RKA

Here are a few of the pics...(more in the link below)
<img src="http://home.pacbell.net/tmblue/pana0152.jpg">
<img src="http://home.pacbell.net/tmblue/pana0154.jpg">
<img src="http://home.pacbell.net/tmblue/pana0155.jpg">

That plastic doo-hickey that's sticking down into the center of the tube is part of the factory MAF...and you're saying that whatever you would machine, that piece would still remain plastic, as would anything near the MAF element itself?<ul><li><a href="https://forums.audiworld.com/s4/msgs/791759.phtml">https://forums.audiworld.com/s4/msgs/791759.phtml</a</li></ul>

ModifiedA4

he gets rid of the plastic air guide.

VAP

And I'm not totally convinced that the sensor assembly in the Hitachi unit couldn't be swapped into a 471A MAF housing with a little machine work. But I'm presuming much and getting ahead of myself.

I can't know if the Bosch harness assembly can be re-wired to accept the Hitachi sensors pin-outs. If it could I think the Hitachi would likely perform better/longer. How's the track record/failure rate on the Hitachi vs Bosch in the S4? If significantly better I think "adapting" likely the easiest, most efficient path to pursue. Get a Hitachi unit working on a Bosch equipped car. Once accomplished successfully then look for a better, larger or more free-flowing and efficient housing.

Has anyone accomplished a Hitachi-to-Bosch conversion? Has anyone tried or even experimented with the possibility? Ideally it would only be a pin/lead swap in the harness plug at most. Once an alternate sensor assembly is found that works well, gives acceptable service life it's an easy process to fit it in a better-flowing housing. And some, if not many, I'm sure would likely "settle" for just a MAF that works, flows similarly and to hell with additional flowor performance.

VAP

And if thats the case I don't use one in any of my Stage 3 conversions. I opt instead to use velocity stack inlets which aren't restrictive like debris screens and laminar diffusers and actually increase volume, velocity while imparting a smoothing affect on the induction air to allow the sensor to sample a smoother, less turbulent sampling of air. It also has a tremendous reducing affect on boundary layer disturbances which are both created and aggrivated by the laminar diffuser.

ModifiedA4

audi engineers wanted the MAF to work. pretty interesting.

RKA

people have talked about it, but AFAIK, they are not interchangable. I think there is programming in the ECU specific to the MAF itself, but I can't give specifics. Anyway, the Hitachi MAF is likely what I have...2001 and newer S4's have it, and the Bosch elements were used in the 2000's I believe (may early 2001's as well).

As far as a significant difference in service life...I believe both will fail at 20-40K, but nobody has compiled detailed failure rates. Both are too prone to failure.

VAP

finding an alternative may prove incredibly difficult. Sourcing an alternate 5 pin sensor assembly with similar voltage outputs for a turbo application lessens the possibility exponentially.

Do you have a Bentley for your model? Can you get me the pin-out description of what each wire goes to or what component its designed to control?

We may be doing an exercise in futility but long as we've gotten this far let's carry it out til we have some conclusion.

RKA

not sure if Bentley every released an updated version that covers 2001-2002 S4's (I believe they did for the 2001 A4's).

xr4tic

For the A4's, I know what the stock transfer curve is, and what the 3" housing curve is, so theoretically, you could use a Ford MAF along with a PSC1-003 with no problems. I say theoretically because I haven't tried it with a stock ECU....yet

RKA

nevertheless.