AFM before or after TURBO which is the proper place and why
 

is there a reason behind having to mount the afm before the turbo?
i assumed that all the AFM does is measure the air entering the engine.
As long as its mounted flat due to the flap inside opening sideways (like a door).
Before, or after the turbo.. i assumed it would measure the same exact amount of air at either place.
For me, it just seemed more of handy place to put it Right in front of the throttle body, so i'd be able to mount the piping easier.
also, if any piping would just so happen to pop up, it wouldnt affect the drivability since it happens BEFORE the afm, not after the afm.

is there any legit reason to mount the AFM before the turbo?

Not really sure why people keep it there. I have heard of people in Japan mounting it into the intercooler system, not sure how exactly, or if any different tuning is required for that, but it would seem like a good idea because then you can just put a filter on the turbo and call it a day..

The AFM should be mounted before the turbo for a more accurate air flow reading.

The reason for this is because when the turbo needs to compress air it needs to consume air and this is what the AFM will measure, how much air the turbo is compressing.

If you put the AFM after the turbo the air is MUCH denser since its more compressed and the AFM is not calibrated for this dense air nor can it comprimise for pressure. You will be running leaner if you put it after the turbo than if you put it before the turbo.

If you have means of tuning the fuel than I wouldn't worry to much about this but if not, keep it before the turbo.

well i have a Neo AFC that i was planning on using it since i have a pair of 680s on the secondaries anyways.
the only other reason i wouldnt put it before the turbo would be because of the fact that it would run momentarily lean when ever the bov would go off.

IF the BOV opens arn't you releasing the throttle anyways? So going lean would be alright while releasing the throttle....?

I don't know much about turbos systems so I ask more questions than giving answers.

The AFM can be mounted either way. There is a temperature sensor in the AFM which in theory could be effected by higher intake temps after the turbo but I don't think I've ever heard of someone having issues because of it. It would never be my first choice for mounting (I doubt it's designed to handle that much pressure) but has been done a lot in the past. Very common before standalone systems were cheap.

There is some good evidence that moving the AFM closer to the engine results in better throttle response.

blow-through setups are common on other cars, but mostly ones with a hotwire or Karman vortex type AFM

so then, to make it a short answer..?
its okay, eitherway.
its purely preference?
i'll be sure to let you guys know if i notice anything fishy from the way this is set up.
thanks for the help guys.

I wouldn't say it's "purely preference." Nobody who responds to your thread has actually done it, so we are speculating about any issues you may encounter. But be advised that the 87-88 AFM is a lot more sensitive to the way it is positioned than the s5 AFM. so you are being a bit of a pioneer here.

personally, I'm not sure what you hope to benefit from this.

For best results, mount the AFM in the trash can and use a speed-density standalone EMS. The outdated 1980's method of mounting the AFM after the turbo and adding a separate fuel controller, ignition controller, and boost controller, will also work, but it is not very efficient in performance or economic terms.

No, this was done a long time ago before the standalone EMS was readily available. You are just not familiar with the process because it has been long outdated, just like you are probably not familiar with leaf springs and bias-ply tires, lol.

I've been there and done that on a turbo-NA setup before. No issues. Again, not my preference but it was the only choice in that case...

Not to thread jack but how critical is it that the AFM be mounted horizontally (either right-side-up or up-side-down)?

Is the S5 AFM a direct swap or would you need to splice some wires to make it work?

86-88 AFMs should be mounted as level as possible either upright or upside down.

you need to splice wires to get the s5 afm to fit an s4, there is a really simple diagram around somewhere if you interested in this i'll help you look for it (i'm bored). The s4 afm need to be mounted so that the flap door swings like a house door, if you mount it sideways then gravity will affect the door and throw off readings

No, this was done a long time ago before the standalone EMS was readily available. You are just not familiar with the process because it has been long outdated, just like you are probably not familiar with leaf springs and bias-ply tires, lol.[/QUOTE]

Wow you're old. Thats like the flintstones era.