Blow through AFM *now with dyno sheets, 14.4kb users beware*

[Malcolm]

this article refers to the vane type AFM as measuring air volume:

http://www.autoshop101.com/forms/h34.pdf

[fivebob]

this article refers to the vane type AFM as measuring air volume:

http://www.autoshop101.com/forms/h34.pdf

Still can't see how it can measure volume only and be unaffected by mass, the damping chamber might make a slight compensation for pressure, but that's only temporary, you still have to overcome spring pressure, and that requires mass. A Karman vortex based sensor might be able to be volumetric only, as would something with some sort of pressure compensation chamber.

But it still gets back to the point that it works, so by that very fact it must measure mass.

*edit maybe they don't take into account that it would be used in other than a open to atmosphere application, suppose you could then claim it measure volume, when in fact it's measuring mass.

[sergei]

AFM is designed to work under atmospheric pressure, if you use it in pressurized application, it would result in incorrect output due to bernoulli equation...

[fivebob]

AFM is designed to work under atmospheric pressure, if you use it in pressurized application, it would result in incorrect output due to bernoulli equation...

So explain why it works when used in a pressure situation

The proof is there, so it must work somehow. Don't think Bernoulli has much to do with it.

[sergei]

It works becuase (atleast in my theory), AFM does not actually play biggest role in ECU calculation, it is the combination of things in play here (TPS + WTS + Air temperature sensors, RPM), again in my theory ECU will output similar (read: not far different) results, say 75% throttle @ 4500rpm with 35% AFM opening vs same throttle/rpm but 10% AFM opening...
From experiment of my own, with AFM not connected to air intake (on my 20V without plenium), I could make it idle by pushing the flap open with finger and the range was relatively big before it would either stall because too lean or stall because too rich. Also I had APEXI SAFC, and it wouldn't make much diffrenece, especially on higher RPMs. One day I had wire brocken on my WTS (due to meremere), on cold it would not idle, so I thought what if I would compensate with SAFC to temporary fix the idle on cold, I had to enrich by 35%!!! to make it idle (considering 20v AFM will max out ~60% of SAFC input)...

[Bazda]

do you know what, who cares about all this mumbo jumbo,
the guy just wants to know if you can run it blow through and nearly all the 4agte setups that have afm and a standard ecu are done like this.
I originally got this idea from NITE PARTS my old man asked around if this was ok (ralliart, lynn rodgers, edgell racing etc) and they said its fine on the 4agze afm, also Quest 4 had done a few and said blow through was the way to go also.

[slighty_sykotic]

Thanks bazda.

And to the rest of you, i accutly belive that sergei may be onto something. I think that maybe its a mix of the others theorys.

Fivebob, you may be right, the denser air causes the flap to open more, but like all fours said:

I wonder if the denser air does cause more deflection for a given volume, but not to the same ratio as the increase in pressure, so air at 2bar abs. might increase deflection 50% more than air at 1bar abs. for instance.

Maybe its not a full 1:1 ratio, like 2 bar isnt going to be twice 1 bar, but because of the fact that it doesnt matter as much as we might think it does (like sergei said) it doesnt have enough of an effect in the real world. Remembering mixtures are normally abit rich from factory anyway (bit of lee way).

Whatever the reason, thanks for the info. Be interesting if anyone can find out for sure, but im convinced enough to run it like that. (and if you have any a/f ratio plots on teh dyno do ya want to chuck them up bazda?), if not, I will get some on my car once it's done to keep people happy

--Sykotic

[Bazda]

they never got recorded down on paper.

But on 12psi it was 12.5:1 maybe even nearly 13.0:1 without the extra injector.

With the injector i ran it at 10.8:1 thats where it seemed to go at its best. We tried making it leaner for more power but that didnt quite seem to work.

[vvega]

just to be the devils advocate
a afm based system is still a analog setup

that means that the heart of the system is the afm not the ecu
the ecu mearly interprits the signal makes the waveforms and adds corections

as for what they can tell with this setup
on my st165 it has a turbo light
no matter the condition the turbo light comes on right at the transistion from vacum to pressure
it has no pressure sensor in the intake

so in realitly its all measured at the afm...........
this also means it must measure mass

oh and sergie just for intrest
at full throttle they go into a closed map mode
what it mans is that at 3/4 to full throttle it disregardes the afm and rums of the tps and revs and temp corrections
thats why you didnt get any differance

they are a very basic ecu
the gen3 is the first proper non analog setup with a 3d map
it woudl also seam apprent that the rev 2 gen2 ecu was the test bench for this

this is just from my findings
ive dune a lot of resurch on this tring to get rid of the fuel cut on the 165
(hence the playing with injector sizings)

i hope that helps your disscussion

personally im desided
but it woudl be good to see some other ideas

v

[slighty_sykotic]

As I said I would, I put it on a dyno to check the A/F ratios.

I will post the graph tonight as soon as I can get to a scanner to scan them in, but the ratios are really good on 12.4 psi of boost.

So blow through works, no matter HOW it works, it does.

--Sykotic

[drftnmaz]

seen this done on mates cars. and gone for a drive with no bonnet and watch the platic cover buldging under boost and evently it flew clean off. found it down the road and glue it back on and put it back to how it was ment to be.

[Adydas]

Very intresting comments there drtfnmaz

[evil_si]

i have set up afm gtz's both ways, and didnt have more or less effect either way,

blow thru was easier because of the piping setup
suck thru can be a pain to setup, especially with my manifolds as i tend to face the inlet to the drivers side.

if you blow thru id suggest drilling a small hole in the black afm cover, some of them tend to pop off as drftnmaz described. they arnt completly sealed between the guts of it and the intake tube, so boost pressure gets in there
check your a/f at the boost you run to make sure its safe.
injector controllers are cheap, and generally the easiest way to increase fuel under boost.

[slighty_sykotic]

*mods, these pics are 70ish kb...they are not huge... plus I have a warning on the title, so don't remove them without a good reason please*


The proof

Only revved to 6grand cause of newish engine, and with my rangi intercooler (lol, its like 20cm by 10cm....), rangi piping, and just generally abit rough around the edges, im very impressed, and surprised that the power is still heading for the sky at 6 grand.

Go to shitty old td04 and backyard mechs

--Sykotic

[Bazda]

whats this 153hp................

[slighty_sykotic]

O yeah, and thats on 12.4 psi of boost (stable the whole way to 6 grand)

--Sykotic

[slighty_sykotic]

whats this 153hp................

???

I dunno how accurate that is, I don't mind, wasnt doing it for that, was doing it for a/f.

Its a hub dyno if it matters (was told that they read lower?)

--Sykotic

[Dell'Orto]

Nup, hub dynos will read higher than rolling road.
113kw isnt bad for, what you've described, a pretty average setup, untuned. Decent cooling and a tune and another couple of psi will have it rocking

[slighty_sykotic]

Yeah, we started to do a run on 14.5 psi, and the graph scared me, it was pulling 150hp at around 4500, but it was backed off then cause the mixtured leaned out.

*shrugs*, it feels fast as $&#$%, the torque figure isnt bad is it?

--Sykotic

[Caveman]

td04 13g? in other words gsr turbo?