# MAF befor or after turbo



## natevw (Oct 23, 2001)

I have heard it is better to mount the maf meter after the turbo and bov. Has anyone done this and what did it do. I know it is supose to keep the maf from getting a bad reading form the bov venting into the air. Is there anything else to gain from doing this.


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## XSiVE (Nov 1, 2000)

*Re: MAF befor or after turbo (natevw)*

it wont read correctly after the turbo. the maf meters air as it flows past it, air velocity. when it is past the bov and turbo it will not accurately measure air flow because on boost it is more pressure than moving air. yes air does have to move into the engine. but the dynamics change a lot once pressure is introduced.


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## Patrick (Apr 28, 2000)

*Re: MAF befor or after turbo (ventoGT99)*

For what it's worth the VR6 supercharger kits mount the MAF after the charger. It works...not the ideal setup in my opinion, but it works.


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## speed51133 (Feb 18, 2000)

*Re: MAF befor or after turbo (Supercharged VR6)*

it is NOT a good idea to run the MAF in the boost pipes. I know vr6's do, but to my limited knowledge, they go through MAF's much faster than stock vr6's. 2.0t's that have the maf in the intake pipe see the same longevity out of the MAF as stock 2.0's.


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## Patrick (Apr 28, 2000)

*Re: MAF befor or after turbo (speed51133)*

I agree, I'm on MAF number 2 with my charger and it's showing signs of death already.


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## Stephen Webb (Apr 12, 2001)

*Re: MAF befor or after turbo (natevw)*

Mounting it after the turbo lets you run a BOV without needing to reroute it into the intake (before turbo). Many people run a BOV anyway, without re-routing. It's hard to say how this affects things. (you run rich for a moment - high emissions, somewhat (but negligible, almost certainly) reduced fuel economy, etc.
The real logic (from my standpoint) is to improve throttle response - putting it closer to the intake valves - but not so close to encounter wild intake pulses (ie near the throttle body). Good computer control and a TPS should be able to give you good throttle response, though. (The '98 Jetta I drive from time to time has very poor throttle response, FWIW)
Now, is it a good idea to put the MAF *after* the turbo? Not sure. Speed says the supercharged VR6 does it, but they wear out faster, which is not acceptable in my book. If I were going to do it, it would be after the intercooler to be sure. 
The MAF uses a hot film or hot wire circuit that calculates mass airflow by heating a wire up to a certain temperature, and monitoring the current required to keep it that hot (incoming air cools it in proportion to the mass of air and the temp of air). Since turbos produce very hot air (way outside of the range of "normal ambient air temperature", I wouldn't be surprised if the MAF can't correctly compensate at such high temperatures. Also exposing PCBs to extreme temps isn't necessarily good for them (maybe explaining why they fail).
To be safe, I would put it before the turbo and consider using a bypass valve to re-route the blow off back into the intake (so you don't run rich).
-Steve


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## speed51133 (Feb 18, 2000)

*Re: MAF befor or after turbo (Stephen Webb)*

to take advantage of putting it in a spot where you can vent the BOV and "fool" the ecu, it would not only have to be after the turbo, but after the BOV as well. since BOV's are SUPPOSED to be as close to the throttle as possible, forget it.


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## Stephen Webb (Apr 12, 2001)

*Re: MAF befor or after turbo (speed51133)*

quote:[HR][/HR]to take advantage of putting it in a spot where you can vent the BOV and "fool" the ecu, it would not only have to be after the turbo, but after the BOV as well. since BOV's are SUPPOSED to be as close to the throttle as possible, forget it.[HR][/HR]​Yes, it's supposed to be near the throttle plate. Enough cars have them not near the throttle plate that I tend to think it's not a big deal, though. If it is important, then routing the blow off to the turbo intake will fix the fuel problem. 
Again, the main reason I would consider doing this is for throttle response. Enough cars have the MAF away from the throttle, though, so maybe it wouldn't really improve throttle response.
-Steve


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## NorthDakota2.0 (Nov 6, 2001)

*Re: MAF befor or after turbo (Stephen Webb)*

So, where is the best place to put a MAF sensor? After the intercooler and BOV and before the T/B -or- before the turbo and re-route the BOV to vent near the intake?


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## Stephen Webb (Apr 12, 2001)

*Re: MAF befor or after turbo (NorthDakota2.0)*

quote:[HR][/HR]So, where is the best place to put a MAF sensor? After the intercooler and BOV and before the T/B -or- before the turbo and re-route the BOV to vent near the intake? [HR][/HR]​I don't know the answer to that. 
I would expect that the closer the MAF is to the throttle body, the better the throttle response would be. In light of the problems some people (supercharged VR6) are having with the MAF after the compressor, I may avoid it alltogether.
If I had problems with throttle response, I would probably be experimenting with putting the MAF closer to the throttle. If the results were noticable / good, I might go out of my way to keep it there (ie put the BOV before the MAF). I don't know how much it matters if the BOV is 1" or 5" away from the throttle plate, but if I found that it affected performance, I would just use a bypass valve and return the air back into the turbo inlet. (The BOV sound is cool and all, but I wouldn't keep it at the expense of performance.)
I don't know if all of the 2.0 engines are this way, but the throttle response on the one I drive is pretty bad - it can't touch my CIS setup. 
-Steve


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## jcorallo (Jan 17, 2001)

*Re: MAF befor or after turbo (Stephen Webb)*

the supercharged vr6 setup can damage MAFs as the crankcase vent is put on the suction side of the charger, thus not only drawing more oil mist through, but also putting it through the MAF.
Putting the MAF inbetween the charger and TB on the supercharged set up is OK, but you tend to need it as far away from the blower as possible, as there seems to be a lot of turbulent air in there confusing the MAF, particulary at tick over.
I can stand by this, cos I bought a new MAF for my z-eng set up, and it runs perfect with no MAF, but idles rough when the MAF is conected.
You can put the MAF before the charger and this works OK, but the software needs to know about it otherwise you can run rich on the overrun, or if you want to use a BOV.
Cheers,
Jules


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## natevw (Oct 23, 2001)

*Re: MAF befor or after turbo (natevw)*

I am putting this on a 2.0 16v setup that is going along very well the only reason I asked is that I have herad of it helping the MAF read the air better. For a better throtle responce and better af mixture. They also said it would let you run higher boost with out the MAF reading to much a throwing a code.


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## sporter (Feb 5, 2001)

*Re: MAF befor or after turbo (natevw)*

well this thread kinda died but im very interested in getting to the bottom of it!! Since I'll be shortly putting my xflow 2.0 turbo together running motronic, I was also under the impression that running the MAF right before the TB was the best way to go (with the BOV shortly behind it). I'll be using an i/c aswell, so what is the general consensus on this issue? I assume there are people out there running both styles of setup - so tell me whats up!


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## TheDeer (Sep 21, 2000)

*Re: MAF befor or after turbo (natevw)*

I did this exact thing when I had the z-eng on the car, just moved it in front of the blower and put a recirculation valve in. The car ran like crap, really rich. It was like a spy hunter smoke screen, it was bad.


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## natevw (Oct 23, 2001)

*Re: MAF befor or after turbo (TheDeer)*

Which way was bad in front of it or after it.


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