General topics » Engine braking

Why do engines with fewer cylinders have greater engine braking effect than those engines with many cyclinders.
A twin will have more baking effect than a four or six cylinder bike.

The only logic I could cone up with was, twins have more torque than fours, so engine braking could be reverse torque.

I cant find any learned or technical documentation, just a load of internet tosh.

Oh and from someone at the meeting who said “2nd Moment of Inertia!”, but wouldnt expand on that.
He all but said ”Its far too complicated. You wouldn’t understand”

I think you need to control for other factors like stroke. Compared to an inline 4, a boxer twin will typically have a longer stroke so it's pulling against the manifold vacuum more.

I don't have the full picture of all the dynamics involved here so I wouldn't try to give an opinion as to why twins generally have more engine braking effect than fours.

My thought is that for two equal displacement engines with similar bore/stroke ratios, the average amount of engine braking over a given time in a closed throttle (over-run) situation would be the same.
The four-cylinder engine would deliver its engine braking "pulses" At twice the frequency but half the "amplitude" of the twin.

Seat of the pants experience tells me that the twin has more perceived engine braking effect, however.

The true explanation runs deep, methinks.

I think it has to do with greater "pumping losses" in an engine with fewer cylinders.
I think pumping losses are also the reason that a four can also generally deliver more power than a twin.

I found this:-

"It has been found that a smaller number of cylinders (<4) has higher pumping losses in principle, even with the same turbocharger efficiencies. The lowest pumping losses can be achieved with four-cylinder engines. It has also been shown that this issue is completely different for diesel and gasoline engines".

and this:-

"Pumping loss in IC engines is the difference in work done to pump out the exhaust gas and the work done to induce the fresh charge (fuel+air mixture) into the intake manifold".

Odd…I never gave this any thought.

Zitat von Steady Eddie im Beitrag #4

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I don't have the full picture of all the dynamics involved here so I wouldn't try to give an opinion as to why twins generally have more engine braking effect than fours.

My thought is that for two equal displacement engines with similar bore/stroke ratios, the average amount of engine braking over a given time in a closed throttle (over-run) situation would be the same.
The four-cylinder engine would deliver its engine braking "pulses" At twice the frequency but half the "amplitude" of the twin.

Seat of the pants experience tells me that the twin has more perceived engine braking effect, however.

The true explanation runs deep, methinks.

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I found it interesting that on some new bike models, I believe that the R1000RR is an example, you can dial in the amount of engine braking that you want to experience on overrun. i assume that is accomplished by the computer adjusting the idle speed when the throttle is closed and the engine is above idle speed rpms.

BTW, my Zero electric motorcycle has a custom setting where the rider can adjust the amount of motor braking (regeneration) with both the throttle closed on "overrun" and when using the brakes to slow down.

Zitat von Steady Eddie im Beitrag #5

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I think it has to do with greater "pumping losses" in an engine with fewer cylinders.
I think pumping losses are also the reason that a four can also generally deliver more power than a twin.

I found this:-

"It has been found that a smaller number of cylinders (<4) has higher pumping losses in principle, even with the same turbocharger efficiencies. The lowest pumping losses can be achieved with four-cylinder engines. It has also been shown that this issue is completely different for diesel and gasoline engines".

and this:-

"Pumping loss in IC engines is the difference in work done to pump out the exhaust gas and the work done to induce the fresh charge (fuel+air mixture) into the intake manifold".

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Zitat von Richard230 im Beitrag #9

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I found it interesting that on some new bike models, I believe that the R1000RR is an example, you can dial in the amount of engine braking that you want to experience on overrun. i assume that is accomplished by the computer adjusting the idle speed when the throttle is closed and the engine is above idle speed rpms.

BTW, my Zero electric motorcycle has a custom setting where the rider can adjust the amount of motor braking (regeneration) with both the throttle closed on "overrun" and when using the brakes to slow down.

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Zitat von wessie im Beitrag #11

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Zitat von Richard230 im Beitrag #9

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I found it interesting that on some new bike models, I believe that the R1000RR is an example, you can dial in the amount of engine braking that you want to experience on overrun. i assume that is accomplished by the computer adjusting the idle speed when the throttle is closed and the engine is above idle speed rpms.

BTW, my Zero electric motorcycle has a custom setting where the rider can adjust the amount of motor braking (regeneration) with both the throttle closed on "overrun" and when using the brakes to slow down.

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more likely altering the compression with some sort of valve system - my S1000XR does that to a certain extend as they artificially create pops and bangs on the over-run by squirting a bit of unburnt mixture into the exhaust when you close the throttle. The amount of popping increases as you go up the engine modes. You get more with E10 fuel as well.

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Zitat von Steady Eddie im Beitrag #5

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I think it has to do with greater "pumping losses" in an engine with fewer cylinders.
I think pumping losses are also the reason that a four can also generally deliver more power than a twin.

I found this:-

"It has been found that a smaller number of cylinders (<4) has higher pumping losses in principle, even with the same turbocharger efficiencies. The lowest pumping losses can be achieved with four-cylinder engines. It has also been shown that this issue is completely different for diesel and gasoline engines".

and this:-

"Pumping loss in IC engines is the difference in work done to pump out the exhaust gas and the work done to induce the fresh charge (fuel+air mixture) into the intake manifold".

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Thankyou for all the comments.

We all know it to be true but there isn't a definitive explanation for the cause.