Aftermarket intake questions

Apparently he's one of the "faith-based" fundamentalists he talks about.

well does it filter?Several readers have responded with concerns about the K&N's ability to effectively filter dirt out of the air compared to paper filters. After all, engine protection is the reason engines have an air filter to begin with. K&N insists that their filters are rigorously tested to meet OEM filtration standards.Expert opinion: Not an issueI discussed the issue with the owner of a reputable engine rebuilding shop. In his experience, the engines that suffered from premature wear were those in which the filters were routinely ignored. He didn't see any significant difference in wear in engines where the filters were routinely cleaned or changed, regardless of type. (He personally runs K&N filters in his own cars.)===================================================================We rebuild dozens of engines on off road motorcycles in the '70s and noticed the same results, engines with neglected air filters had dirt inside, those with maintained filters didn't. We sold a lot of K&Ns and Uni filters and never noticed any difference. Lots of links here:

When I was racing dirt bikes (national enduro circuit), I used both K&N and Uni until the bike manufacturers caught up and started providing decent foam OEM filters. You're correct, rigorous maintenance was the key. But no one expected a dirt bike engine to last more than a season under the best of conditions--the real breakthrough from K&N was the ability to keep the engine running even when the filter was caked with dust, because the flexibility of the gauze and the rubber mounting collar ensured that chunks of oily crud would fall off under the pounding of off-road racing. We were more concerned with finishing the race than facing an early rebuild. Piston rings were cheap and easy to replace.

These filters did what they were designed for: keeping enough dirt out of an engine so it could finish a desert race. Protecting automotive engines on the street for 200k miles was not a consideration...until they discovered that clever marketing and manipulation of magazine content could expand their market past their wildest dreams.

Note that overoiling a foam or gauze filter can ruin a 1.8 Miata's mass airflow sensor.

No. This is an internal flow, not flow around a car. Speed is irrelevant here, it is total pressure that counts. The total pressure loss must be greater for the smaller flow volume.

And resistance is a meaningless term here also. The throttle is not trying to move through the air. What counts is head loss, not force. (Although the head loss of course finally shows up as a reduction in pressure on the top piston surfaces.)

Think of taking the Miata to Denver. If it takes in the same number of molecules of oxygen, in Denver the throttle might be wide open, and there will be no real pumping losses. In Florida it will be partly closed at exactly the same produced power. Pumping losses, here we come.

Then consider the fact that for *the air resistance of the car*, your argument above *does* apply. The air resistance in Denver will be much smaller too, and you are probably going at a good clip on this highway if your throttle is wide open in Denver. We in Florida suffer. :(

But then, we do not freeze to dead in winter as they do in most of the rest of the country. :) But then we freeze to dead in Summer. :( But you can always go outside to warm up some in your Miata. :))

Leon

Common sense says that it should be very small. 30 degrees Centigrade is about 50 or so Fahrenheit, and that changes the density, so the pumping losses, by about the same percentage. That limits it to just a few miles per gallon, and then pumping loss is only one item for which fuel is used.

I was not saying it is something to worry about, just responding to suggestions that common sense says an aftermarket intake would improve fuel mileage.

I have no clue. There must be lots of much more important variables.

I am somewhat mystified what you are asking here. Did I not already note in another post exactly the same that you are saying here? Your final sentence seems to be exactly what I said there. If the intake air temperature is the same, the effect of the intake should be the same, except for effects that would take a fanatic to measure.

Leon

Internal flow follows the same laws of fluid dynamics as external flow does.

No, but the pistons are trying to draw air through the throttle. In doing so, they must use power.

In Denver, the resistance will be less (not none, BTW), but the air must be moving much faster to make up for the change in density. Power expended goes up in proportion to resistance (which has fallen) and up in proportion to the square of the velocity (which has risen).

if you're in a non-FI Miata, no. Your throttle will indeed be wide open, but you'll be in third or fourth gear, engine gasping for breath.

We now resume the counting of pinhead-dancing angels, already in progress...

Actually, when I was in Denver, I spend hours in endless traffic jams. Fuel efficiency was most definitely *not* enhanced. The rest of Colorado was great, though.

Leon

I had to sort of laugh at this thread -- An untuned air intake may allow more air in at wide open throttle and low engine RPM. At higher RPM, and wide open throttle, things change. The properly tuned intake system takes over. Why do y'all think the 99's had long and short tuned air passages inside the intake? Naturally, adding a supercharger or turbocharger changes things quite a bit, since they can "cram" air into the intake, and it becomes a pressure instead of a vacuum system. Still, the long and short air passages can be utilized, but most likely at different points in the engine operating envelope. How much change in gas use will occur? Don't know, because every test I've ever seen had the difference in the same range as the variation from one test to another.

Things worked a bit differently on the carbureted engines. Mooney A/C had a real working Ram air intake that did add a few HP. Naturally, if you have

120-140 mph airflow and very cold clean air, you can bipass restrictions in the intake, and actually get an effective ram air intake.

D>

I already mentioned in a couple of my posts that you would lose any optimization Mazda would have done. I meant primarily acoustics, (or tuning, if you want,) though temperature regulation may be another. I do not know how effective it is, but I am aware that it is generally considered an important thing to do. The design project students around here tell me so, and they should know, coming up with a radically different intake design every new year and new group of students. :) I would think it is very hard to do well since the range of operating conditions of the intake is so wide. Does anyone make a variable intake?

I believe it used to be difficult. Then they invented computers to mess around with the engine at random, and I guess it is probably impossible now. :)

Actually, before Moss took over, the Jackson Racing intake added 9 horsepower, and 5 more when your car speed started compressing the air, (i.e. ramming the air down the throat of the intake.) If you believed the advertising, at least. One poster said that Jackson in private mentioned 6 or 7 hp; I don't know whether it is true. However, it was widely complained that the numbers included the effects of advancing the timing by 4 degrees, which is a free thing anyone can do themselves.

And then of course, everyone with even a basic familiarity with some Bernoulli law has posted the fact that cars driven by people who want to stay out of jail don't get close enough to the speed of sound to have any ram effect to speak off. (Though I am not sure whether this motorcycle driver they caught doing 200 mph or so was thrown into jail. Ram effect at that speed would be more appreciable. However, you have to drive 1000 mph to really start seeing a somewhat major, still relatively minor, effect.)

But the latter point was satisfactorily resolved when Moss took over. Moss simply claimed the intake would give you 14 hp and more as your airspeed started compressing the air. (Note the ambiguous reading of this statement.) I assume it was very, *very*, cold outside when they measured that. (Sure they measured that. You must believe people.)

What year Miata? And what modifications?

I guess I am chicken. I have driven neither of my Miatas near the speed they are supposed to be able to do. Then again, I am not on the interstates that much, and anywhere else does not seem like that hot an idea. On track days, there is not enough time to build up speed, and I tend to have my eyes on the track instead of the speedo. Also, I usually have to use the straight parts to let much faster drivers pass.

Leon

I believe that, although every manufacturer wants the best possible performance AND fuel economy from their engines, the EPA/DOT regulations have been very strong toward noise and I think that, right now, sound levels *MAY* be the overriding criteria....

I've seen some pretty complex and restrictive intake systems designed to overcome noise rather than provide performance.

Leon,

"GPS" ..... is that Gallops Per Second ??? :-)

Was that with the top up ? I know when we did the "tuffing test" on my '91, there is little over 5 MPH faster with the top up and almost 9 with the hard top on.

Bruce Bing '03 LS

You may well be right. That would favor aftermarket intakes. I guess it is mainly an issue for larger cars, though. Surely Mazda could easily raise intake noise a bit without going over exhaust noise on the Miata?

Leon

Actually, you are replying to Chuck's text.

Don't be silly. Of course it stands for GigaParsec/Second. Chuck is a fishing man, and I believe him unconditionally.

I'll leave it to Chuck. But you are right, there is a difference in drag coefficient of that order between top up and top down, and at that speed, resistance is all drag.

Of course, in Bozo and Bess, resistance is futile. :)

Leon

I would thing Mazda would have a worse problem with the Miata, particularly the NB. Trying to keep the car light means they can use less sound deadning than other cars, the NB has no hydraulics to eliminate valve noise, Mazda rightfully believes the exhaust sound is important to sales, etc. etc. I think they'd have more sound problems with the feds than other cars?

As far as aftermarket intakes and exhausts, I recall years ago a manufacturer of motorcycle exhaust systems (Hooker Headers) commented to me that the factory did an excellent overall job, the aftermarket systems were best at increasing power and or torque in specific rpm ranges so they could tune a motorcycle exhuast for motocross or roadracing or ??? depending on the need of the racecourse. Interesting comment, it's stuck with me for 30+ years and I'll bet it applies to all vehicles, even today...

I am sure it is right. If you only optimize for a narrow range of conditions, you can do a much better job at it.

Leon

Actually the graph is showing horse power as well the scale is just not part of the photo I took. The unit is in metric horsepower meaning the top at 7095 rpm is 142.5 BHP. The missing scale gives 60 HK at 90 Nm, 80 HK at 120 Nm and so forth.

I have put the kit on my car now and I do like the difference.

There is a little more "omph" in the exhaust but mainly at higher revs and during acceleration so when taking it slow it does not make me feel like a noise terrorist. Also there is a sucking noise from the new filter which can be heard at idle and even a second after the engine is turned off.

As for power I think there is a slight improvement but it could well be wishful thinking.

The rolling road I used in the test without the kit is closed for the holiday but I have booked a time for August 8'th so by then some hard facts should be available (I want to use the same place to ensure the most accurate result).

Kind regards Bruno

Looking forward to seeing the results. Sounds like you had the same experience as me! It's when you put your foot down the filter change is most obvious...

Cheers, R.