Thinking hi-flow filter? Look at this!

[DailyE36]

i hope this is not a re-post, but is helpful for those that want to change out there air filters for something that is more "high flow"
this test was done with a e30 airbox.

http://www.max-boost.co.uk/max-boost...er%20tests.htm

enjoy..

[Boland01]

Very interesting and surprising giving the claims of the oiled filters.

[coconutmnky]

Obligatory spoony

Ask yourself this question: What does a cold air intake do, and how?

Provides guaranteed cooler air to the intake than what is roaming around the engine bay. Sure, okay… this is assuming the system is as static as when you are looking at it. Consider you are moving at 30mph, stick your hand out the window. Fair bit of airflow over your hand, yes?

Air is constantly being pushed through the kidneys and chin scoop (as well as any gaps in the bodywork), mostly forced by the underpanels and side curtains to pass through the radiator stack and then forced by the pressure of the engine bay and the shape of the firewall downwards and out under the car. There is actually quite a lot of air being scooped even at relatively low speeds so this system moves pretty quick.

The stock airbox has a snorkel that draws air from between the radiator and the driver's headlight. There is just no way, at any appreciable speed, this is pulling hot air. I would say that even if you remove the snorkel the airbox is sucking ambient temperature air (cold air intakes don't make your air cooler than ambient temperature). There is just a heck of a lot of cool air being forcefully rammed into the engine bay, enough to easily displace almost all of the hot air (pockets and eddies will still exist).

Wait, why do we care about cold air again? Because it is denser and thus a cooler charge will have more oxygen per liter, thus more fuel injected by the ECU, thus more boom, thus more zoom. It's all about power. So when you are parked, or in traffic, or cruising through a residential area slowly a CAI definitely provides you with "more power". Do you care about power in any situation where you are going slow enough for it to matter?

No, nobody cares. We care about power when we're really shifting. When we're going that fast the intake already has plenty of cold air to work with. I put to you that the only thing your CAI will do is change your exhaust note and possibly decrease the efficiency of the intake system (whole other can of worms - when you start dealing with the actual fluid dynamics of how the intake works… BMW tends to do a pretty good one, but this is for a different thread…).

(Dyno tests are inherently flawed in this application. On a dyno a car is sitting still, and even a very large fan cannot emulate the car traveling at 30mph. You will get hot air sitting in the engine bay so the CAI will post better numbers… even if it doesn't in the real world.)

At some point I plan to find somebody's E36 and install some temp sensors around the stock intake to figure this out empirically. Note that we also want to filter the air here, and a good MANN drop-in filter is verifiably excellent at that.

Well I said this was for another thread, but I lied. There are a huge number of principals governing good airbox design. It is my opinion, by looking at the design, that BMW actually designed their airbox to filter air well, not keep noise down.

Don't we want our engine to last a long time? It is actually important to filter the air going in to it. Most people who know something about intakes swear by a good paper panel filter. They simply filter the best. One of the ways a CAI will offer more flow is to filter much less well. You compromise some flow here for cleaner air. I think this is a fair compromise for the longevity of the engine.

Does the M/S52 really need all that much flow? The displacement is not especially large, if it is getting enough air then the increased flow of CAI wouldn't really help anyways. There is such thing as 'too much flow' as well, something around 200 ft/sec is too much. BMW's engineering of this intake is quite good, I imagine the pipe size is pretty ideal.

Consider valve resonance. Pressure waves moving back through the intake system created by air momentum reflecting off of the valves when they close. These will reflect off what they hit. This can be the back of the intake plenum (determining runner length to some degree), the throttle plate, or the next surface which will be the air filter. Pressure waves not only disrupt airflow, they confuse the MAF which cannot tell the difference between air moving 'back' down the intake system, or air moving up it. It only knows how much air is moving over it. The funny little handle on the stock airbox has a purpose. It is a helmholtz resonator designed to reduce the force of these pressure waves as they enter the airbox. This way they do not reflect back up the intake and confuse the MAF readings further.

The position of the MAF and its environment determine how well it reads. The short straight run of pipe between the stock airbox and the MAF is therefore not for show. It is to ensure that the reading is correct, and that little kink that most CAIs have will cause disruption and confuse the reading. I am not certain of this, but I have read that the angle of the MAF within the pipe makes a difference as well. Ten o'clock is the commonly quoted 'correct' position, which is just about where stock placement is and I believe it. The stock airbox acts as a secondary plenum to a degree, this can be both good and bad for a MAF-based system (as opposed to MAP). There is a bell mouth at the entrance of the intake port out of the stock airbox, this is good.

Where to draw air from also counts. You CAN select places that are worse than stock. Drawing air from directly behind the radiator stack probably isn't a good idea, nor is it smart to draw from too low. The road surface gets hot and radiates heat very heavily. Pulling from the brake duct or similar will probably result in a higher temperature air than ambient. The stock location looks pretty darn good for an intake.

In short, BMW designed this thing pretty well. I'm sure if you removed some of the design constraints you could make it better. Who has the R&D budget to do this? BMW does, but I haven't seen anything else that looks too promising. Certainly most of the home-brew and commonly available intakes are not designed properly.


Note that heat soaking of the intake components can matter, and should govern materials selection more than wrapping the intake system or something. Wrapping it with reflective material or protecting it may help slow down heating of the intake piping, but if you run for long enough (probably not that long) it will eventually become heated anyways. Better to select a material that does not readily transfer heat, something like nylon or the sort of plastic the stock manifold is made of.

[mynameisBMW]

Lol. Yes, this is one of those situations (well almost all of the "aftermarket" parts are in this situation) where a part designed by professionals at BMW is almost certianly better than the one designed by a CAI manufacturer.

[sunbrn]

Lol. Yes, this is one of those situations (well almost all of the "aftermarket" parts are in this situation) where a part designed by professionals at BMW is almost certianly better than the one designed by a CAI manufacturer.

Or better yet, a 17 year old with Home Depot tubing.

[keeslinger31]

What about the e36 filter anyone seen a flow test of dyno comparison of that and a shielded round filter. And maybe a Modified e36 canister like cut open the side>??

[sunbrn]

What about the e36 filter anyone seen a flow test of dyno comparison of that and a shielded round filter. And maybe a Modified e36 canister like cut open the side>??

If it flows more air then it flows more dirt. Can't have one without the other.

[keeslinger31]

If it flows more air then it flows more dirt. Can't have one without the other.

Makes more power too

[sunbrn]

Makes more power too

Not necessarily. If the filter is NOT a restriction, then it will not make more power with a more porous one.
I read a report somewhere on here where they dynoed it WITHOUT a filter and it didn't increase HP.

[DailyE36]

someone should do a flow test of the e36 airbox with OEM filters vs aftermarket pod filters. that should come up with interesting results.

[keeslinger31]

well you would think a k&n panel filter with some extra holes in the stock airbox would be good right?

[DailyE36]

i know that extra holes in the stock airbox will make the induction noise louder. but not sure on flow.
this should also be included in the next flow test. any guinea pigs?
as the e30 test shows more flow through the OEM vs the K&N, that will not change if the airbox had extra holes. the OEM will still flow more. but maybe the airbox will flow more with extra holes? providing it still has the velocity stack left on.

[hammy1]

correct me if I'm wrong.. but from what i understand just drilling holes into the intake box will actually reduce fuel economy and make the vehicle run rich. heres why, the intake box has an intake line connected to it on one side which takes in fresh air and the other side is connected to the engine, engineers designed the air box to have optimal air "flow" which with momentum actually allows the cylinders to have maximum air in it on the intake stroke. (think of it as a bottle your injecting water into once its full you leave the tap on overflowing the bottle and then closing it while its overflowing.) as a result the engineers had to increase the fuel intake to compensate for the "extra" air in the cylinder. hence why you get worst fuel economy with random holes.

now with that being said I'm sure its not completely optimal because bmw doesn't want to sell cars that have loud intake noise, so what i think they did is reduced the air box intake hole to reduce noise almost like what most manufacturers do with their mufflers.

[Found94]

So it seems that the knowledge slap us coming from the pro airbox people. I tend to agree with this view and so I have a question. I realize there are probably massive amounts of air hitting the snorkel but more can't be bad right? So it is possible to increase flow into the snorkel without ruining the front body work? I was thinning about picking up a euro snorkel with the extra bit that goes into the brake duct. Would this help with airflow? Also, thr general consensus is that removing thr baffle kills midrange throttle response, but does removing it help up top? Is there a way to keep throttle response and increase airflow up top? If my quick and dirty math is correct the engine needs rough 100 liters of air per second at 5000rpm which seems like a lot. The more the merrier with airflow

[sunbrn]

The more the merrier with airflow

Why does everyone think the engine is lacking in this area? All cars for that matter?

[Jam Boy]

Very cool read, thanks!

[Jam Boy]

Very cool read, thanks!

[Nomade30]

Why does everyone think the engine is lacking in this area? All cars for that matter?

More air = More fuel that can be ignited

and

more air + more fuel = more power

[keeslinger31]

^ exactly. I dont see how cutting holes will hurt hp

[mwood]

Had a big write-up here and hit a bad key...

Anyway, more air does not always equal more power.
Air velocity and flow quality will be of more benefit.

Had a V8 ( 6.56 liter/390ci )with a 750cfm carb, put a 625cfm carb and gained tons of throttle response and torque. just sayin'

[StaceyOverbeck]

i know that extra holes in the stock airbox will make the induction noise louder. but not sure on flow.

[FLYINV]

So does this mean all of us who did the debaffled airbox mod should put the baffle back in?

[sunbrn]

More air = More fuel that can be ignited

and

more air + more fuel = more power

True. With a turbo and SC you are able to increase the pressure to the intake track.
Drilling holes in a filter box does not do this.
Removing the box does not do this.

[DailyE36]

So does this mean all of us who did the debaffled airbox mod should put the baffle back in?

i think its the induction baffle that needs to stay on for better flow.
m42 box.

looks like a velocity stack.

[hammy1]

So it seems that the knowledge slap us coming from the pro airbox people. I tend to agree with this view and so I have a question. I realize there are probably massive amounts of air hitting the snorkel but more can't be bad right? So it is possible to increase flow into the snorkel without ruining the front body work? I was thinning about picking up a euro snorkel with the extra bit that goes into the brake duct. Would this help with airflow? Also, thr general consensus is that removing thr baffle kills midrange throttle response, but does removing it help up top? Is there a way to keep throttle response and increase airflow up top? If my quick and dirty math is correct the engine needs rough 100 liters of air per second at 5000rpm which seems like a lot. The more the merrier with airflow

lol @ "the more the merrier"

theoretically longer induction hose the more torque you'll get. but the question is how much and is it noticeable. many of the time be noticeable isn't feeling the power the vehicle has but watching you fuel consumption change.

so with that being said longer induction hose also takes longer for the air to get from point a to point b thus creating a lag. probably not a big thing but still has a lag. shorting the induction hose will make the distance from point a to point b shorter but the vehicle won't be getting 100% air in the cylinder it'll be more like 97-99% again not a big deal but its how you look at it and what matters more to you.

in short from what i understand and again i could be wrong so correct me if I'm wrong, cold air intakes are designed for increased torque aka low end and short rams are designed for hp or better know as high end.

and as said before me in a previous post quality is better than quantity




o and just a little clarification on power for everyone that thinks hp means power. hp is just a measurement of power that the engine creates, where as the power that everyone speaks of and we also call pick up is really torque. and torque is measured in lb-ft