Fuel Economy Improvement

[Richard L]

Justjimmy,

It's OK to disagree. I disagree that there are places all over the country where you can drive a constant 70 without interference from other traffic. Those kinds of places hardly exist east of the Mississippi river. Even here in Texas, it's almost impossible to find places like that. There is just too much traffic. The only time I have ever been able to do it was leaving my house at 12 midnight and found stretches on I-35 heading north and then on I-30 heading east out of Dallas. I was traveling between 70-75 MPH and got better than 22 MPG in my ST. By about 4:30am-5:00am that ended as traffic picked up.



I did not say that you would not get better mileage driving at 70, I said there was not much of a mileage difference between driving at 60 and at 70. When you are driving at 70 you encounter too many other vehicles that will require you to slow down and speed up and that causes a greater mileage penalty than driving at 70 mph. When you drive at 60 mph, you encounter far less traffic going slower than you are, and therefore get much better gas mileage.



I find that I actually get better gas mileage on my Mercedes driving at 70-75 mph than at 60-65 mph as long as there is little or no traffic around. Since my car is equiped with a fuel mileage gauge I can see instantly the difference in MPG cruising at 70 vs cruising at 60. Aerodynamics is a factor as is the 7 speed overdrive automatic transmission and a car designed for high-speed Autobahn cruising.



As for using the old vacuum gauge, it still works but really does not show exactly how much gas mileage you are gaining or loosing. That's why I recommend an accurate digital gauge that gives exact MPG readings accurate to a 10th of a MPG. You can actually see what your MPG are during a fast acceleration vs a slower more gradual acceleration.



...Rich

 

[Jimmy Lavoie]

It's OK to disagree. I disagree that there are places all over the country where you can drive a constant 70 without interference from other traffic. Those kinds of places hardly exist east of the Mississippi river. Even here in Texas, it's almost impossible to find places like that. There is just too much traffic. The only time I have ever been able to do it was leaving my house at 12 midnight and found stretches on I-35 heading north and then on I-30 heading east out of Dallas. I was traveling between 70-75 MPH and got better than 22 MPG in my ST. By about 4:30am-5:00am that ended as traffic picked up.

Exactly what I said - depending on the time of day.

When you drive at 60 mph, you encounter far less traffic going slower than you are, and therefore get much better gas mileage.

Again, exactly what I said - you'll get better mpg at 60 then 70.



So you do agree - but just worded it differently? :banghead:

 

[Johnny O]

I think that the less aerodynamic a vehicle is, the worse the gas mileage penalty at higher speeds.

You won't see as much mpg difference in a Benz from 60 to 70 as you would a much less aerodynamic Sport Trac. Heck, my Trac gets better mpg than my daughter's 4-banger Jeep Wrangler. OTOH, my Dad's V8 Cadillac will knock down 27 mpg at a steady 70 mph.

 

[Richard L]

Just Jimmy,

Yes I agree that you can usually get better gas mileage going 60 MPH than going 70 MPH, but not for the reasons you claim. You want to believe that all the mileage increase is based on the slower speed, without regard to the volume and speed of the other traffic. If you could drive the same vehicle under a controlled environment without any traffic and cruised once at 60 MPH and once at 70 MPH, you would find there would only be a slight increase in gas mileage while driving 60 MPH. That is because once you get the momentum of the vehicle going there is very little fuel penalty to keep it there. But if you are driving 70 MPH and the traffic around you is driving only 60-65 MPH, you will constantly be slowing down and speeding up. That's really why you get worse mileage trying to maintain 70 MPH. A good trip computer will quickly show that your average speed was probably only about 62 MPH, but you used more fuel because you were trying to go faster than the traffic around you.



JohnnyO,

Yes aerodynamics does play a part and a more aerodynamic shape will have less drag but I am not trying to compare a more aerodynamic, ligher car to a heavier, less aerodynamic truck. What I am suggesting is that the earodynamic drag on a Sport Trac going 70 MPH is not that much greater than the same Sport Trac going 60 MPH. The biggest difference in MPG when trying to drive 70 MPH vs 60 MPH is caused by trying to drive faster than the traffic is moving around you.



If the traffic around you is only going 55 MPH and you are trying to maintain 60 MPH you will get much worse mileage then if the traffic was going 60-65 MPH. Then your gas mileage at 60 MPH could be as bad or even worse than your mileage while try to drive 70 MPH when the rest of the traffic was doing 60-65 MPH.



Here in Texas, the speed limit on most Interstate and major highways is 70 MPH, however most traffic moves at about 75 MPH. I find that driving at about 72-73 MPH gives me great gas mileage because I only occasionally encounter slower moving traffic. That's usually a slow moving 18wheeler passing another even slower moving 18-wheeler :angry:



...Rich

 

[Jim parnell]

:argue: nice kids lulz

 

[Jimmy Lavoie]

ohhh kay



I'm done. :banana:

 

[Jake Fluchel]

I personally experienced a ten percent increase in fuel economy when I removed the intake silencer from my WRX. I usually set the cruise in the high 70's and very often had passing bursts of 90-120mph with the a/c on and still got 28mpg. Before I removed the silencer I was getting 24/25mpg max on the highway. The better an engine can breathe the more efficient it can be. Thinking back, when I had the silencer on I drove the car as efficiently as I possibly could for one week(1 tank) and I got 26mpg. I then determined that the resulting increase in mileage wasn't worth the lack of fun. Since my ST isn't nearly as much fun(but I still love it), I drive in a more efficient manner. my 2c.

 

[Bill Koonce]

Rich:

All performance modifications are based on WOT...

*sigh* That still doesn't mean that you must drive around at WOT all the time. :banghead:



Believe it or not, but there are other performance upgrades than just those for drag racers.



From what I've seen, the stock intake is probably OK when it comes to fuel economy. By the same token, adding the usual freer-flowing aftermarket intake parts that work with the stock MAF sensor and stock injectors will not reduce fuel mileage.



The exhaust system is a different matter. It does take power to force exhaust gasses out of the stock, highly restrictive exhaust system. It does take horsepower to move around that big heavy muffler. IME with other vehicles with big, heavy luxury car style exhausts can be made more efficient with lighter, freer-flowing parts. If I was one to wager, I'd bet that's what will happen when I do just that to my ST. Stay tuned.



Although it doesn't hurt to mention that spending a lot of money on the most expensive parts can be false economy, please understand that is not the question that was asked. Besides, there are economy-only tuners that cost only $50 or so. A budget replacement muffler will cost a lot less than a full dual exhaust, and offer a good amount of improvement. It doesn't have to be a show quality job.



IIRC, I did mention that losing weight also improves economy. Hold on...yep, I sure did.

It is really not much difference in mileage driving at 60 and driving at 70...

The force of drag increases as a function of the cube (^3) of velocity. That's not an opinion, that's the law.

Of physics, that is.

I like to recommend that anyone who wants get better gas mileage, investin in something like a ScanGauge or other accurate fuel mileage computer that gives instantaneous MPG updates.

That flies in the face of the "it costs money" argument. The "instant fuel economy" page of the info display uses data from all of the PCM computers, and costs nothing extra. And you don't need any guage to tell you to drive smoothly and avoid excessive acceleration (in any direction).

 

[Bill Koonce]

Most of the ST mods are for WOT HP only...

I'll bet you a nickel that there are more cosmetic mods! :bwahaha:

 

[Richard L]

Mustang Guy,

From what I've seen, the stock intake is probably OK when it comes to fuel economy. By the same token, adding the usual freer-flowing aftermarket intake parts that work with the stock MAF sensor and stock injectors will not reduce fuel mileage.

I never said that performance mods that increase HP will reduce fuel mileage (assuming you keep your foot out of it) My point is that most mods designed to increase HP do not give any significant improvement to gas mileage, and if they do give a marginal improvement, rarely ever pay for themselves in gas savings.

The force of drag increases as a function of the cube (^3) of velocity. That's not an opinion, that's the law. Of physics, that is.

So what is your point? I said that there is not that big of a fuel savings driving 60 MPH vs 70 MPH. The reason you may see a significant difference is not so much the aerodymanic drag, but the fact that other vehicles are driving slower and you will constatantly be slowing down and speeding up...and that will be very noticable bite into your gas mileage. More than the drag associated with going faster.



And I never disputed that vehicle weight played a big factor in mileage. It takes more HP to move a heavier vehicle down the road at any speed. But, most of that fuel use is lost in accelerating to speed. Once you reach your target speed and begin to cruise, the vehicle's momentem contributes to it's forward motion and less fuel is required to maintain that speed.

That flies in the face of the "it costs money" argument. The "instant fuel economy" page of the info display uses data from all of the PCM computers, and costs nothing extra. And you don't need any guage to tell you to drive smoothly and avoid excessive acceleration (in any direction).

Not all vehicles have fuel mileage displays (Early Sport Trac's did not). My suggestion is if you are getting crappy mileage and think you need to buy speed equipment, you are better off buying a trip computer or ScanGauge (if the vehicle does not have one) and it can help train you as to exactly how fast or slow you can accelerate and save fuel, and what other bad driving habits you may have that are sucking up your gas that you might not be aware of.



While you may know how to drive to save gas, some people don't or don't realize how much gas they are using in various driving situations.



The reason I recommend buy a ScanGauge or similar fuel mileage monitor is that not all vehicles have them or may not have the instantaneous mileage readout, and they can be removed and put into another vehicle or simply sold to recoup some of your money.



My point is that everyone keeps recommending performance equipment that increases HP but does little to improve mileage. Most of the poor fuel economy can be based on poor driving habits which you can correct if you know which ones are costing you extra gas. Traffic, you can't do much about it, but if you drive to keep up with the flow of traffic but just a bit slower, you will save more gas. If everyone is driving 70 MPH, then don't drive 60 and get run over. You can drive at 67 or 68 MPH and you can still save a lot of gas.



...Rich