Stock Airbox vs Hot K&N?

[bondheli]

As you all know, the stock airbox gets somewhat cold air from behind the drivers headlight. My question is; will a performance intake elbow and K&N filter make any improvement since it will be right next to the hot engine?

I'm talkin an $8 elbow and a $9 K&N filter so cost is not an issue.

[Rory535i]

No, you'll probably lose performance because it'll only be drawing in hot air from the engine bay. Unless you get a pipe running down to the front grille where it can draw cold air you might as well stay with the stock airbox.

[Beez540]

I've really been pondering this issue as well. AND I know it's been talked about ad nauseum... however, I've looked at some of the designs that place the cone filter (with a heat sheild) right behind that little venturi air outlet... and I wouldn't think it would be sucking much hot air at all, at least while in motion.

Plus, I really want to hear my V8 growl a little... makes me feel better about every day on the road. So, I'm on the case to find a manufacturer with a suitable air filtering element on one of those cones.

[willobmw]

Try ITG foam filters. The best. Eurosport in Salt Lake City can get you one. Do a search or go ITG's Web site. I have a replacement(still in the air box) in the 535i.
Willo

[Hector]

to increase engine performance. I agree with Rory535i, you don't want to draw hot air into the air box as this will make the incoming air thinner, and therefore the combustion chamber won't get the optimum amount of air required for peak denotation. Remember, that the density of air is temperature-dependent. One of the reasons why the engine performs better in the morning is that incoming air is denser when cold and you get that right air amount and boost as a result of this.

I have the K&N filter the goes in the stock box. I also have the stock filter. The jury is still out on this one as far as noticing a performance increase when I have the K&N filter installed. Sometimes it seems that I can feel a slight increase in power and sometimes I don't. But in any event, I use the K&N filter from time-to-tiem specifically when I go on a ling trip. The stock filter is used for in-town driving when air quality is at its worse.

There are threads/posts that the K&N filter has inefficient filtration of air particulates and can cause harm to the engine with prolonged use. This may be true but in a conversation (was trying to replace an existing one for free because of its lifetime warranty) I had with one of the K&N filter representatives here in SoCal said that the filter has been qualified to filter out 98% of particulates just like it is done with its stock counterpart. So does one believe him this dude?

I've read that airflow is directly proportional to filtration media surface area. If you were to stretch the stock pleated filter and a K&N filter you would notice that the stock has much more filtration material area. If you were to plot the amount of airflow versus time, you'd note that although the K&N filter has a higher rate of airflow at beginning of life, the stock filter has the higher rate at end of life because it has more surface area to filter out particulates over time. But then again you can clean the K&N filter when it gets dirty.

I've also read that people rate the oiled foam filters over the stock pleated filters and the stock pleated over the K&N filter when it comes to filtration efficiency. Having said/read this, I'll just stick with the stock filter for most of the time.

[Hector]

that the air box has a black aluminum shield attached to it next to the exhaust manifold. Between painting the intake with a metallic aluminum (to reflect heat) and stripping the paint off the air box shield I believe I noted a miniscule increase in engine performance.

[bahnstormer]

can u send me some of those filters for that money?
KN wanted 70 bucks for a open cone type filter last
i checked =\

what you'd need to have is a heat shield seperating
then intake filter from the rest of the engine bay

[infinity5]

The only thing about a cold air intake is that the piping and airbox are either plastic(stock) or metal(a/m). metal conducts heat better than anyhting, and thin plastic doesn't insulate spectacularly either, so doesn't the air just get heated on its way from the shielded intake area behind the headlight to the intake manifold? and then the manifold is toasty hot as well... the air is flowing quickly, but its not flowing super fast, and either way its got a few feet of burning burning hot engine bay to cross in thin little plastic/metal tubes.

Seems like a true cold air intake would need heavily insulated pipes that started outside the car (maybe a scoop somwhere, i.e. no highbeam), and continuted to be insulated up until they hit the TB. I wonder if i could just wrap attic airduct insulation around my system... hmm would trying to cool the inbcomming air be worth it? you could use the exsisting AC system, and use a tiny condensor(is that what its called?) inside the airbox to considerably chill the incomming air. just like the car's ac. whats our ACs lowest temp? and with a tiny little radiator the coolant flow would be extremely fast.....

also, the little plastic divider (on the m60) that "sheilds" air right behind the headlight isn't exactly air tight, its more along the lines of very loosely cliped in place.

[bjl4776]

There is a system that I have seen that ricers use for high boost turbo engines that is basically a freezer coil running through the intake manifold to cool the air intake temperature to freezing temperatures just before is enters the engine. Im not sure about any specifics but sounds like it would be a cool effective idea. Im sure it would be easy for somebody to retrofit there ac compressor to run a cooling coil through the intake manifold, especially on the M50 manifold, and the expense of not having ac in the cabin, and would the strain on the motor from the ac, be worth the cooling properties of the cold air, or would it take major mods for it to be worth it?

[Johntee540]

Brunos site has all kinds of data disproving any kind of improvement with the 4.0 motor for CAI and the Cone filter.

They dont filter as well as the stock airbox and actually restrict the airflow your engine can process. Jim Conforti did some dyno passes with both stock airbox and CAI with KN Filters showing the 5% loss. I will look for the links to these and post them. But I found them when I was wondering the same thing - if its good for the rice machines it must be better for my 8. Clearly - I was wrong. On Roadfly there are also several discussions about this with links and resources. But the consensus is that for the BMW 8's the CAI and the KN are not a good mix - JT