Engine braking?

[Robobble]

hahaha, whatever. I can live with using the brakes, It's just what I was used to. I do miss the obnoxiously loud gargle gargle CRACK gargle gargle of a straight-pipe 5.0.. lol, pretty sure everyone who lived on that hill (right by my house, went up/down it every day) hated me! Thanks for the replies!

[RichBinAZ]

I agree with Norm about trying to not let it go past about 4K rpm, your engine will last a lot longer that way. Pumping the brakes on the way down the hill is also good, with as much free wheeling time in between pumps as possible. That will save the brakes from burning up - hence your question about engine braking: Yes it's a good thing.

Well the engine is small and despite the high compression ratio, the actual compression ration is much lower than that. Think of all gasoline engines as variable compression engines and you are only getting full compression at wide open throttle. (Diesels are opposite)

Going downhill, the throttle plate is closed and the only air going thru the engine is what can leak around the edge of the plate and the air going thru the idle air valve. None of this is a lot, so there really isn't a lot of engine braking. It's also quite fuel efficient to do this too.

If you want engine braking, get one of these. I literally have to drive it down the hills that cars and trucks run away on, otherwise it will stop on its own. Must be a low mass thing.

[Iceracer]

In CDL school, we were told that lightly riding the brake is better tham "pumping" the brake.
Compression ratio is a fixed mechanical number and is not changed by throttle opening. You may be thiking of mean effective pressure.
Engine braking with a closed throttle is just the reistance of the pistons compressing the air in the cylinder. Friction is also a factor, increasing with rpm.

[FXSTi]

I may be wrong, and I'm sure someone will point it out if I am. Here is my theory. Our cars have variable valve timing, and I suspect that it is set up to keep the valves open longer during deceleration. With the valves open the engine pumps less air than it would with fixed valve timing.

Remember this is just my theory, I waited to post, hoping someone would explain it better than me. Nobody posted so I am probably wrong.

[Iceracer]

It doesn't change the duration of the cam. So early or late, the valves are open for the same amount of time.

[FXSTi]

Thanks Iceracer,

I'm no expert on these things it was just a thought.