MAF on pressure side?

[Henka]

Hey.. Can I move the MAF to the pressure side just like that? I mean - there is no difference in what it's meassuring if it's on the pressure side or atmospheric side. Or?

[Greg_S]

have a word with Tom on this one

[SteveH]

Mark H has this setup too. He may be able to give you some info...

[91_S2]

You can put the MAF between the IC and the plenum. The advantage is measuring mass flow close to where it goes into the cylinders.

As I understand it, the MAP and the MAF measurements are compared. If flow is unusually high for a measured pressure, the Motronics diagnoses an air leak in the system and cuts fuel. Mihnea can correct me if I am wrong.

Obviously, this system can only detect leaks that occur BETWEEN the MAF and the MAP. So what happens e.g. when you put the MAF between the IC outlet and the Intake?

Imagine you have an air leak between the turbo and the MAF. The MAF and MAP won't detect the leak. Flow is low, pressure is low. Motronics will try to raise boost. The turbo spins up but still there is low pressure, low flow.

The WG won't crack open because it isn't getting high boost. The WGFV won't relieve pressure because Motronics doesn't see high pressure. Turbo spins more. Sounds like an unstable feedback loop to me.

Do the designers have another system that e.g. compares TPS with pressure to prevent this from happening?

[audiman]

Not worth doing unless you HAVE to IMHO. It could cause problems as above. Also the ECU needs to be remapped to compensate for changes. BTDT, my car drove very badly on part throttle until mapped by the Motronic God

[Mark Halligan]

Not worth doing unless you HAVE to IMHO. It could cause problems as above. Also the ECU needs to be remapped to compensate for changes. BTDT, my car drove very badly on part throttle until mapped by the Motronic God

Well just to throw a curve into the discussion, I have recently just moved mine to the pressure side and have noticed no problems at any throttle setting, in fact the motor runs better than ever before .
Although I should point out that the car is not my daily drive anymore and I have only done ~ 1K miles with it like this so far, so my comments above may not be definitive.

I did the mod for space considerations as it has tidied things up a lot in my ever changing engine bay.

But Rich has a good point about the turbo over spinning if there is a leak between it and the MAF, only way I can think of getting around this is some sort of turbo tachometer......if such a thing is available??

Mark.

[91_S2]

Also the ECU needs to be remapped to compensate for changes. BTDT, my car drove very badly on part throttle until mapped by the Motronic God

Tom,

R U sure it was the changed MAF position that was the sole cause of the probs? I have heard anecdotes that Mark's experience seems to confirm.

Rich

[Henka]

Well I posted this question at a Swedish forum and the answers point to the same thing - it can be moved and it won't need a remap.

This whole boost leak thing got me scared though. Beeing able to put a airfilter directly in the turbo is mighty tempting too. Would definently work better...and look better.

[91_S2]

Frankly I don't know if Tom's or Mark's conclusion is the right one. Both guys tend to know what they are doing. But I agree it will certainly clean up the turbo side of the motor.

[Mark Halligan]

As I said earlier, I have had mine in that position for only a short time and have not covered a lot of miles with it like that yet............but it has behaved very well.

The only problem I had was getting the hoses to stay on the MAF, initially they blew off when under boost as there is not a lot for them to grip onto on the MAF ends, but it seems to be OK now, maybe I was being a bit of a pussy not wanting to tighten the clips up too hard in case of cracking the plastic MAF body.

Mihnea can probably tell us why the map might have to be tweaked when doing this, all a bit beyond me, I am just a spanner monkey .

Mark

[WabTheKing]

could this be a differance between ABY and 3B? i no a couple of people who have done it but they are all ABY engines and they have said it ran fine after,

is this a coincidence?
if this sounds like crap dont rip me as im not well up on ecu programing - it just crossed my mind

[Doug_RS2]

Mark - if your car runs "better than ever" with the MAF moved it has caused a difference.

There is a difference in velocity, density and temperature of the air in the 2 positions so it WILL make a difference.

[sorens2]

I run MAF on pressure side.... Ohh what a feeling. Needed a remap.

Søren S2

[Henka]

Doug: Yes there is a difference in those things... But it's still the same air mass! I reall y don't see why it wouldn't work.

[Mark Halligan]

Mark - if your car runs "better than ever" with the MAF moved it has caused a difference.

Don't think I said that there wasn't a difference.....I did say that I had no problems, in fact the opposite, it ran better, and yes maybe I was 'lucky' and the car ran better instead of worse.