Here is the results of some testing done by consumer reports on a Camry ICE4.

http://www.consumerreports.org/cro/c...-406/index.htm

While they did not try to increase the air pressure in the tires, some of the other things they tried would be relevant for the Hybrid as well.

 

Thanks for the good link.

 

Keep your air filter clean. According to our tests, driving with a dirty air filter in modern engines doesn't have a significant impact on fuel economy, as it did with older engines. While fuel economy didn't change, however, power output did. Both cars accelerated much more slowly with a dirty air cleaner. We drove both vehicles with their air cleaners restricted and found little difference in gas mileage with either engine. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow, therefore, caused the engines to automatically reduce the amount of fuel being used.

I checked the link for tips. I'm not sure I follow their logic. First they say dirty air filters don't affect FE, that it just makes the car more sluggish. Then they say it simply causes the engine to reduce the amount of fuel being used.

I'm not sure these guys are mechanical engineers but it seems like what they are really saying is if one whould clog up their air filter then your auto's computer will decrease the amount of fuel to the engine and increase your FE? I know that's not what they meant, but it sounds like they have conflicting statements?

 

Using air conditioning while driving at 65 mph reduced gas mileage in both vehicles by about 1 mpg-it might make more of a difference if you drive faster.

This is also something CR said about using AC. I can understand that in a Camry getting 35 mpg that 1 mpg is not much concern. However if using AC in the Mountaineer V8 which is probably getting 15 mpg then a 1 mpg difference is significant. Not that I would forgo using my AC but I don't see rational logic in their reviews.

 

There is a missing part of the equation that links the two statements. The driver's gas pedal foot. If restricted airflow results in less fuel being used, most drivers respond by pushing down more on the pedal thus compensating for the reduced air/fuel flow. I think what was meant was "for a given throttle position" a plugged air filter simply results in less air/fuel, but in real world the driver compensates and therefore in the end no real difference occurs (unless the driver spends quite a bit of time with the pedal on the floor.

 

This is why articles quoting the effect of various things in "MPG" makes no sense. They also said that they would expect the mileage hit from air-conditioning to be more pronounced if you drive faster -- the AC should use nearly the same amount of power no matter what (there will be some variation based on the efficiency curve of the ICE), so it shoudl reflect a smaller percentage of consumption at a faster speed, meaning less MPG difference.

Also, reporting that air-conditioning costs 1mpg in an SUV, and 6mpg in a hybrid suggests the air conditioning is less efficient in the hybrid, when in reality they both burn about the same amount per hour to cool the same amount of space. Report air-conditioner consumption, and other accessory loads in gallons per hour makes sense, as those things are not at all related to distance covered or speed. It's also a lot easier to compute the actual cost that way.

Reporting the cost of other things in "mpg" is also an oversimplification. For example, the effect of low tire pressure, or grippier tires, will increase linearly with respect to speed. The impact of roof racks etc. will be proportional to the square of speed, as it adds to drag. Hauling around unnecessary weight all the time will hurt acceleration times, and impact mileage dramatically for someone who does a lot of hill climbing or stop-and-go acceleration, but minimally for someone who drives on flat highways for a long time (it would add a bit of rolling-resistance by loading the tires more, but that's all when at a fixed speed).

This is how I read it -- driven the same way, a clogged versus a normal intake will have about the same fuel consumption, but the clogged one will have less power in reserve.

 

First of all CR didn't make a bunch of theoretical guesstimates and then explained it. They did real world measurements and then attempted to explain what they saw.

This makes sense to me. A car has an optimum ratio of air to fuel. In the olden (carbeurators and no computers) if the airflow was restricted the engine did not receive enough air and it did not run efficiently. With the sensors and computers in today's cars each is monitored continuously. If not enough air flow is received the car will adjust how much fuel is injected. Yes, the result will be to press harder on the gas pedal, but that's only when accelerating.

 

Double-Trinity,

The article didn't claim a 6 mpg penalty for A/C in the Camry. It was a 6 mpg penalty for the car-top carrier. The A/C in both vehicles caused about a 1 mpg drop.