SuperL98

Here is my recent adventures with Mass Airflow Meter screens.
Hopefully, some may find it interesting.
Tried to keep the word count down & the picture count up.

Short Background: I have an 1988 Corvette with a ZZ4 crate engine, TPIS manifold & runners, full modified MAF (screens and fins removed), Paxton Supercharger, and headers. Built and tuned in the early 1990's (old school), it's probably right at the edge of what a MAF system can handle, and with the elbow duct, heat and turbulence from the supercharger, a worse case environment for the MAF as well.



The car has always had a bit of a stumble on "light" acceleration from a stop, and I felt that the throttle response was never as sharp as it should have been, so a friend and I recently decided to poke around with the tuning and components looking for answers.

The interesting test is we replaced the Modified MAF with a borrowed completely Stock MAF (friends 58,000 mile L98), and saw a significant improvement in light throttle acceleration and throttle response, so the question was why?

Comparing the TPS Volts (throttle position) to the AFGS (MAF readout) in a bunch of data scans for both MAF meters, it was clear that the Modified MAF signal was much noisier than the Stock MAF and didn't shadow the throttle position as closely as the stock MAF either. Actually was a very dramatic difference between the two.

Original Modified MAF data and fuel calibration results for a test run. We kept this chip tuning for all the tests.


The borrowed "Stock" MAF data and fuel calibration results for a test run. The meter made the tune go LEAN in most Cells, meaning it was reading generally lower airflow than the Modified MAF meter.



Next, using a piece of aluminum window screen, I put a temporary screen on the inlet of the Modified MAF, and the data cleaned up considerably, and the light acceleration and throttle response was much better than the unscreened Modified MAF but not quite as good as with the Stock MAF. The calibration tended to move LEAN, but not as far as the "Stock" MAF did. Note. the window screen material was very close to the screen used in the Stock MAF (.009 inch dia. and about 15 x 15 openings/inch)



Figuring that if we had to put a screen back in, we could make it less restrictive by increasing the area. We had the bright idea (the kind you get when you over think things ) to make a cone shape inlet screen that would have about twice the open area as stock. Six inches in diameter instead of the stock three inches.
Made it as shown bellow.



The test data shows a little dirtier signal than the single flat screen, but the throttle response was just about as good, the fuel calibration went surprisingly RICH in all the cells ( MAF reading much higher than the original Modified MAF).
I have no explanation for why this one went in the opposite direction of the other two screened MAF's.
Perhaps something about the flow pattern from the cone shape affecting the sensor wire?



We also figured we would try a "Crude" flow test of the different screens, on the Modified MAF, using two big ShopVac's and a piece of Pvc pipe.
We took velocity measurements with a wind speed meter fixed to a three inch exhaust pipe, the idea being just to compare one to the other and not test the ultimate flow rate, which we couldn't do with the ShopVac's.



Unexpected that the Cone Screen didn't flow much better than the single flat screen?
It had twice the open area, but also has twice the wires in the flow path, which may have something to do with it?
We decided to go with the single flat screen for now, and tweak the fuel calibration to go with it.


Possible Conclusions:

* In this particular case (SuperCharged ducting) the MAF screens made a big difference in MAF signal quality, low speed acceleration and throttle response.

* The MAF sensor calibration is very sensitive to what is in front of it (Screens).

* Cone screen was not worth the effort in airflow and possible tuning mystery problems.

* We still didn't get as smooth an MAF signal or as good throttle response as the Stock MAF gave. Either our Modified MAF still has another issue, or the rear screen and cooling fins also contribute somehow to the calibration? I might try a rear screen test if I can get some more free time.

Klyde

My understanding of the screens purpose after a lot of research is to generate straight line air flow before and after the sensor causing a more accurate reading. Most think they are to stop dirt from getting to the flow sensor but that is what your air filter does and of course you would not need one after the sensor. You should never remove them because it would or could cause misreading of the air mass. By you adding the screens you are cleaning up the airflow around the sensor. The screens on the original are researched and designed for the most stable and therefore accurate reading.

GREGGPENN

and and and

(The last picture icon is because of all the pictures! )

I'm trying to figure out why it went lean versus rich? If the engine sees (and gets) less air, then you'd have MORE fuel in relation to the lower air input. The coned screen that went rich is what I would have expected.

Did you modify your tune in respect to each screen ... or just observe the results? How much does that screen affect the "bottom-line" of power production on the top end? What is your thought of the benefit of a screen at this point? Are you sure you can't improve light-throttle any further with tuning? Have you tried more fuel in low-load acceleration enrichment? (or less)

Can more rows be added to an individual BIN function to fine tune a given table like this? (What if you need more low, less high or vica-versa?

I'm thinking the coned screen may actually "appear" like a deflector to high-speed "wind". IOW, the surface turbulance is going to try and deflect air away from entering the screen. Because it's clamped in a tube, you might have way more air traveling down the MAF walls versus the middle of the tube?

For the flow question, I'd consider what the cone screen looks like as veiwed straight on. As you mentioned, it's going to have more screen per square inch "blocking" air from traveling a STRAIGHT PATH into the MAF. (Hmmmm....the exception would be close to the "tip" where it might flow better -- and help to compensate for my prior turbulence theory. Hmmmm....)

Did you measure the stock screen MAF to get a feel for how much percentage loss it would induce compared to your modified unit?


(Also how did you secure the window screen for that first test? Is it siliconed to the front rim?)

SuperL98

Try to answer as many ??? as I can, but these are only my opinions ....

First, as I stated, we used the chip tuned for the Modified MAF for ALL tests.

I have to visualize things, words can be very confusing when we start talking lean and rich, compared to what? So this is how I see what is happening.




So, if my chart is true, the Stock MAF & Flat Screen Modified MAF created slower airflow @ the element (center of the bore) and cooled the wire down less (for a given air flow) compared to the Modified MAF.

The Cone Screen MAF had a faster airflow @ the element (center of the bore) and the wire element was cooler (for a given air flow) compared to the Modified MAF.

Keep in mind, it's what is happening at the wire element (center of the bore) that matters.

Yes, I think the Flat Screen distributes the flow more even across the bore, and somehow the Cone Screen is either blocking the edge flow or something wierd I can't visualize ?

These two videos helped me to visualize what might be happening (open vs flat screen).





Here is a bigger picture of the Cone Screen.
I used a two part marine epoxy, oven cured to speed things up.




I didn't flow test the Stock MAF because the minute I started drilling drain pipe and dragging ShopVacs around, he decided it was safer back in his car.

Going to stay away from the chip tuning in this post, that's a whole other subject.

leesvet

Yessir,

I've seen data that tells us that the flat screen does indeed "fix" the turbulence and also provides some equality for the boundry layer effect that causes air molecules that stick to the walls and do nothing more than cause drag...making the flow better toward the center and slower at the walls...like a smaller passage. The screen tends to give the entire diameter an equal ability to flow the air through the tube.

The SIZE of the screen holes is what would make an interesting experiment! Try this with different size mesh.....bet you get some wide variations.. in the resulting data !

The cone....

Think of EACH wire in that cone as an airfoil. If the cones shape means there is twice the area, that's twice or ten times the surface area that air is forced to go around...creating DRAG.
Look at the grill on the "other wanna be cars" in the driveway. The grill serves a purpose. As air passes over each grill plate or vein, it MUST accelerate therefore hitting the radiator faster increasing the efficiency of the cooling system. Same principles as flight. Air rushes around something, and depending on the shape and whats immediately behind the airfoil, you can manage what the air does for you. In a wing the air moves faster over the top because of the shape then it does under the bottom where its flat and tends to compress and build pressure (lift). In grills the shape is even top and bottom so you just get speed both sides of each wire or fin or whatever the "thing" is that's been placed in the airstream.

In the case of the flat screen, you get the desired reduction in turbulence. With the cone, you increase DRAG to the point of negating any benefit of the grate effect...

Damn good research ! Great work!

DanZ51

Real interesting. I like the videos. You should try it with cone reversed, I would think this would "center" the flow.

Corvette40

Good info, but darn, now I gotta go buy a MAF with screens. Just yesterday I was reading your thread on when you repainted your car. That was an excellent thread too. Now I gotta fill in the waves in my front bumper. I gotta stop reading your theads SuperL98.

GREGGPENN

I thought the same thing.

Later, I had the vision of a lightly-sprung dual valve flap (like a carb throttle plate). If you designed it so it left a sizeable gap in the middle (1"?) then lower speed air would funnel away from MAF walls and across the wire element. With higher speeds, the flaps would open -- allowing more air to pass.

gerardvg

Hi
I have a vortech blower with an intercooler, the maf is installed after the intercooler just near the cooling fan and below the alternator so it cuts the 90 deg c air from the blower to around 30 deg c to the maf.
The only change from standard is a inline fuel pump and a vortech FMU that restricts fuel return per psi boost (5-8 psi fuel per psi boost) forcing more fuel thru the injectors that allowed me to run the standard ecm and fuel injectors.
I have run this setup the last 7 years with 8 psi boost without issue, yes the maf has the standard screens. When it was dyno tuned the emissions are really good, only getting a touch rich at max boost.
Standard ecm and standard chip.

Yes i know the standard air filter and flexible hose is not a good thing, (blowers hate to suck) but to be legal in Australia the original air filter has to be used. It has not really lost h/p compared to a pod filter i used to use on the blower, its a lot quieter with the standard filter.

No flat spots or hesitation more rpm = more go.

89L98TPI

Couldn't of said it better. Very cool thread.

leesvet

Actually there IS such a thing...

Nissan uses a flapper type MAF on the Z cars, or at least they used to.
It metered flow by the flap and was VERY sensitive...there were adjustments and calibrations that you never ever messed with, or the thing was never the same again. The flapper was managed by a coil spring that was set to an exact tension and that somehow was monitored by the system as part of the reading.

Cliff Harris

My '90 Supra had that same setup. I had an '85 Celica GTS before that and I think it did too -- can't remember for sure.

Those flow videos are fantastic. They dramatically show how the screen removes the turbulence in the air duct. Very nice.

mrc24x

Interesting. So the de-screened MAF increases flow to the engine by 4.9% and the down side is a stumble during light throttle tip in?

That sounds like it could be tuned out and if not, a worthy trade off.

Am I thinking right?



Thanks for the post!

bjankuski

SuperL98

If the Modified MAF was just reading high or low, even if it wasn't linear, that could be tuned out.
But because of noise (or whatever) it's not following what the throttle is doing during small changes very well.
Don't think we could predict that well enough to tune it out.




Been driving this (with the single screen) for a little while now and it is a pretty dramatic improvement in how the car responds to throttle.


I never cared much about light throttle tip in, or throttle response either (when I was younger).
Live with "whatever" to go faster and stop faster.
Funny thing happened ... I turned into an OLD MAN.
Now mufflers that drone, brake pads that squeak like a school bus, and no Catalytic Converters leaving me smelling like an exhaust pipe, found me driving my C4 less and less.
I'm working on changing that ...
The car that is ... can't change being an OLD MAN

GREGGPENN

Matt, The SuperFlow bench tests at a NorthWestern Ohio University posted 658cfm unscreened and 517cfm screened. http://www.gmtuners.com/pda/flow.htm

Your increase in flow is more than 5%. It's more like 25%. But...you'd also need to upgrade the stock TPI airbox (which is in the lower 500cfm range). If you can't GET more than 500cfm to an increased capacity MAF, it's pointless.

That's why it's a worthwhile mod to experiment with -- especially when your engine is modified and NEEDS the extra air!

WDYWFL

Good solid info‼️I however failed to state that I have a open air box with a K&N filter, 160° T stat, smooth inlet hoses, bypassed coolant to throttle body and a full width airfoil. After all was said n done I reprogrammed the computer to the minor adjustments. However I'm curious about how the window screen would work so I may have a rainy day project.