Is the s14 (320is / M3 e30) AFM a restriction to the intake?

[france320isco]

Greetings from Rome.

After nine years since last time I took this matter seriously I'm back with a test.
Managed to make the engine running smoothly by fitting 0280120418 and a couple of days of tuning by real time emulation and lambda gauge, "down and out in Rome" .
Actually CARABINIERI and POLIZIA stopped me a couple of times but with no legal consequences - the fact that I don't drink, helped.

Eprom updates: AFM transfer function, injection (PT throttle hot and cold), idle (hot and cold), WOT, max load constant, min load constant, acceleration enrichments and a couple of maps with strange german names (spotted by trial and error process ).

I tuned the lambda with the stock AFM in place, but not connected. When finished, I removed it. Absolutely negligible changes in lamdba while idling, PT throttling or WOTting. The mixture was not leaned by removing AFM.

https://www.youtube.com/watch?v=iVf7BKGJFsQ

Sorry, italian only video (intended for italian e30 whatsapp group. And Italian is better than my english ).
And sorry again for the wrong shot / poor filming - when I realized it was too late. Next time I'll give Oliver Stone a call.

[Mick]

That doesn't make sense. I see lambda changes if I just change the position of my air filter relative to the radiator support.

You're probably not seeing much because the car isn't under load. Try putting an air filter on it and driving it that way. It should feel much better under your foot without the AFM, especially when you quickly step on the throttle as you won't have to wait for the plenum to generate enough vacuum to open the AFM door.

When I removed my AFM the difference was night and day. It felt like the car had been broken all along and I had just fixed it.

[france320isco]

That doesn't make sense. I see lambda changes if I just change the position of my air filter relative to the radiator support.

You're probably not seeing much because the car isn't under load. Try putting an air filter on it and driving it that way. It should feel much better under your foot without the AFM, especially when you quickly step on the throttle as you won't have to wait for the plenum to generate enough vacuum to open the AFM door.

When I removed my AFM the difference was night and day. It felt like the car had been broken all along and I had just fixed it.

Well it may not "make sense", but it's just an "engine response", I can't help with that.
The lambda may change (a little) also during re-start (the ECU enriches the mixture for a few seconds)...or for a number of EMS reasons which is indipendent from you playing with the intake.
I yes put the car under load, also in the end of the video, and then test driving.
It's true: faster pedal response, but that's the pot directly linked to your feet, doesn't mean that the car was choked, and in fact even with the AFM still in place the car really seems a cannon ball above 3500/4000rpms.
Potentiometers existed also back in the 80s, so, as an engineer, I don't know why BMW engineers would have engineered something that had to be "fixed", especially when talking of a born-F1 2000/300/500cc aspirated engine that is up to 180/190/200/250 hp. Or why they would have used a sensor restrictive (and I think it is, taken alone) without thinking a big intake plenum. Maybe they wanted an EMS with the exact (as far as possible) measure of the air flowing in.

Then: if you put a new intake duct (different lengths, volumes, eg. carbon plenums) toghether with a better ign - inj map, tuned on a braked dyno, anybody knows that you'll end up with more power both due to torque increase and torque shifting toward high rpms. Let alone head porting, cams, injectors, etc, which radically changes everything and nullify the restriction topic: it would be like talking of a bird fly during a storm.

I would just like to see myself if this cursed AFM was really a (hell of a) curse - as always described - on a stock S14 engine, that was a nonsense to me, and (for now) I find that I was right. True restrictions are head ports, valves lift, as always.

[jimmy p.]

I'm not really sure what you are trying to say, but if you are trying to say the AFM is not a performance impediment but its been proven over and over again that simply removing the AFM and changing nothing else yields more power.
The AFM opening that it makes the car breathe through is about 1.5" x 2.5" (its been a while since I looked at one) and its got a spring loaded hunk of metal in the way, but how can it not breathe better by breathing through a 4" opening?

On my street cars I run the old school chip AN and which nothing else changes except remove the AFM, put in a pipe and swap a chip.
Its like a completely different car.
I seem to remember it being dyno'd at 17 hp increase back when the first guys did it.

[france320isco]

I'm not really sure what you are trying to say, but if you are trying to say the AFM is not a performance impediment but its been proven over and over again that simply removing the AFM and changing nothing else yields more power.
The AFM opening that it makes the car breathe through is about 1.5" x 2.5" (its been a while since I looked at one) and its got a spring loaded hunk of metal in the way, but how can it not breathe better by breathing through a 4" opening?

On my street cars I run the old school chip AN and which nothing else changes except remove the AFM, put in a pipe and swap a chip.
Its like a completely different car.
I seem to remember it being dyno'd at 17 hp increase back when the first guys did it.

AFM removal needs remapping: so, from a technical point of view, you can't say if better performance is up to remap (most eprom ONLY tuners offers(ed) +10/20hp, proved) or up to the AFM removal or both.
And for those who add a bigger plenums, longer runners...say goodbye to any before-after comparison on the "restriction" topic. It's a different intake with different resonances, etc.

The engine response is absolutely faster: the reason is the pot directly connected to your feet (like I said above).
The intake plenum is the "air accumulator" (in the ETK): this name itself explain anything one needs to know, e.g. that the trumpets inside are not breathing on a 1,5"x2.5" opening and neither on a 4" one (maybe closer to the 4" ).

One final and very interesting (at least for me) test, and maybe a "counter evidence", should be to measure the difference between the pressure at the trumpets (or inside the plenum wall in front of the trumpets) and the one close to the AFM exit on the intake boot on a stock S14. I'm pretty sure that BMW engineers of the 80s didn't want an s14 engine to breathe from a 1,5"x2.5" opening

Again, after mapping an A-N with AFM in place and than removing airbox + AFM, I saw no significant change in the mixture. This means two things to me: the first is that BMW gets it right and the second - related to the first - is that AFM is not that horses plague form outer space often reported. So one has to carefully understand what he intends for "restriction".


Some A-N very old dynos.
http://www.maxbimmer.com/forums/show...6ab59e3994a&p= 70486&postcount=24
I suggest to read the whole vintage thread too.

[HANDBLT]

Engines do not 'pump air', as in, they do not create a 'suction draw' through the AFM opening. Atmospheric pressure is all the ingest pressure you have on an NA engine. What is happening with removing the AFM, is allowing the engine to have a larger volume of 'air' available, in the lower revs mostly, for the process of filling the cylinder's vacuum on the intake stroke. This is why everyone notices the HUGE increase in lower RPM drivability, when removing the AFM and going to anything else (MAP, MAF, AN....etc).

If nothing else is changed besides removing the AFM a dyno plot will show the 30%+ increase in torque below 4500 RPM and area under the curve in part throttle. This is the number one butt dyno change, along with the audible change in the sound from the airbox, which also in turn will make your senses think there is mo powah as well. Transducers in your couch while watching movies late at night with the audible bass turned down? Same effect on your brain.

Now, when you increase the volume of air anywhere in the revs, you have to adjust the volume of fuel and the delivery of spark to match the changes. When you remap a chip to match the removal of he AFM you will get more power on the top end as well. With the stock setup, from OG airbox all the way through the cats and muffler, the AFM flows just enough for the stock mapping that BMW tuned for longevity. They could have optimized more power and torque with a more aggressive mapping of the chip but they wanted stable and predictable performance all over the world and conditions.

T

[france320isco]

What is happening with removing the AFM, is allowing the engine to have a larger volume of 'air' available,

At least when designing, the volume available is the volume of the entire intake and the AFM is very small. So: if you are just removing AFM and keeping what's left in place (connecting airbox to intake boot for sure), you are not adding that much volume.
If you have a bigger airbox, runners, etc, things change obviously, even if you are just connecting a bigger tank to the same neck of a 2, 2.3, 2.5L steel bottle.

in the lower revs mostly, for the process of filling the cylinder's vacuum on the intake stroke. This is why everyone notices the HUGE increase in lower RPM drivability, when removing the AFM and going to anything else (MAP, MAF, AN....etc).

This is new to me: from what I learned there is no significant gain below 4000 rpms, but everybody knows that changing volumes/lenght of intake/exhaust ducts can shift the maximum filling up and down...so, set aside a remap that improve torque at low rpms (on engines that are known to be low on torque at low rpms) anything can happen, depends on the setup, not only AFM removal.

If nothing else is changed besides removing the AFM a dyno plot will show the 30%+ increase in torque below 4500 RPM and area under the curve in part throttle.

To increase 30% an engine torque is quite a challenge: usually you need what is needed, a lot of work (and re-work).
I'd like to see a dyno plot of such a performance on a removed-AFM+mapping-only setup (regardless if its a pot of MAF setup), trusting that it's a "only-AFM" setup. If such an increase exists, can be only due to mapping, cause my experiment (at least on a little 2.0L s14) shows what above (and it's not me): no such radical changes in mixture, which is no more air and so no need of more fuel to exploit it, after AFM removal.

When you remap a chip to match the removal of he AFM you will get more power on the top end as well.

Yes if you are a good tuner

With the stock setup, from OG airbox all the way through the cats and muffler, the AFM flows just enough for the stock mapping that BMW tuned for longevity. They could have optimized more power and torque with a more aggressive mapping of the chip but they wanted stable and predictable performance all over the world and conditions.

This makes absolutely sense and they did a hell of a job giving ~100HP/L...

Like I said: you remove AFM -> you remap. It's two works, together, that have given, measurable effects. But which one is leading?
To answer that, I didn't remove the AFM, I installed the pot and remapped. Once I got to a nice mixture reading, I removed the whole airbox + AFM. On my lambda gauge was not like removing a cork. Now: why BMW would have designed a such Hp killing airbox + AFM?
This, really, make no sense. And in fact it isn't.
Maybe they designed a conservative map, like you say, which is just as likely, for longevity.
Now I'm scared because any A-N or remap could shorten the life of my car.

[france320isco]

Done one last test on the highway yesterday, WOTting several times a pot+map+AFM (disconnected, but in place) VS WOTting a pot+map-AFM (removed airbox and the intake boot too).
The lambda reading was the same (from 1500 to 7000 rpms).

I got what I expected, but wasn't happy.

The removal of the boot produced a very uncomfortable noise from the intake from 3500 to 4500 rpms (nothing to do with the carbon airbox sound).

So, for me it stays that the A-Ns systems, or anything you what to replace the stock EMS with, may improve performances for a number of reasons but a restrictive AFM/airbox.

[HANDBLT]

Done one last test on the highway yesterday, WOTting several times a pot+map+AFM (disconnected, but in place) VS WOTting a pot+map-AFM (removed airbox and the intake boot too).
The lambda reading was the same (from 1500 to 7000 rpms).

I got what I expected, but wasn't happy.

The removal of the boot produced a very uncomfortable noise from the intake from 3500 to 4500 rpms (nothing to do with the carbon airbox sound).

So, for me it stays that the A-Ns systems, or anything you what to replace the stock EMS with, may improve performances for a number of reasons but a restrictive AFM/airbox.

Are you running in open loop or closed loop on the WBO2?

T

[france320isco]

Are you running in open loop or closed loop on the WBO2?

T

Open.

And I really wouldn't know how to close it, ever

[france320isco]

And I wish to add something just for the sake of S14 technics: after I reinstalled the stock EMS (AFM, stock map, idle/WOT switch), I re-WOTted the car and I noticed a stable lambda 14/14,6 above 4000 rpms and all the way up to the rev limiter. Againgst this stability the stock injection WOT map is shaped like a dome, max injection (3480rpms - 4480rpms) and cutting after 5000rpms following the cylinder filling which is max at 4000/4500rpms (I'm sure that one was a given).


Back to the A-N testing, I'd like to add a carbon airbox in the same setup (map+pot) and check lambda again.

So A-N dealers will be happy, they get a new market segment (experiments )

[hardtailer]

Good to read you still have the 320is and are doing these tests, Francesco!
As an engineer you will appreciate this argument:
Power required to flow Q cubic meters of air per second through the AFM equals the pressure drop across the flap inside the AFM:
P=Q(p2-p1)

The pressure delta across the flap must be equal to the force of the clock spring divided by the area of the flap as there is an equilibrium when the flap is at a constant opening, when throttle opening and vehicle speed are constant. (Disregarding 2nd order effect of oscillating of the flap due to varying vacuum per intake stroke and 2 intake strokes per each crankshaft revolution on this 4cil 4 stroke engine)

The power required to open the flap is provided by the engine and therefore is not available to drive the rear wheels.
This amount of power to open the flap will be very little (1,1 Watt at 6000rpm for the 2l s14, volumetric efficiency of 1, flap area 6x4.5 cm2 and 3N for the clock spring force. Last 3 numbers are guesstimates by me).

It is obvious that this is negligible compared to the 141kW of peak power an S14B20 generates.

So it's not getting rid of only the flap (for example by locking it in the fully open position but keeping the afm itself) when using a throttle potentiometer to measure engine load (I.e. using alpha-n) that is responsible for any power increase.

However, pressure drop across the AFM flap does mean that less air is sucked/pushed into the engine than would be the case if this pressure delta would be (almost) zero as would be the case if the flap is removed.
Let's try and calculate how much less power is generated by the engine due to this pressure loss.
Going by above calculations the pressure drop across the flap is 11Pa=0,1 mbar, so basically nothing and going by the numbers further down it means the engine can generate 0.4bhp less. Again that is not the sort of power increase people report when going aN, so it is neither the reduced air intake caused by the sprung flap that isresponsible for the power increase of getting rid of the AFM when going aN.

Comclusion
Based on the above numbers I agree that the flap/vane/barn door inside the AFM does not rob power.
BUT the cross sectional area inside of the AFM still causes a pressure drop between its intake in the airfilter housing and the rubber intake tube.*

Reducing the pressure loss in an intake upstream of the throttle butterflies will result in more air inside the combustion chamber for any given engine load and rpm which in turn can burn more fuel per combustion cycle and therefore will yield more engine power.
aN provides the possibility to do this by fitting a larger intake (ranging from the rongineer airbox to a dtm replica box on a stock engine).

Found these numbers on pistonheads from a contributor who appears to be a professional regarding engine calibration

"The typical induction system loss of most modern engines at wide open throttle, the Aston is no different, is 3.0 kPa. The relationship between a reduction of 1.0 kPa inlet manifold depression = approx. 4.0 BHP improvement.
So, when the ITG filters are fitted, like to my GT4 cars, around 0.5kPa depression / vacuum is measured in the inlet manifold, hence a power increase of 10BHP (inline with my sports air intake element of my performance kit due for release anytime soon)."

Source: https://www.pistonheads.com/gassing/topic.asp?t=978848&i=60

So I agree with you that replacing the AFM as the engine load sensor with a throttle pot ('going aN') does in and by itself not increase engine power output but it does offer the possibility to reduce pressure loss in the intake path and it is the latter that allows the engine to generate more power.

*the very very early M3s had an airbox where the size of the opening for the rubber elbow was identical to that on the AFM side. This opening was then increased. I can only guess but I presume it was done to lower pressure losses in the intake path by improving the inflow into the airbox.
Another fact is that the intake elbow has been changed at the same time in that it received more ribs/webbing on the outside to prevent it from collapsing under high load and high (engine compartment) temperatures. Collapsing shows that there is lower than ambient pressure UPSTREAM of the throttle bodies, which reduces power output. And I don't mean by the reduced cross section of the collapsed rubber intake hose, obviously).

Here is a picture of the very early airbox, easily identified by the tube that connects the crank case vent on the cilinder head cover directly to the airbox instead of down to the air/oil separator.
I have such an airbox as a spare part that's how I know although the picture doesn't show it.

[HANDBLT]

Open.

And I really wouldn't know how to close it, ever

So have you logged RPM/RPM_SEC to see if there is a torque increase for a given throttle opening/RPM? Log a part throttle pull at various steady state throttle before and after removing the AFM and see if there is an area under the curve increase in torque. If you have the stock EMS in the car with the O2 sensor hooked up it is compensating up to +/- 10% so you wouldn't see an O2 change, just a pulse width change in increased fuel needed.

T

[france320isco]

So have you logged RPM/RPM_SEC to see if there is a torque increase for a given throttle opening/RPM? Log a part throttle pull at various steady state throttle before and after removing the AFM and see if there is an area under the curve increase in torque. If you have the stock EMS in the car with the O2 sensor hooked up it is compensating up to +/- 10% so you wouldn't see an O2 change, just a pulse width change in increased fuel needed.

T

I don't know what RPM/RPM_SEC is: I used tuner pro SW, ostrich emulator and an old german DAMOS file for mapping while looking (by eyes) at the lambda response via WBO2 sensor and gauge. I only install the 0280120418 where the stock ignition switch is.
To see if there were errors in the gauge readings I double check with my mechanic's lambda equipment before the tests.
I didn't install an EMS with lambda feedback to compensate for injection and keeping lambda stable, it's the stock ECU (never compensate for unmetered air flowing in . An intake leak, even tiny, is sufficient to see it).
But I don't quite get your message.

Mapped the engine by looking at lambda response to get it to work with pot and AFM in place, but disconnected (as in the video), then removed the whole airbox and AFM to check for any lambda changes. Couldn't spot any.

[france320isco]

Hi Hardtailer,

The fact that I'm an engineer doesn't imply that I can explain everything nor absolutely that I'm always right. I don't know engine electronics, especially modern ones.
Not knowing what happens in the intake path of my engine while moving it, let the engine tell me.
The principle beyond so big intake plenums is, among others, to increase static pressure, recoup pressure losses, to make the engine breathe right.
It's the Occam razor.
Why would BMW get the intake path wrong?