[QUOTE=vishnus11,Jan 22 2007, 09:20 AM]Those who claim

 

Aerodynamic drag, tire pressures, load on the engine (from other components on the drive belt), weight of the car, combustion efficiency, rate of acceleration, hmm what else?

 

What I have noticed, so far.

As I put more miles on the S, gas mileage has continued to go up. When new, the best I could muster was 26mpg. Now with about 20,000mi on the clock, I easily get 29mpg on the highway and have gotten just over 30mpg on two occasions.

On longer trips the car can get exceptional gas mileage at higher average speeds in the 80, 85mph range.

Several long trips, car fully loaded with two passengers and a full trunk, or solo and mimimal luggage, top up for the entire trip, or down. All seem to average within 2mpg of each other. Too close to call.

I will be checking mpg using my gps for the next trip (Dragon in Apr). With so much beeing said about the Honda odometer error and the class action suite. See how much differance that makes.

I have never taken any trips with low average speed, say 45, 50mph so I can't say what might happen.

That this car can get the same average mpg on the highway that I get in my xB (automatic) is pretty increadible.

 

Ok to clear up the confusion, (and for those of you commenting on xViper, this was the conclusion that we as well as others came to in a previous thread) the faster = better mpg theory only applies to ap1's, and even more so to '00 and '01. The reason while these specific S's will see more benefit from going faster is not specifically the speed, but rather the rpm. In earlier ap1's the fuel curves a/f ratio is very rich in the lower half of the rpm range (which is why early ap1s will see greater improvement from piggybacks like a vfacII compared to ap2s). However the ratio leans out significantly as it approaches vtec engagement. So as you approach vtec engagement in 6th gear (mechanical advantage > rpm advantage, so higher rpm in 5th with not likely save you gas) your mpg will improve.

 

I've heard other people make this statement before. More likely than not, the novelty of the car has started to wear off and you're not driving it as hard. Therefore, your fuel efficiency appears to be getting better.

 

I've noticed this too. I first noticed a equal phenomenon with my 2001 Honda Prelude. I got 33 mpg at average speeds of 85 mph in that car on a trip this past June. 85 mph puts the needle at 4200-4300rpms, just below VTEC (5200 on the H22A4) By comparison I get a steady 29-30 mpg at 65-70 mph. The car is supposed to get 26mpg highway according to EPA estimates. Around town it gets 24 mpg so 33 on the highway is excellent!

 

Here's a better explaination.

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

Check out the chart linked at the bottom of the page. Even small, light cars get worse mileage at speeds over 50ish. I believe that the S's most efficient speed will be slightly higher than average due to good aerodynamics, but 85mph is a joke. Energy requirements due to drag go up by a factor of 2...

Vtec engagement and RPM at a given speed won't make much difference. Remember, I can put it in 5th, or 4th and get to the same RPM range at a lower speed... Ram air will increase power, but not significantly increase efficiency, as you need more fuel to burn that larger air charge.

Wind, air density, and up/down hill will make a HUGE difference, and probably accounts for the anecdotal evidence offered by drivers here. I will bet anyone their pink slip that in a controlled test that 55mph is more efficient than 85mph.

-b

 

anyone up for the challenge? he's racing for PINKS!

 

That's a decent explanation for power required. But it's less complete for efficiency.

First of all, what are we looking for?

Gal/mile.

Gal is proportional to the energy required.

Power = energy/time.

So efficiency is proportional to power*sec/miles ... in other words, efficiency is not proportional to power, it is proportional to power/V.

Now let's assume the engine efficiency does not vary with respect to vehicle speed.

Then the correct term to be looking at is not aV+bV^2+cV^3, it is a+bV+cV^2.

Now to find the best efficiency, we look at the derivitive w.r.t. V, which is b+2cV.

Where that equals zero we should find a best efficiency. But assuming b, c, and V are positive, then it never equals zero.

What's wrong? What's wrong is the assumption that the engine efficiency is a constant. In fact, it's not.

So let's try again.

energy required = energy of the gas (constant) / engine eff (function of V)

power required = energy of the gas / (time * engine eff)

efficiency = power required * time * engine eff / distance
= power required * eng eff / V
= eng eff * (a+bV+CV^2)

So you need to factor in the engine efficiency w.r.t. vehicle speed. That's why it is quite possible for a car that reaches it's peak engine efficiency at a high speed to have a maximum mpg at a high speed, even though the power requirements also go up very quickly.

 

Engine efficiency changes with engine speed, not vehicle speed. There should be at least 6 different vehicle speeds in an S that will produce the best engine efficiency. One for each gear. I don't think the highest one is the best choice for overall vehicle efficiency.

What was left off of the equation you quoted, and was expained in the body of the article, was the energy cost of just keeping the motor running. Otherwise the optimum speed would be near 0mph.

Wanna take my bet?

-b