Aftermarket intake questions

No. Parts that are out of spec will normally increase fuel consumption.

Same response as to Alan Baker.

Leon

Yes.

If you argue that admitting colder air would decrease flow efficiency then you're also arguing that admitting warmer air would increase it.

Please feel free to quote anything you think I should have read.

Sorry. That's obfuscation, not explanation.

Just out of interest, how many of those miles were with the K&N filter? I've just bought one (Typhoon) so anything that makes me feel happier about it's filtering ability is good ;)

R.

Leon,

True. What you did was obfuscate a simple question by attempting to send the discussion in several directions that do nothing to answer the inital question(s). If you don't have an answer to the question(s) asked, why do you hinder the process by confusing the isuue - answering simple questions with divergent questions? I have plenty of my own reasons for not purchasing a system to date; I am simply trying to get real-life information/data from owners who have actually tried the systems and have opinions on the results.

I was talking about myself starting a useless thread - why would YOU take the comment personally?

Here is an appetizer:

Supposedly it's real easy to fit so if you got it cheap there certainly is no reason not to try. Just make sure to keep the original parts in case you don't like the new sound (or performance somehow suffers).

Kind regards Bruno

I bought the car with just over 100,000 miles over 7 years ago and installed the K&N soon there after. So, the K&N has been running in the car for over

Gus

There is simply too much obfuscation so, I'm starting with a clean slate. What I hear Leon saying is that at any given velocity of a car, lets say a Miata for interest of this group, the power output from the engine is the same, assuming all other external factors are the same (e.g., engine modifications don't change the profile and thus the drag of the car). Also, assuming similar fuel mixture in the combustion chamber (which is controlled by the ECU to meet exhaust and performance criteria), the amount of air entering through the intake system stays the same (e.g., same power, same fuel to air ratio, and therefore same air volume). Thus, the throttle plate in the air intake will be further closed in a less restrictive air intake system compared to stock.

Now for the difficult part. I believe Leon is stating that at constant power output, the engine with the less restrictive intake system will need to work harder to pull in the air due to lower vacuum needed to pull the same volume across the trottle plate. Put another way, more fuel is needed to the same net power output to the wheels since more power is used to pull air into the enginer. If this is the case, then I can understand Leon's argument. For maximum fuel efficiency, the intake system should be designed to minimize pumping losses at the designed optimum speed.

What I don't understand, is why moving restriction from the intake system to the throttle plate results in the engine having more pumping losses. I understand that the pressure loss across the throttle plate will increase, but at the same time, the pressure loss across the rest of the system is less. Therefore, couldn't the vacuum down stream of the throttle plate to be the same in both cases. Why isn't it the other way around where the restriction across the throttle plate actually results in less total pressure drop than the restricted intake system?

Now, of course, this entire argument is only valid for the steady state case (e.g., the car at constant velocity and the engine at constant power output). From my experience, even at what appears to be constant velocity (e.g., driving on the highway at say 65 miles per hour), the engine output varies to adjust for other factors (e.g., incline of the road, wind, passing cars, etc.). Average fuel consumption is thus the average overtime as the engine output and thus fuel efficiency vary to maintain constant speed.

Gus

K&N actually filters slightly better than OEM. There's a very large amount of FUD about K&N filters, one being that they allow dirt in the engine which is untrue and the other that they will give big increases in HP which is also untrue although if you have an unusually restrictive intake system (Miatas don't) the K&N will help.

Yes, let's get the facts straight. You NEED to get an aftermarket intake system otherwise the manufacturers won't make money and the world economy will collapse so get one right away, do your part to avoid the end of civilization.

That should be clear and free of obfuscation, right?

I couldn't agree with you more. After all, that's what a free market economy is all about. The choice whether to spend hard earned cash on a product is 100% up to the buyer. And since we are all individuals with free choice, our individual decisions may be different with neither being better than another, just different. The best we can do is make sure that facts are available for people to make wise decisions. The worst would be for everyone to stop make decisions to wisely spend their money because the facts were obfuscated. That is when our economy and the world would collapse. So yes, go out and spend your hard earned cash today for the good of the country and the world, but first do the research, learn the facts, and spend our money wisely.

Gus

Oh, LORD NO! If we were spending our money wisely nobody would have a Miata at all!!!! We'd all be driving vanilla 4 door sedans with wimpy

Geez, man, stop preaching intelligence, our economy is designed to run w/o it and cannot survive educated consumers.

Yes so far.

No, this misses the exact point. It is the *amount of oxygen*, not the *volume* that stays the same. By design a Miata engine wants to take in 1.8 L air by volume every cycle. When it really needs only a fraction of that, during highway cruise, say, the throttle keeps out the excessive air. That means that the engine fights the throttle, which costs power, hence fuel. Now if the intake air goes down say 30 C in temperature, the volume that the engine needs becomes even smaller by about 10 percent. So the throttle must let the engine get even less volume, so they fight harder, so fuel consumption goes up.

Leon

You posted the above remark in a public newsgroup. It is definitely wrong. You get the facts. Thanks are not necessary since I too post to a public newsgroup.

I think it would not be obvious to everybody that you were addressing this to yourself. Note the reference to spending people's time. That was the thing I was doing, remember? With good justification, and this is a public newsgroup, so I can. But anyway.

Leon

Because while resistance goes up, the speed of the flow goes down. And power required to overcome the resistance to the flow is proportional to the *square* of the speed of the flow, but only directly proportional to the friction.

IOW, double the density of the air, you halve the required flow by doubling the resistance. Thus you get an increase by a factor of two from change in resistance, but a decrease by a factor of four from change in flow, for an overall decrease in pumping losses by a factor of two.

You know, I think you are right. I should have suggested maximizing personal satisfaction and enjoyment not the use of wisdom. Forgive my poor choice of words.

Gus

You are right, the important variable is mass of oxygen not volume of air. I was being lazy in my analysis and basically assuming the conditions were similar enough that the density didn't change signficantly. I also understand that the same mass of oxygen requires less volume of dense air. How significant is the reduction in fuel efficiency with lower intake air temperature? Do cars get lower gas mileage in the winter in cooler climates?

I still do not understand your point for the case when the temperature is the same and the only change is a less restrictive intake leading to more restriction across the throttle plate. I do understand that fuel efficiency is impacted by pumping loses, which a greater at low power when the throttle is closed, and by friction loses which increase with engine speed. I also understand that more restriction across the intake system (e.g., closing the throttle) results in more pumping loses. What I don't understand is why it matters where the restriction is in the intake system. I'd think that what would matter is the restriction across the entire intake system not just the throttle. What am I missing?

Gus

Interesting, it's what I expected, only more so! Although that is a torque graph, I'd be interested to see the BHP equivalent (although I would expect similar curves). My car is a 2002 1.8, approx 59,000 miles on the clock, no alterations expect for a Racing Beat exhaust. This test might as well have been done on my car...

I'll try it and see, may well be standard again next week though :-p

Cheers, R.

(What's FUD?!)

K&N claim this: The K&N will filter dust as fine as talc which is between half and one micron

The Paper filter will only stop dust as big as 5-6 micron

Fear, Uncertainty and Doubt.

The best example used against K&N was a "report" widely circulated on the internet showing a mining company in Utah (I think? Could have been Nevada?) used K&N filters in their heavy equipment and found sand, dust, grit, etc. in the vehicles oil and a lot of engine damage. K&N responded that they had never made filters for that type of equipment and it later turned out that no such company existed.

Never the less, the fake report hurt K&N to some extent and the mis- information is probably still circulating around the internet, some urban legends never die.... I'm a bit surprised it hasn't shown up here, maybe it will later?