Relocating AFM inline (after turbo + intercooler)

[Fodder]

I've been pondering ways of improving my engine bay (and there are a lot of them), and I recently saw a thread on ozcelica where someone has moved their air flow meter to just before the throttle body, after their turbo and intercooler. Sounds like it's been running fine so far, but it's only been a few days - just wondered if anyone else had any experience with toyota AFMs in this sort of position.

I've seen it done a lot on dirty nissans with no reported dramas, though to be honest I don't even know what sort of meters the nissans use - whether they're a flap system like mine, or a hot wire setup.

Anyone able to weigh in with thoughts or (even better) experiences?

[Harreh]

From my understanding it's going to end badly, very badly if my knowledge is correct of course.

AFM's cannot measure the density or the speed of air, simply the volume of flow. Moving it post turbo will cause it to measure the flow of the air after it's been compressed and not the volume of the air since the AFM cannot determine if the air is compressed or not it will most likely run lean, pre turbo it measures the flow of uncompressed air.

I could be completely wrong through

[MWP]

Dont try it... itll be a world of pain for the reasons Harreh mentioned.

[jonathan yee]

interesting, i have a pic in my hyperrev mag and there's one of such a thing done with an mr2 gen2 3sgte.

how does the flow change pre/post turbo? for it to run lean your saying there is less flow post turbo?

[Harreh]

The flow will likely be more of less the same, or within an immeasurable difference but the point is that the air will be compressed.

It measures flow, not density or pressure.

[Fodder]

Makes sense that there would be lower air speed but higher air density after the turbo, guess I'll keep an eye on this other guy's thread for a while - would be interesting to see what his air fuel ratio is like.

[jonathan yee]

yes which to me says it will work, as the flow isn't changing and it's fuelling according to said flow. it doesn't matter if it's compressed or not, as that's not what it needs to measure?

[boxh34d]

yes which to me says it will work, as the flow isn't changing and it's fuelling according to said flow. it doesn't matter if it's compressed or not, as that's not what it needs to measure?

By my way of thinking, an AFM is not really measuring flow per say, it is measuring velocity and calculating flow much like an oriface plate does. If the air is compressed (post turbo) the engine will be flowing the same volume of air, but it will actually have a lower velocity than if it were uncompressed (pre turbo).
I would see this ending badly, but am curious to see the results of the other celica, and whether the fuel mixtures have leaned out or not - proving or disproving my theory.

[Valkyrie]

As you have said, the Nissan guys often do it. I've seen this on Sr20s, RB25s and RB20s. All that use this setup swear by it. Having said that, all have some form of tuneable management. The Nissan ones are hot wire or whatever it is called. How it would work with the Toyota AFM who knows. There needs to be a first

[andrew_mx83]

yep all the vl boys love it for the dosing.... as above i think they are all hotwire tho.

i dont see it working so well with a flap type meter, wont it just blow the flap wide open as soon as it comes on boost? there isnt a lot of spring pressure in those things (altho you can change it for some ghetto tuning)

[mullett]

I think that the hotwire meters are much more forgiving to higher pressures. I also think that if you're going to do it, why not just buy a proper computer and ditch the thing?

-RM

[Fodder]

The same reason most people try to do things on the cheap, funds Already gone overbudget for the moment due to an offer that came up I couldn't refuse, but if I could tidy up my engine bay a bit for effectively no cash it would've given me something to tinker with while I get back to where I'd like to be money-wise!

ECU is definitely on the list, but behind a few other things so probably a few years away.

[thechuckster]

fwiw: an MS1 ecu running MS Extra Hi-Res code would be sufficient for a 3SGTE donk - would let you eliminate the AFM and only require fitting an air temp somewhere (plenum preferably). And cost would be minimal except for any dyno time.

Also, the 3SGTE AFM is a strange thing - the track the AFM arm slides over isn't a simple logarithmic resistance change. It rises up then drops down several times (mapping AFM arm movement against resistance shows a kind of saw-tooth pattern). It does suggest that the ECU uses it for rate of change as well as bulk airflow. Given that the ACU would have to cope with occasional data loss from the AFM, it wouldn't rely on (also a guess) counting the number of saw-tooth transitions to work out the overall position of the AFM arm. I suspect that it would require the inlet side of the AFM to have no restriction between itself and the atmo.

Might be easier to tidy the engine bay by removing the battery to the boot allowing you to reposition the airbox and AFM (in preparation for the eventual deletion of the AFM).

[Fodder]

Battery is already out of the way, under the passenger seat. The main benefit for me moving the AFM closer to the engine would be freeing up my choice of intake path between the filter and turbo without having to extend my AFM wiring, but that may be the path I go down.

Edit for dodgy pic of dodgy bay with what I was thinking, but if it ain't gonna work it ain't gonna work

[thechuckster]

there's only 5 wires going to that particular AFM, none are shielded so would be an easy job to extend it.