Performance air filters

[B21]

I have a K&N air filter in the standard airbox; are we saying that an OEM BMW one is better?

In almost all cases for quite some time an OE air filter will do a job that at least 99% as good if not better than a K+N..plus filter far far more dirt than K+N..the exceptions are possibly with a very major performance update that is limited by the airbox design or filter size..

 

[Nodzed]

I have a K&N air filter in the standard airbox; are we saying that an OEM BMW one is better?

If I remember correctly (and @Pingu is the man to answer) the oiled K&N actually reduces airflow and potentially reduces performance, I'm sure this difference would be unperceivable for most if not all owners but for me if there was no benefit or performance from a performance filter then the hassle of cleaning then re-oiling the K&N was a total waste of time and effort, so may as well use paper filters.

 

[the Nefyn cat]

I've always been perfectly happy with OEM filters, just keep shoving clean ones in, more often than the manual says may help. It's fairly easy to see if a filter is full of cr4p or not. If I wanted more performance I'd have bought a Z with a bigger engine, but the 2.2 seems quite capable of breaking the law as it is, and I've grown out of trying to emulate the TopGear/Fast and Furious type to55ers. Having the VTR helps, too.

 

[Richard29]

I have a K&N air filter in the standard airbox; are we saying that an OEM BMW one is better?

Good question. I have the same.

 

[Pingu]

I have a K&N air filter in the standard airbox; are we saying that an OEM BMW one is better?

It depends what you want. If you want noise, use a K+N. If you want filtration, either is probably good - I' don't have any way to measure filtration. If you want the highest flowrate, use a dry K+N, but sacrifice the filtration. If you want highest flowrate and good filtration, use a BMW paper filter.

I think (only my thoughts) that the noise is caused by what I call the "syringe effect". It is actually a form of cavitation. It's the effect that you get when you try to suck water through a syringe, but pull the plunger back too fast. You can't fill the syringe with water, as you have exceeded the magic Mach 0.3, which is the speed at which the fluid starts to become incompressible. The solution is to use a bigger nozzle, make the fluid less compressible, or to pull the plunger back more slowly.

In car terms : Bigger nozzle = less resistive air filter. Less compressible fluid = make the air hotter. Plunger slower = less revs.

Bigger nozzle is mostly gains for a performance high speed engine, but the slower air velocity will penalise you in a normal speed engine. You want the max flowrate at approx Mach 0.1, so you want a max air velocity in the region of 70mph (30m/s).
Hotter Air is mostly losses, as it's less dense, so less fuel, so smaller bang.
Slower plunger speed is a slower revving engine. That is mostly losses (IMO), but it's the way large Yank V8s used to go. They sound great, but are big and heavy. Power-to-weight losses.

 

[Ianmc]

Blimey. Think I will stick with the K&N filter until it gets dirty then replace with OEM. Can't say I have felt (or heard) any difference anyway!

 

[B21]

FWIW on the Z4 E89 (yes I know later car, maybe better design of inlet system)..on both the N20 powered version I had (2 litre 4 cylinder) and the N54 version (3 litre 6 cylinder) I did about 50 dyno runs over a 4 year-5 year period with all sorts of changes to exhausts and inlets (as well as turbos and mapping)..

Every induction system, every engine and every exhaust system has its limits in terms of flow etc..what's more complicated is that these systems are not simple steady flow, steady state systems..at certain points either constructive or destructive interference effects happen as in the case of resonance of systems..so you get standing waves, pulse effects based on all sorts of fluid dynamics which hopefully the manufacturer understood by design or testing.

It seems from what I saw that most systems are reasonably balanced and taken overall the systems work well.

Its a lot lot easier to make power despite inlet and exhaust issues with turbos..but it still not without effort..you can see this in the waste gate duty cycle of the turbos, ie how hard they having to work to make the boost asked for...you can also see how asked for boost compares to delivered boost.
The beauty is if you marry the data logging to a dyno then you can see how these things effect torque and therefore BHP.

What I found in summary (for the E89s) was that the stock air box and factory filter did a pretty good job at stock power levels and there were only marginal gains..and often losses in different parts of the rev range.

What we saw was that typically K+N , no filter and Pipercross impacted in a positive way a small amount at peak torque and then often lost it at peak RPM.

When the engine was asked to deliver substantially more than stock..on the N20 from 184 BHP to 280+ BHP and the N54 from 340 BHP to 400 BHP that there was a minor increase in peak BHP..on the n54 from 400 BHP to 406 BHP.

What was interesting on the twin turbo N54 was that when seperate dual cone intakes were used outside of an airbox then there was a marked improvement in peak torque..we surmised by the removal of interference effects of one inlet or another that occue in the common airbox for both turbos.

We did find on the n54 after 400 BHP somewhere the stock system started to limit power..so at 500 BHP we found that by adding an auxillary inlet to the existing airbox and filter we suddenly got an extra 25-30 BHP..but that was an extreme example.

 

[Rodders67]

The N54 has chilled DME like my N63? I have flat KNs in mine and performance is relatively same as OEM, but cheaper.

I am regretting my Cosmo CAI purchase, but will give a go with a box and some piping.

 

[B21]

The N54 has chilled DME like my N63? I have flat KNs in mine and performance is relatively same as OEM, but cheaper.

I am regretting my Cosmo CAI purchase, but will give a go with a box and some piping.

I don't know the N63 but its the same vintage as the N54 and I believe it uses broadly the same DI components..I assume its DME is related to the MDS81 fitted to the N54.

If you are bored /interested / have time or money then its fun to play around with these things.

At power levels of 250 BHP + its difficult to really check these things out on most UK roads..I used the same dyno boys so there's a degree of consistency and since they've tuned and dno'd hundreds if not a thousand plus cars there's a body of data for comparision.

There chief tuner / owner who claimed they had done much bench marking of various manufacturers' intake systems and filters stated that teh vast majority failed to live up the manufacturer of the dyno operator's expectations..

My 'Mr.5' mod on my N54 surprised them (and me) with its impact on the uprated turbos and plumbing on my 35is..

 

[TriumphZ3]

K&Ns were always a problem with my older cars running carbs; you could never get the mixture to a good setting and there was a dubious benefit if any. Many owners just went back to paper filters which the factory settings were designed for.

 

[Mike Fishwick]

Yes - as the OEM filter is also used on the E36M3 etc, it is more than adequate for the smaller-engined models. If the filter internals of a K&N and an OEM filter are cut out and compared, the OEM filter has about five times the area. For a felt filter of less area to match the OEM airflow rate it has to have less filtration. Even if the K&N did have more flow, it would only be apparent at large throttle openings, which may happen once a year!

This is why a K&N loses a lot more flow when slightly fouled than does the OEM type. Add in the risk of fouling the airflow sensor wire, and all you are left with is more intake noise . . .

 

[Rodders67]

Yes. BMW paper filter is the best.

The improvement that I made was to modify the internals of my airbox.

The improvement was from 444CFM to 485CFM ay 28"H2O

Air Filter Box Modification

Looking at the intake system of the M Roadster, I thought that the air filter box could do with some improvement... I built a flow bench to measure the flow rate through the air filter box... but this rig would only measure comparative differences. So, I built another rig. The data from...

www.zroadster.org

After 4hrs of attempting Cosmo CAI installation and removal of my Z3M airbox and pickup ducts… I think I have more questions than answers and a deep appreciation of Pingu airbox modifications.

Shame me, but I didn’t realize there was a forward facing pickup for induction air on the Z3M. The 55mm duct in the brake duct is only 1/3 of air supply. Pardon me for criticizing also the headlamp box, but the push of air in/behind the light housing seems like a bad idea for lights.

both of my intake light bulb access doors were open, so OE induction was handicapped. So after failed CAI installation, I returned to stock airbox and pickups and sealed up the doors. The Pingu article makes more sense and I will share that pushing air into light housing seems better than pushing rain and or grime into CAI when you sandwich the filter into the underside of wheel liner.

Maybe someone can share photo of their installation that helps me understand where the CAI should go, but at present time, I have surrendered to the fact the OE induction system need only some air funnel mods and it will surpass a piped CAI with regards to flow.

I do want the induction sound, but reserved to saving the engine.

thanks

 

[Pingu]

After 4hrs of attempting Cosmo CAI installation and removal of my Z3M airbox and pickup ducts… I think I have more questions than answers and a deep appreciation of Pingu airbox modifications.

Shame me, but I didn’t realize there was a forward facing pickup for induction air on the Z3M. The 55mm duct in the brake duct is 1/3 of air supply. Pardon me for criticizing, but the push of air in/behind the light housing seems like a bad idea for lights.

both of my intake light access doors were open, so induction was handicapped so after failed CAI installation, I returned to stock airbox and pickups. The Pingu article make more sense and I will share that pushing air into light housing seems better than pushing rain and or grime into CAI when you sandwich the filer into the underside of wheel liner.

maybe someone can share photo of their installation that helps me understand where the CAI should go, but at present time, I have surrendered to the fact the OE induction system needs some funnel mods and it will surpass a piped CAI.

I do want the sound, but reserved to saving engine.

thanks

I treated "Cold Air Induction" and "High Flow Induction" as separate, but tried to design them so they are complimentary (one doesn't adversely affect the other).

I made the existing system as high-flow as I could, and then used shielding to try to keep the air cool.

Page 2 shows the shielding that I used to keep the engine's heat away from the induction area (plenum, MAF and airbox).

Pingu's M Roadster

I've just copied the HTML from "across the road", so the links still point there. Jobs done so far on my M roadster... -----------Winter 2010/2011----------- Inspection 2 Service - £100 ---Crankshaft Turning Tool Fuel filter replaced - £50 Vanos filter replaced - £7.50 Valve clearances...

zroadster.org

 

[Rodders67]

I treated "Cold Air Induction" and "High Flow Induction" as separate, but tried to design them so they are complimentary (one doesn't adversely affect the other).

I made the existing system as high-flow as I could, and then used shielding to try to keep the air cool.

Page 2 shows the shielding that I used to keep the engine's heat away from the induction area (plenum, MAF and airbox).

Pingu's M Roadster

I've just copied the HTML from "across the road", so the links still point there. Jobs done so far on my M roadster... -----------Winter 2010/2011----------- Inspection 2 Service - £100 ---Crankshaft Turning Tool Fuel filter replaced - £50 Vanos filter replaced - £7.50 Valve clearances...

zroadster.org

Respect… regarding your liberal use of Gold insulation and knack for data, would you anticipate insulating the OE box has merit? I plan to modify the inlet funnel to distribute incoming air over entire filter vs 1/3 in OEM configuration. #Mr.Obvious

 

[Pingu]

Respect… regarding your liberal use of Gold insulation and knack for data, would you anticipate insulating the OE box has merit? I plan to modify the inlet funnel to distribute incoming air over entire filter vs 1/3 in OEM configuration. #Mr.Obvious

You may already know that I've done that modification inside the airbox, as well as twisting the internal trumpet.

Reference the insulation "is it worth it?" -

The graphs in the first post show the results of the mod...

TestO Datalogger - what do you think?

As anyone who does performance mods should know, keeping the intake air temperature low and the exhaust gas temperature high are two of the many improvements that you can make. I've just done a mod to keep the intake temp low and TestO proves that it works!!! Intake Temp Graph before... You...

www.zroadster.org

 

[Rodders67]

I’m geeking out over data. As an equipment OEM, I have heat insulation foam for ovens. I will be wrapping the Air Box.

The note about exhaust… have you wrapped the exhaust manifold as well, maybe missed it?

i do want to see if anyone has CAI picture with bracket securing tubes/filter.

I do think the OEM airbox with trumpet mod and insulation is the best option.

 

[Pingu]

...have you wrapped the exhaust manifold as well, maybe missed it?

No. I did consider ceramic coating, or exhaust wrap, but I read that this is really a thing for race cars.
It would be a good modification on a mild steel system, but stainless steel is prone to heat cracking, and I would rather not have that problem.


More stuff to think about...
Suck and Blow seem to attract the most modifications, as they are easy for an amateur, and they are external. Squeeze and Bang are just as important, but they are much more difficult for us amateurs to improve.

The easiest way to improve Squeeze and Bang is to adjust the valve clearance correctly.
Tight valve clearances, but in tolerance = Valves opening to designed maximum lift and maximum time, but still closing properly.
Tight valve clearances, but out of tolerance = Valves may not fully close, leading to escaped gases and valve seat burning. VERY BAD.
Loose valve clearances, but in tolerance = Valves fully open 0.05mm less than design maximum, and is open for less time than design maximum.
Loose valve clearances, but out of tolerance = Valves will not open as far, or for as long as designed, but valves are guaranteed to close.

This shows the valve opening and closing times for the S50B32.

https://www..porterbility.co.uk/htdocs/Files/XLS/M_Roadster_Valve_Timing.xls

Hopefully, you can imagine the effect of the segments being a few degrees longer or shorter. I thought I had done the actual measurements of different shims, but all I have are the actual measurements of the camshafts (Exhaust = 47.19/36.25, Inlet = 47.18/36.00)

This means that the exhaust valve can open between 10.61mm and 10.66mm, and the inlet valve can open between 10.95mm and 11.00mm. The simple maths of cylinders makes you think this is only a 1% improvement, but it's more than that. You have to include the extra time the valve is open, and the corresponding increase in area under the "Bell Curve".

 

[Rodders67]

Sooooo… I have access to some very effective insulation rated for temp above 400F. It’s adhesive backed, so felt like wrapping the engine side of intake box.

 

[Pingu]

Sooooo… I have access to some very effective insulation rated for temp above 400F. It’s adhesive backed, so felt like wrapping the engine side of intake box.

That looks like excellent stuff. Have you any way to measure the effect? Ideally, you should do everywhere upstream from the inlet manifold gasket. A lot of work , but I think it would be worth it .

I'd be very happy to use that stuff. Is there a name that I could google. The stuff I have found, after a few seconds of research, looks like it would be around £300...

ADHESIVE REFLECTIVE GOLD HEAT BLANKET | Dreamscience Motorsport

ADHESIVE REFLECTIVE GOLD HEAT BLANKET | Protect components | Stop Heat Soak | Increase Overall thermal efficiency.

www.dreamscience-automotive.co.uk

or a lesser insulator...

Adhesive Gold Reflective Heat Barrier Sheet 24 x 24"

T7Design Adhesive Gold Reflective Heat Barrier Sheet Protection Against Radiant Heat

www.t7design.co.uk

 

[Rodders67]

I dug around the Amazon and found this, which is similar and more economical. Mine is from Mcmaster Carr, but I don’t know the exact number.

I will look at BOM when I go to office….

Mine is scrap from oven shielding.

thanks @Pingu for the excellent analysis of airbox dynamics and simple mods. I just had time to swing car around. Although 40F/18C The induction sounds is improved. I can tell the car breathes better as seems little more torque when on power. Above 3500 the induction is noticeable with hardtop on and windows up both on throttle and engine rev matching.

Side note, in addition to intake trumpet mod, I have removed butterfly valve on ABS throttle body as well. (It keeps the brakes active, no warning lights and doesn’t choke car).

Thanks for sharing. Worth the 30minute mods.

Amazon Link