Engine braking and fuel consumption?

Hi,

Is it better for fuel consumption to use engine braking or to to use brakes then build up speed again?

Cheers

Usually use engine braking and try to make your riding style as smooth with throttle and brake as possible.

I do but just wanted to know if it uses more fuel

For what it's worth I was informed during a driving test for work, that when coasting to a halt in gear with modern FI car engines, the ECU stops the injectors firing fuel into the cylinders. It's part of the way they increase MPG figures.

I was picked up on it as I allways used to knock it into neutral, then coast/slow on brakes. But the modern FI units go into a default idle mode when neutral is engaged, so still use fuel. Part of the test consisted of 2 identical circuits, one with me driving normally, then after instruction repeating the route following recommendations. I can't remember the figures, but the MPG on the second run was an improvement in the first.

Not sure if it applies to the SV FI system though.

This also contradicted what I was taught when learning to drive.

Replacing brake pads is cheaper and easier than replacing a gearbox!

engine braking is very little to do with friction in the gearbox and engine so no.. its more to do with it sucking air in, throttle position-induced vacuum etc think trying to breathe through a small straw.. engine breaking only wears out old 2 strokes cos its starves them of fuel and subsequently oil thats in the fuel to lubricate the engine.

but to answer the original. nearly all modern engines use so little fuel it can be considered as using NO fuel at all when engine breaking.. and has the added benefit of saving your breaks.... typically if you're breaking alot you will be using more fuel on your journey

[yorkie_chris]

Originally Posted by lammypie

engine braking is very little to do with friction in the gearbox and engine so no.. its more to do with it sucking air in,

So what happens when exhaust valve opens?

IMO it is pumping losses from moving air in crankcase that gives engine braking as well as frictional losses. Sucking air losses are negligible.


As to which is better for mpg, it depends whether FI injects some fuel, some do this to make pickup smoother I believe. Not sure though. Ideally you'd find out by using a lambda sensor, maybe someone could have a look next time they're at a dyno.

However, considering the amount of gas flow is low, the mixture could be rich, and still not use much fuel in absolute terms.



And another point, how does using engine braking result in needing to replace gearboxes? I would suggest you learn to ride the bike properly...

was replying to what "johnnyfartpants" 's instructer told him

I was talking in terms of car licence, taken 19 years ago in a 750 mini. Compared to 2l mondeo 2 years ago for work.

I've learnt some mechanical sympathy in those years, and gearbox quality has moved on.