legacycentral bbs

I removed the little wire screen from my MAF, and it made a pretty noticeable difference, car seems to pull just a little harder than before, plus it chirped 2nd

That's new . . . I thought the MAF screen was there to smooth out the airflow to the MAF, plus to catch any large debris in case (and this prolly would never happen) the air filter was punctured.

boostjunkie wrote:catch any large debris in case (and this prolly would never happen) the air filter was punctured.

I'll take my chances on that one

Hmmm... interesting! I have 2 extra MAFs laying around, I might just ruin one to try this.

I doubt that a large piece of debris can get into the fender, be sucked into the snorkus, get sucked out of the snorkus instead of falling to the bottom of it, get sucked into the airbox instead of falling to the bottom of it, then cut through the air filter and get sucked into the engine...

The wire screen is also a place for oil droplets to condense.

Reusable filters like K&Ns usually use an oiled gauze or foam to catch particulates. An unavoidable consequence is that a small amount of oil comes off it. A frequent problem with overoiled filters is dead MAF sensors; the oil just gets all over the sensor element.

I imagine you could deal with this by just cleaning your MAF sensor out every once in a while; like every time you change or clean your air filter.

I really do think the screen is there to smooth out the air flow. I know I heard that somewhere.

subyluvr2212 wrote:I doubt that a large piece of debris can get into the fender, be sucked into the snorkus, get sucked out of the snorkus instead of falling to the bottom of it, get sucked into the airbox instead of falling to the bottom of it, then cut through the air filter and get sucked into the engine...

Oh, and see my first post:

and this prolly would never happen

The "official explanation" for the screen is that it is there to prevent non-laminar airflow. But there is an article that is probably in AutoSpeeds archive called Negative Boost and in the article they measure the drop caused by this screen and it is real and according to what they found so is the power gain.
AL(CO)
al@iwtu.net

How can a grate possibly "smooth" airflow? Removing it can only be beneficial to airflow.

Having experienced many different fan configurations in the computer field, the quietest and best flowing ones have no restriction whatsoever due to the lack of pressure being built up around the grate.

Dave

I honestly never thought the removal of the screen would make that much of a difference but it's worth a try . . . looks like another project for me this weekend.

They are depending on the screen to straighten out the airflow as there might be turbulence in the part of the intake before the meter. I don't think that there is much turbulence and if there is it is not significant as I can't see any voltage variations on the scope. Also anything that can be done to free up the intake will help the turbo spool up faster and allow more air to be available. I have run my MAF without a screen since reading the AutoSpeed article. I do use a K&N filter because some of the foam filters will shed small particles that I have seen lodged in sensors.
AL(CO)
al@iwtu.net

So how do you take it out? Does it pop-out or do you cut it out?

Since we're talkin about restrictions, what about that reservoir tank after the MAF? Anyone run a straight thru pipe instead? I have a couple pieces of aluminum tubing from an old intake that I was thinking about using (has the attachment for the vaccum hose too) . . . is this worth doing as well?

Theres a ring type thing that holds it in, it has two little holes, just pull it out by one of the holes, and the ring will come off, then the screen just falls right out. I know it seems a little unclear, but it'll make perfect sense when youre looking at the MAF. As for that reservoir tank, I tried to replace it once, but the 2nd hose on the other side of the tank has to have vacuum on it at all times I guess, so that failed.

The tube I have has vaccum attachments on it that seem to fit the stock hoses so I think it'll work. I'll try to get everything hooked up this weekend and let you know what results I get from both of these mods.

Hey I found this at MRT, scroll down to inlet plenum.
http://www.mrtrally.com.au/shop/

boostjunkie wrote:The tube I have has vaccum attachments on it that seem to fit the stock hoses so I think it'll work. I'll try to get everything hooked up this weekend and let you know what results I get from both of these mods.

Yeah, let us know if it works, I'd love to get rid of that damn box.

Looking at the link that -K- found it seems that MRT has a part already fabricated for this purpose (although that doesn't necessarily mean it'll help dramatically). Here's the details:

Inlet Plenum
Suitable for 1993 to 1996 Subaru Impreza model WRX's and STi's. Also early model Liberty (Legacy) Turbo's. It replaces the standard factory plastic resonator part which is quite restrictive to airflow. Although a small increase in induction noise may be heard, low end torque and high RPM throttle response will be significantly improved. Made completely from steel with powder coated black finish. Suitable for road, race and rally. Contact MRT Performance for more detailed information.

The price is posted as $67.20AUD, which means this piece is pretty damn inexpensive!! I emailed a peed shop near me that's an MRT vendor and asked them how much this piece will cost.

Let us know how much when you find out.

I would like to make some comments on the screen issue before some of you get too gung-ho.

Al is correct in how/what the screen does or is supposed to eliminate. You want as laminar an air flow as you can through the MAF sensor so it's readings are correct.

A good real world comparison is the aerator on your faucet at home. With it on, it puts out a nice smooth steady stream of water. Even if you have the water turned up pretty high.

If you take off the aerator and turn the water on to the same level as before, you will get a lot more pressure, but the flow will be very turbulant and most likely splash the hell out of everything.

The basic principle is the same for the grate on the MAF.

But wait....there's more.

On the stock airboxes there is a little metal piece that the MAF actually bolts to. This metal piece also is shaped and serves as a velocity stack which helps speed up the air as it enters the MAF. It may also serve/help in smoothing the air flow out.....but that it just a guess on my part.

Another issue/design trait of the stock box is that the area directly in front of the MAF sensor is relatively small. It's only several inches deep from the screen of the MAF sensor. I believe this was done also to help with the air flow properties and also in maintaining some amount of back pressure on the intake system so that the air entering the MAF region would be more homogenous and exibit more laminar flow.

And yet another thing with the stock box.....which I'm not sure is a big deal or not......but it has slats or plastic vanes that protrude from the edges of the airbox. This again may be some crude method of helping straighten the air flow.

The reason I've mentioned all of this is because if you look at all these things, the stock air box has the potential to be fairly complex and a bit of engineering behind it, which helps the air flow characteristics. So removing the screen may not be a big deal.

The issue arises if you have an open style intake/filter. You have now elminated all of these things to help air flow characteristics.....so it's very possible the screen on the MAF is actually working the way it was designed to.

Without actually taking some readings from the MAF sensor.......you wouldn't be able to tell for sure whether what I said has merit, or if it's just a hypothesis/theory on how things work.

Closing note.....MAF sensors are not cheap....they're a little over $300 new. Yes you can them used but you'll still probably be looking at $150 or so.......Take it from me.....I had an intermittant MAF failure.....plagued me for over a year.......$300 later......no problems.

So keep all this in mind before you just go ripping the screen off.

So Legacy777 was the one who told me about this before!! I knew I heard this explanation somewhere!! Good write up!!

I'll tell you guys what the shop says about the intake plenum.

I remembered the title for the Autospeed article it was called "Negative Boost" and they studied all of the restrictions that they could find in the intake system and measured them with some good equipment. Altogether they came up with some pretty good figures on flow and added performance.
AL(CO)
al@iwtu.net

Do you need a subscription to get in and read the article?

Yes, you need to be subscribed.

In the Autospeed article "negative boost" the test car was an Audi S4 2,2liter, so the airbox is slightly different, but the synopsis would be as follows. And this is a compilation of the actual Autospeed Article.

Key Points:

1. Most of the restriction occurs after the airfilter.
2. As is the case with most cars, the filter element itself poses little restriction.
3. The greatest flow restriction of the intake system was occurring between the exit of the airbox and the turbo.
4. The airflow meter was causing the majority of this restriction.
5. Removing the airflow meter screens made a major improvement.
6. The airbox exit bellmouth could not be easily improved upon.
7. The new added ram-air duct to the airbox reduced the full-load intake snorkel pressure drop to zero.
8. At less than full load, a positive pressure is generated in the airbox.
9. Power did not respond to the better intake flow, with initially knock-triggered ignition retard, and then falling ECU-controlled boost the suspected culprits.

SO, more power would be available only if the ECU does not control the boost itself, but is controlled manually.

Of course what most worries me is the knock-aspect of this mod. Without Knock-Link (or similar) you can just gradually blow your engine WITH high boost and WITHOUT good grade gasoline.

I had read about that and it seems to be another case of an improvement causing a problem maybe this is why some mods trigger more. But this was an Audi and some of the German ECU's seem to be a little behind the times as far as I can tell. What I eventually did was build my own MAF that was larger and gave even more flow but also corrected the output voltage to compensate for the additional air. I really don't think that the air obtained by the screen removal would upset the AF ratio that badly as this system is adaptable to a lot of conditions such as high altitude but it would be something to check.
AL(CO)
al@iwtu.net