K&N air filter in 308?

Yep. '79 GTS. Love it.

 

many times on the several i have owned.

 

Mine has been in for at least 8 years.

 

Have one on my QV, better performance above 5500 rpm.

 

As long as you don't buy into the marketing hype, they are OK but they DON"T filter better than a paper filter. The advantage is that they can be cleaned and reused they have no other advantage despite what they may claim. We did TONS of dyno tests with air filters and never once did a K&N increase performance over a NEW oem filter.

 

Let in more grit and particulates for no performance gain. What's not to love about it!

 

I have had them in all my cars, but I don't think there is any measurable performance gain. I too have heard that they don't filter as good as others...I don't know for sure. It might have to do with how well/much they are oiled. I don't think these flow any worse than OEM filters, so if anything, they will help more than hinder. I think the only proven advantage is is they can be reused. Their own advertising is kind of iffy, they say: "DESIGNED" to increase horsepower.

 

If you have a carbed car it make a noticeable difference in response time. The UFI paper is as thick as cardboard the K&N you can see through. I try not to drive in dusty areas or in high winds etc. I love it!!!!

 

It's kind of an odd psychological thing with cars and car guys.

Most car guys *start* with the presumption that the stock air filter is "choking" their car. I.e., that if you took the air filter out completely, the car would "breathe" more air and make more power.

The problem is, that presumption has no basis. For anyone who is making that presumption, on what data are you basing it on? Remember, there are a ton of restrictions in the air flow of an engine, from the little throttle body, the heads, the valves, the exhaust, etc. The air flow is only going to be as much as the "weakest link" in the entire chain will allow. It's odd that so many people assume that the air filter is that weak link. They will quickly accept that claim or presumption with absolutely no data to back it.

It's easy to see, if the stock air filter can already flow more air than the engine can process, increasing the flow capacity of the air filter will do nothing.

As far as filter effectiveness, KN will NEVER claim their filters are effective as the stock OEM paper filters. They'll make a lot of claims (many misleading IMO), but they won't claim they are as effective at filtering as stock filters. I think that's because it's just not true and they want to avoid lawsuits on something that is easily proven. I corresponded with them many years ago when I was curious about their effectiveness, and even in emails they would not make that claim.

They sent me some data at one point, that showed in some standard filter test the OEM paper filter filtered 99% of particulates in their testing, while KN did 98%. Which sounds good on its face, but that's a 50% (or so, my math is bad) increase in particulates passing through.

It's always surprised me that so many people that are so particular about their cars, and OEM equipment, so quickly accept tossing their OEM air filter, based on no good data or real information.

 

(That being said, as applied to a 308, I don't know if the stock filter is the "bottleneck" in the system or not. I've seen lots of dyno data on other cars (porsches) running with stock filters, no filter and aftermarket, and it's made no difference in those cars. We had a BMW CCA dyno day and did some runs many years ago, and no ones car did any different on the dyno with or without air filters in place. But as to the 308 specifically, I don't know. But in the absence of real data, I would not start with the presumption that the air filter is the bottleneck.)

 

On the gt4 with the 8 carb throats if you put your ear to the body air intake at idle it sounds like a monster sucking air, at full throttle it is more like a screaming monster. I am only going by my seat of the pants but with the tubi and K&N it seems each other complimented the other and the car SEEMS to breath allot easier. I in know way was trying to save money just get more response.

 

Although I agree with most of what you say, there is no way that eliminating the air filter makes NO difference.

An air-filter is by itself a restriction, and if there is flow through it, there is resistance and hence a drop of pressure. If a filter has enough paper-surface or filter medium, the drop is minute, but by the nature of things it has to be there.
The reason why some cars may not show a performance increase on a dyno could maybe be explained by the fact that you didn't re-tune the engine for running with more air (little as it may be, depending on the quality of the filter)

It is not only the biggest restriction in the air-path that limits the amount of air that enters the combustion chamber, it is a product of all the restrictions in the path.

 

Exactly. Loss is additive. A filter can flow more and more air, but with a greater pressure drop. That pressure that's "lost" to resistance through the filter is just like climbing another 1000' in altitude, there's less air pressure downstream.

If you look at the threads here where some of these guys are flowing cylinder heads and whatnot, you'll see that they occasionally say things like "it flowed x cfm at y inches" (of mercury pressure drop).

 

"I am only going by my seat of the pants but with the tubi and K&N it seems each other complimented the other and the car SEEMS to breath allot easier"

"Louder is faster" Sells a lot of performance parts and is one of the cornerstones of the aftermarket exhaust/air filter marketing "bible."

As noted earlier, if the engine requires say 450CFM of air at WOT and the oem filter can deliver that, changing to a filter than can deliver 10,000CFM of air will make no difference at all. Neither will removing the filter completely.

 

Mike C and I already dyno'd this back in 06.

The K&N gave a consistent 5 or so HP.
It's here in the archives

 

and, yes, I use one

 

At what pressure drop?
You can flow a lot of air through a paper filter before it disintegrates, but you'll have a big pressure drop, and loss of flow compared to no filter, or something designed for high flow. Similarly, reducing the pressure drop across the filter in a stock engine will increase airflow and, potentially, performance.

The assertion that a conventional, restrictive filter is good enough as long as it lets air through is incorrect. Taking it to the limit, at what point would a higher flow filter be required? I get the impression that there is a belief out there that, as you add more and more flow, the filter will just QUIT passing air, and at that point, and only at that point, a higher flow solution is called for.
I hope this shows the fallacy of such a theory.

 

The K&N filter topic seems to be almost as common as the timing belt thread. I don't have the graphs, but somewhere around here is a thread that has a series of graphs comparing several filter types in a single vehicle. In a nutshell, the K&N allowed more flow than the other filters when brand new. It was a lot more free flowing compared to some filters and marginally so against others. However, it also allowed the most debris to pass through, and as soon as it became slightly dirty, it became exponentially more restrictive than ALL of the other filters.

So, if you want 5 HP that you won't be able to notice and you don't mind getting more dirt and grime into your engine to do so. Have at it. Depending on where you drive, you might want to replace it every couple of thousand miles.

 

If you do a WOT dyno pull on an engine with an airfilter, do it again with a different filter, do it again with no filter, and the results do not change, then you have proven that changing the filter makes no difference.

We used to do such dyno tests constantly with airfilters, exhaust systems, etc. As I said earlier, we never saw a K&N result in higher HP on a dyno over an oem paper filter assuming NO other changes were made to any components. I agree that a K&N might easily produce more power over the oem filter when engine changes are made that now require higher airflow.

I will admit that I have never done a single dyno test on a ferrari engine - all my experience is with US V8s but based on that I'd suggest that if the K&N really produced 5 more HP on a stock engine, than the Ferrari airbox design is really poor (filter too small) or the paper filter was extremely dirty or very poor quality. I'd like NOT to think that the oem airbox is the issue...

 

I think I've identified the fallacy in the argument that a stock filter will flow as much as a low restriction filter.

The engine (at WOT, not concerning ourselves with things like intake pulses, plenums, whatnot) is not a constant FLOW device, it's a constant vacuum source with a flow limit.
In other words, the engine doesn't do whatever is required to suck a given number of CFM, it just sucks with a given effort (cams, RPM, volumetric efficiency, etc) and takes what it can get. If you stuck a tennis ball in the intake tract, that would be hard for it to suck the air by, and would produce a vacuum behind it (exactly what the vacuum gauge measures at part throttle!). Now, if you take a thousand BBs and packed them into an air filter shape, they would let large particles through, but also lots of air could get through those big gaps, right? If you packed it with sand, the spaces would be much tighter, so far fewer foreign particles would get through, but so would much less air, just like the tennis ball would keep a bird out, but not a mosquito.
That's not to say that you can't make a better media for an air filter, but I hope it will show what's the driving force (vacuum created in the cylinder) and how restrictions in the flow path affect the result (airflow).

Note that I'm not making any claims here of what value a K&N or other high flow filter has on a stock or modified engine.
P.S.- I think it HAS been noted before that the stock airbox is a restriction in and of itself as it doesn't have enough space above the trumpets.

 

Mike, as long as you are testing K&N vs. NEW OEM paper filter I completely see your point and agree. But try this one (we have). Run a race or a race weekend with a new OEM paper filter then take them back and dyno vs. yet another new OEM paper filter. Your results will be markedly different. The paper filters do a better job of cleaning the particulates and as a result, load up (much)faster than the K&Ns. K&N (or any of that type) just give better performance for a longer period of time. The trade off is the K&N will pass more small crap to the motor. Which is in part, a small reason we freshen motors every 20-25 hours and rebuild every 500 miles... . But a small price to pay for improved/prolonged performance. They don't give trophies for the best air "filter" at the end of the race.

That said... I don't really like K&N type filters for street cars.

Rick

 

I totally agree with your evaluation re the fact that a paper filter will load up faster and therefore reduce power more quickly. As you noted, it's a primary reason not to run an air filter for competition purposes - it's not because the airflow is better without a filter it's because the filter will load up and performance will drop as the day goes on.

A few years back we ran a filter on on an SS/A Hemi Barracuda drag racer (mid 8's/155MPH) for a couple of meets and found exactly what you described. At the end of the weekend, power was down over the beginning. We were curious to try a filter, thinking that cleaner air would reduce wear and keep power up but unless you changed filters frequently, the loading up of the filter was a net loss overall.

 

This is the complete opposite of the data I've seen.

 

Yes, that's seems to be opposite of what many say and data shows.

But, it's still just guessing. If we're guessing, my guess is that the stock paper filter is designed to flow more air than the engine can use, both when it is new and at the end of it's OEM recommended mileage/replacement limit, under normal usage. My guess is that the factory mfrs have plenty of room to place a large air filter and don't make one so small as to be right at the limit of flow. OEM paper filters have large pleats with give huge surface area, which is designed to make them efficient over their recommended service life. Is my guess right, or is a contrary guess right? Impossible to know for sure without a real test and data.

Since 99% of the K&N debates that have raged since the beginning of the internets is based only on guesses, those guesses are just as good as any (although IMO they are a little better in they give auto engineers a little credit for being smart enough to not leave "free" HP and efficiency on the table by simply fitting a large enough air filter).

Bruce Anderson is a 40 year porsche mechanic, including factory race team mechanic, shop owner, written numerous books, etc. on Porsches (including many that are considered mechanical "Bibles" for the cars). He has dyno tested countless Porsche models over the years with stock, KN, and no filter at all. Jim Conforti of BMW fame has done the same with BMWs. It never makes a measureable difference on those cars.

(Again, that's those cars, and while the results are consistent and predictable, that doesn't mean it would be the same for every model of every car ever produced. But IMO odds are the results would be the same).