vaccum, you may only get atmospheric pressure).
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Richard

CBR1000FM

[sickpup]

Internal friction caused by the cams and cam chain, generator etc.
as well as weight of internal parts being accelerated and de-celerted are higher than a four-stroke.

Note. Engine braking happens with a closed throttle although friction is always there. Theres an interesting piece on it in one of John Robinsons books.

[palmer]

my ar50 2t has engine braking, it back fires too

think its on its last legs, i thrashed the hell out of it yesterday, started it up today and a VERY load pop came out of the exhaust :s