TRUEBLUE3934

I agree with Cliffy. Throttle position is critical. If you roll into throttle gently and only as much as "required", you will maximize your fuel economy. In general, if your motor doesn't drop to somewhere around 2000rpm after a shift, you have consumed more fuel than "required." Increased rpms does increase fuel usage.

Wind direction would not have anything to do with the impact of weight. Wind would just be another force acting upon the car (weight would neither increase nor decrease that force).

Dragonus18

Why does the amount of cylinders play a role in fuel consumption when you have a 6 cylinder getting worse fuel than a 8 cylinder?

Ex. Posche 6 cylinder.
14/20 mpg

My car. 03 mustang GT V8
16/23 mpg

What gives?

BraMas

Allot of that has to do with Torque. A V8 has more torque and it is easier to get the car moving therefore using less gas. A V6 has less torque and has to use more gas to get it moving again.

TRUEBLUE3934

I think BRAMAS is heading down the right path there. With more torque, you can run a V8 less rpms by using taller gearing. If you are gentle with the throttle, you can use less gas with the V8 than a V6. RPM for RPM, a small displacement motor tends to use less fuel. Typically, a smaller motor will use less gas if driven with the same gentle techniques, but there are exceptions to most rules of thumb like this.

The bottom line for fuel economy is that you have to drive it with fuel mileage in mind if you want decent fuel mileage. That means darn near all the time. You can't run our cars hard thru the gears a couple of times a day and expect to get decent mileage.

Dragonus18

Interesting but wouldn't having more torque require more fuel to use it? I'm a little lost here. An engine with more torque can move a heavier car. Ok. Understandable but wouldn't you need to more fuel to actually USE that torque?

BraMas

No it is working less to move the mass therefore using less gas. Everyone gets a hard on about HP #'s. But in my opinion TQ is the important # to worry about

cliffyk

They also get their panties all wet about peak HP. A nice number, that happens someplace around or past where you just shifted to another gear. I would gladly give up 10-15 peak HP if I could get them back at 3k rpm...

0949er

Although it will not have a direct impact on the weight of the car, it will ultimately be a factor when it is added to the coefficient of drag. Without going into vector addition, the coefficient of drag will act opposite of our force vector. If you are trying to go a fixed speed, that means more amount of work needs to be done to go the same speed. SO, whit that said, if you are driving into a headwind, it will have the same effect on your car as if it weighed more (in a simplistic kind of way)

cliffyk

Since we are sort of headed that way, here's my "How much HP does it take to \go how fast?" calculator. The formulas have been refined over 10 years or so and it's pretty accurate even if I do say so myself...

Also, please keep in mind that this has nothing to do with your engine's peak HP.

It is how much rwHP is needed to keep the defined vehicle (the default values are for a new-edge coupe) going at the speed indicated in the first column. If your engine can deliver the calculated rwHP, at one of the RPM values in the second column (shown for a 3650 in 5th, and for 3.27, 3.73, and 4.10 gears) then on level ground with no head wind your car should top out at the selected speed.

As this also represents the maximum speed for a given HP it would also mean you would spend some significant time at WOT getting there...

TRUEBLUE3934

Yup, peak numbers are what guys like to brag about, but give me area under the curve and I'll kick your butt down the track.

BTW, HP is a function of torque and rpms. One is related to the other thru the rpms that the motor is running at. HP made at low rpms equates to higher torque values. This explains how diesel trucks make less horsepower but lots of torque (they do it at lower rpms).