Thinking about airfilters

[uk525td]

Dont want a cone filter no no, and fabricating a heat shield... cant be bothered
So, was thinking aobut using another air box from a different car, with an improved panel filter.... hell why not...
cut hte bottom off nad fibreglass to shape :)
however
i just looked up the cubic inch of a K&N for my airbox, comes out approxiamtely 140.5 cubix inch (so relates to filter surface area)
and compared it to a 535 filter which came out at a measly 97.9 cubic inches.....
any huge airboxes from the bmw stables which could be good to use? bearing in mind a RHS mounte box would be preferable as it would be a straight fit....
however im all up for chopping a box up (possibly )

Why you may ask?
well i need a new filter so if i can attempt to reduce any restriction while im at it all the better :)

[zubbie]

Is the current setup that restricted?

This may bring up the whole "engineered design" of the airbox question. I.E. how does changing the flow characteristics of the airbox effect combustion, powerband, fuel mapping and tuning in general. I don't know the answer but I'm sure there are a lot of opinions

[uk525td]

I dont know, BUT if 2 filters off the same construction are compared, the larger should in theory be less restrictive.
as it feeds straight into a compressor wheel im pretty sure a smooth feed to the turbo, large filter area and good cold air feeds are the future :)
at the moment the airbox is fed from a small little snorkel behind hte headlight, i would like ot improve on that and if possible fit a larger filter, now owuld be the time :)
My original options where K&N Panel or an aftermarket cone, but i dont liek hte idea of a cheap cone with no good cold feed...
Obviously the stock air fiter cant be that bad as its 50% larger than a 535 filter!!!
Ah and remember htis is a turbo diesel, i dont give a fluff about too much air, too much air is good :) and everyhting gets blitzed through the turbo and after turbo pipework so the airbox becomes less important imho, cold air and less restricio for winners ;) plus its something fun to work on :D

[E34ührer]

I dont know, BUT if 2 filters off the same construction are compared, the larger should in theory be less restrictive.

That is good in theory....but the stock box is the right box. Plus, you have a turbo diesel....you aren't going to see ANY gains anyways.

[5mall5nail5]

Why not?

Turbo diesel would make more power with NO air filter. Turbos LOVE filter changes. People with big turbo single 3L turbos can see 10% difference with a big K&N vs no filter.

I say give it a go if you can find something large... but I doubt there is much out there that is larger than what you already have

[uk525td]

yer i ran with no air filter once and nothing was particualrly noticible
off course the other benefit.... is to reduce the nasty smoke when i floor it :P but yer i think i may be stuck with stock airbox, i may just mod the hell out of it and get some more cold air fed in, and fit a pipercross panel

[E34ührer]

I just don't think the M51 would benefit from more air. Its pretty much as good as it can get without an M57 swap. The airbox in the M51 is about 4 times bigger than it needs to be anyhoo....

[5mall5nail5]

I would turn the boost and injectors up man

[E34ührer]

Now we are talking....but still an M51....

BTW, anyone know of a M57 swapped car? I really, really want to do this.

[uk525td]

yer the airbox does seem to be oversized compared to other bmw airboxes, remember however a diesel consumes vastly more air than an equivalent sized petrol engine.
And as with all turbo applications, reducing the restriction before the turbo reduces the amount of work hte turbo has to do and therefore the charge temperature is lowered.
Im going to be happy with a pipercross element and some improved ducting i think. My filter atm is almost black so its time to swap it out :D


I would turn the boost and injectors up man

I have!!
:)

[madk0w]

Pulling in cold air isn't as important because as soon as its sucked into the turbo, it is super heated because its being compressed

[paanta]

I'd bet $100 that on a back-to-back dyno run, you'd see less than 1-2 hp.

Engines, turbo or not, are just pumps that extract power from expanding air. Usually, flow through pumps is either limited by the intake, or it isn't. Going bigger on your plumbing gives you exponentially decreasing returns on flow if the system is well fed to begin with. In the case of almost all car engines, it's the pump itself that is the limiting factor.

Why is the intake rarely a problem?

Open your mouth half way and breath in and out. Now open it all the way and breath in and out. Notice any difference in how your lungs feel? No. It's cheap and easy to design a "big enough" intake, so car companies don't bother scrimping on $.02 worth of plastic tubing. They might put some restrictions in place to control intake noise, but anymore those are pretty well designed. It costs a lot of money to get 10hp out of any given engine, so they're not going to screw that up by limiting the air intake before the throttle body (exception: AFM).

[5mall5nail5]

Pulling in cold air isn't as important because as soon as its sucked into the turbo, it is super heated because its being compressed

Yes it is - I forget the relationship exactly but for every degree cooler your intake temperature is, post intercooler temperature is a great deal cooler. Someone did a chart recently.


I'd bet $100 that on a back-to-back dyno run, you'd see less than 1-2 hp. Probably less than 1.

It's been a decade since my fluids or thermo classes, but basically: engines, turbo or not, are just pumps that extract power from expanding air. Essentially, flow through pumps is either limited by the intake, or it isn't. Going bigger on your plumbing gives you rapidly decreasing returns on flow if the system is well fed to begin with.

Open your mouth half way and breath in and out. Now open it all the way and breath in and out. Notice any difference in how your lungs feel? No.

In the case of almost all car engines, it's the pump itself that is the limiting factor.

Why is the intake rarely a problem? Because it's comparatively cheap to design an efficient intake/exhaust, so car companies don't bother scrimping on $.02 worth of plastic tubing. It costs a lot of money to get 10hp out of any given engine, so they're not going to screw that up by limiting the air intake before the throttle body.

Dude breathing you're sucking maybe 1/50 CFM. Make that number something like 800 - 1000 CFM and you'll see why it matters.

You can hop on over to the FI board and talk to some big HP guys there, ditching the filter on a PT76 3L turbo car makes a HUGE difference in power.

[paanta]

Regardless of the amount of air being moved, it's the same principle. Aren't we talking about a stock engine moving more or less stock sized amounts of air?

Of course ditching the filter on a car making 2x the power of stock will make a huge difference! That'd be like if I doubled my lung volume!

[5mall5nail5]

Yes but it can never hurt to make it more free, and he said hes got the boost up

[paanta]

Yeah, it can't hurt unless you live in a world where you can put $100 into a new filter or $100 into tires. :)

[5mall5nail5]

you can get like 7/8 of one tire for $100 ;)

[E34ührer]

5mall5nail5: all too true unless you are talking about a BMW diesel motor. A 114hp diesel car isn't going to react the way a 600+ hp car would to more air.

On an M51, nothing you can do to that car will ever net more than say 30hp...and thats spending some serious $$. Trust me. I have been up and down the M51, and flat out, it doesn't get much better than how it came from BMW.


PS-I like your new sig 5mall!

[paanta]

Or like 1-2 hp. My post said under 1-2 horsepower. ;)

Anyway, I totally agree it won't hurt anything but your pocket. It'd be an easy check beforehand anyway. Just do timed 3rd gear pulls with and without the filter and see. One unfiltered run won't hurt anything.

[attack eagle]

Pulling in cold air isn't as important because as soon as its sucked into the turbo, it is super heated because its being compressed

Pumping losses are critical on the cold side. a reduction in restriction can improve responsiveness (by improving spool) due to less vacuum pre turbo. It also increases efficiency out of boost, since you already have a huge restriction in the exhaust and intake. IIRC on a DSM even with the t25, a K&N FIPK was worth 200-300 rpm earlier spool, moving it to under 1800 rpm for full boost. That can add area under the curve on its own... despite no higher 'peak' hp number.


Superheated is a technical term... I assure you the air is not superheated.
Stock Turbo cars can lose as much as 20 hp just from a 20 degree increase in ambient temp. Partly from the intake and partly from reduced IC efficiency.

on the flip side a nice crisp 50 degree day is about as good as it gets, warm enough for tires to have traction and cold enough to make power.

[uk525td]

Ok Ok
remember we are approaching this from a petrol turbo standpoint... the main goal being more power/driveability

Firstly, my car is not stock, its not anything silly by any means but hte tweaks i have made to it have transformed hte car from an out and out slug to something much better, the only comparison i can make is pushing my friends e36 325 down the road.
its an ongoing project, eventually it will have some exhaust mods done too.... remember free flowing inlet and exhaust improves spool up... what does that do for me? well in theory it improves my fuel economy and performance!! sure i may get 1-2 bhp here and there but a diesel performance is not about BHP its about the area under the curve....and how little fuel it uses to get there :)
i estimate that when i bought hte car you could feel the surge of ttorque at around 2300 rpm.... i wasnt happy with htat and im pretty sure by reducing my wastegate creep and chipping i have got that urgency to under 2k rpm.
What does this really mean? well accelerating through the gears it means pretty much sweet fa??!?! However if i put it in 4th at around 40 mph and floor it its fun.... it is constant acceleration to 100. Cruising at 70 in 5th means nice power on tap for overtaking etc etc.
As somone else said 1 degree pre turbo is worth 2 after the turbo... if its a relatively free upgrade im willing to try it
Fact of the matter is im not getting a bigger filter in that space and it probably is overkill, so ill be hitting diy stores to improve the ducting and put a panel filter in.
Further up it was mentioned its a 114bhp motor.... well yes it is 114 bhp, a tds makes 146 or something and chips for that claim 169 bhp..... thats 169 bhp at sub 4k rpm.... you extrapolate how that would be in a petrol car?
So in theory there is nothing stoipping me hitting the 170bhp mark.....
Id love to find a BB turbo i could use, be like driving an audi quattro with good boost sub 2k :)
what power do i make now? well i figure it has to be 135+ if i can find a good app for my blackberry like hte ones on the IPHONE id try to dyno it with the GPS lol

[uk525td]

meh i took a holesaw and pad saw to my airbox, cut all of hte frontal area away and a lot of hte underside away from the engine :) ill grab a pipercross panel when i get some more paypal money :D

[neockder]

IIRC on a DSM even with the t25, a K&N FIPK was worth 200-300 rpm earlier spool, moving it to under 1800 rpm for full boost. That can add area under the curve on its own... despite no higher 'peak' hp number.

Wow.. I'd love to figure out the derivative of my car's performance! .. Nice! :thumbup:

[93FIM5]

Uk525td, can we get some pics of your engine bay I for one would love to see it?

[uk525td]

some pics from a while back
http://img.photobucket.com/albums/v327/alanthecelt/Beemer/IMG00202.jpg
http://img.photobucket.com/albums/v327/alanthecelt/Beemer/IMG00203.jpg
http://img.photobucket.com/albums/v327/alanthecelt/Beemer/IMG00204.jpg
http://img.photobucket.com/albums/v327/alanthecelt/Beemer/IMG00205.jpg

Ah, these seem to be pics when i ripped a few bits of for maintenence :P

[XR000mb]

:lol

lol bmw OG top mount turbo status.









I would turn the boost and injectors up man

+1.

sereously dude, i think thats all it really takes. i think the ECU can handle the changes.


thats or go stacks. :rofl
afterall.. it is a diesel

[corvettediesel]

Have you concidered using the air box of a 525 tds? It is bolted to the complete length of the valve rocker cabinet over the turbo and has plenty of filter area. You could get an intercooler from the same source.

[E34ührer]

Have you concidered using the air box of a 525 tds? It is bolted to the complete length of the valve rocker cabinet over the turbo and has plenty of filter area. You could get an intercooler from the same source.

This thread is like 6 months old...so good job reviving the dead....

Even more to the point: the OP HAS a 525TDS

[uk525td]

not certain the airbox is any different in all honesty :S
and i do only have a 525td not a tds
anyhoo, i did this as i needed an airfilter desperately and a friend had one kicking around :)
http://img.photobucket.com/albums/v327/alanthecelt/IMG00018-20100105-1308.jpg
http://img.photobucket.com/albums/v327/alanthecelt/IMG00017-20100105-1308.jpg

She sounds like a skyline now lol :)

[E34ührer]

She sounds like a skyline now lol :)

LULZ:buttrock