[s-cars] Re: [Es2] MAF to intake side of turbo

[Phil Mische]

I suppose the idea is that the air mass is about the same on either side...

Let's get one thing absolutely straight: if no additional air is added to (or lost from) the system downstream, the mass of air stays exactly the same, not about the same, no matter where in the system you are.  The pressure, temperature, density, and velocity of that air may change, but it's mass will not.

The MAF will function anywhere in the intake tract.  Audi's ECU programming is based on where they chose to put the MAF; if you stick it somewhere else it will likely provide outputs which are different (for a given mass flow rate) from the original location.  Since the hot wire resistance value implies mass flow, measuring a different velocity & temperature for that same mass flow rate will likely yield a different answer for what's happening - so ya gotta change the programming.  

Is this really worth the trouble?  Makes more sense to me to get a big mamoo MAF (with less impediment to flow) and re-program with that, which has been done.  And don't I remember Trevor Frank (and perhaps others) finding that the MAF didn't have much to do with controlling anything after 1/2 throttle or so??

P


----- Original Message ----- 
From: "Kenneth Keith" <auditude at gmail.com>
To: <CaptMagu at aol.com>
Cc: <es2 at audifans.com>; <s-car-list at audifans.com>; <Elijahallen92 at aol.com>
Sent: Monday, June 06, 2005 12:30 AM
Subject: [s-cars] Re: [Es2] MAF to intake side of turbo


Hi,

Oh my gosh, I can actually comment on something and have it add something. =)

I haven't done the mod, but I have read about the cars that have had
it done.  The airflow on the pressure side of the turbo is actually
less, because it is denser than before the turbo (well, intercooler). 
I believe not ripping out the maf wire is one of the benefits of doing
it.

I suppose the idea is that the air mass is about the same on either
side, but the software can be optimized so that it remains as trouble
free as with the original location.

Elijah, I don't know if you have read through all the past S2forum
threads on it, but it's been discussed a decent amount on there. 
Basically if you can get someone like Mihnea to custom map your car,
you can move the maf there if you want.  It's sort of suggested that
you leave it before the turbo, but I do recall that the maf wire is
less likely to be sucked through than before the turbo, because say x
amount of intake air is slower but denser on that side.

http://www.s2forum.com/forum/showthread.php?t=9471&highlight=maf
http://www.s2forum.com/forum/showthread.php?t=7019&highlight=maf
http://www.s2forum.com/forum/showthread.php?t=8016&highlight=maf

Well anyway, those threads have some info.  From memory, I think it's
healthier for the wire to be on the pressure side, but things like
part throttle driveability might be adversely affected if a remap
isn't done.

It sure makes for a cleaner intake setup in some installs.

Ken

On 6/5/05, CaptMagu at aol.com <CaptMagu at aol.com> wrote:
> Elijah
> 
> I dont think this would be a good idea. There are numerous listers that have
> pulled the hot wire with MAF overflow in its current location. With the
> compression and force of the turbo, won't the air be travelling faster at this point
> in the charge air tract? Its also my understanding that the mass of the
> airflow is read because of the change of resistance in that little hot wire as air
> flows over it. If you change the temperature of that air you should be
> changing this equation a good amount.
> 
> Hap,wit dakine airflow thoughts from Evahboost, Maguire
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