I read something today that said driving at 55 mph saves gas. While this MIGHT be true for older cars i was wondering if this is still true for newer computer controlled cars. Namely our fantastic TSX.

any comments?

 

The faster you go, the more wind resistance there will be so your car will have to work harder.

But really, its more about rpms than speed. So at 55 your rpms will be lower than at 70, or 80, meaning your engine isnt working as hard and you are using less gas.

EDIT: I just posted this in another thread so I may as well post it here. If you are really interested in fuel economoy, sauceman is the king and has a gread write-up on how he is able to achieve crazy mileage figures.

http://www.acura-tsx.com/forums/show...&threadid=2182

 

I think an overly general rule is that the lowest rpms in the highest gear will get the best gas mileage.

 

Hmm...i think the lowest rpm in the LOWEST gear would be better. 2000 rpms in 4th should be more fuel efficient than 2000 rpms in 6th, since you will be going much slower.

 

I totally agree, but here's something I've always wondered:

How this is offset by the fact that when you drive faster (70 or 80 as opposed to 55), you get to where you're going quicker? That is, imagine two people driving the same distance on the same road, one going 55 the whole way, one going 80. Per unit time, I think we'll all agree that the slow guy uses less fuel (as he turns less RPMs and faces less wind resistance). But when we consider the fact that the guy going 80 gets there sooner (and turns his engine off), who uses less gas on the total trip? I'm still not exactly sure how to attack this problem analytically. Any thoughts?

 

I can't drive.......55!!!

 

Exactly. For whatever reason, I have to drive at least a bit faster than everyone else.

 

Traveling at 70 mph requires more power than traveling at 55 mph, due to increased wind resistance and increased rolling resistance of the tires. More power = more fuel = worse mileage. Fuel mileage is barely affected by engine rpm. Throttle position is what really controls mileage. More throttle = more gas = more power = worse mileage.

If you get better mileage at 70 mph than at 50 mph, then the engineers did a poor job of choosing gears for the engine and/or you're in the wrong gear.

 

I'm not so sure about this.

 

I'm sure we can look at physics formulas which relate work to force/and or power, and you'll find your reason there.

But how about we use an analogy?

Lets say there is a store 1 mile from your house. You could walk there, or run there. Which would make you more tired and hungry? Which would require more energy?

 

Exactly, that's while I'll stick with what I previously said. A car at 2000 rpm in 6th gear is working no harder than a car at 2000 rpm in 2nd gear, it is just moving faster because of the gearing.

 

Here's why:

http://www.insideracingtechnology.com/tech102drag.htm

Note that the wind drag is proportional to the velocity squared. So to go twice as fast, you get four times the drag. As a car goes faster and faster, wind drag becomes more and more the inhibiting factor than anything else.

 

OK, I looked for some info online, and here it is from howstuffworks.com:

http://auto.howstuffworks.com/question477.htm

No time to analyze what is says though, I'm off to Texas hold'em night to try and win some money.

 

Right, but I think it needs more fuel to maintain those RPMS when traveling faster, because it needs to overcome wind resistance. In 2nd gear this wouldnt be a problem (or not as much). I'm not saying its a big difference though.

I guess you need to look at a) how often combustions is occuring, and (rpms) b) how much fuel is used during combustion (throttle position, etc).

 

Here's one my link that shows a brief table of good speeds for different size cars. Most seem to peak around the 55mph zone.

http://auto.howstuffworks.com/framed...ning/speed.htm

 

The trick in understanding this is to realize that engine speed doesn't matter. A car at 2000 rpm in 6th is 'working' much 'harder' than a car at 2000 rpm in 2nd gear. Engine rpm is solely a function of vehicle speed and gearing. When you talk about how hard an engine is working, what you really want to think about is how much power that engine is making. At 2000 rpm and 60 mph, your engine is making much more power than it is at 2000 rpm and 20 mph. That is because it takes more power to make your car go 60 mph than 20 mph.

 

While others are talking about the weight, speed and drag of the car that affect mileage. It is also helpful to understand how the ECU controls the amount of fuel delivered to the engine base on RPM and load.

This is a standard Honda fuel map that shows how fuel is added depends on load and rpm. The numbers on top across 21.6, 21.1, 17.7... are the range of vacuum in the intake manifold. The numbers on the left down 500, 600, 700... are engine rpm. As you can see, the higher the load (less vacuum), the more fuel the engine will consume. The same is true for higher rpm. However, if you can modulate the engine speed and load (cruise control?), good gas milage is possible even at higher rpm with light load.

 

Exactly. It's like saying riding your bicycle at 5mph, 80 rpm in low gear uses the same energy (i.e. fuel) as you trying to keep up with Lance Armstrong at 30mph, in a much higher gear, but also at 80 rpm.

 

This is true of course only at a constant speed. At WOT the power is identical (and of course the car won't stay at 20 mph very long at WOT... )

 

i don't worry about it much, after spending $27k on the car, i'm driving it like i stole it!!

 

I have to say, I have noticed an increase in mileage after I installed my intake. If anything I'm driving harder than I ever did but I'm getting about 540-560km a tank with average city driving when I was only getting 500-520km before. I was expecting the opposite to happen so I'm plesantly surprised.

Has anyone with an intake noticed any increases? I have yet to do a long road trip with it since the upgrade but I will be heading to the cottage next weekend so I'll report back with what I get on the highway.

 

Holy old thread.

 

Today is resurection Friday. I think there have been a lot of old threads brought back to life today.

 

I cant think of any reason why a CAI would increase gas milieage. But I can think of reasons why it would hurt it.

 

I can: less pumping losses. It takes less work to pull the air in.

 

I can't explain it either but I have been getting better mileage. Oh well, probably just a fluke.

 

pumping, what pumping?

 

Could also be that your engine is settling in. I've noticed better mileage and power compared to last year.

 

On the intake stroke, the piston creates a vacuum in the cylinder in order to draw fresh air in. Since there's a pressure imbalance between that vacuum and the crankcase, it requires work to create that vacuum and pull that fresh air in. If your fresh air is flowing in more freely (i.e. you have a freer-flowing intake), then the pressure imbalance is not so big and not as much work has to be done to pull the piston down.

Your engine is a pump. It pumps air from the front of your car out the back of your exhaust pipe (and it happens to do some other good stuff in between). That's why I say "pumping" losses. Make sense?

 

Holy crap, some of you need to take some time, sit down, and read a book on gearing or something. You know how many MORE RPMs you would have to turn to go a mile in 2nd at 2000rpms, than if you were in 6th at 2000rpms??? To get the best gas mileage, get your car into 6th, don't modulate the throttle at all, and try not to do 90mph down the freeway...