Yes, you are partly right here, when you are decelerating in gear, it is through the transfer of friction, that makes the engine turn.. Thats where you're right. But the engine is STILL using gas. And it is using this gas through Internal Combustion. It's still internal combustion(you don't see the explosions outside of the engine(backfires excepted))

If there was still NO combustion going on in the engine, then it would free spin. IT's these little explosions that actually slow the car down. The reason, is as the wheels turn the engine(slower and slower) the engine is still firing, naturally trying to accelerate(or at least in this case stay running), and the force of the explosions is counteracted by the force of the wheels slowing down from the effects of gravity and friction.

The reason this happens is because the engine is firing with minimal gas being delivered into it and the wheels are making it 'tach' at a higher range than it should with that minimal gas. The only thing the engine can do is slowdown, cause the car is still turning it, and it's not getting enough gas to accomodate the rpm at which the wheels are making the engine turn.and you thus have Engine Braking.


http://www.rx7club.com/showthread.php?t=459749

i guess he forgot about compression and engine vacuum.

apparently without the force of those 'tiny explosions' all engines would just freespin!

man i wonder why it didnt do that when i was trying to crank my engine over by hand! damn compression!

:rofl: :rofl: :rofl:

The pumping loss throught the closed throttle provides a lot of engine braking at higher engine speeds. Turning an engine by hand won't see that, but it makes a big difference when coasting. Now we just need to convince one of these "tech experts" to try timing how long it takes to coast down a hill with the engine off, throttle closed and repeat the test with the throttle open. We'd probably get some genious that would lock the steering column, drop the keys on the floor and run his ass into a tree. Darwinism at it's finest.

What
The
Fuck!

IIRC, two stroke engines will just free spin and not provide compression braking.

at least in motorcycles anyway.

The engine braking problem (lack of engine braking) with an unthrottled engine like a diesel is that the compression also pushes back down on the piston during the power stroke. This is why Jacobs Engine Brakes (retarders) open the exhaust valve near the top of the compression stroke. The opening of the exhaust valve(s) while the cylinder is under high pressure also makes for a lot of noise. Diesels that don't have provisions for this type of retarder often retrofit an exhaust brake that simply creates a lot of back pressure in the exhaust. A throttled engine has pumping significant losses when there is intake vacuum as the engine has to perform work and consume energy to pull air past the throttle.

IIRC, two stroke engines will just free spin and not provide compression braking.

at least in motorcycles anyway.

no two strokes do engine brake same as a fourstroke.



i'm #9
http://www.illstreet.com/forums/attach-1186

nice pic man! :D

no two strokes do engine brake same as a fourstroke.
eh, what little two stroke riding i've done they didn't do any engine braking compared to the four stroke, so i wasn't going text book, just going personal experience.