pilchardthecat's MAF screen mod

"M" Specific discussion
User avatar
exdos
Senior Member
Senior Member
Posts: 2788
Joined: Wed Feb 22, 2012 12:58 am

Re: pilchardthecat's MAF screen mod

Post by exdos » Sun Jun 02, 2013 10:56 am

daz05 wrote: More noise must mean less pressure?
Many engines and intake systems rely upon "resonant effects" for optimal performance and high volumetric efficiencies. As I understand, all of BMW's ///M cars with the S54 engine incorporate such resonant effects, particularly with the runner lengths inside the plenum, immediately in front of the throttle bodies.

There appears to be a strange phenomenon specific to the Z4M, related to the recorded powerband, which shows a drop in power at around 7200rpm followed by a rebound around 7600rpm, as shown in a typical dyno plot, as below. This doesn't seem to occur in the E46 M3, and so I wonder whether this phenomenon is caused by resonant effects which are related to the Z4M's unique air intake system upstream of the plenum? Since pilchardthecat's CF air-filter box mod will have different resonant characteristics to OEM, it would be interesting to know, what changes to performance, if any, this mod has?

From datalogging in "real world" driving conditions, this drop in power at around 7200rpm is clearly shown by a reduction in air-flow rate through the MAF coupled with a slight deceleration of engine rpm, followed by a surge in airflow and an increase in engine rpm acceleration, as if the engine has taken a sudden gulp in air for a "second wind".

Image

pilchardthecat
Member
Member
Posts: 583
Joined: Wed Jun 02, 2010 11:28 pm

Re: pilchardthecat's MAF screen mod

Post by pilchardthecat » Sun Jun 02, 2013 3:21 pm

Changing the material wont have any effect on the resonant effects you are talking about, as long as the replacement material has the same rigidity - the phenomenon you are referring to are caused by pressure waves bouncing around inside the system - when these waves are in phase with the opening/closing of the valves, there is a beneficial effect. The same is true on the exhaust side, hence the position of bends etc in manifolds
As long as the dimensions and the rigidity of the materials are unchanged, nothing should change in the shape and size of the internal pressure waves.
Of course the downside of using this approach in the design, is that for any given dimensions, certain parts of the rev range will be in the opposing phase, and there will be a negative effect. This is probably the cause of the flat spot you are talking about :-)
On the intake side there will probably only be significant wave characteristics inside the plenum, and possibly between the plenum bend and the maf screen. I doubt that anything as far from the valves as the airbox itself will have much of an impact
Z4M Roadster.

User avatar
exdos
Senior Member
Senior Member
Posts: 2788
Joined: Wed Feb 22, 2012 12:58 am

Re: pilchardthecat's MAF screen mod

Post by exdos » Mon Jun 03, 2013 9:20 am

pilchardthecat wrote:Changing the material wont have any effect on the resonant effects you are talking about, as long as the replacement material has the same rigidity - the phenomenon you are referring to are caused by pressure waves bouncing around inside the system - when these waves are in phase with the opening/closing of the valves, there is a beneficial effect. The same is true on the exhaust side, hence the position of bends etc in manifolds
As long as the dimensions and the rigidity of the materials are unchanged, nothing should change in the shape and size of the internal pressure waves.
Of course the downside of using this approach in the design, is that for any given dimensions, certain parts of the rev range will be in the opposing phase, and there will be a negative effect. This is probably the cause of the flat spot you are talking about :-)
My point is: the E46 M3 and the Z4M both share the same engine and plenum, where the resonant effects you've described are beneficial to cylinder filling in both platforms, but there is a loss in performance in the Z4M at around 7200 rpm which doesn't occur in the E46 M3. So what's different in the Z4M which is causing this to happen? Is it intake/exhaust/ECU differences?
pilchardthecat wrote:On the intake side there will probably only be significant wave characteristics inside the plenum, and possibly between the plenum bend and the maf screen. I doubt that anything as far from the valves as the airbox itself will have much of an impact
If, as you say, your CF airbox lid mod has changed/increased the induction sound, then surely the resonance of the entire air intake has changed? Surely the sound characteristics of the intake as a whole, from inlet to throttle plate, is because it acts like one large sound chamber? Whether or not the difference has any impact on performance neither of us knows.

pilchardthecat
Member
Member
Posts: 583
Joined: Wed Jun 02, 2010 11:28 pm

Re: pilchardthecat's MAF screen mod

Post by pilchardthecat » Mon Jun 03, 2013 9:57 am

Resonance and sound are not the same thing - resonance is specifically the relationship between the frequency of pressure waves and the dimensions of the space they occupy. Neither of these things have changed.

Sound is more general, and is effected by timbre, amplitude, reverberation, etc. You can change the external sound without having any effect on internal resonance
Z4M Roadster.

User avatar
exdos
Senior Member
Senior Member
Posts: 2788
Joined: Wed Feb 22, 2012 12:58 am

Re: pilchardthecat's MAF screen mod

Post by exdos » Mon Jun 03, 2013 10:23 am

pilchardthecat wrote:Resonance and sound are not the same thing - resonance is specifically the relationship between the frequency of pressure waves and the dimensions of the space they occupy. Neither of these things have changed.
Sound is more general, and is effected by timbre, amplitude, reverberation, etc. You can change the external sound without having any effect on internal resonance
Does CF have the same resonant characteristics as the OEM ABS plastic air-filter box?

User avatar
BMWZ4MC
Lifer
Lifer
Posts: 5890
Joined: Sun Sep 13, 2009 4:24 pm
Location: Back in the sunshine

Re: pilchardthecat's MAF screen mod

Post by BMWZ4MC » Mon Jun 03, 2013 10:33 am

pilchardthecat wrote:...As long as the dimensions and the rigidity of the materials are unchanged, nothing should change in the shape and size of the internal pressure waves...
I would think that you've changed the rigidity of the air box significantly with this mod. More than that, what once was an airbox with walls of equal reflectivity to pressure waves (at least with respect to material properties although not in shape), is now a hybrid which will deform and reflect differently in the carbon fibre sections from elsewhere. I suppose it is conceivable that the filter will serve to "damp" the of effects of the carbon fibre section since you've only altered the airbox before the filter. It's interesting to speculate on the effects of your mod, but I'd love to hear it in person and see data logged before and after your modification :thumbsup:
Image
Z4MC - heavily fettled for track use, now in Sydney; Modified RS4 Avant - back in Blighty;
Westfield SEiW track car currently in hibernation; S2000 GT - sold

pilchardthecat
Member
Member
Posts: 583
Joined: Wed Jun 02, 2010 11:28 pm

Re: pilchardthecat's MAF screen mod

Post by pilchardthecat » Mon Jun 03, 2013 11:22 am

Gutting the bends from the exhaust back boxes will have a much bigger impact, as this is changing the internal dimensions significantly. I doubt there is much difference in reflective/rigidity characteristics on pressure waves between plastic and CF. And of course the pipe between the plenum and the airbox/maf is rubber, and will deform, as well as changing is deformation properties with age, temperature, etc
Z4M Roadster.

User avatar
exdos
Senior Member
Senior Member
Posts: 2788
Joined: Wed Feb 22, 2012 12:58 am

Re: pilchardthecat's MAF screen mod

Post by exdos » Mon Jun 03, 2013 12:14 pm

pilchardthecat wrote:Gutting the bends from the exhaust back boxes will have a much bigger impact, as this is changing the internal dimensions significantly. I doubt there is much difference in reflective/rigidity characteristics on pressure waves between plastic and CF. And of course the pipe between the plenum and the airbox/maf is rubber, and will deform, as well as changing is deformation properties with age, temperature, etc
I know that reducing the exhaust length and making it more free-flowing by gutting the silencers does have a measurable and significant impact on performance, but it hasn't changed the fact that there is still a dip in performance at 7200rpm with a rebound at 7600rpm. Therefore, I'm simply attempting to explore the possible reasons why the Z4M has a different torque/power curve to the E46 M3, with the same engine/plenum, and if modifying the exhaust doesn't give the answer, then it seems logical to me that the answer must lie in either the ECU mapping or the air-intake upstream of the plenum.

From reading postings of other Z4M owners elsewhere, this dip in power is still a feature after having various remaps by different tuning companies. Likewise, I've not seen the dip in performance in dynoplots of supercharged Z4Ms, which eliminates the OEM air-intake system and mapping. So, it seems logical to me that the Z4M's OEM air-intake, which is significantly different to that of the E46 M3 looks like the most likely cause. I still observe this dip in power with my own air-intake mods (which are all different to yours) so I'm wondering if your CF mod might shed some light on this?

pilchardthecat
Member
Member
Posts: 583
Joined: Wed Jun 02, 2010 11:28 pm

Re: pilchardthecat's MAF screen mod

Post by pilchardthecat » Mon Jun 03, 2013 1:45 pm

I am much more interested in what happens when you improve the maf screen (no maf on supercharged cars either....) this really is a huge restriction. The top end "dip" you refer to is noticeable when driving the car, but since i changed the screen it feels much more free revving at the very top.

I would be very very surprised if the CF makes any difference at all other than to the external noise.

Very much looking forward to your datalogging.
Z4M Roadster.

AlienZed
Senior Member
Senior Member
Posts: 1273
Joined: Tue Oct 25, 2011 4:39 pm
Location: Tameside,Cheshire

Re: pilchardthecat's MAF screen mod

Post by AlienZed » Mon Jun 03, 2013 2:42 pm

Honeycomb just ordered.I'll have to be patient now for a couple of weeks .
Many thanks guys
Moz

Sent from my GT-I9300 using Tapatalk 2

User avatar
exdos
Senior Member
Senior Member
Posts: 2788
Joined: Wed Feb 22, 2012 12:58 am

Re: pilchardthecat's MAF screen mod

Post by exdos » Mon Jun 03, 2013 2:44 pm

If the dip in power is caused by a restriction in the air-intake I'm presently puzzled to know why this is then followed by a rebound at 7600rpm? The rebound is confirmed by the datlog of airflow through the MAF. After all my modding, in 3rd gear I now see a maximum airflow of over 34lbs/min in comparison to 31.2lbs/min when my car was OEM.

Anyway, I've just bought some honeycomb mesh off ebay for £2.65 and I've also ordered some of that 4.1 honeycomb from saxonpc at 22.53USD (£14.77) so I'll make a couple of MAF screens and I'll datalog them both. :thumbsup:

pilchardthecat
Member
Member
Posts: 583
Joined: Wed Jun 02, 2010 11:28 pm

Re: pilchardthecat's MAF screen mod

Post by pilchardthecat » Mon Jun 03, 2013 3:13 pm

The rebound could be due to resonance being in-phase. Are the plenums significantly different between the e46 M3 and the Z?
Z4M Roadster.

mmm-five
Lifer
Lifer
Posts: 11876
Joined: Sun Nov 30, 2008 1:03 pm
Location: South Liverpool
Contact:

Re: pilchardthecat's MAF screen mod

Post by mmm-five » Mon Jun 03, 2013 3:28 pm

So, we need someone to create a full CF airbox, with a top-switchable Eureka mod (which is what I'm planning to do with it), and a honeycomb MAF screen!

BTW, my data logging of the 'before' failed due to the app crashing on the iphone when I tried to save the log in DashCommand. No trace of the 4 hours of logging I'd just done, but the good news is it looks like I'd used the wrong setting anyway and it would only have recorded my speed & fuel consumption.

Will try to capture at least an hour's worth of 'before' figures on the way home this/next Thursday and on Monday, to compare with similar runs over the next 2 weeks.
Trigger’s Z4MC
Some bits now over 163,000 miles, some less than 1,000 miles.
Individual Ruby Black, Individual extended champagne leather, plus many options

Image

User avatar
exdos
Senior Member
Senior Member
Posts: 2788
Joined: Wed Feb 22, 2012 12:58 am

Re: pilchardthecat's MAF screen mod

Post by exdos » Mon Jun 03, 2013 3:31 pm

pilchardthecat wrote:The rebound could be due to resonance being in-phase. Are the plenums significantly different between the e46 M3 and the Z?
No difference at all. Part number: 11 61 7 835 819 shows same for Z3M, E46 M3 and Z4M. That's why I'm wondering if the resonance of the air-intakes (pre-plenum) make a difference, because there's a very significant difference between all the three variants using the same plenum. The Z3M is restricted to max revs of 7600rpm, so any drop off above 7200rpm doesn't have any rebound, so no comparison possible here.

pilchardthecat
Member
Member
Posts: 583
Joined: Wed Jun 02, 2010 11:28 pm

Re: pilchardthecat's MAF screen mod

Post by pilchardthecat » Mon Jun 03, 2013 3:49 pm

Anything the wrong side of the MAF screen is going to have a tiny impact on resonance - there's just too much between there and the valves.

However if there were packaging issues with bonnet space, it could be the length of the pipe between the plenum and the first bend, or the first bend and the MAF screen (are these different?). If you really wanted to test this, you could fabricate a short section (say 2 inches) of the oval pipe that connects the intake to the plenum, and make it a bit longer. This would change the internal dimensions and alter the alignment of any pressure waves with the valve timings (although if the wavelength was exactly the same as your extension length it wouldnt do anything, so probably best to try a one-inch long section too)
Z4M Roadster.

Post Reply