MAF De-Screening

[Holksvagon]

Hmmm intersesting... what are the downfalls

[R_Ethug]

CEL more than likely and car running rich or too lean

[Fluidic Digital]

You car will NEVER run too lean on a "back-up" air/fuel ratio plot.

You will get a CE light, your ASR light will turn off and the light will appear and you will get BAD, and I mean BAD fuel economy. I ran this solution on my car for a while... no good for the stock turbo.

Peter

[Kor]

Sean, your advice is awesome, since you can speak from experience! Can I just replace the screen with a less problematic screen maybe? I don't think I will remove the MAF just yet...

[Holksvagon]

Well i guess thats not for me.... if i wanted my car to break down i would have bought a 67 Nova.....

[1.8Trip]

Hey Guys, just wanted to throw this theory up on the purpose of the screens.

I've been thinking about why there would be 2 identical itty bitty screens to protect the turbo and combustion chambers from debris.

IMO, you'd be better off putting two much larger air filters in series if this was the purpose of the screens. I mean that is the sole purpose of the airfilters right? Two tiny screens just doesn't seem right to me. Also the idea of flow straighteners seems kinda strange to me. My work takes me to measure noise at turbine driven compressor stations and also examining HVAC systems. Since noise is a function of turbulent flow, we look for ways to make the flow smoother. The flow straighteners I've seen seem to resemble more of a fan blade turned parallel to the flow. A screen would create more turbulence than straighten flow.

Instead, I propose this hair-brained idea. If I were an engineer designing the MAF assembly, I could care less about crap getting into the turbo. That's the job of the dude 2 cubicles down. I would be concerned about the function of the MAF. The MAF is supposed to measure the amount (mass) of air entering the combustion chambers. I would want to measure this as accurately as possible. Since you can't block the entire cross-section to measure the instantaneous flow at every possible location, you pick one location and assume that it's uniform across the entire cross-section. Well, I remember from good ol' fluid dynamics that when a fluid flows in a pipe, that there is friction along the walls of the pipe. This area is called the "non-slip condition". The velocity of fluid at the surface of the pipe is zero. The velocity increases non-linearaly to the centre of flow (middle of pipe). My wild-ass idea is that the purpose of the screens if to flatten the velocity profile so that the assumption of uniform flow is a little more accurate. Thus, the MAF reads the proper amount of air.

...stands triumphantly waiting for reaction.....Well, what do ya think?

[CalgaryB5]

Originally posted by seanfournier
Recomendation. Disconnect it MAF and take out the air box all together and run a 3" pipe straight to the inlet of the turbo with no filter... you'll get kick ass power!

How about re-route your air-condition outlets to the intercooler then that will make the ECU think the car is driving in the North Pole. :whipped:

[CalgaryB5]

I removed the snow screen which located on middle of the elephant hose after the driver side headlight. I removed that after a day of the ownership of the car, K&N in on the same day. Removing that snow screen was not new on the TDIClub because will get problem when it clog. I did a test when the snow screen clogs which I used a plastic bag to cover the snow screen I cut out. The car still can drive by using the vent with a spring on the side of the air box. That is cool. Then I got very boring on a winter holiday in Home Depot. I built a 2” cold air intake to the air box from PVC pipe and hardware. The cost is $5 CDN.

On topic. MAF de-screen( wire mash ) does not make a difference but snow screen does because it will clog in some time.


:mrpimp:

[Boy Racer]

The laminar air flow that the screens create is important. If you read carefully, you can see that the person ended up with a lot of worse results, it is obvious from Sean's words here that this would be the result. The person was measuring very small changes in pressure (.2psi across the air flow meter) without investigating the effect of changing measurement points. We know that a narrowing of cross section will create higher velocity air flow and lower pressure, the reverse is also true; therefore the area at which the pressure is measured will effect the measurements. Note also that conservation of energy is important and increases/decreases in area can be detrimental to this. The cross sectional velocity changes that 1.8Trip mentioned are also important when considering any bends in the pipe whereby the pressure profile will shift away from the concentric. This can be problematic for MAFs (even with the screens) connected to aftermarket intakes that are poorly designed, throwing calibration way off.

So, ways to improve intakes in turbo cars (therefore intake (Helmholtz) resonance charging is not an effect as things get really complex at this point). I would say to choose an appropriate diameter that flows well enough under full boost conditions and maintain that diameter as close as possible with minimal internal (ribbed pipes etc) distribution. Note that the start of the intake creates it's own disruption and should be slightly horn shaped to help mitigate this effect It may be possible to use the MAF without screen provided that the intake is straight enough for a long section before and after the MAF. The readings may be off but will be somewhat linear wrt. to the screened version and the ECU should adapt using closed loop A/F adjustment. If there is any bend close to the MAF then the air profile around the sensor will change as the air velocity (throttle, load, rpm and boost) change and therefore the ECU will probably not be able to apply a correction factor that keeps things running well.

These pessimistic comments have been brought to you by "The Engineering Skeptic" and after all is said and done, anything is possible. I just bring you one side of the arguement.

[Smartiepants]

Wow that was a brainful

[Kor]

Most intakes ARE fairly straight before the MAF...