Downshifting

[coolieman1220]

random question, so when you down shift, just wondering does it effect your gas usage. When you downshift, your RPM's fly up high but the throttle is not open because no throttle is pushed. so when you downshift your gears, do you use more gas because your engine is revving higher?

[johnnynumfiv]

If no throttle is being pushed, its not using gas.

[baddabang]

The engine is at high RPM's because the Transmission is turning at high RPM's. That's why when you push the clutch in you drop to idle RPM's.

[Niko_Fx]

No gas consumption, less brake consumption

[Sledgehammer]

That doesnt make sence to me. If you engine is turning faster, that means that more gas is injected into the engine in a given amount of time. Do cars stop injecting gas during a downshift? If the formentioned is true, then does that mean that idle uses more gas than downshift? That is the only senario that would make Niko's statement true.

[johnnynumfiv]

Originally Posted by Sledgehammer

That doesnt make sence to me. If you engine is turning faster, that means that more gas is injected into the engine in a given amount of time. Do cars stop injecting gas during a downshift? If the formentioned is true, then does that mean that idle uses more gas than downshift? That is the only senario that would make Niko's statement true.

If you aren't pressing on the gas, you aren't putting any gas into the engine. It's not rocket science.
When you downshift, you aren't pressing on the gas, the rpm's go up right after the shift, but then go down because you aren't pressing on the gas.
The idle is a given amount of gas just enough to make the engine run, so that is being put in at all times.

[Quiggs]

Originally Posted by Sledgehammer

That doesnt make sence to me. If you engine is turning faster, that means that more gas is injected into the engine in a given amount of time. Do cars stop injecting gas during a downshift? If the formentioned is true, then does that mean that idle uses more gas than downshift? That is the only senario that would make Niko's statement true.

Throttle plate closed = no fuel. Engine becomes a big air pump. Bosch Motronic ECUs have been like this for years.

Originally Posted by johnnynumfiv

If you aren't pressing on the gas, you aren't putting any gas into the engine. It's not rocket science.
When you downshift, you aren't pressing on the gas, the rpm's go up right after the shift, but then go down because you aren't pressing on the gas.
The idle is a given amount of gas just enough to make the engine run, so that is being put in at all times.

Troof.

But it's all about the rev matched downshifts. <3

[Sledgehammer]

Originally Posted by Quiggs

Throttle plate closed = no fuel.

Ok, I was unaware that it closed completly. I assumed that their was always a small amount of gas being put into the motor each cycle.

[Sledgehammer]

So how does downshifting in a jake brake work? I thought that the valves opened late or something like that to help the engine slow down sooner. Are jake brakes done with combustion or without?

[jediali]

Originally Posted by Quiggs

Throttle plate closed = no fuel.

blocked intake (closed throttle) = no air, which = stall. The throttle plate will allow a small amount of air to enter the engine. for newer engines (efi enabled, not just fly by wire throttle) the fuel injectors shut down meaning no fuel on no throttle input. The air only mixture runs through engine being compressed and providing engine braking and no fuel consumption.

[ZeTurbo]

I read somewhere that it actually is better to use your brakes only, and not downshifts when slowing down. This because it will cause unnecessary stress on the engine, and brakes are chaper to replce than an engine.
Is there any truth in this?
it was a "metro" paper so it probably isnt the most reliale source in the world, but it still made me wonder...

[baddabang]

Originally Posted by ZeTurbo

I read somewhere that it actually is better to use your brakes only, and not downshifts when slowing down. This because it will cause unnecessary stress on the engine, and brakes are chaper to replce than an engine.
Is there any truth in this?
it was a "metro" paper so it probably isnt the most reliale source in the world, but it still made me wonder...

No. Like quiggs said as long as you match revs or double clutch the downshifts to take it easy on the synchronizers, and not do something stupid like downshift into 2nd at 70mph it should be fine. Brake parts are cheaper but at high speed's it won't make a difference because you'll eat the up real quick.

[nota]

Originally Posted by Sledgehammer

So how does downshifting in a jake brake work? I thought that the valves opened late or something like that to help the engine slow down sooner. Are jake brakes done with combustion or without?

Valves closed for compression braking

In the old trucks I drove, disengaging the clutch while using the jake meant an instant stall

At a guess, if newer trucks provide for downshifts during compression braking then there has to be some sort of new fangled computer program or gizmo that recognises when you're downshifting while using the jake?

[ScionDriver]

Downshifting doesn't use gas; My dad said when he was a trucker back in the day that the truckers said that engine braking was always better than using your actual brakes because it help saved fuel.

[Waugh-terfall]

Surely you are pressting the throttle when you downshift to match the revs so you get a nice smooth gearchange or to avoid the wheels locking...