Tom Steele

Ok,

We have beaten to death ram-air myths, and cold air speculation. And there are plenty of folks running low 12's and even high 11's with the stock air box on an 02+ Z06... Plus there are dyno tests that indicate the stock box is within 1hp of some of the other air boxes out there. Without dredging up all the old arguments, let's say that there is at least an argument for using the stock air box on the car.

So... what air filter element is the best.

I did my first oil change (early, since it is the "break-in" oil change) and also plopped out another $11 or so for a new air filter.

The Autozone only had Fram and STP there. The STP was a buck cheaper, but looked $5 cheaper in construction in my eye. The Fram actually looked pretty good.

Anyone have any knowledge, tests or opinions on this?

If the stock air filter flows as well as, or nearly as well as some of these aftermarket options, then it would make sense just to change the air filter every three thousand miles. It would take 150,000 miles at that rate to pay for a vararam...

Bertrand

I would just keep using factory paper filter element. I will try to dyno test mine with the air box lid on and off (using tie wraps) but the air box is really not that restrictive in our cars IMHO. 01s are a different story.

IMHO, the paper element is large enough on our cars to limit gains from intake mods. With the open screens at the front, we are already getting cool air in the intake... I personally plan on paying the extra for the OEM filter replacement but I guess any quality element would work fine. Based on the pattern to date, I plan on changing filters about every 10,000 miles (I have 9000 miles on the car right now and it looks about due for a new one).

Tom Steele

Greenville is adding lanes to 385, my route to work. I go through clay dust nearly every day. Mine was looking dirty at 4,000 miles. So at least for the time being, I plan to change more often - probably 5,000 miles max.

Do you think the factory element is better than the aftermarket units?

Bertrand

I don't know...And probably not. However, I figured that considering the fact that dust is the number one cause of engine wear in street automobile engines (it gets into the oil and mucks things up pretty good - cold starts is the number two cause of wear), I choose to stick to the factory spec on this one (at least for now).

Changing every 5000 miles is probably not a bad idea in a dusty area. Ideally, you would change it every time you change the oil. Premium oil filter, clean factory air filter and Mobil 1 should go a long way to keeping our engines like new - even with a fair share of WOT...

Just my opinions of course; I have done a little reading on the subject but I'm no mechanical engineer though. :cheers:

Tom Steele

Good point (about the reading) - I'm going to do a little reading too.

Another question. What do race cars run? NASCAR, The Corvette R team? Indy cars, etc...

Tom Steele

Ok, here is the first site I have found... interesting. They are testing 14 inch diameter filters, but the info is of interest.

One thing I found...

"Who claims what? When K&N tests at 0.3" H2O, using a standard, cylinder head air flow conversion formula and extrapolates to 1.5", they may not be making a correct assumption. We are dealing with a restrictive medium, not a free flowing cylinder head port. They claim 50% greater flow with a K&N over paper. Our results show this claim to be quite a bit off! Most paper filters rated between 80 % and 90% of the cotton gauze types. Amsoil claims to marginally outflow K&N but this could not be shown in our test. Both Accell and Amsoil foam filters flowed about as a good as a premium paper filter, around 90%, indicating that the foam filters are getting better."
http://www.fordmuscle.com/archives/2...s/index2.shtml

Tom Steele

"The established performance brand of choice has quickly become K&N. They claim a substantial flow advantage over paper. Our results show this to be fairly accurate. The only filter to outperform the cotton gauze filters are the Nascar qualifying filters by WIX Racing. Unfortunately, these Wix glass fiber filters are very expensive and not washable. However we tested it to obtain the highest possible flow value in each category. As the results show, the K&N 14x3" and 14x4" are down only 25 cfm, flowing at 97% of the Nascar filters. Nearly even are the AIS (Air Inlet Systems) prototype versions of the same material.

Tom Steele

From the same test...

"In conclusion, the cotton gauze filters are the best flowing filters when new. Being reusable, and with proper maintenance, it may be the last filter your hot rod needs. Paper, if you are willing to replace it often, will flow very close to cotton gauze. The foam filters are also reusable and probably more resistant to washing damage. Foam is down 10% on airflow capacity, which puts it about even with a quality paper filter. "

Bertrand

I don't disagree with any of this information but I have also read that a K&N type filter only outperforms a good quality paper filter for the first 2000 miles after a cleaning (or when brand new). By 2000 miles, they are comparable to paper in efficiency from what I read.

Additionally, the improved airflow is only useful if the paper filter surface area is less than optimal. For example, in my IS300, the 3 liter in line six has an air box with a filter medium about 1/4 the size of the Z06. So an engine with over half the displacement of the LS6 and improved breathing from DOHC with VTTi has a filter about 1/4 the size of ours :jester

In those cars, I installed high performance filters and can tell a difference. However, the filter size relative to the engine created an airflow bottle neck which the better flowing K&N style filter improved. In our vettes, the filter surface area is so large that I don't believe it represents an airflow bottle neck.

If anything, the airbox itself may be more restrictive (though less in 02/03 than 01) and the airbridge/valves may be the limiting factor. This would explain why a more agressive cam with the stock filter element still achieves excellent performance gains - in other words, the paper filter is more than adequate for the required airflow - and then some. I had started a filter thread with similar questions some time ago and the feedback was that you could gain 2-3 hp max with a K&N and the stock air box.

Just food for thought... :cheers:

SWCDuke

There's no reason why the industry cannot give of flow data - like carburetors and throttle bodies. I think it's part of the SAE J726 test.

OEM's typically size filters to provide the engines air flow requirement at somewhere in the range of three to six inches H2O drop across a new element. On heavy duty engines, rather than replacing filters at a specified mileage or operating hours, mechanics test the depression across the filter and change them at 15 to 20 inches H20 depression. Some HD engines have a permanent pressure gage mounted on the filter housing to continuously read filter depression.

Being as how low speed (air flowing in the incompressible range) airflow is driven by the square root of depression you can easily extrapolate a given flow rate @ depression to any other reasonable value. The actual flow is a function of the type of media and the total media area, so filters for the same application can have different flow rates even though they may look the same to casual observation and fit the same housing.

The other issue if filtration efficiency. The K&N apparently meets SAE J726 when new, but its filtration efficiency is highly dependent on the oil, and as the oil dries out with time, filtering efficiency goes to hell and you start breathing DIRT, and cleaning and reoiling is a hit and miss proposition. Like I've always said, if you're willing to clean an air filter in solvent, oil it and reinstall it, why not do the same with your oil filters. Most guys would cringe at the thought of washing out an oil filter and reusing it, but reusing a "cleaned" air filter is the same thing! It's just a matter of whether you want the particles in the bearings or the rings. Take your pick.

It's also noteworthy that paper air filters will not reach full filter effciency - say 98 percent single pass at 10 microns, until they have trapped some initial particles, but this usually happens in a few hundred miles of operation on normal streets and highways.

Duke

Power Shifter

SWCDuke, As allway's you wright a good post. The point for some(me) is I ran quicker times with a K&N than the stock paper, and better still with the VaraRam. If washing the K&N bothers you(wasen't a problem for me)keep your paper replaceable filter or new K&N's. The K&N still is better flowing than stock washed and re-oiled. If you don't think you can properly re-oil an air filter, your deffinatly on the right track staying stock. :crazy: :jester Ric

SportsCars

I researched the K&N's a while back and found that they can in some circumstances flow more air, but they always flow more dirt: this was shown via engine oil analysis. It's a classic trade-off.

I would agree with SWCDuke regarding cleaning and reusing the K&N, more so that it's a pain to clean and re-oil *properly* (I used to do it years ago). Many people have had problems when using too much oil causing a malfunctioning MAF sensor. Perhaps a recycleable filter would be better for most people and as well as the environment.

The WIX filters sound interesting. A better flowing, better filtering, one-use recycleable filter would be highly marketable.

SportsCars



[Modified by SportsCars, 1:50 AM 9/9/2002]

Tom Steele

The Wix website shows a filter for the C5, but it doesn't say if it is fiberglass or not...

rbartick

Here we go again. Nice jab... :jester

ZO6LS6

How about a different take...............
I agree with Duke, the K & N is a good filter.......but, it will allow more crap in........
If you are running the car at the strip....use one, or any other high flow filter.........
When on the street....use the OEM..........
Best of both worlds......and you are assured of best protection 98% of the time.....
If you aren't gonna keep your ride for a long time........then use whatever filter flics your bic. :yesnod:

Tom Steele

I thought that was fair. Ram air at automobile speeds IS a myth. Cold-air is speculation, meaning it MAY make a difference (actually, cold air WILL make a difference, the question is whether the CAI's out there actually bring in colder air than an 02 Z06 is already getting via the screens).

Tom Steele

Good suggestion. Easy swap. You don't have to clean the K&N as it likely won't get dirty in most people's use at the track.

I'd even go a step further, and say run the K&N on weekends and the paper element on weekdays...

RG in Dallas

I think Tom loves engaging discussion with a conclusion. I would guess that that stems from his profession somewhat, Radio Announcer in the profile.

I don't get the feeling it's anything more than that. Besides, you need a good cold air, ram air discussion once in awhile.:)

RG


[Modified by RG in Dallas, 5:09 PM 9/10/2002]

rbartick

The problem I have with your statements is that they are based entirely on stuff you've read on web sites.

Your statements are not based on any real world testing. I am willing to bet that you have not even logged any data with your still stock car.

SWCDuke

I can tell you with no uncertainty that "ram air is a myth" is based on the science of fluid dynamics! I does exist, but not below Mach numbers of at least 0.3.

Duke