What RPM to maximize fuel efficiency?

S

Stu C

Member
Let's face it, there's no reason to beat on the car in traffic. However, I'm constantly having to remind myself not to run this car at Honda RPM's while cruising. So those that have been getting killer MPG, what RPM are you cruising at?
 
As low as possible without bogging it. If I am on a flat road maintaining a constant speed I try to keep it under 2000 rpm. Around 16-1800 seems to work good. You just want to keep off of the turbo as much as possible. Drive like this guy would. (smoke)
 
I just set mine on cruise and my RPMs are usually low 2K...
I've gotten over 28 MPG...though, I live in Florida with long straight flat roads and minimal traffic...
 
I am normally cruising at around 2,000 rpm or below in 6th, sometimes 5th if traffic is slow along the backroads. I stay off the turbo for most of my driving (for real) attempting to maximize gas mileage. Only seeing 22/23 mpg. (nuts) I took a 150 mile drive to my girls parents house 2 weeks ago and got just shy of 27mpg. I've got about 1,400 miles on my motor if it makes any difference. Will this get better with time???
 
lestat13 said:
I am normally cruising at around 2,000 rpm or below in 6th, sometimes 5th if traffic is slow along the backroads. I stay off the turbo for most of my driving (for real) attempting to maximize gas mileage. Only seeing 22/23 mpg. (nuts) I took a 150 mile drive to my girls parents house 2 weeks ago and got just shy of 27mpg. I've got about 1,400 miles on my motor if it makes any difference. Will this get better with time???
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supposedly, you will get better gas mileage (like 2-3 mpg better) after an initial break in period, and then it will slowly degrade over the lifetime of the car, but every car is different. it honestly probably doesn't make that much of a difference, but what does make a difference is that as you own the car longer, you are more used to it and are better at keeping the RPMs down when you don't mean to romp on it.

another important thing to remember is: use engine braking! when you engine brake on a fuel-injected car, you're basically not consuming fuel and still moving forward. it saves your brake pads and also adds to fuel efficiency. i consistently get 22-24mpg on mixed driving with my car and 28-30mpg on the highway now because i'm used to keeping my RPMs where i mean for them to be. when i'm going through stop and go traffic, i allow myself to rev up to 3k-4k rpms (without going heavy on the throttle so the turbo stays off) so that i have plenty of engine braking available for slowing down at lights and because of slow traffic.

in the end, there isn't a magical "fuel efficient RPM" that you need to stay at...it's a combination of RPM management so that you can stay in the zone for engine braking, cruising, etc.
 
Sacrilicious said:
another important thing to remember is: use engine braking! when you engine brake on a fuel-injected car, you're basically not consuming fuel and still moving forward. it saves your brake pads and also adds to fuel efficiency. i consistently get 22-24mpg on mixed driving with my car and 28-30mpg on the highway now because i'm used to keeping my RPMs where i mean for them to be. when i'm going through stop and go traffic, i allow myself to rev up to 3k-4k rpms (without going heavy on the throttle so the turbo stays off) so that i have plenty of engine braking available for slowing down at lights and because of slow traffic.

in the end, there isn't a magical "fuel efficient RPM" that you need to stay at...it's a combination of RPM management so that you can stay in the zone for engine braking, cruising, etc.
Click to expand...

Why is engine braking more fuel efficient than coasting? If you are coasting you are at idle RPM which is less than when the engine is engaged while slowing down. Also, while you are putting less stress on brake pads, you are putting more stress on the transmission and engine downshifting, right? Brake pads are easy to replace.
 
PeterC said:
Why is engine braking more fuel efficient than coasting? If you are coasting you are at idle RPM which is less than when the engine is engaged while slowing down. Also, while you are putting less stress on brake pads, you are putting more stress on the transmission and engine downshifting, right? Brake pads are easy to replace.
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when you idle, you're actively burning gas to maintain the 700-800 rpms that the engine turns at. when you engine brake on a direct-injection car (synonymous to taking your foot off the accelerator), your car basically stops injecting fuel into the engine cylinders. what keeps the engine rolling at X rpms is simply the forward momentum of the car traveling through the transmission and into the engine. in order to keep the engine turning without detonating gasoline in the cylinders, it bleeds off the kinetic energy from the car's forward movement (thus the "braking" effect).

now, i should have mentioned that i do not downshift just to engine brake, since that would indeed be unnecessary wear on the transmission (which is why i was trying to emphasize the careful management of RPMs so that you have enough engine speed handy for effective braking without downshifting). if you don't downshift to engine brake and simply take your foot off the accelerator, the wear to the engine and transmission is negligible. i mean, if you think about what your engine+transmission is built to handle (hard acceleration created by blowing up loads of gasoline crammed into the cylinders with heavily-compressed air), engine braking is a complete cakewalk! where you run into noticeable wear on transmission parts is when you shift gears, disengage/reengage the clutch, etc. when it's fully engaged and running, the wear is basically negligible.
 
Sacrilicious said:
when you idle, you're actively burning gas to maintain the 700-800 rpms that the engine turns at. when you engine brake on a direct-injection car (synonymous to taking your foot off the accelerator), your car basically stops injecting fuel into the engine cylinders. what keeps the engine rolling at X rpms is simply the forward momentum of the car traveling through the transmission and into the engine. in order to keep the engine turning without detonating gasoline in the cylinders, it bleeds off the kinetic energy from the car's forward movement (thus the "braking" effect).

now, i should have mentioned that i do not downshift just to engine brake, since that would indeed be unnecessary wear on the transmission (which is why i was trying to emphasize the careful management of RPMs so that you have enough engine speed handy for effective braking without downshifting). if you don't downshift to engine brake and simply take your foot off the accelerator, the wear to the engine and transmission is negligible. i mean, if you think about what your engine+transmission is built to handle (hard acceleration created by blowing up loads of gasoline crammed into the cylinders with heavily-compressed air), engine braking is a complete cakewalk! where you run into noticeable wear on transmission parts is when you shift gears, disengage/reengage the clutch, etc. when it's fully engaged and running, the wear is basically negligible.
Click to expand...

Engine braking by downshifting does not cause any harm to the transmission. There is no more wear on it (in fact there is less) than when you are at a similar RPM / gear and accelerating. This is because you are braking at the same time to assist the transmission in slowing down the vehicle. Larger vehicles have been doing it for decades. In fact, newer large trucks have automatic engine braking built in. The slight increase in wear on your transmission is more than worth the amount of wear you will save on your brakes and rotors. I alway engine brake. (now) I have never had a transmission issue on a car ever, and my brakes last a heck of a lot longer than before I did it. In many cases at slower speeds, I never have to touch my brakes.
 
Sacrilicious said:
when you idle, you're actively burning gas to maintain the 700-800 rpms that the engine turns at. when you engine brake on a direct-injection car (synonymous to taking your foot off the accelerator), your car basically stops injecting fuel into the engine cylinders. what keeps the engine rolling at X rpms is simply the forward momentum of the car traveling through the transmission and into the engine. in order to keep the engine turning without detonating gasoline in the cylinders, it bleeds off the kinetic energy from the car's forward movement (thus the "braking" effect).

now, i should have mentioned that i do not downshift just to engine brake, since that would indeed be unnecessary wear on the transmission (which is why i was trying to emphasize the careful management of RPMs so that you have enough engine speed handy for effective braking without downshifting). if you don't downshift to engine brake and simply take your foot off the accelerator, the wear to the engine and transmission is negligible. i mean, if you think about what your engine+transmission is built to handle (hard acceleration created by blowing up loads of gasoline crammed into the cylinders with heavily-compressed air), engine braking is a complete cakewalk! where you run into noticeable wear on transmission parts is when you shift gears, disengage/reengage the clutch, etc. when it's fully engaged and running, the wear is basically negligible.
Click to expand...


One more thing, it is the fact that you take your foot of the gas that causes modern vehicles to shut off the fuel. The RPM level (being in or out of gear) is irrelevant. Therefore, it is better to engine brake for the sake of your brakes, as it will not affect your MPG either way.
 
camrycev6 said:
Engine braking by downshifting does not cause any harm to the transmission. There is no more wear on it (in fact there is less) than when you are at a similar RPM / gear and accelerating. This is because you are braking at the same time to assist the transmission in slowing down the vehicle. Larger vehicles have been doing it for decades. In fact, newer large trucks have automatic engine braking built in. The slight increase in wear on your transmission is more than worth the amount of wear you will save on your brakes and rotors. I alway engine brake. (now) I have never had a transmission issue on a car ever, and my brakes last a heck of a lot longer than before I did it. In many cases at slower speeds, I never have to touch my brakes.
Click to expand...

although, it's not harm persay, it's added wear. just the simple fact that you slip the clutch a little bit as you downshift puts a little bit of wear on your clutch. over time, this starts adding up. i'm not saying it's going to be an significant kind of wear, but i was simply confirming the guy's post about downshifting causing some sort of wear on the clutch.
 
camrycev6 said:
One more thing, it is the fact that you take your foot of the gas that causes modern vehicles to shut off the fuel. The RPM level (being in or out of gear) is irrelevant. Therefore, it is better to engine brake for the sake of your brakes, as it will not affect your MPG either way.
Click to expand...

my understanding was that your engine will always try to maintain a minimum of idle RPM. if you're above idle RPM, then my understanding was that it will actually pull fuel a little farther past what it does to maintain idle. given that, if you engine brake instead of braking with your pads + rotors, you would actually save some gasoline too. if i'm wrong on the additional fuel cutting thing, then you're definitely right about the brakes being the only thing saved.
 
I did a little research (including Popular Mechanics) and all versions collaborated the version that modern fuel injected cars cut off fuel feeding (beyond what is necessary to keep the engine running) once the accelerator is released. It doesn't matter if you are at 4000 RPMs or not. If your foot is off the gas, it is the same thing as idling.
 
Sacrilicious said:
when you idle, you're actively burning gas to maintain the 700-800 rpms that the engine turns at. when you engine brake on a direct-injection car (synonymous to taking your foot off the accelerator), your car basically stops injecting fuel into the engine cylinders.
Click to expand...
Oh, I see. I think this explains why when I let my foot off the accelarator when in gear, the ignition timing in my other car (not a Mazda) drops all the way down to 3 (It's 15 at idle), and the fuel injector pulse % drops as well.
 
Sacrilicious said:
my understanding was that your engine will always try to maintain a minimum of idle RPM. if you're above idle RPM, then my understanding was that it will actually pull fuel a little farther past what it does to maintain idle. given that, if you engine brake instead of braking with your pads + rotors, you would actually save some gasoline too. if i'm wrong on the additional fuel cutting thing, then you're definitely right about the brakes being the only thing saved.
Click to expand...

I hear you. I just think the benefits outweigh the negatives. Not to mention, engine braking is a MUST if you are going up and down a lot of hills. I have smelled many a person burning up their brakes going down a large hill / mountain. I just engine brake all the time...
 
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