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Old 27th August 2009, 14:48   #1
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Default Effect of Air Filter condition on Vehicle fuel economy.

Looked around for threads on this, but didn't find any. Here is a very interesting link I came across when I was hunting for something. It a comprehensive test done to show how the condition of the air filter effects the fuel economy of the motor. Interesting result.

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Results show that clogging the air filter has no significant effect on the fuel economy of the newer vehicles (all fuel injected with closed-loop control and one equipped with MDS). The engine control systems were able to maintain the desired AFR regardless of intake restrictions, and therefore fuel consumption was not increased. The carbureted engine did show a decrease in fuel economy with increasing restriction.

http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf
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Old 27th August 2009, 15:02   #2
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This is news to me. But I will keep the filters of my bike (carb) as well as car (MPFI) clean nevertheless.
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Old 27th August 2009, 15:02   #3
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Does the reverse also hold true then? Custom intakes that are larger than stock would not have any impact on the performance?
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Old 27th August 2009, 15:23   #4
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Quote:
Originally Posted by mclaren1885 View Post
Looked around for threads on this, but didn't find any. Here is a very interesting link I came across when I was hunting for something. It a comprehensive test done to show how the condition of the air filter effects the fuel economy of the motor. Interesting result.




http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf
It's been also shown that Fuel efficiency of a motor with an engine management system running on a clogged filter goes up. It is true that a clogged filter only reduces efficiency in older engines without engine management systems. The newer engines maintain AFR so that excess fuel is not injected when the air flow is reduced such as when the filter is clogged. This results in an increase in FE - lower volume of air results in less fuel injected. Thus performance decreases and mileage increases. But severe restriction is known to have a detrimental effect on this.

The clogged filters that went through the WOT test look pretty bad eh ? Wouldn't want that to happen..

Last edited by di1in : 27th August 2009 at 15:29.
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Old 27th August 2009, 15:24   #5
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Originally Posted by amitoj View Post
Does the reverse also hold true then? Custom intakes that are larger than stock would not have any impact on the performance?
Doesn't it mean that modern engines adjust the fuel to the air quantity. Might lose on performance if its clogged.
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Old 27th August 2009, 15:31   #6
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Originally Posted by srishiva View Post
Doesn't it mean that modern engines adjust the fuel to the air quantity. Might lose on performance if its clogged.
Point. So, for FE to remain constant, performance will reduce. But if the driver wants to keep performance constant, FE will go down.
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Old 27th August 2009, 15:32   #7
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Quote:
Originally Posted by srishiva View Post
Doesn't it mean that modern engines adjust the fuel to the air quantity. Might lose on performance if its clogged.
That is why you need a ECU remap or a external device like Pete
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Old 27th August 2009, 16:34   #8
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Not very surprising since the ECU tries to keep the emissions within limits - i.e. the fuel-air ratio within limits. With a really bad case of choking you will have loss of power and ultimately the ECU will give up. In the case of more air getting in (larger manifolds, freer filters) the ECU will increase the fuel flow to compensate. So expect a bit of more power, but do not expect your mouse to become a tiger!
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Old 27th August 2009, 17:04   #9
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An interesting article and a good read. Every month, I remove the filter and blow air over it using a vacuum cleaner in blower mode. I change the OEM air filters on my vehicles half way (20,000 kms) of the recommended change interval which is 40,000 kms.
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Old 27th August 2009, 17:27   #10
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@gpa - every month! Good for you. I make sure I do it every three months, and am more fussy about the turbo diesel engine, where the filter processes huge amounts of air. But its free, so monthly is fine if you are able to do it. A suggestion - clean it by blowing air from inside out, against the direction in which air passes through it. That will dislodge more dust particles, than the other way, which will embed some of them into the filter material. What works well is taking it to the closest tyre shop and running the compressed air jet against the air flow direction of the filter.

Last edited by Sawyer : 27th August 2009 at 17:29.
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Old 27th August 2009, 17:31   #11
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Why don't guys change it for a newer one every service ? Hardly costs anything.
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Old 27th August 2009, 17:37   #12
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Quote:
Originally Posted by prince_pervez View Post
Why don't guys change it for a newer one every service ? Hardly costs anything.
People with aftermarket high performance filters can't afford to do that!
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Old 27th August 2009, 17:40   #13
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Quote:
Originally Posted by 1100D View Post
People with aftermarket high performance filters can't afford to do that!
Ooops! My mistake, I thought the guys were running stock filters.
Well I change em every service.
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Old 27th August 2009, 18:08   #14
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Shocking news. Now for a moment consider that the filter is clogged, so definitely the required amount of air is not going into the motor. This means overall, the performance will reduce. The hike in FE is because of less amount of fuel being used. Here again the engine is not working in the optimum manner.

Also if one really wants to know the effect of clogged air filter, dont clean the filter for long, take the car to hills with full load. Here one will realize that even if the FE is slightly better, what a clogged filter can do.
Air filter is like nose to car engine. You might save on a few breaths, but when you are asked to perform with a clogged nose, you are not able to give your best.

Best is to keep it clean.

For a vehicle without MPFi and the modern ECU, a clogged air filter is not a good thing. I know this from personal experience with 800 and Spirit.
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Old 27th August 2009, 18:12   #15
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Yup it can be true.

If you're used to a cruising speed of say 100kmph, with a clogged air filter, the engine will consume less fuel for a given throttle position (since less air is entering through the filter).

But in order to maintain 100kmph with a clogged filter, you will need to use a bit more throttle than you would with a good filter. So finally, you end up spending the same amount of fuel from point A to point B.

But on the downside, the engine will feel un-responsive and rate of acc will also be slower.

Shan2nu

Last edited by Shan2nu : 27th August 2009 at 18:14.
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