new manual driver: does this destroy my tranny?

[serialk11r]

Originally Posted by Thunderchicken

Read more: Coasting in Neutral or Gear to Save Gas - Coasting and Fuel Economy - Popular Mechanics

That's if you want to slow down. Energy is not free. For a mile long hill, I hope you're not allowing the car to speed up indefinitely. For shorter hills though, if you coast in neutral you end up with more speed at the bottom, and will need less gasoline to maintain your speed in the future.

The way to think of it is this, it takes more energy to spin the engine at 3000rpm or whatever it is at highway speed than the 700rpm it spins at idle. If you aren't stopping (aka throwing away all the vehicle's kinetic energy), then you want to optimize both energy usage (speed, engine braking) and energy production (engine load).

[Thunderchicken]

Originally Posted by serialk11r

That's if you want to slow down. Energy is not free. For a mile long hill, I hope you're not allowing the car to speed up indefinitely. For shorter hills though, if you coast in neutral you end up with more speed at the bottom, and will need less gasoline to maintain your speed in the future.

The way to think of it is this, it takes more energy to spin the engine at 3000rpm or whatever it is at highway speed than the 700rpm it spins at idle. If you aren't stopping (aka throwing away all the vehicle's kinetic energy), then you want to optimize both energy usage (speed, engine braking) and energy production (engine load).

Since you didn't read the whole artical.

I've replicated these conditions with instrumented cars, both with scan tools and with an oscilloscope, measuring the leads leading into the fuel injectors. The signal controlling the injector is a 12-volt square wave. It's pulse-width-modulated, varying from 5 percent or so at idle to around 80 percent or so at full throttle. The higher the percentage of on time to off time, the more fuel. There's one on pulse for every cylinder firing, so the consumption also varies with engine speed (rpm). All vehicles show a short pulse width at idle, regardless of whether they're sitting in traffic at a red light or coasting downhill—at idle—in neutral. (Actually, they use a fraction more fuel sitting in drive at a traffic light, because of the drag in the torque converter, but I digress).

Almost all vehicles show a pulse width of zero when coasting while in gear. Zero, as in there is no fuel injected at all. Yes, the engine is turning over, the pistons are going up and down, the water pump, alternator and a/c compressor are working, so technically you can say the engine is running, sort of. But it's not consuming any fuel. And that goes for automatic or manuals.

Okay, eventually, at the bottom of the hill or as you creep up to the traffic light, the engine finally will slow to idle rpm—at which point the fuel injection will wake up and start adding fuel to keep the engine from stalling. That usually starts at around 1000 rpm, and if you pay attention, you can sense when it's happening as the engine will rev up slightly. And that's when the scan tool or oscilloscope will show injector dwell rise from 0 to 5 to 10 percent. So you're actually wasting gas by putting your car into neutral.

I hear this argument as well: My car-mileage-information computer goes wild with increased mileage while coasting.

The algorithm the trip computer uses is not based on how much fuel is actually consumed, but on some calculated value based on airflow past the mass airflow sensor, manifold vacuum and engine rpm. And it's not accurate under these coasting conditions. That's why when we report fuel economy here at PM, we never just print the numbers we read off the trip computer's display: We use the gallons pumped into the tank divided by the mileage on the odometer—which we check against a handheld GPS.

I use a Scangauge II for a lot of diagnostics and general tinkering. It's a great tool—but I've learned not to trust the economy or gallons-used function too closely. That's why the Scangauge has a function that allows you to tell it what the engine-idle cutoff is for your particular car to get somewhere closer to the truth.

Bottom line: Don't coast in neutral. It's dangerous and won't save fuel. Turning off the key at traffic lights might.


Read more: Coasting in Neutral or Gear to Save Gas - Coasting and Fuel Economy - Popular Mechanics

[serialk11r]

Jesus christ, when were we talking about coasting to a stop light? I was talking about on the highway, and I said that many many times. Reading fucking comprehension. I know what deceleration fuel cutoff is.

[Thunderchicken]

Originally Posted by serialk11r

Jesus christ, when were we talking about coasting to a stop light? I was talking about on the highway, and I said that many many times. Reading fucking comprehension. I know what deceleration fuel cutoff is.

My reading comprehension is just fine. The same thing applies on the highway you run your car up to XYZ speed release the accelerator and when you feel like you need to speed up you press the petal again. The time you are off the accelerator you are not consuming fuel because your injectors aren't running. There is no reason to be out of gear unless you are changing gears. It's plain unsafe to be coasting in neutral.

[Thunderchicken]

Originally Posted by serialk11r

That's if you want to slow down. Energy is not free. For a mile long hill, I hope you're not allowing the car to speed up indefinitely. For shorter hills though, if you coast in neutral you end up with more speed at the bottom, and will need less gasoline to maintain your speed in the future.

The way to think of it is this, it takes more energy to spin the engine at 3000rpm or whatever it is at highway speed than the 700rpm it spins at idle. If you aren't stopping (aka throwing away all the vehicle's kinetic energy), then you want to optimize both energy usage (speed, engine braking) and energy production (engine load).

unfortunately, at idle your car runs much much richer then at 3000 rpm. Think of it this way. You run your car to 70 mph put the car in neutral and coast to 60 mph the ECU knows there is no load on the motor so it has to run the injectors every 5ms with X amount of fuel in order to stay at 14:1 AF, but the ECU has to run richer to achieve that. Lets say it takes 10 seconds to decelerate.

While I run my car to 70 mph let off the gas the ECU knows there is a load, but knows that the motor doesn't need to fire the injectors to keep the motor from stalling the car is happy to stay in motion without fuel because the load keeps the motor in motion. Yes my kinetic loss is going to be more but lets say it take 5 seconds to decelerate before i have to get back on the accelerator.

so in summary I got 5 seconds of no injector spraying while you got 10 seconds of very rich idle fuel.

[Saibot]

enough talking lol; i actually went out and did an experiment yesterday.

I did three types of highway cruising; Each test was along a flat section of the highway. I did the experiments consistently across roughly a 30 km (18.6 miles for you americans) stretch each (i was driving from niagara falls to toronto and was bored). All windows were open, Air conditioner was off; and stereo was off. After the results of each test, id reset the mpg counter and restart the next one.

The tests:

1. in 6th gear; accelerating to 120kmph (74.56 MPH), lifting foot off pedal and letting car slow to 90kmph(55.92 MPH) without touching clutch or gear shifter. Average speed was ~105kmph (65.24 MPH).

2. Cruise control on 6th gear set at 105KMPH (65.24MPH).

3. Accelerating in 6th gear to 120kmph (75 MPH), putting it in neutral, coasting down to 90 (56MPH) ; then rev matching and accelerating back up to 120kmph (75 MPH).


The results:
1. Coasting in gear: 32.7 mpg
2. Cruise control: 33.1 mpg
3. Coasting in neutral: 38.6 mpg


After deciding coasting in neutral was the most efficient, i drove the remaining part of my trip like so. I turned on AC for the last bit noticed my idle rpm when coasting in neutral went from about 800rpm to 1.1k rpm. This dropped my coasting in neutral mpg from 38.6 to 37.8


Those are the results guys.

p.s ive already started heel toeing two weeks into learning manual (^^,)

EDIT:
regarding thunderchicken's post.

Sure you get 5 seconds of no fuel, while we get 10 secs of rich idling, but at the end of the day; you have to get on the accelerator pedal twice as many times as we do.

[EsoBOFH]

Originally Posted by ThatGuy

Look ahead and adjust speed before you have to (try to max speed transition as slow as possible, or remove them altogether) **** This is the BIGGEST factor in real world fuel economy.****

Exactly... in other words - don't brake, ever.

The right pedal is an investment, the middle pedal throws your money away

This car is quite capable of whipping around corners at speeds, and you can use that to your advantage by braking only when necessary, or only to the speed necessary to safely negotiate a corner. Braking is evil!

[Thunderchicken]

Originally Posted by Saibot

enough talking lol; i actually went out and did an experiment yesterday.

I did three types of highway cruising; Each test was along a flat section of the highway. I did the experiments consistently across roughly a 30 km (18.6 miles for you americans) stretch each (i was driving from niagara falls to toronto and was bored). All windows were open, Air conditioner was off; and stereo was off. After the results of each test, id reset the mpg counter and restart the next one.

The tests:

1. in 6th gear; accelerating to 120kmph (74.56 MPH), lifting foot off pedal and letting car slow to 90kmph(55.92 MPH) without touching clutch or gear shifter. Average speed was ~105kmph (65.24 MPH).

2. Cruise control on 6th gear set at 105KMPH (65.24MPH).

3. Accelerating in 6th gear to 120kmph (75 MPH), putting it in neutral, coasting down to 90 (56MPH) ; then rev matching and accelerating back up to 120kmph (75 MPH).


The results:
1. Coasting in gear: 32.7 mpg
2. Cruise control: 33.1 mpg
3. Coasting in neutral: 38.6 mpg


After deciding coasting in neutral was the most efficient, i drove the remaining part of my trip like so. I turned on AC for the last bit noticed my idle rpm when coasting in neutral went from about 800rpm to 1.1k rpm. This dropped my coasting in neutral mpg from 38.6 to 37.8


Those are the results guys.

p.s ive already started heel toeing two weeks into learning manual (^^,)

EDIT:
regarding thunderchicken's post.

Sure you get 5 seconds of no fuel, while we get 10 secs of rich idling, but at the end of the day; you have to get on the accelerator pedal twice as many times as we do.

How are you calculating your fuel usage. If you are using the computer your fuel usage is incorrect and isn't based on fuel, but MAF voltage values and rpm. To get true fuel usage is to actual milage divided fuel used

[Saibot]

Originally Posted by Thunderchicken

How are you calculating your fuel usage. If you are using the computer your fuel usage is incorrect and isn't based on fuel, but MAF voltage values and rpm. To get true fuel usage is to actual milage divided fuel used

? I'm not stating instantaneous mpg, but average over a trip. Instantaneous would have infinate or near infinate mpg during coasting.

[Thunderchicken]

Originally Posted by Saibot

? I'm not stating instantaneous mpg, but average over a trip. Instantaneous would have infinate or near infinate mpg during coasting.

since you are not using distance gone divided by fuel used your number mean nothing it's just assumed milage. Unless you are calculating these numbers they are just number that the computer is spitting out.

315.2 miles driven / 11.223 gallons filled = 28.09 miles to the gallon by the way that was my '02 Honda Si just filled up this afternoon with no highway miles on this tank.

[Thongpocket]

If you are that concerned with gas mileage, I think you should have gotten a VW diesel. Seriously? That much effort to save MAYBE $1.00 per tank?

[serialk11r]

Originally Posted by Thongpocket

If you are that concerned with gas mileage, I think you should have gotten a VW diesel. Seriously? That much effort to save MAYBE $1.00 per tank?

I think he finds it entertaining possibly? I dunno. I'm too lazy to do it personally.

[7thgear]

Originally Posted by serialk11r

I think he finds it entertaining possibly? I dunno. I'm too lazy to do it personally.

but you'll spend half an hour writing up a scientific argument?

[serialk11r]

Originally Posted by 7thgear

but you'll spend half an hour writing up a scientific argument?

No, it only took 15 minutes (I do it pretty often on this board though ) Amazingly, I typically hate writing up notes in LaTeX and stuff because I feel like it's too tedious. Contradictions...