When you are slowing down for some traffic lights with out using the brakes that's engine braking (or gravity or wind resistance) :)

See thats where i got confusd. Just slowing down i always attribute to air resistance/friction. But in essence, I guess there is an element of engine braking in there. Then again, I'm lazy and put it into neutral as I coast to a stop.

I was told never to coast to a stop in my driving lessons! :) That was 13 years ago though! god I'm old!

Unless you are at a very high speed where wind resistance would be greater its engine braking that slows a car down. Its easy to see the difference. Whist going a long dump the clutch and see how quickly you slow down and then get back to the same speed and drop a gear (making sure your are initally a low enough revs that when you do the engine doesn't blow up) as well as the inital force of getting the flywheel up to speed there will be a significant increase in braking (as long as the revs are high enough). You can do this by also keeping it in he same gear. Have the car at 4-5000rpm and dump the clutch and get back up to speed and just take your foot off the accelerator. you will notice the difference.

Have a quick google on it and see what pops up :)

I'm sure you're right, i'm not disputing you. Just a misconception.

:) I'm just bored at work!

I agree the act of squashing a pint of air to a tenth its size a good 15-25,000 times a minute does create notable engine braking in itself.

The point i was making to start this whole debate off is simply that initial engine braking,during the absorbsion of kinetic energy into the flywheel,is reduced to notable effect with a kilo taken from the weight of the flywheel.

Sure,the lighter flywheel doesn't harness the stored energy for as long as the heavier one,so an engine slowing down with a closed throttle,once the initial void from the flywheel has been spent,will do so more quickly. But that's far less noticeable.

The difference is kept more the minor because heavier flywheels have more rolling resistance,preventing the heavier flywheel from sustaining the full extra percentage of its weight.