LEARN BEFORE YOU SPEAK. YOU can be dumb and "ride the clutch" but to anybody who does not feel like destroying their clutch DO NOT RIDE THE CLUTCH. Anybody who has learned to drive a manual should know this.

Mark

 

The value on time would be the amount of gas you consume.

Say if you are travelling at 65 miles/hour you are consuming 2.5 gallons per hour. If you travel 60 miles at this speed, it will take you about 55 minutes, and you will consume 55/60 * 2.5 = 2.31 gallons of fuel.

Now say you are travelling at 75 miles/hour and consuming 17% more fuel, or 2.93 gallons hour. If you go 60 miles at this speed, it takes you 48 minutes, and you will consume 48/60 * 2.93 = 2.34 gallons of fuel.

This amounts to an difference of only 0.03 gallons of fuel for the trip. I am not saying I subscribe to this theory (because I don't), but I believe this is the point that Matt was trying to make.

 

also wanted to throw in the thermodynamic aspect of an engine turning at a higher RPM. the efficiency of burning fuel increases as burn time increases, and of course decreases as time-to-burn decreases (or as RPM's increase). By crusiing at say 80 mph w/RPM at roughly 3000, the fuel burn time is decreased compared to traveling at 55 w/RPM's at ~2000. Lower RPMs allow for a longer time for fuel to burn, aka more efficient, complete burn. Also contributes to better efficiency at lower speeds and is the reason you want to shift at the lowest possible RPMs.

You could also increase the compression ratio of your engine, as that also increases engine efficiency :grinnp: may be a tad expensive, but it'll get better mileage (in theory - not w/me drivin!)

 

My point was that Matt was trying to do something incorrect, as you are as well. You made the fatal flaw of saying you are consuming 2.5 gallons per hour. Most cars fuel efficiency is not given in gallons per hour, but instead, miles per gallon. The 17% Matt is talking about does not factor in time (hence the gallons per hour), but instead the distance per unit of fuel (hence the miles per gallon).

RxMan was correct in saying that unless you assign a dollar amount to to the unit of time saved, it would be impossible to come up with a complete efficiency rating because the time saved is relative to the person driving.

 

Please tell me how you can make the above conclusion from reading Matt's post? All he said was 17% more. 17% of what? Who knows.....could be 17% more in mpg as you are implying. It could also mean 17% more as related to time. You are assuming it is MPG just because that is what is typically used. I am not saying you are wrong, just that there is not enough information to make the conclusion that you have made.

 

Understood. You are correct in saying that it *could* be either, but it doesn't take a genius to come to the correct conclusion. The Autozone 17% figure was given to demonstrate the effect of saving gas by driving slower. If the 17% was 17% based on gallons per hour, then that 17% is very deceiving as you showed earlier - saving only .03 gallons per 65 miles.

In addition, we ALL know that driving faster uses more gas, time AND distance wise. Also, taking into consideration the drag equations that TriangleMan so generously shared, we can easily come to the conclusion that the 17% the Autozone figure is referring to is 17% distance per gallon. Common sense.

 

drive slow.

 

I agree 100%.

 

funny how I keep on putting in 10 gallons every 2 days and get 270 miles out of it... I do 80MPH all the time on the highway, I don't go past 3K RPM, and I tend to shift into 2nd kinda late- at 25MPH, where I seen people shift at 10MPH already. Luggn the engnie at low RPMs puts serious amounts of stress on the internals of the motor- wearing out the rod bearings and at times even detonating and causing damage to the piston rings. At the same time engine under high load will use alot of gasoline, so driving in 5th gear at 750RPMs is not a good idea for ya 5spd people. I get 30MPG constantly when driven slower and on longer trips, my car has 100K miles, all bolt ons.

 

take the bus and leave the max at home..............