jlin101

you don't save any gas by shifting into neutral while going downhill--the engine is coasting in either case. As far as the 30 lb saved from removing the spare, that's miniscule too. One G35 forum members once gave a quick tip to remove 250 lb from his car--telling his GF to get out of the car.

Lets Drive

iTrader: (3)

That and a few other factors. But we'd also have to keep in mind that it would be extremely difficult to calculate how much each factor affects the slowing of the car (I at least don't want to do it ). I'd be more inclined to say, that if you're coasting, you're usually doing it before coming to a stop, making engine braking valuable if for some reason you're trying to save brakes on the street. Otherwise, if you're proceeding at a given speed, and begin going downhill, a few other factors would dictate that you gain or 'maintain' speed (overcoming the engines ability to slow the car), until you're ready to accelerate again.In a few cases, you're absolutely right with the idea, but if one is trying to make it a practice, I'd just stay out of neutral in an automatic car (and for days when not driving lazy, a manual one too)...more work than necessary.

Ichigo

Thats a REAL big GF.... shoot im 6'0 and I barely weigh 200.

jcreech

if you really want to save gas in your 350...try snow mode. i get considerably better mileage.

C280to250

that was Funny

Regarding Conserving Gas have you guys used unocal 76 use premium ofcourse.
My take on this two Gas station
Chevron=Aggressive Driving 24mpg Normal driving 27.5mpg

Unocal 76 =Aggressive Driving 23mpg Normal Driving 28.8mpg
Im going by the Tank Average

I Use Chevron all the time.
The only thing i dont like when i put unocal is the Power to get up and go seems to be less.
Try unocal i bet it will give you more MPG

2Fast0

You are wrong.

2Fast0

assuming what u said is true. it doesnt change the fact that my engine drops down to 600rpms when in neutral. I think an engine in gear going at 2500rpms will use more gas than an engine in neutral going at 600rpms, assuming they are both going at the same speed, say 70mph.

and like someone else said, there is engine break when the car is in gear, so even though i'm going down hill with my foot off the accelerator, my car's speed is decreasing due to the engine break. on the other hand, if i'm in neutral and going down this same hill, i might gain some speed if not maintain my current speed. when i get ot the bottom of the hill, i just put the car back in D and keep going.

Lets Drive

iTrader: (3)

You're missing the idea a bit- RPM is not a measure of fuel injection, its a measure of how fast your engine is rotating. Coasting is to move without the use of propelling power. An engine turning at any RPM can be done so via the drivetrain, because the wheels 'stay connected' to the motor in an automatic car. If you roll faster while in gear, the drivetrain will turn the engine faster, obviously raising the RPMS...however, your injectors are not injecting fuel, because you are not pressing the throttle...remember, you're not accelerating or cruising, but coasting.

An example would be my other car, where I have an ECU which also has a commander visual display which shows the injector duty cycle, just as the ECU sees it. At coast, at any speed, in any gear, at any RPM, it will read 0%, because the drivetrain is doing the work, in combination with gravity and momentum. If I want to accelerate or cruise, then pressing the throttle will subsequently inject fuel, and the duty cycle (fuel used) will raise according to how much I'm trying to accelerate.

You'll engine brake, but if you're coasting in the first place, then you're most likely trying to go slower anyway... In the process of coasting, you will save gas, but if you put it in neutral, you'll 'go faster' (defeating the purpose of getting off the throttle), and also burn gas. Either way, I'm just offering the truth about coasting and shifting into neutral (which is not the best for auto trannies when throwing it back into gear), when ones car, by design, is engineered and fully capable of taking on such task by itself.

2Fast0

how can the engine rotate without burning fuel? I thought it's the combustion of gasoline that creates the force to push the pistons downward. therefore, the faster the engine is revolving up and down, the more fuel it needs to perform the mechanical work. right?? You said the injectors are not injecting fuel cuz i'm not pressing the throttle, but I would think fuel is being fed to the engine via some other route. the throttle can't be the only mechanism that is controlling how much fuel is being fed to the engine.

Lets Drive

iTrader: (3)

Have you ever turned your key, and heard the engine cranking, but not turn over? Thats your engine being spun by the starter motor. Have you ever seen a person push start a car in order to get it running? Thats essentially using the drivetrain to rotate or turn the motor over. Torque is what rotates your engines crankshaft, and that can be created by an outside motor, a person pushing, or combustion. Keeping this idea in mind, remember that your drivetrain is always connected to your motor when in gear, and as such, has the ability to rotate the motor (by applying torque), so long as the car has enough momentum behind it...meaning the car does not need to inject fuel, since torque is being applied to the crankshaft from elsewhere. This is a mechanism engineered into cars, which among other reasons, saves gas. Its easier to demonstrate with a manual car, but its the same reason why you will stall an engine if you don't put a manual car into neutral when stopped- the engine is halteded by the drivetrains lack of twisting motion. Placing the car in neutral allows it to rotate freely under its own power, but to do so, it must now consume fuel. This is why when coasting, it doesn't make sense to put the car in neutral...since the car is rolling, you can use that 'free' energy to rotate the engine, instead of having it turn by itself. RPM will just let you know how fast its turning, whether it be by the drivetrain, or its own power, in case you need to select your gear again.

Yes, but thats when you've used your right foot to depress the gas pedal, and open the throttle. As air enters, your ECU senses the throttle position via a sensor, and along with a host of other sensors, it injects a specific amount of fuel, which is then ignited for our familiar end result. The more you depress the gas pedal, the more air is allowed in, and your engine rotates faster (rpm) to allow more air in over a shorter period of time, for what amounts to stronger acceleration. However, the key here is mechanical work, which can also be done by other portions of the car now that its already in motion. You cannot accelerate or even cruise (maintain your exact speed 'indefinately') without using fuel (unless you're going downhill), but you can coast (slowly losing speed at a gradual pace) for a pretty good distance from most speeds depending on your gear.

Try accelerating to 60mph, then just let off the gas, and you'll see how far you travel on a fairly flat road in an automatic car...you'll be hard pressed to find your engine braking dramatically, as your car will most likely be in its final gear (again, engineered for fuel savings). It will downshift into the next lower gear before the engine slows too much (stall), but with each drop in gear (due to the different ratios), your engine will have more leverage on slowing the car. In a manual car, its even eaiser to see this.

Without making it too complicated, in a nutshell, your right foot is the main contributor to how much fuel your ECU is deciding to inject into your motor. There are a HOST of other mechanisms which work in conjuction with your right foot, which read everything from air temperature, to how much oxygen you have in your exhaust, which dictate how much fuel is injected, but for all intents and purposes, your right foot dictates how much air comes in, and your car does its best to match that.

SKYTECH

The coverter unlocks so not much engine brake happens. If youre that worried about gas, get a motorcycle.

gshb

even a 600cc bike will get only about 40-50mpg, but is much more fun and dangerous than a comparable car (prius). as for shifting to neutral, you dont save fuel. coasting downhill in 6th means your RPMs will drop to above idle, but below 2000rpm. you would have to go pretty fast downhill for the rpms to climb when youre not adding gas. at the stop light, again no savings because the car is idle whether you put it in drive or neutral? ....

2Fast0

Thanks for that clarification and detailed explanation. You have officially persuaded me. Appreciate ur help.

Lets Drive

iTrader: (3)

Hey, no problem. Glad I could help.