September 19, 2007

Gas mileage question

After years of having the shortest commutes in LA history, we now have to do some serious driving, so I've been thinking about gas mileage, but I'm making no progress with my thinking.

Hopefully, my 10 year old sedan won't collapse anytime soon, but it's making weird shimmying motions, so I've started to look at car ads again, and, what the heck happened with horsepower in this decade? The Toyota Camry V6, the most generic middle of the road car of them all, is rated at 268 hp. My old sedan has 200 hp and goes 0-60 in 7.8 seconds, and that seems like plenty.

So, does all this extra modern horsepower consume more gas, all else being equal? I could look at the federal mileage ratings, but I've never come close to the numbers they claim. The federal test track must start on the top of Pike's Peak.

Is this purely a physics problem of how much the car weighs, how fast you accelerate it, and what your wind and road resistance is at top speed, so that horsepower doesn't matter? I should just accelerate like I have 168 hp instead of 268? Is that it?

Even if that were so, it doesn't sound very realistic for a mediocre driver like me. I mean, you could probably drive some state-of-the-art bat-out-of-hellmobile in a sensible fashion, merging into traffic off the onramp at a moderate pace, but I'd likely continue to stomp it for all it was worth even if I had a Bugatti Veyron.

Or was this just an error by the car companies? Did they forecast that gas would $1.50 per gallon in the wake of a successful Iraq War and wind up with a line of gas-guzzlers?

My published articles are archived at -- Steve Sailer


rkillings said...

Steve, just get a Prius and stop worrying about gas mileage.

Anonymous said...

The man has a family. I think it's unfair to stick them all in a Prius. I get great milage out of my minivan if I don't go over 55. It's all self-discipline. I had a Honda CRV that generally got close to 30 mpg but that was because the thing had no power. Just try to merge into Houston freeway traffic with a pathetic engine like that, too steep a hill, a sudden loss of power just as you're reaching the top.

Get a vehicle with a little power so you can get out of tricky situations and keep your foot off the accelerator. Consolidate your trips to the grocery store, drycleaners, etc.

Dennis Mangan said...

This won't answer your gas mileage question, but buying a car that's a few years old will more than make up in price anything you spend on gas. That's the Prius's fatal fault: the gas savings can't possibly make up for the price.

Anonymous said...

Steve, the Federal rules on how MPG is calculated has just changed. I believe it happened about a year and a half ago. So the new numbers that you will see with the latest releases in September should be the updated numbers. However, that is all I know about the new numbers.

On the old way of calculating MPG, yes, I believe it was a Mathematical formula that did not need to have a whole lot of real world testing.

And, on the Prius and other electric-hybrid cars, make sure to ask how long the battery will last and how mucha replacement will cost.

Those batteries can be EXTREMELY expensive.

Anonymous said...

HP ratings are huge marketing gimics. So, the effect on your mileage depends on what they've done to get the hp. If they've just spun the engine up to a higher peak RPM, then that's not going to effect real world mileage any. If they've added a turbo charger that's going to effect it considerably. In between is air intake tuning. The short answer is gasoline engines need to burn a given amount of fuel in relation to their effective displacement. The higher the displacement, the more fuel they must burn, even at low idle.

Also, the more moving parts, the more friction the more fuel waste. That is why big diesel engines have 6 massive cylinders. It is more fuel efficient than 12 of 1/2 the size. It is also why overhead cam engines using a little rubber belt are more fuel effecient than rows of lifter rods reaching up from the bottom of the engine.

If you really want to dig deep, you need to look at the torque curves. But how-to is too long an explanation. And this is probably more than you wanted to know already. :-)

Regarding the EPA numbers, they changed their test methodology this year to better reflect "real world". So be aware comparing between model years will make this year look worse than last, even for vehicles and engines that are absoletly identical. Don't worry about it. The numbers are still good for comparing cars of the same model year though. And while no one expects to get EPA numbers, they are good as relative comparisons between models.

As the minivan driver noted, the biggest effect on mileage is wind drag. The taller the car, or the wider the car, the more the drag. The faster you drive the more the drag. Obviously faster has the biggest effect. I think it is a power to the 3rd root: doubling your speed has 8 times the drag.

Not sure if any of this helps. Of course the easiest and most obvious way to save money is to not fixate on fuel costs and buy a 4 year old Toyota. But boy, is that ever boring.

Anonymous said...

Hopefully, my 10 year old sedan won't collapse anytime soon, but it's making weird shimmying motions, so I've started to look at car ads again, and, what the heck happened with horsepower in this decade? The Toyota Camry V6, the most generic middle of the road car of them all, is rated at 268 hp. My old sedan has 200 hp and goes 0-60 in 7.8 seconds, and that seems like plenty.

Auto manufacturers have been increasing horsepower due to increased car weight and technology improvements.

Cars have become heavier due to more and more standard features, larger size and increased crash protection. To move that weight they bumped up the horsepower. There was also a ripple effect where the extra power required a stronger drivetrain.

The fact that fuel economy has only decreased a little bit is actually very impressivejajhdg

Anonymous said...

Get this;

The TFSI/FSI new engines yield an excellent mileage with surprising power.
Or go diesel:
Any WV TDI engine will do, but this is one USV you might be interested in:

Anonymous said...

Yes Steve, more horspower consumes more gas. A car with 300 hp spends more fuel than a 200 hp car going at the same speed. Not 50% more but still, more. Bigger engines have larger cylinders and that means they take in more gas for each revolution.

Anonymous said...

Don't get a Prius.

Hybrids are horrifically complex, two power systems and tricky computer controls to merge them. A number of incidents where power is lost at freeway speeds have been found with all hybrids, but mostly the Prius and Civic hybrids.

Repair and reliability on those things are awful as well. Gas savings likely to be overwhelmed by repair/service costs.

Buick makes good sedans, high reliability and decent cost-performance, you can put your family in them and they have better driving feel than a top-heavy minivan or SUV. Resale value sucks but I assume you'll buy and hold.

Mazda has some nice models, also the Ford Taurus or Pontiac GTO. Which has bland styling but good mileage and performance.

Anonymous said...

Is getting something with a stick shift an option for you?

Small cars with small engines perform better without having the extra strain of an automatic transmission...

Anonymous said...

I drive a 12 year old Lexus that runs great, even though it has 175k miles on it. Last spring I bought $8k worth of stock in a gas refining company Frontier Oil. The dollar amount I'm up on that stock is more than I will spend on gas all year.

My advice: Since you live in a state with the highest gas prices in the country, buy an older, cheaper car (but one ranked highly by Consumer Reports for reliability, like my Lexus ES 300), and invest the difference in something that will provide a hedge against higher gas prices.

Glaivester said...

As I recall from a discussion on Matt Yglesias' blog, engines are most efficient when being used close to capacity (this is engine efficiency, not necessarily car efficiency, so wind resistance is not taken into account).

For a given speed, a small, lower horsepower engine will be working at closer to capacity, and so would tend to be more efficient.

James said...

Watched a show today on armored transport vehicles and the US military "Stryker" weighs over 16 tons but only has 350 hp.

Anonymous said...

Engine size per se has little to do with mileage. In modern engines with efficient fuel delivery and combustion chamber design, the brake specific fuel consumption is relatively consistent across a wide range of power settings. The amount of total horsepower-hours is what you are paying for.

Steady state fuel burn is a matter of BSFC vs aerodynamic drag and rolling reesistance. However, fuel burn under acceleration is determined by mass of the vehicle and the accelerating force.

Hybrid vehicles do relatively better in stop and go driving vis-a-vis the conventional ones. But the higher price destroys the economic advantage of that efficiency.

For what it's worth, my daily driver is a 1974 Olds 98. It's been modified in what would be unacceptable ways in California-it has no catalyst, AIR pump or EGR. But I get a steady 20 mpg in the city and even at $3.50 a gallon, it's economical. It's paid for and I can fix anything on it myself.

Once last year I broke a U-joint and couldn't drive it to work. I had to take the hobby car-my 1936 Graham.

Anonymous said...


Get a new diesel VW. They get around 50 MPG on the highway, and are much cleaner than the VWs of old. I was next to one at a traffic light recently, and I could not hear the diesel at idle. They are that good.

Or get a new Saturn mid-size. Highly rated, and GM products have a 100,000 mile powertrain warranty to insure piece of mind. The Saturn will fit your whole family. Read about the new Saturn Aura in Car and Driver online. Just google it.