Think you need a new air filter? Maybe not....
 

I like beating dead horses. If you choose to read this report, pay attention to the very last paragraph. 8D

It isn't necessarily a 6637 filter argument, and no diesel engine tests were done, but it is very interesting to find air filters aren't as restrictive as people think they are, even when dirty.

http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf

Looks like it says a dirty air filter may have a measurable affect on fuel economy.

I'm pretty sure I needed one. I even gained 1-2 psi of boost after putting in the new one. :eek:

http://inlinethumb33.webshots.com/43...600x600Q85.jpg

http://inlinethumb02.webshots.com/43...600x600Q85.jpg

The way I read it, for it to have a significant effect the vehicles suffered from driveability problems where there was something obviously wrong. They called it severely clogged, and it was mostly on the carb engine. The FI engines were something like 1-2% difference in economy between a dirty filter and engine filter. Hardly anything really.

I think Izzy's might be one of those severely clogged filters they referred to? :-missingt

I just thought it was a good read even though it might not apply to a turbo diesel engine.

Taken from the last paragraph.

Looking at the tests, there are two distinguishing factors: there's a difference between fuel economy and performance.

With clogged air filters, every single vehicle saw performance suffer. Naturally that's expected.

However, the newer vehicles didn't really see much of a drop in fuel economy. Why? Here is your answer:
The electronic fuel system cut back on the fueling to maintain proper air/fuel ratio. So when the air was cut back, fueling was also cut to maintain proper stoichiometric ratio. This decreased performance, but did not affect mileage. The older Pontiac without electronic fuel controls did see a drop in mileage. So there's the difference.

However, the test is incorrect to a certain point. At higher speeds when more HP is required to maintain speed on the highway, a clogged filter will reduce fuel mileage. Even in the tests, the operators limited the speeds to the point of misfire. Once a misfire was detected, they did not accelerate any further. Try driving on the highway, maintaining a speed, with a filter clogged enough to cause misfires, and your fuel mileage will be zapped away very quickly (even on electronically controled fuel systems).

Now, try the same test on a diesel, and you will see a drop in fuel mileage. Diesels do not operate on a set stoichiometric AFR. Reduce the airflow, but you'll still keep the same amount of fueling. With less air, you lose power. In order to maintain the same speed, you have to bury your foot deeper in the pedal, which of course, increases fueling (and EGT's), and thus reduces fuel milage. A boost leak is a good way to duplicate these results without clogging the air filter.

from the read it says it affects power and fuel economy.

Dyno testing on a Cummins engine at various air filter restrictions up to 25" H2O has shown that HP remains approximately constant as air filter restriction increases... http://www.filterminder.com/bulletin...estriction.pdf

So why do some dyno tests show a rather large HP difference of 10 HP or more when the air filter is removed? The reason is that those tests are done on high HP engines that are extremely over-fueled and air-flow limited and they're operating at an AFR of 10 or less and in those cases the engine is able to make some additional HP with each and every additional air molecule because these air molecules can find some fuel to combust with.

At AFRs above 15 there's more air than fuel and for AFRs above 18 almost all of the fuel is combusted so that any additional air is only used for its capacity to absorb heat from the combustion which reduces the temperature rise in the cylinder. This reduced cylinder temperature limits NOx production which is why my CAT C7 with its AFR=25 can meet the 2003 EPA NOx spec without using EGR.

At WOT maximum load a typical chipped 7.3L engine has an AFR of about 18 and my 7.3L engine model shows that for an AFR=18 there's only a 2 HP decrease as air filter restriction increases from 0" to 20" H2O. Or said another way if you were running a moderately dirty air filter with a 20" H2O restriction at WOT maximum load and you removed it and ran without a filter the extra air would only be able to find enough unburned fuel to produce an additional 2 HP!

The bottom line is that if you want reliability and longevity for your engine you'll chose an air filter based on its ability to filter 10 um and smaller particulate matter and not on it's restriction at some arbitrary predefined flow rate.

What I take from this testing is that it confirms what few people, including me, have been saying for years. Which is dropping in a K&N filter or wasting money on a 'hot' air intake system does squat for mileage or performance. Even a dirty OE filter showed little difference on an EFI engine. They had to wrap the filters in shop rags to mimic a crazy situation that would most likely never occur, to create a filter so clogged it deformed the filter to get a significant difference.
If I was going to put effort in to an air cleaner system, it would solely be to pull in as much outside air as I could and increase it's filtering capability if possible. Seems most people do just the opposite.
I know most don't agree, but I'd hope at least it confirms for most a K&N filter is hype. Not to jump on Eugene's bandwagon, but I don't know what I was thinking clamping a 6637 filter on a stick, it went against my better judgement.
Seeing as how I'm at WOT about .5% of the time I'm not buying it helps make more power and gets better mileage.

If at some future date you should decide to make the leap please be advised that "reservations" are definitely not required as there's still plenty of room!

With all the obsession about air filter restriction that I read about in ads and in various posts and claims of large HP increases by reducing restriction just how much does air filter restriction effect your engine's HP? Well my above post of the Cummins dyno testing data says air filter restriction doesn't effect your engine's HP in a measurable way but then I'm sure some will say that test was done on a Cummins and I drive a 7.3L power stroke!

So just for grins I went to the K&N web site and entered in 1999 F350 7.3L to see if they're still claiming the same large HP improvement as when I fell for their ad and bought one of their cone filters many years ago and if you click this link... 57-2530 - K&N 57 Series FIPK, Performance Intake Kit ...you'll see a picture of the filter I ran for several years until my turbo blew and sure enough nothing has changed because they're still claiming ...Estimated Horsepower Gain: 14.86 HP @ 2925 RPM! Here on FTE I've seen claims of a 15 HP gain for a 6637 so I guess a 6637 is 0.14 HP better than a K&N! See I can say something nice about a 6637 after all but lets see if there's any "Physics" to back up such claims.

Lets define a term AFHP=Air Flow HP as the HP that's required to "suck" a given VAF=Volume Air Flow ft^3/min=CFM through the restriction of an air filter element. In a turbo diesel operating at very low boost levels most of this AFHP comes from the crankshaft in the form of a "sucking" action provided by the pistons during their intake strokes and at higher boost levels most of this AFHP comes from the hot exhaust gases in the form of a "sucking" action provided by the spinning compressor wheel. In simpler words this AFHP is just the air filter pumping loss HP!

Some day I'll show how to derive the following AFHP equation but for now just accept that...

AFHP={(R)(VAF)}/{(TCE)(6,343.4)} HP

...where R=Restriction Inches H2O of the air filter element and TCE=Turbo Compressor Efficiency a ratio between 0 to 1.

Lets assume a typical TCE=0.65 and calculate the WOT full load AFHP for a stock FA-1750 filter and for a K&N filter. As verified by independent lab testing ...see page 7 for the CFM airflow versus Inches H2O restriction graph for a stock 7.3L FA-1750 filter... http://www.thetruthaboutfilters.com/...andAFE_Dry.pdf ...and note that when the turbo applies an R=15" H2O suction to a stock FA-1750 filter the VAF=580 ft^3/min=CFM.

For a stock FA-1750 filter flowing a 580 CFM this gives an AFHP={(R)(VAF)}/{(TCE)(6,343.4)}={(15)(580)}/{(0.65)(6,343.4)}=2.11 HP which means that when a stock FA-1750 filter is flowing 580 CFM it's producing a 2.11 HP parasitic drain on the engine!

Lets be generous and say it only requires an R=5" H2O suction for a K&N filter to flow a 580 CFM which gives an AFHP={(R)(VAF)}/{(TCE)(6,343.4)}={(5)(580)}/{(0.65)(6,343.4)}=0.7 HP which means that when a K&N filter is flowing 580 CFM it's producing a 0.7 HP parasitic drain on the engine!

Well saving 1.41 pumping loss HP is nothing to brag about! There's more to this air filter restriction vs HP story but I've probably already exceeded the average attention span. If anyone expresses an interest in hearing the rest of the story I'll continue it at a later time!

:-X14 We always enjoy reading your comments Gene. (although we do miss the duct tape pictures:)) If nothing else, it always brings on a good discussion, which is where the knowledge & understanding really comes from. It's been my experience there is usually a difference in lab results compared to real world application, but the more you understand from both sides is how to gain the proper insight.

And for the record, there is more reason than just supposed power or increase airflow to move away from the stock intake air box. You also have to factor in filtration. I switched to the 6637 when my factory box started to allow dirt to pass. I built a cold air type box around it when the drone from the open element got on my nerves.

I keep reading about how crappy the stock airbox is, but I'm not comprehending it. I have a 00 with over 170,00 miles and the lid and tube are clean and the compressor wheel is good. My dad has a 99 and a 00, the 99 with 300,000 and the 00 with 200,000 miles with the same deal. And dad's have been all farm use in central IL. But now I digress....

Somewhere around 230k miles I noticed the lid on my box was starting to warp just a bit. It didn't look like it was seating down like it should, and I noticed a small trail of dirt where the warp was. That's when I changed over.

When I was looking at trucks for my wife, I saw some stuff that was just downright scary. Broken tabs, missing clips, basically no filtration at all. Just something to be aware of so you can keep an eye on it.

I always love it when you post something, there is always math and facts to back it up.

Dang Joe, that's dirty...lol