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Zeffer's Product Review: K&N Short Ram Intake

14K views 40 replies 12 participants last post by  WoodinvilleDan 
#1 ·
"When you floor it, and it keeps suckin'."


K&N Short Ram Intake

What is it?
K&N is one of many companies (Corksport, AEM, Injen) offering an alternative intake solution for our cars. It's a tube with an open-element cone filter at the end, and a heat shield. They'll claim to make more power, but they won't without a tune. Mostly just sound, which for some (myself included), is enough justification. We don't drive racecars.

What's nice?
I've owned a K&N intake in my previous car, and will not buy another brand without heavy influencing. I love this thing. Sparkling metallic silver tube, deep red cone filter, and a metal heat shield that uses OEM attachment points! Wonderful. The sound is incredible. People hear you coming, and won't think this is a 2.5L sending out that sort of noise. It growls, it screams, and it's so much fun to stomp on it. When you push the pedal past the mechanical switch to get that extra rev limit, this thing screeches. Ah man. I love it. Makes me feel some type of way. This is what I would call the first mod for any car, ever. Being an SRI, it's out of the way of splashing water in the rain. In addition, filter cleaning is every 50,000 miles, as opposed to the stock filter replacement interval. The filters are good for 100k+ miles too.

What's not nice?
It's an SRI. It's not being fed any cold air. Though the heat shield helps keep the radiator heat away, one might need supplemental tubing (see below). It's an open element, so it's vulnerable to water and the elements. This can be remedied by a pre-filter, or hydroshield, for an extra thirty bucks. Competitors such as Corksport and AEM have entire boxes around the filter, with an inlet leading to the factory air inlet (hmm). Less parts with the K&N though. With this kit, some assembly required. No big deal, but you're piecing everything from the rubber to the element together. Price is high compared to other tubes-with-filters. There's quality to be had though.

Ease of install:
It's easy. It really is. It's not a bear to remove the stock, and it's easy to install this in and enjoy it. Would probably take an experienced DIYer thirty minutes, new guy an hour or two. Minimal hand tools required.

Overall, I love this thing. I would buy another in a heartbeat. I ran some extra tubing, and it's been sexy ever since. Might be in my head, might be butt dyno, I don't know. Highly recommended.




 
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#3 ·
I'd like to say they did, if not only in throttle response. It's winter here in FL, so it's in the 70s. Once it gets hotter I'll know for sure. They're three 3" tubes, running from two inlets on the bottom, and one from the factory inlet. It looks like butts, but I'd like to think it helped. It's a lot of air to be forced up there, especially since other cars get their air from in front of the front wheel as well. Who knows. Butt dyno best dyno.
 
#4 ·
Cool. Yea I am in FL too but I live in Tampa where the coldest day in 2016 was like 60. So for us a cold air vs short ram vs stock vs replacement filters is all pretty much the same. I don't think it looks bad either. I think it actually looks very cool once the bumper cover is off.
 
#8 ·
Data says these things do exactly zero for power and in fact likely do harm. Yes, I have logged data to back that up.

If you just want sound, and perhaps direct and provable harm to engine life (those "gauze" filters are radically inferior to factory-style paper ones in terms of actually filtering out dust from the air) then go ahead and pay the money. But after paying the money and putting the noise-maker on do check a UOI for silicates (dirt) and see if your levels have gone up. If they have you're taking real and measurable mileage off your engine life.
 
#9 ·
I'm curious about the data you've mentioned! To state that filter A allows more dirt than filter B would require controlled testing of each. One would need the same amount of particulates and dirt and dust, thrown in a wind tunnel, sent through the filters, to see if one or the other accepts more or less dirt. All filters let through some amount of dirt; in fact, brand new paper filters for OEM require a certain amount of dirt in order to work properly. I would imagine a well maintained cone filter would do the same, being made from similar materials. An open element cone filter gets maintained and replaced just the same as a regular filter would.

Since you say you have the data I'm very curious about it! I'd hate to purposefully damage the vehicle, as you claim it can.
 
#12 ·
That was a very informative read! Thank you for the explanation, article link, and chart you submitted as well. Certainly all factors to consider.

I would suggest that on our cars, at least, there's no restriction of air flow compared to stock, on a comparable lightly used filter. Our stock airbox only lets in that small inlet of air through the front; the rest of the box is sealed. With an open element like the K&N, you're pulling air from all directions, at all times. This runs the risk of hotter air, yes. There's also the issue of hot weather and not enough air reaching the filter. I won't deny any of that. I would say that it's not restrictive by build sense.

Based on the reading of the article, the K&N didn't last as long as the other filters did by a fair margin. Most of that can be solved with regular cleaning. What really stood out to me is how much dirt accumulated beyond the K&N filter. That's what's concerning.

Thank you for the read. There's a lot of good information in there!

Since it talks specifically of filters - was there an OEM standard comparison included? If not, I'll likely swap the K&N filter for an applicable filter that's better performing. It seems ACDelco doesn't sell cones, and neither does Baldwin. AFE and AMSOIL sell cone filters, and judging by the tests, performed far better than the K&N did. Looks like I have some shopping to do!
 
#13 ·
A cone filter has less surface area than the panel filter. ALL the aftermarket panel filters outperformed the cone (by a lot) and it's physics that are responsible.

The OEM paper did better than the aftermarket, and given that the surface area is likely similar between the two the difference there is media. Simply put the OEM costs a few dollars more and that extra money went into better media, which matters.

You can't get around physics. More surface area means less velocity at any given location through the filter, which in turn means the filter can be designed to be more effective at a given level of airflow restriction. I'll pay the few extra dollars for the OE air filter given that it's good for ~30k miles or thereabouts. I check it when I change the oil and that's about the change interval I've wound up running on my car.
 
#14 ·
Just to play devils advocate here...

Two things: one, the link posted is to a series of tests run on replacement panel filters, not complete intake systems. The test, to me, shows two things visa-vie oiled cotton gauze filter material. It allows in more dirt...and more air. That sort of makes sense. The difference in filtering efficiency between the best (most restrictive) paper filter and the K&N is about 2%. (99% vs. 97%)

Two, regarding the claim that there are no hard dyno numbers to prove that the K&N intake does anything...K&N actually publishes dyno results for their T-69 intake on the Mazda 6 2.5. K&N 69-6032TS Air Intake, Intake Kits
It shows a peak gain of about 5 hp/7 ft-lbs of torque on the vehicle they tested. They do, of course, point out that these numbers "may" vary.

So, what are we to make of this? Well it seems like there are several important points to consider...

First and foremost - "Figures lie and lairs figure." Both dyno graphs and column charts can be manipulated to show predetermined outcomes...or, at the very least, bias the viewer into making assumptions that are not completely borne out by the data. I'm not saying that anybody has done that here, but I'm just saying that I tend to take every chart and graph I see with a grain of salt.

Next, does the K&N intake actually improve the performance of my car? Hard to say. K&N says "yes, and we have the dyno chart to prove it." However, I already know that this dyno graph only shows one particular run on one particular vehicle. "Your results may vary." Some folk's anecdotal evidence says "yes" some says "no"." Now my personal impressions tend to back up the K&N dyno. I've owned cars where intakes seem to do nothing but make noise and I've owned cars where intakes actually seem to reduce low-end performance. However, on my car the K&N does "seem" to pull harder from about 4000 - 6000 rpm at full throttle. And I've tried both back to back and there is a viseral difference to me. Whether this as actual increase in power or just the motor climbing out of a big torque pit created by the intake, or my own wishful thinking, I don't know. I would need to actually put my car on a dyno and run back to back pulls with the OEM intake/filter and the K&N intake/filter. That seems to me to be the only way to "prove" the claim to my satisfaction. Unfortunately, that's not going to happen in my near future.

Then there is the issue of filtration. The K&N filter does seem to allow in both more air and "dirt." Like I said, this makes sense. But, how much dirt is too much? - this seems like its the real question here. Well, as mentioned before, we are looking at about a 2% difference in filtration. Well, what does that mean? Will 2% more "stuff" sucked into my intake cause my motor to be worn out at 200k miles? Or 100k? Or 50k? I guess the only way to prove this would be to take two identical Mazdas and run one with and one without and see what happens over the life of the cars. Actually, we'd probably need to run a whole fleet of cars to get a better idea. Sorry, way out of my price range.

Finally, there is the issue of intake air temperature. We know that the Skyactive engine is very temperature sensitive. The SRI sucks in more air - but its likely to be heated engine compartment air, and ambient air temp. has a huge impact on this. The stock intake is more restrictive (maybe) but is better able to regulate intake air temperature. So, it looks like its another case of "this or that." Cooler air vs. more restriction...maybe.

Just some stuff to think about. I'll leave you with these words from the 'Sage of Baltimore,'

"We are here and it is now...beyond this, all human thinking is moon-dust."
 
#15 ·
@tickerguy

I won't deny a smaller surface area on the cone filters compared to paper. That much is likely true, especially depending on the paper filter you have installed. What I'm saying though, is that on our cars, the air inlet only brings in X amount of air. No matter how big a filter is, it'll only let through that X amount of air. The bigger the filter, the more air it lets through, yes. But if a filter is being fed a constant stream of air, it doesn't matter how large it is. It'll only take in that constant stream of air, i.e. our factory filter inlet.

Another question. One could have a bunch of pleats/folds on a paper filter, but if they're so close, how much air are they really letting through? They could have a monstrous surface area, sure, but isn't the total passage of air determined by the square dimensions of the filter? Such that no matter how many folds there are, it can only let in up to the size of the filter L x W? More pleats would just mean more surface area to allow for more filtering. But does that mean that there's more air coming in before there are more pleats (surface area)?
 
#16 · (Edited)
@tickerguy

I won't deny a smaller surface area on the cone filters compared to paper. That much is likely true, especially depending on the paper filter you have installed. What I'm saying though, is that on our cars, the air inlet only brings in X amount of air. No matter how big a filter is, it'll only let through that X amount of air. The bigger the filter, the more air it lets through, yes. But if a filter is being fed a constant stream of air, it doesn't matter how large it is. It'll only take in that constant stream of air, i.e. our factory filter inlet.
Correct. The engine only flows "X" amount of air at a given RPM. Without forced induction that's a physics problem and is resolved by arithmetic -- the engine displaces "X", it turns "Y" RPM, and if there is no restriction (1 ATA) then the amount of air that flows through it is a known number. Restriction lowers the total airflow by volume. Temperature, given constant restriction (which cannot be less than zero, obviously) controls *MASS* of air, and it is mass of air that is consumed in combustion. In other words cooler intake air is always better if the goal is to maximize the number of available molecules of oxygen for combustion.
Another question. One could have a bunch of pleats/folds on a paper filter, but if they're so close, how much air are they really letting through? They could have a monstrous surface area, sure, but isn't the total passage of air determined by the square dimensions of the filter? Such that no matter how many folds there are, it can only let in up to the size of the filter L x W? More pleats would just mean more surface area to allow for more filtering. But does that mean that there's more air coming in before there are more pleats (surface area)?
Yes, if there was no filter in there at all! But there is.

Filters are pleated to increase surface area. The reason for doing that is two-fold -- you want to increase the area of the filter because you want to increase the amount of dirt it can hold before the restriction reaches the service limit but you *also* want to increase the surface area because the more surface area you have the lower the velocity of air passing through a given square inch of media. All other things being equal the slower the velocity the more effective the media is.

Depth-based oil filters are set up on a bypass system for heavy equipment for exactly this reason. You cannot get that sort of effectiveness with a full-flow oil filter because the size of the filter would be prohibitive to get the velocity down enough for it to work. So in those applications you rig a second filter, this one with a restrictor fitting on the inlet, that bypasses a small amount of oil through a second, much-more-densely packed filter at a slow rate. This allows you to run a very small pore size and the velocity through that filter is very low (comparatively), which removes a LOT more of the crap from the oil than the full-flow filter does.

This is why the cones always lose; they have (far) less total surface area (which is easily determined; disassemble it and unfold the pleats, laying both out) which means they are forced to run a higher velocity of air through a given square inch of media. This means they are less effective. If the media on a cone filter is 40 square inches while the media on the pleated paper filter is 200 square inches then the paper filter has a huge advantage both in terms of the amount of dirt it can hold before restriction becomes unacceptable and in filtering efficiency.

As to how much service life you're giving up in terms of engine longevity that's a much harder question to answer. One decent qualitative answer can be had by looking at silicon levels in your used oil, because some percentage of the dirt that gets into the intake will wind up in the crankcase oil, and you can detect it there. You can also get some sort of read on whether it's impacting your service life by the wear metals in your oil as well, which a UOA will also tell you.

But the real question to ask here is why buy such a device at all? If it's simply for the noise factor then *perhaps* it's worth it. But here's the thing -- I have an OVT tune on my car, which means I have a Tactrix that can log data at high speed. There is a large thread here with other people's results, some of whom have and still are running SRIs. None of them have put up any sort of statistically valid difference in power output .vs. what I get without one, and between all of us there's a HELL of a lot of data exposed for anyone who cares to look.

If AFR is constant and so is RPM then given that fuel rail pressure is regulated and fixed then injector duty cycle is truth (unless you've replaced the injectors with ones that flow more fuel, of course!)

What's interesting is that a few people with various SRIs have reported statistically-significant "improvements" in MAF. However, we know those numbers are bunk (that is, they're gamed by the geometry of the SRI) because they have not resulted in commensurate increases in fuel flow and output. The problem with trying to "trick" airflow numbers into the ECU with a modern engine is that it doesn't work because the ECU manages fuel in order to produce a given AFR and it has closed-loop sensors downstream in the exhaust to allow it to do so with very high accuracy. The result is that if you tamper with the MAF sensor output by tricking it (e.g. by using a venturi) you gain nothing because the ECU will very quickly reset its internal mapping multiplier. Remember that MAFs, like all other instruments, have tolerances and drift over time, so the ECU has to be able to compensate for that -- and it does, almost immediately.

In short the DATA says that an SRI makes no more power in this particular application because there is no appreciable restriction in the stock intake that can be improved upon. The DATA also says that a cone filter on an SRI allows in more dirt. Whether that dirt translates into materially-less engine life is an open question but since the gain is zero in terms of output and in fact may be a net loss, especially in warmer areas, due to hotter air being ingested then what possible purpose does putting one on the car have, other than emptying your wallet?
 
#17 ·
Correct. The engine only flows "X" amount of air at a given RPM. Without forced induction that's a physics problem and is resolved by arithmetic -- the engine displaces "X", it turns "Y" RPM, and if there is no restriction (1 ATA) then the amount of air that flows through it is a known number. Restriction lowers the total airflow by volume. Temperature, given constant restriction (which cannot be less than zero, obviously) controls *MASS* of air, and it is mass of air that is consumed in combustion. In other words cooler intake air is always better if the goal is to maximize the number of available molecules of oxygen for combustion.


This is exactly why the aftermarket SRI or CAI would provide a benefit though. MAF/MAP sensors may regulate the amount of fuel being fed into the chamber for combustion but the cooler, denser air should trigger more (stronger) combustions. This would intern translate to more power.
 
#18 ·
This is exactly why the aftermarket SRI or CAI would provide a benefit though. MAF/MAP sensors may regulate the amount of fuel being fed into the chamber for combustion but the cooler, denser air should trigger more (stronger) combustions. This would intern translate to more power.
Except that you don't GET colder air with a SRI. You get HOTTER. And thus far it has proved to be damnably difficult to get even equally-cool air than the stock intake provides with an aftermarket airbox replacement. That's what the data shows.

In short the stock intake is surprisingly effective at doing the job of getting air at or near ambient into the engine.
 
#21 ·
@tickerguy is doing a great job with all of this data, so I'll add mine:

After removing the K&N intake and reinstalling the OE airbox, my instances of exclaiming "fuck this piece of shit car" while the engine bogged from a stop went down significantly. The reduction of instant torque due to the hot engine bay air getting pulled in initially is hell for MTX drivers.
 
#22 ·
Oh god, so much this. Not the bogging, but the exclamation. I'm fairly handy, but when I run into a snag I get stuck on, it's always that. "F**k this bullshit dumpster fire of a car."

On the bogging, never had the issue with an AT transmission, even in sunny Florida in 100 degree days. It would go whenever I asked it to.
 
#23 ·
The AT masks the seat of the pants feeling, but not the impact on your acceleration times.

There's nothing like sucking a big chunk of 150F air down the intake to screw you; the ECU instantly pulls timing (if it didn't you'd blow a hole in a piston from detonation!) and there goes the torque.
 
#24 ·
I was thinking it'd be a more numb drive. I floor it all the time. I don't drive like a dick, but when I can get on it, I will. Haven't noticed any changes in acceleration, except for today.

You know how when you press the mechanical kickdown, it raises the rev limiter? Mine was hesitating at the top of the range. It would pause as if unsure, and then rev up again. Strange. It was 50 degrees out too.
 
#25 · (Edited)
It's 50F out but it's 120F (or more) in the engine bay..... especially if you're in the city (e.g. not moving fast enough to turn over the air in the engine bay quickly.) The air in the engine bay has passed through the radiator and of course the job of the radiator is to take the heat in the coolant and transfer it to the.... air!

BTW there is no "mechanical" kick-down on these cars. AT vehicles have a fake "kick down" detent at the bottom of accelerator pedal travel but it isn't wired to anything. The ECU does read the last few percent (beyond the detent) however, as "downshift if RPMs are safe to do so". MT cars do not have the faux detent "switch."
 
#26 ·
Well, naturally. I'm pulling cold air from three inlets: factory + two more, with heat shielding. I don't think it's a temperature issue. This was also while cruising back roads.

What else is it called? It's a physical kickdown. This is my first A/T vehicle with a kickdown, and in our 6, it downshifts to the lowest gear possible, and raises your rev limiter (or at least shifts later) as long as it's held down.

My issue was that, while pedal to the metal, when it hit that rev limit, it hesitated, then continued to gas. A similar effect to the fuel being cut, rather than being starved for air.
 
#27 ·
I really wish there was more knowledge out there from the general public on SRI's. The public is broken up into three groups.

1.) Those that know the truth and wouldn't touch one if it was given to them for free. 2.) Those that know they are getting robbed performance but don't care because they like the sound. 3.) Those that swear their car is faster because of their SRI (this group is the most frustrating because their butt dunno is way off). I also swear that the last group are paid moles by K&N themselves.

The reality is these things are completely pointless in modern cars and do absolutely nothing other than offer a really cool sound upon acceleration. I've been a part of over a dozen car forums in the last 10 years and each forum has people that fall into these groups. However cars that are more performance oriented usually have more group one followers where cars such as the Mazda 6 that don't have a lot of upgrade options usually have more group two and three followers.


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#29 · (Edited)
Its funny how different people can perceive the same thing in radically different ways, isn't it?

I've run K&N intake products on many cars that I've owned and have had all three of my95tsi's impressions. I had a GTI where the intake actually degraded low end performance (actually not a K&N product, btw) - but this wasn't noticeable until I switched back to the stock box. I've had cars where the intake didn't seem to do anything but make noise. And I've had cars where the intake "seemed" to enhance performance on the top end. My M6 is one of those cars, seeming to pull stronger from 4k on up with the K&N intake on vs. the stock box.

I'm open to the idea that what I'm feeling may not, in fact, be what's happening...but, has anyone actually run back to back dyno sessions (stock box vs. K&N) on a 3rd gen M6? The only one I've ever seen is the one published by K&N.
 
#31 · (Edited)
Zeffer's Product Review: K&N Short Ram Intake




Dynoing your car after an SRI install is like taking your car for a new top speed run after adding a rear spoiler. If you do see any power increase, maybe 2-5 horsepower it won't translate to the real world.

You would need to do 4 dyno runs to make any claims. One with stock intake on cool day, one with stock intake on hot day, one with SRI intake on a cool day and one with SRI intake on a hot day. I'm willing to bet any amount of money that the stock intake will beat out the CAI in both categories. Adding a heat shield or some tubing below won't make a lick of a difference. Anyone that feels any type of change in power after a SRI install is delusional. The mind and body will play tricks on you when your ears hear something they are not used to.

As much as I don't recommend it, if you really are that dead set on having a "cool sound" you're better off drilling some holes into your stock intake box than you are buy a SRI.


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#32 ·
Ok...my question is in all this.... does this all apply to the CAI? When I bought my car i got the Corksport SRI and was getting bad heatsoak. So I pulled it of and put on an Injen CAI.... there was a night and day difference..and I'll admit I love the growl.

Im in sales and when i get stuck doing the city driving I notice my car getting pissed and loud and laggy from a stop...BUT i DO notice the "butt dyno" gains above 3-4K RPM's

I love reading what you all post on this and I learn a lot from you guys.... so Id love to hear your opinion.
 
#34 ·
You're much better off going this route but I really hope you have the Injen made hydro sleeve over the air filter that protects the air filter from potential water intake. I had a friend hydrolock his engine with his CAI during a big rainstorm with all plastic shielding on his car fully intact. Definitely not a risk I'd be willing to take.


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#41 ·
First, I want to commend @Zeffer for a nice write up and a cool way to mitigate some of the drawbacks of an SRI (get cooler air). It's actually got me thinking about how to route more cool air to my intake.

I also commend Mazda for how well the stock setup works, truly it is well engineered and staying within there parameters (quietness & budget) it cannot be beat.
All due respect @tickerguy, and I do respect/appreciate all the data you bring into the discussion, rightly pointing out that the stock setup is quite impressive, but your arguments are only capturing a part of what is happening and thus leading to only partially correct conclusions.

The problem is quantifying performance of an air intake purely based on peak flow is not measuring lots of other mechanisms that are at play. In any engine, and especially the Skyactiv 'Miller cycle', there are pulses from the valves opening/closing and there is turbulence. One of the reasons for a cone shaped filter is the effect it can have on shaping air flow and affecting flow dynamics. One reason for SRIs not helping in the low end is because the Miller cycle generates stronger pulses (from the intake valve staying open during compression) and if there is not as much air mass coming into the engine (short tube, smooth tube) then the pulses can momentarily stall the incoming air charge, creating worse turbulence at lower RPM. So, if the SRI has better flow characteristics (and you mitigate the heat issue) then at lower RPM it's net gain or loss of nothing, but at higher RPM where the pulses from the intake valve are shorter then the SRI is no longer at any disadvantage and flexes it's flow.

In my case, I went with the Injen CAI (with Hydrosock) and love the gain in power & responsiveness across all RPMs. In fact a few weeks ago I put the stock intake back on to see how it felt, but took it off the next day because I missed the low end power and reduced throttle latency from better flow characteristics.

About the ECU, this Skyactiv ECU is awesome IMO, and if you change anything about your engine I highly recommend resetting the computer in some way (clear DTCs, disconnect battery for a while, etc.) to get it to re-learn how it's operating. This ECU has a hard-coded base RANGE of operation (known as the "tune"), then it has the adaptive part that essentially runs in RAM which adjusts to how the system is operating (obviously there is a limit to how much the ECU will adapt, but I've experienced this engine running worse after changing something, until I disconnected the battery for a while).

Intake does not happen in a void: In my experience airflow related improvements tend to compound each other. If you do nothing else to your car but put a better flowing intake the difference will be very minor, and if you do nothing but put a better flowing muffler the difference will be very minor, but both together will have a little extra effect because having air flow out more easily will help more flow in. Also getting a tune that is more aggressive means you generating more power, and leveraging the small flow gains even more.

About Dynos, the reality is I'm likely never going to waste the money on a Dyno as that same money could pay for two days of Autocross!!!.
I also don't think a Dyno is a good way to measure the overall impact of good changes to Intake/Exhaust. A better way to quantify it would be to do a series of timed runs on a track with each set up (it would have to be a lot of runs, where you through out high and low times, then average the rest), because in my experience the difference in 0-60 WOT is not nearly as big compared to the difference in throttle responsiveness in the real world and the effect on lap times!
 
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