On available power. But the engine itself cannot tell if the throttle is 80% and the filter 40% clogged or the reverse. It sees the same manifold pressure either way. So if you want more hp, then a clogged filter will be a problem. Or if the filter is so clogged it keeps the engine from reaching the most efficient rpms. But your milage doesn't care where in the air intake the bottleneck is, either the filter or the throttle.

 

The engine can get enough air under full load at max rpm.

So... a partially-obstructed filter at, say, 4000 rpm may not present much resistance to air flow.

Does anybody know how much extra resistance a dirty air filter even adds?

 

I'm assuming the findings of the study is that the same vehicle under the same conditions with and without a clogged filter will get the same mpg when achieving the same set speed. This is more than likely true.

What is not being said is the clean filter is getting to the set speed quicker and traveling a shorter distance than the clogged filter using the same amount of energy.

In the real world what will happen is the driver will compensate for the lack of power due to a clogged filter and have a heavier foot resulting in lower mpg.

 

The heavier foot will only change things if its enough to go to wot/open loop operation. But as long as you are in closed loop operation, a heavier foot with a clogged throttle is no different from a lighter foot with clean filter. ie, the acceleration profile looks the same because the engine sees exactly the same thing.

 

I suppose when using the same amount of energy that both would travel the same distance.

 

and do so with the same acceleration times, etc. A clogged filter can't do a whole lot till you get to WOT situations. That's why racing teams want something like the K&N, because they need every bit of power they can get, so the more open the filter, the better.

 

There is a few things you guys are forgetting. 1. There is 10 percent ethanol in the gas which is almost 17 percent of the air required. 2. The CEL light will come on when the fuel trims get lower than a 11.1 fuel air mix or other sensors get out of whack. The ecu wont let a clogged air filter ruin the motor with out letting you know.


The air filter never gets fully clogged, even in the tests they used a towel which still allows air in. It the vacuum form the pistons get high enough it will blow out a seal somewhere to allow air in. In my car there is 2 air tubes made out of rubber so when the vacuum gets high enough 1 will leak and it wont be filtered air.

In my truck at work a air filter lasts 200,000 miles, they clean it once and then replace it. We have a vacuum gauge that tell the mechanics when to replace it. Keep in mind the air filter is the size of the engine block in the Fit.

A K&N air filter has oil to hold the dirt but the cotton still breaths and the oil moves allowing enough air to sneak by with out the dirt. There is more surface area that allows a lot more air than a stock filter.

 

no no, these are the important things:

1. There's a man in a smiling bag.

2. The owls are not what they seem.

3. Without chemicals he points.

Remember these three things.

 

The study has to do with a partially clogged filter. A completely clogged filter would cause a malfunction. If the study is correct and there would be no change in mpg just a decrease in performance...then my question is at what point would the ecu not be able to handle the level of being clogged. I would have liked this study more if they would have taken it to the breaking point.

 

And the cheese chases the dog.

(Ocean's Eleven anyone?)

 

According to consumer reports testing, they had to completely cover the air filter in duct tape to get anything other than reduced power. Air Filter Gas Mileage | Myths on raising gas mileage - Los Angeles Times

 

If that was true there would be no such thing as fuel trims.

Seems huh? You were a participant in the oil thread where I spelled out everything. Do you remember our discussion on the stribeck curve and fully formed hydrodynamic lubrication?

 

Right, the engine adjusts home much fuel gets injected based on what it sees. How does it know or why would it care the relative pressure drops across the filter vs throttle body.

 

You are right the throttle body is a big restriction on airflow, that is the whole purpose of its existence although that is (very) slowly being phased out of spark motors. That however is a completely different discussion..

The filter assuming it was sized properly, being that is the OE filter we are discussing (at least I am) it has been properly selected.

So it should when clean create minimal pressure differential across the filter media.

Placing a MAP sensor in the pipe behind the filter is how you determine this. The right filter, when clean, should create less than -1inHg vacuum.

I have a write up in at least one other thread about how to size your intercooler (if applicable), charge piping and air filter for your application that covers this. Basically you want the face velocity of your charge (at whatever density) between 200-300fps through the charge pipes and approaching .5 mach as they enter the runners leading up to the valves.

 

Because with the throttle (anticipated by the ECU) already choking the engine, literally, it now has to increase the plate angle to get the same mass of air in.

The engine is working harder (how much depends on how badly it is clogged) as it directly affects VE.

VE is one of the main bits of the equation which directly affects torque and fuel economy. Which go hand in hand.

On GDs which run exclusively on speed density, the MAP sensor tells it. On GEs which are a MAF/Speed Density Hybrid it at least has a sanity check with the MAF sensor to compare what the MAP is telling the ECU.

Otherwise MAF sensors have to compare the mass of air oxidizing the hot wire element to the VE table and it is basically guessing which is what hurts fuel economy most.

On a filter that is too small, or is borderline.. a little clog can make a big difference. Make no mistake OE engineers do not always get their say. Compromises are made to satisfy budgets. When I pull the stock airbox and plate filter I'll do some measurements and try and put this one to rest.

The bottom line is you want to make the intake path as free flowing as possible because less energy will be wasted on pumping the air.. this doesn't account for charge velocity, wave tuning the intake, etc. But it is important.

 

Why is the engine working harder, rather than just seeing a less opened throttle though? What the consumer reports and oak ridge labs studies seem to show is that the ecu learns that the throttle position equates to an effectively less opened throttle.

 

The engine is working harder because while one piston is seeing combustion, another is trying to draw in the charge.

As mahout said earlier... try using two balloons of exact dimension with the same volume of air under the same conditions and evacuating them with different diameter straws of the same length.

That is effectively what is going on. The less combustion energy wasted drawing in a fresh charge the better.

You only want the throttle plate its self acting like, well.. a throttle plate.

 

But again, you're ignoring the throttle.

edit: putting the straw analogy in perspective, imagine two straws of different diameters, both with a valve in them. Why would I expect the straw to be the largest blocker of air given there's a big valve in the way specifically there to block the flow of air.

 

Yes, and at the time I didn't comment on how off that seems. There are engines that produce only 50-100 hp (the Fit being at the high end of that range, my old diesel rabbit at the low end). And you think that frictional losses could eat up much of that? Rather than, say, wind resistance at speed and the forces required to accelerate the vehicle to 50-100 mph? You can turn an engine by hand, but you can't produce even 1 hp unless you're really, really, really strong. And that would be with more than just your arms.

Somewhere, somebody may have misplaced a decimal point or two in a calculation, and throwing all the fancy terminology isn't going to overcome that. Most of the engine's power isn't used to overcome internal engine resistance, they're not that inefficient. Keep in mind- two people can probably push-start a Fit, those people producing less than 2 hp between them, and the force they put into the car is enough to turn over the engine. (as is a small electric starter motor)

So, 14 hp per bearing? Maybe if each engine has only a tenth of a bearing. Otherwise, I question the conclusion.

 

I don't think you're quite grasping it, and you clearly have not done the math on it as this is a quantifiable topic..

It will change depending on the brake mean effective pressure of the engine, the width and diameter of the journal as well as the speed the engine is turning to name the key components. The oil and the style of bearing also play apart and I have accounted for this.

My figure was 12HP per main bearing at the crank on a comparable four cylinder, with admittedly higher BMEP.

If that seems excessive, consider that ~70% of the energy from a gasoline engine is lost to friction and heat. Turbodiesels are considerably better but few will best the 40% TE mark.

So for a ~100HP SAE Net engine to lose ~50-60HP to friction at wide open throttle on its biggest and most abused bearings is not unrealistic.

In the case of your diesel rabbit, that 50HP measured at the crank is what is left to move the car after all the other parasitic losses have had their piece of the pie.