Downshifting LS3

[two_wheel_mayhem]

Doing a lot of engine braking is bad for your car. That's why they put Brembos on the cars for us to use on the street, brake pads and rotors are much cheaper than driveline components.

On a racetrack it is what it is.

[NC_SS]

Originally Posted by two_wheel_mayhem

Doing a lot of engine braking is bad for your car. That's why they put Brembos on the cars for us to use on the street, brake pads and rotors are much cheaper than driveline components.

On a racetrack it is what it is.

Engine braking makes that nice popping noise on decel though, soooooo

[two_wheel_mayhem]

Originally Posted by NC_SS

Engine braking makes that nice popping noise on decel though, soooooo

Some like it, some don't. With stock tune it decel pops by simply letting off the gas with it in gear, no engine braking required.

I think it sounds like turd.

[xinfamousxi]

New to driving stick. What I have been doing is throwing it in N and coasting to the stop

[rebelyell22]

I rev match and downshift

[Nor Cal ZL1]

Originally Posted by xinfamousxi

New to driving stick. What I have been doing is throwing it in N and coasting to the stop

Thats ok take your time. Here is a video on the heal and toe method.

http://m.youtube.com/watch?v=8By2AEsGAhU


Don't worry about downshifting until your ready and know the gearbox well because a mistake downshifting gets expensive if you screw it up. That said I have never had an engine or drivetrain related issue caused by downshifting. Downshifting is perfectly fine on the engine and drivetrain as long as it is smooth. The cars are capable of hundreds of thousands of miles of downshifting.

[i2disturbedSS]

Originally Posted by xinfamousxi

New to driving stick. What I have been doing is throwing it in N and coasting to the stop

That's fine.

[ytown87]

Originally Posted by Bodywerks

This is why you don't ask this type of question in the general forum...

ACCORDING TO GOOGLE

Downshifting can save fuel, as when you are in gear and coasting, many cars shut off the injectors or only fire minute amounts of fuel. At idle, the engine must inject enough fuel to keep itself running. The amount of fuel used at idle is significant enough that many manufacturers are moving to a start/stop system that automatically turns the motor off when you are sitting at a stop on the brakes.

In order for downshifting to a be a net fuel gain, you have to do one of two things, either not use the gas (which makes for a rougher downshift, as the inertia of the car's forward movement gets bled off as you let the clutch out (or put the DCT in a mode where it doesn't rev match) is traded to spin the motor and all of it's reciprocating parts up to an appropriate speed. Or, you have to coast long enough that the fuel saved during coasting with the car in gear is more than you'd spend simply idling the motor.

[GVA 45TH 2SS]

As others have said Fuel cut off kicks in, the innertia of the car keeps the engine moving till RPMs hit certain level or Accelerator is pressed.
Now as a side note when winding down from the mountains, I dont shift into neutral or push the clutch in. In theory the fuel cut off should save fuel.

[762SPR]

For the record, the term is engine braking. NO it does not harm the engine or the transmission (assuming you don't screw up shifting...). Instead of adding fuel (energy) into the equation to be combusted for acceleration, instead the kinetic energy of the car moving forward is going back through the drivetrain into the engine and into the compression cycle. Since there is no (or little) fuel in the mixture, therefore no extra energy added, this slows the car down. Basically it turns the engine into an air pump. On some engines (like commercial trucks) it is possible to open the exhaust valve near TDC on the compression stroke, releasing the energy that was put into compressing the air in the cylinder, making the engine braking even more extreme (used for long downhill sections to keep from cooking the brakes).

Does it burn fuel? In short NO. Well ok a little depending on the engine's specific programming (FI) While there may be some environmental or economy settings to shut off the injectors completely, generally speaking, on a fuel injected motor there is very little fuel being put into the equation during engine braking. Certainly not as much as it burns when you mash the skinny pedal and accelerate, even if the engine is rotating at the same speed. Think of it this way: The RPM is a function of energy going into the engine, either it is coming from the fuel/air charge during acceleration, OR it is coming from momentum, and slowing the car down.

Fun fact. Hybrid cars often capture the energy from slowing down and use it to charge the battery a little... If only a V8 could fill the tank from engine braking...

Regarding carbureted engines, it is a little different. Instead of pumping pressurized fuel into the air charge with injectors, the fuel is pulled into the charge by a pressure differential in the carburetor as the air flows through it. So it is a little different, but for the most part the result is the same.


Does all this save more or less fuel than using the clutch and brake to slow down? I'd imagine it really depends on circumstance, but at the level of fuel burn for either it is just splitting hairs. It will save your brake pads some ware though... Assuming you can shift, don't go trying to go from the top of 6th and try to slam it into 1st to save a little money or brake pads will likely be the least of your worries... But you know what they say: If you can't find it, GRIND it!

[Spec]

Originally Posted by ytown87

ACCORDING TO GOOGLE

Downshifting can save fuel, as when you are in gear and coasting, many cars shut off the injectors or only fire minute amounts of fuel. At idle, the engine must inject enough fuel to keep itself running. The amount of fuel used at idle is significant enough that many manufacturers are moving to a start/stop system that automatically turns the motor off when you are sitting at a stop on the brakes.

In order for downshifting to a be a net fuel gain, you have to do one of two things, either not use the gas (which makes for a rougher downshift, as the inertia of the car's forward movement gets bled off as you let the clutch out (or put the DCT in a mode where it doesn't rev match) is traded to spin the motor and all of it's reciprocating parts up to an appropriate speed. Or, you have to coast long enough that the fuel saved during coasting with the car in gear is more than you'd spend simply idling the motor.

Well there you are...

Who is this google guy and why does he know everything?

[Nate76]

Originally Posted by 762SPR

For the record, the term is engine braking. NO it does not harm the engine or the transmission (assuming you don't screw up shifting...). Instead of adding fuel (energy) into the equation to be combusted for acceleration, instead the kinetic energy of the car moving forward is going back through the drivetrain into the engine and into the compression cycle. Since there is no (or little) fuel in the mixture, therefore no extra energy added, this slows the car down. Basically it turns the engine into an air pump. On some engines (like commercial trucks) it is possible to open the exhaust valve near TDC on the compression stroke, releasing the energy that was put into compressing the air in the cylinder, making the engine braking even more extreme (used for long downhill sections to keep from cooking the brakes).

Does it burn fuel? In short NO. Well ok a little depending on the engine's specific programming (FI) While there may be some environmental or economy settings to shut off the injectors completely, generally speaking, on a fuel injected motor there is very little fuel being put into the equation during engine braking. Certainly not as much as it burns when you mash the skinny pedal and accelerate, even if the engine is rotating at the same speed. Think of it this way: The RPM is a function of energy going into the engine, either it is coming from the fuel/air charge during acceleration, OR it is coming from momentum, and slowing the car down.

Fun fact. Hybrid cars often capture the energy from slowing down and use it to charge the battery a little... If only a V8 could fill the tank from engine braking...

Regarding carbureted engines, it is a little different. Instead of pumping pressurized fuel into the air charge with injectors, the fuel is pulled into the charge by a pressure differential in the carburetor as the air flows through it. So it is a little different, but for the most part the result is the same.


Does all this save more or less fuel than using the clutch and brake to slow down? I'd imagine it really depends on circumstance, but at the level of fuel burn for either it is just splitting hairs. It will save your brake pads some ware though... Assuming you can shift, don't go trying to go from the top of 6th and try to slam it into 1st to save a little money or brake pads will likely be the least of your worries... But you know what they say: If you can't find it, GRIND it!

That all makes sense to me. The only part where I'm confused is where is all the sound coming from? When you downshift, it sounds wonderful and loud similar to when you're accelerating. So if the sound isn't from gas being combusted in the cylinders, then what's making it? Is it just the car inertia causing the cylinders to move and that makes the noise? I assumed the beautiful growl of the v8 was made by the explosions of gas in the cylinders.

[rebelyell22]

Originally Posted by Nate76

That all makes sense to me. The only part where I'm confused is where is all the sound coming from? When you downshift, it sounds wonderful and loud similar to when you're accelerating. So if the sound isn't from gas being combusted in the cylinders, then what's making it? Is it just the car inertia causing the cylinders to move and that makes the noise? I assumed the beautiful growl of the v8 was made by the explosions of gas in the cylinders.

go turn a lawnmower engine with the ignition off

[gajagfan]

I think the amount of fuel saved here over a year of engine breaking vs. using the clutch / brakes is about enough to buy one Happy Meal from McDonalds. Hardly worth the discussion is it? To me, using the opportunity to practice your rev matching down shifts is much more valuable.