Maximizing Fuel Economy

[IFMJohn]

So, I come from the v8 world. My previous vehicles are a v8 titan and a v8 jeep. I'm used to feathering the throttle to try to maximize fuel economy.

I'm wondering what physical modifications can be made to the vehicle to increase fuel economy?

-Air Filter (Picking up a K&N today at work)
-Amsoil Engine Oil (Fluke or does this really increase fuel economy?)
-Amsoil transmission fluid (same question as above)
-??

I'm not going to lower my car. I'm not going to spend $1000 on something that might get me a few more mpg.

I've been working on cars my whole life, I'm going to school for diesel mechanics, and I work at an auto parts store. I have a pretty good understanding of this kind of stuff. Just wondering what you guys who have been driving 4 bangers for years have discovered.

Also, Are the factory service manuals through toyota's technician website downloadable?

 

[kyoo]

I usually do notice a pickup of 1 or 2mpg when I switch to Amsoil - can't say I've noticed much with the Corolla though. The trans fluid is on my list of things to do once the weather gets nice again.

Weirdly, I've noticed that at 75mph, the car tends to do significantly better in MPG. I can only imagine this is due to the engine running hotter (more efficiently) and it seems to outweigh the cost of increased air resistance. Trying to get others to corroborate, but no one's responded as of yet.

Also, keeping a Fuelly might help as far as keeping track of everything, comparing averages, trends, etc.

 

[Richard]

Well do you have manual transmission or automatic? if manual i would shift at 2700-2900 rpm if your going for fuel economy. Do not floor it obviously haha, drive 60-75 miles per hour too get the best out of your engine. Purchase the best gasoline, not the cheaper stations because they seem to burn quicker for me or maybe I am wrong. keep track of how many miles you drive on one tank of gas and divide it by how many gallons you fill up when you go to the station, that will tell you your miles per gallon based on that tank of gas. Mine usually gets 31-29. doesnt drop lower unless im flooring it all the time.

 

[kyoo]

^
I have auto. Right now I'm averaging around 31 mpg or so. I was just commenting on the fact that it seems like I get much better mpg cruising at 75mph than I do at 60-65mph. I wonder if anyone else has found the same. Always do Shell or BP, and am using fuelly to keep track of mpg with the trip odometer. I used to get 42mpg solid on my '08 Mini Cooper on the highway, kinda disappointing I haven't been able to break 36mpg in the rolla

 

[IFMJohn]

I've been getting around 36 when I drive like a grandpa (60 mph freeway) (90%+ freeway miles). I've gotten it down to around 32 when I'm going 80.

 

[Donabed Kopoian]

Check it again. Several things affect mileage, could be a fluke. Car needs more fuel to move at 75 then at 65. If the car was in a different gear at both speeds it is possible, but even things like ambient temperature and humidity affect mileage.

 

[kyoo]

Check it again. Several things affect mileage, could be a fluke. Car needs more fuel to move at 75 then at 65. If the car was in a different gear at both speeds it is possible, but even things like ambient temperature and humidity affect mileage.

Noticed on more than one occasion. I definitely agree it is odd. While it does need more fuel, it runs hotter and produces more torque, which requires less "throttle" (I use cruise control the whole way). I'll test again in the summer when the fuel is normal and more stable.

 

[Donabed Kopoian]

Best way to truly tell would be to keep as many things constant as possible.

Use the same gas pump, fill to first cut-off. One tank stay at 65, noting outside temperature and humidity.

Next tank, do 75, noting outside temperature and humidity.

Find average temperature and humidity during 65 tank and again for 75 tank.

The colder it is, and the more humid it is, the more fuel you'll burn because of denser air and weaker charge, respectively.

 

[livevil904]

There are several factors at play with fuel economy.

Firstly, engines are most efficient, in terms of work done per unit fuel, when working their hardest. This means with the pedal floored and the engine turning at whatever rpm makes peak power (5000-6000 most likely). However, some of that power is going towards overcoming friction in the engine, and the more rpm, the more friction.

Secondly, you have to accelerate somehow. The engine has to change the cars kinetic energy from x mph to y mph. You have basically two options on how to do that: using a lot of power and fuel for a short period of time, or using a small amount of power and fuel for a long period of time. Ignoring several other factors, these are equivalent.

The advice of accelerating slow and granny shifting at 2500 rpm is not going to help you get good gas mileage, though I doubt you will get "bad" gas mileage driving that way. It will also be boring.

So a hard working engine is good, but high rpm is bad, to me this would suggest that the most efficient way to accelerate is to sandwich your torque peak between shifts. This is typically about 4000 rpm in most toyota corolla engines, that would mean shifting at 5000 rpm would be reasonable. I personally wouldn't shift below 4000rpm.


Now as for cruising speed. It's a simple balance between a engine that is working harder and closer to it's peak torque and peak efficiency, and the increasing force of wind resistance. The force of wind resistance quadruples when you double your speed, this means it takes 4 times the power to go twice as fast. If the force of wind resistance was linear, then there would be no adverse effect of driving faster because even though the engine is working harder going, say, twice as fast and using using twice the fuel, you are also traveling twice as many miles. 2*miles / 2*gallons = miles / gallons.

The reason cars with lower powered engines get better gas mileage is because the engine has to work harder to do everything and is therefore more efficient. It's not as though a higher powered car is using all it's power to it's potential (and using more fuel than a lower powered car), it's just that it isn't as efficient when using a small percentage of it.

Like others have said, it takes time and diligence in documentation to find the most efficient cruising speed. In my RX7, I've gotten my best gas mileage going 75-85mph. In my geo prizm 3sp auto, I get the best going 55 and would probably get the very best going 47 (right after the torque converter locks up), but I don't drive under the speed limit.

 

[livevil904]

Also, across all my testing, I've found very insignificant difference between gas stations. Any actual difference would be most likely overcome by the fact that the gas is cheaper.

 

[Donabed Kopoian]

That's not right at all.

First, when I say use the same pump, that is to keep your car at the same level and get the exact amount of fuel in your car to a consistent shut-off point. When you change pumps, you can inadvertently add more or less fuel, which means your calculations will be off.

When I floor it up to the speed limit I get around 315 miles out of a tank. When I shift at 2500 rmps and use light throttle to the speed limit, I get over 340 miles, and this is consistent.

Most cars will use the least fuel at the lowest speed in the highest gear possible that doesn't lug the engine or keeps the converter locked, manual and automatic transmission respectively.

If you lug the engine, you are burning more fuel having the engine trying desperately to get power, so you downshift, then upshift after the hill, keeping your speed consistent.

 

[Donabed Kopoian]

With an RX-7, you need rpms to keep the engine from lugging or dumping in fuel to just keep speed because their is no torque in rotary engines. That is why having more rpm benefits you in that car as opposed to a four-stroke Otto engine that can produce some torque down low in the rpm range.

 

[livevil904]

1) Miles per tank is an unreliable and inconsistent measurement of gas mileage. Gas gauge accuracy? Do you fill up at exactly the same gauge location each time? Are you able to accurately tell when you're at that location on the gauge?

2) You probably will get less gas mileage if you floor it up to the speed limit, because the ECU then tunes for power rather than efficiency. I never talked about throttle position, that's a whole other conversation. Also, stop lights are timed for someone accelerating slowly, and so you'll most likely hit more red lights if you accelerate quickly. Also, accelerating quickly means that it is typically more difficult to adjust to traffic conditions, resulting in more brake use. So yes, in the real world it is likely you will get slightly better gas mileage accelerating slowly while in city traffic.

3) "Lugging an engine" to me just means driving at an rpm that does not make very good oil pressure. Typically this is below 1500 rpm. It's not as though your fuel economy changes significantly if you drive at 1400 rpm versus 1500 rpm, and the engine is certainly not "dumping" any more fuel into the engine when you're lugging it compared to not. The engine is most efficient in terms of power output per unit fuel at peak torque RPM, why else would it make peak torque at that RPM?

4) Rx7's have rotary engines. A rotary engine IS a FOUR stroke otto cycle engine. Yes it burns oil in the combustion chamber by design. Yes many times people premix their gas. Yes it is high revving and is not a low rpm performer (though it does have a very flat torque curve on stock ports). Where do people get the idea that it is a two stroke engine?
I do agree that the reason I experience good gas mileage at high speed is because the rotary engine is more efficient at high load and high rpm, just like a piston engine except to a lesser degree.


My main point is this,
If wind resistance was a linearly increasing force with respect to velocity, then the most efficient cruising speed would be in top gear at peak torque rpm. Since it isn't, there is a balance between engine efficiency and wind resistance that you must find. I doubt there are many cars that are most efficient at speeds above 55mph.

 

[Donabed Kopoian]

1) I keep track of the gallons I put in the tank and I fill to the first shut off on the pump.

2) Yeah, coasting helps as well instead of stop and go

3) Lugging the engine is when it groans from being in too high of a gear and having too much throttle. You'll hear it, and can't confuse that sound with anything else. And yes, if you go up a hill and the engine is lugging because you are in too high of a gear, people will floor it to keep speed, which dumps a ton of fuel into the engine, as opposed to downshifting a gear and being lighter on the throttle. Also, efficiency isn't equal to torque nor horsepower. Torque = (HP * RPM) / 5252. Engine design is what causes peak rpms for torque and horsepower to be different, and it has nothing to do with efficiency (also, that number only exists at that rpm under full throttle. When you let off the gas the numbers drop ... that is why dyno pulls are done under wide open throttle in a high gear).

4) A rotary engine IS NOT a 4-stroke nor a 2-stroke. A rotary engine doesn't even have pistons. Look up the design on Google and you'll see what I mean.

 

[Donabed Kopoian]

This is a rotary. The rotor spins around the casing of the engine on an eccentric gear. One edge is doing intake, the other edge is doing compression/power, the other edge is doing exhaust. The rotary is sealed via apex seals, as opposed to piston rings.

That is why rotaries lack torque, but can spin at a really high rpm and make horsepower.

With a piston, the explosion of the fuel occurs and forces the piston directly down, which is what gives them their bottom end power. When a rotary goes through ignition, the explosion occurs but pushes the rotor along at an angle instead of directly.

The advantage is that you get 3 explosions per revolution (albeit smaller one), while an Otto 4-stroke engine gets 1 every other revolution, with a 2-stroke getting 1 every revolution.

 

[livevil904]

Efficiency in terms of power output per unit fuel is what I'm talking about. There are many different types of efficiency.

A rotary engine is a 4 stroke engine. It has an intake stroke, a compression stroke, a ignition/power stroke, and an exhaust stroke... go ahead and count them. A 4 stroke engine has nothing to do with pistons. There are also two stroke rotary engines, they just were not used in rx7's. Please don't try to explain an engine to me that I've rebuilt and driven for 3 years.

Rotary engines don't so much "lack" torque as they just rev so high that they make much more HP than ft lbs. We are accustomed to engines making about the same amount of HP as ft lbs. That said, my rotary engine, when it was stock, makes peak torque at 3800 rpm. The 1zz-fe makes peak torque at like 4200 or something like that.

Rotary engines DO NOT have 3 explosions per crankshaft revolution (which is what RPM measures). Yes there are 3 explosions per rotor revolution around the eccentric shaft, but it's irrelevant when comparing it to a piston engine. Rotary engines have 1 explosion per rotor per crankshaft revolution. That means, for every production rotary engine produced by mazda except for the 3 rotor 20B in the mazda cosmo, there are 2 power strokes per revolution in your typical twin rotor engine. This happens to be the same number of power strokes in a 4 cylinder piston engine (4 cylinders, each firing every other rotation)

 

[Donabed Kopoian]

The stroke is in reference to what the piston is doing inside the cylinder (engine displacement on a piston engine is measured as pi x (bore/2)^2 x stroke).

You are wrong. Rotaries are called just that, rotaries. They do not have a stroke at all. The chambers rotate, hence the name of the engine.

Just because you rebuilt it doesn't mean you know the proper terminology. You can learn something from me, or you can get laughed at when you tell other people this when they know better.

 

[Donabed Kopoian]

Also, not all engines make the same amount of peak torque as peak horsepower.

Ford 5.0s always make far more torque than horsepower because the engines were designed for bottom-end power, and they never span past 6000 rpm (I shifted my '82 at 5,200 rpm because it ran out of breath after that engine speed).

 

[Donabed Kopoian]

Now if you said that a rotary is a 4 CYCLE engine, that would be one thing.

But anybody that uses the term stroke, is wrong.

 

[livevil904]

I should correct my previous post first, the rotor rotates the eccentric shaft 1 time for every three eccentric shaft revolutions, not the other way around.

Yes, pi * r^2 * h is the volume of a cylinder.

As for being laughed at? Please, if I posted this conversation on any rotary engine forum you would be laughed at for days for thinking rotaries have 3 power strokes (or I guess you prefer the term cycle) per revolution.

Rotaries are widely called 4 stroke and 4 cycle among both rotor heads and piston heads. And they're widely but incorrectly called 2 stroke engines by people who notice similarities between a 2 stroke piston engine and the wankel.

Yes, not all engines make the same peak hp as peak ft lbs. But generally engines with more peak ft lbs than hp are considered to be torquey and vice versa. That was my point and you seem to support it with your example of the 5.0. If the 5.0 revved to 8k and still maintained a relatively flat torque curve, then it would still have plenty of low end torque, just much more top end power.

Cycle and stroke are used interchangeably. You may associate stroke with pistons, but that doesn't mean it actually is associated. Read the first sentence under design:
http://en.wikipedia.org/wiki/Wankel_engine#Design

Actually, just go ahead and do a control-F and type in stroke like I did. I found 45 occurrences of that word being used. Since you will probably criticize wikipedia as a source, here is a quote from a mazda webpage:
"At the time, he had no fundamental knowledge about internal combustion engines, but he intuitively believed that an engine could achieve four strokes--intake, compression, combustion, and exhaust--while rotating."
http://www.mazda.com/mazdaspirit/rotary/story/

 

[Donabed Kopoian]

Yes, I made a mistake. Rotary has 1 combustion cycle per revolution (spaced out that the crankshaft spins faster than the rotor itself).

The problem with calling a rotary a 4-stroke engine is ambiguity between the Rotary and the Otto engine (Otto specifically refers to a piston and valve 4-stroke engine, named after the engineer first credited with the design). That's why you can refer to an Otto as a 4-stroke, a 2-stroke as a 2-stroke, and a Rotary as a Rotary. It eliminates ambiguity between the two engines.

The stages that occur during the run of a rotary engine should be called cycles, not strokes. The term is incorrect, period.

Just because other people use the term stroke, doesn't make it correct. All it means is that there are a lot of people out there that don't know what the word "stroke" actually refers to. I'm actually surprised Mazda has that err on their website.

 

[livevil904]

We'll have to agree to disagree then, but really it's not that important to me as long as you don't call it a 2 stroke engine. It shares three major similarities with 2 stroke engines (burning oil in the combustion chamber by design, high revving low torque, and a power cycle every revolution), and so people think they are 2 stroke engines.

Back to the original post topic, I'm curious if you agree with my statement that if wind resistance was a linearly increasing force, rather than a square law, that you would (at a minimum) not get worse mileage driving at a cruising speed up to peak torque rpm in top gear.

I get very good mileage when going over mountain passes, because the engine works hard and efficiently going up the hill, and basically stores all that energy into potential energy. Then, on the way down, all of that potential energy is put to use in letting me coast down the whole way down. I have a fuel pump switch that cuts the fuel and I leave it in 5th so that it keeps my alternator, power steering, and power brakes working... in the rx7 at least. With the geo and it's automatic, it's a pain. I switch between nuetral and 3rd depending on engine braking needs.

Moral of the story, an engine working hard is efficient IF that energy is going to be put to use.

 

[Donabed Kopoian]

If we assumed that fluids could exhibit linear resistance, then that is possible.

You'd also have to assume that, as vehicles speed increases, that the engine, transmission, tires, and wheel bearings do not increase in friction.

If you have all of those things held constant, then your mileage would be the same in your highest gear no matter how fast you were driving, provided that the speed stayed constant.

When I go up a hill, I downshift to keep speed because, like I said before, I don't have to keep the car floored trying to keep speed going up the hill, so I downshift and even though my engine spins faster, I'm light enough on the throttle to balance the fuel injectors firing quicker, once I am past the hill, I go back into 6th. I only go into neutral if the grade is long enough.

There is a hill on my drive from Reno to San Diego, that I kill the engine on going down, not that it's recommended, but the car gets up to 90 mph and stays there for 10 minutes going down this grade, and I'm strong enough that I can live without power brakes and power steering.

 

[livevil904]

"You'd also have to assume that, as vehicles speed increases, that the engine, transmission, tires, and wheel bearings do not increase in friction."

No, we'd have to assume that as vehicle speed increases, these forces increase linearly with speed. Of course there is going to be increased resistance, and thus fuel consumption, when you drive faster, but this is compensated for by the fact that.... you are going faster.

Go as light as you want on the throttle getting up that hill, it doesn't change the fact that you have to get up the hill at some point and you have to put X amount of energy into the car to do that. People forget too easily that there are two factors in MPG. Miles and gallons.

Power steering isn't necessary when you're traveling over 20mph or so. Power brakes are in my opinion. You can be as strong as you want, but your physical braking reaction is going to be faster with power brakes than with manual brakes.

A fuel cut switch is nice because you can have the ignition 'on' and the car in gear (for engine braking).

 

[kyoo]

There are several factors at play with fuel economy.

Firstly, engines are most efficient, in terms of work done per unit fuel, when working their hardest. This means with the pedal floored and the engine turning at whatever rpm makes peak power (5000-6000 most likely). However, some of that power is going towards overcoming friction in the engine, and the more rpm, the more friction.

Secondly, you have to accelerate somehow. The engine has to change the cars kinetic energy from x mph to y mph. You have basically two options on how to do that: using a lot of power and fuel for a short period of time, or using a small amount of power and fuel for a long period of time. Ignoring several other factors, these are equivalent.

The advice of accelerating slow and granny shifting at 2500 rpm is not going to help you get good gas mileage, though I doubt you will get "bad" gas mileage driving that way. It will also be boring.

So a hard working engine is good, but high rpm is bad, to me this would suggest that the most efficient way to accelerate is to sandwich your torque peak between shifts. This is typically about 4000 rpm in most toyota corolla engines, that would mean shifting at 5000 rpm would be reasonable. I personally wouldn't shift below 4000rpm.


Now as for cruising speed. It's a simple balance between a engine that is working harder and closer to it's peak torque and peak efficiency, and the increasing force of wind resistance. The force of wind resistance quadruples when you double your speed, this means it takes 4 times the power to go twice as fast. If the force of wind resistance was linear, then there would be no adverse effect of driving faster because even though the engine is working harder going, say, twice as fast and using using twice the fuel, you are also traveling twice as many miles. 2*miles / 2*gallons = miles / gallons.

The reason cars with lower powered engines get better gas mileage is because the engine has to work harder to do everything and is therefore more efficient. It's not as though a higher powered car is using all it's power to it's potential (and using more fuel than a lower powered car), it's just that it isn't as efficient when using a small percentage of it.

Like others have said, it takes time and diligence in documentation to find the most efficient cruising speed. In my RX7, I've gotten my best gas mileage going 75-85mph. In my geo prizm 3sp auto, I get the best going 55 and would probably get the very best going 47 (right after the torque converter locks up), but I don't drive under the speed limit.

aaaanyway, on topic - in general i do agree with this post. seems like different cars have different "sweet spots" as far as the engine work/efficiency vs speed/wind resistance goes. for the 4 speed automatic corolla, it too seems to get the best mpg around 75mph - just wanted to see if anyone else has found the same. my evo also gets the best mpg around 75-85 - a lot harder to be certain for the evo since it doesn't have cruise control.

but in general yes, it's not just the lowest cruising rpm the car can manage, while staying under 60mph or something like that.

 

[Donabed Kopoian]

<shrug>. That is how I get my best mileage. Lowest speed possible at highest gear (that isn't under the speed limit).

 

[Scott O'Kashan]

So, I come from the v8 world. My previous vehicles are a v8 titan and a v8 jeep. I'm used to feathering the throttle to try to maximize fuel economy.

I'm wondering what physical modifications can be made to the vehicle to increase fuel economy?

-Air Filter (Picking up a K&N today at work)
-Amsoil Engine Oil (Fluke or does this really increase fuel economy?)
-Amsoil transmission fluid (same question as above)
-??

I'm not going to lower my car. I'm not going to spend $1000 on something that might get me a few more mpg.

I've been working on cars my whole life, I'm going to school for diesel mechanics, and I work at an auto parts store. I have a pretty good understanding of this kind of stuff. Just wondering what you guys who have been driving 4 bangers for years have discovered.

Also, Are the factory service manuals through toyota's technician website downloadable?

Hi IFMJohn - Sorry your threat got hijacked. Somehow I didn't see your post here.

What year is your Corolla?

Yes, AMSOILK synthetic motor oils, synthetic automatic transmission fluids and gear lubes do increase fuel economy and that has been documented in controlled SAE fuel economy tests. I can e-mail you copies of the test results if you wish, (or anyone else here if you'd like your own copy). I can also provide you or anyone else in the Corolla Forum with wholesale prices on the entire AMSOIL product line with an AMSOIL PC membership. Contact me for details.

Today's vehicles have the fuel delivery to the engine closely monitored by the onboard computer and unless an air filter is really, really plugged up with dirt, fuel economy gains from an air filter will not be seen by using a racing air filter.

By the way, hold that cotton gauze air filter up to a strong light and you may see unobstructed beams of light passing right through the, "filtration media". If that is the case, it would seem to hold that airborne ingested grit and dirt can also flow through those holes and into the engine, causing abrasive wear and tear, shortening the engines life. With a race car engine this isn't so important as they are rebuilt comparatively often, but with a street driven car this is of paramount concern.

The air that your Corolla's engine ingests in an average city contains 400 tons of fine dirt particles per cubic mile! So having an air filter that really does a good job of filtering out abrasive engine wearing dirt is very, very important for the engine and your wallet. If left unchecked, the ingestion or airborne abrasives can reduce the life expectancy of an engine by a 60-80%!

Below is a video from my YouTube channel that discusses air filter technology that will provide you a lot of information on this topic. Enjoy.