Brent94Z

Yes, sure does! The debate typically isn't whether porting the MAF housings messes up the calibration (most all agree on this one that it DOES) but rather removing the screen negatively affects the calibration or the way the sensor behaves. I don't see it affecting the calibration but can see how it *could* affect the way it behaves. However, I have found (with crude testing I'll admit) that removing the screen doesn't seem to change the way the sensor behaves. I just did my testing with Diacom and other similar laptop scanners. With those, I saw no difference for all ranges of sensor operation. It would be cool to see more "scientific" testing with like an o-scope or something The screen is an odd one because the majority of people don't see anyting negative with removing it but there are a few who can remove it, get crappy results, then stick it back in and everything goes back to good again. Very strange

InjectedSS

Honestly, I did some testing with the screen in the same manner as I did my other tests and I didn't see ANY ISSUES at all... If there was ANY difference, it was VERY VERY VERY minor cause I didn't notice ANY changes...

MentalCaseOne

Somewhere I did read about Ford recalling MAF sensors due to contamination..... has anyone seen this before?? What kind of contamination? and does it affect our MAFs too?

Could this be the reason why some people get a different result than others??

I cant remember the website..... Its about Ford cars I remember clearly.


Marvin

slimdawson

I am curious. If the gps get lower due to porting, is that a bad thing? It seems that velocity would slow because of the larger opening the air had to pass through.

I admit, I know nothing of fluids.

InjectedSS

YES it is lower... Actually a buddy of mine was having me tune his car and I told him that he HAD to get stock ends because his were ported and at idle he was seeing like 5gps and at WOT he was only seeing like 210 gps where most cars will show like 240-250 etc Which means that the ECM think's there isn't that much air coming in so it doesn't add enough fuel in turn causing the car to run LEAN AS $HIT

Brent94Z

Yes, you are exactly correct and the slower velocity is WHY it messes up the calibration. The sensor is calibrated for a certain cross sectional area AT the sensor location. If you port the housing you increase the cross sectional area at the sensor. The sensor then sees a lower velocity air flow across the sensor for the same overall amount of air going into the intake. Because the sensor doesn't know you increased the cross sectional area, the lower velocity flow is seen as less flow when you are really putting in the same (or maybe *slightly* more due to the reduced intake restriction) amount of air to your engine.

Usually lightly modded, just bolt on cars can get away with porting the MAF housings and actually seeing a gain. The car is programmed to run a little rich from the factory. This will make you run a little leaner which is usually seen as an increase in power. Lightly modded cars can get away with this but once you start getting some more serious mods (like above 400 hp for example) it becomes more important to make sure the PCM sees actual air flow... when you are cranking out good hp, you don't want to not have that margin there IMO. That is why I like the Granatelli. While I'm not saying you'll see the advertised gains with a Granatelli or if it is worth its cost, it is a way for people (without LT1 Edit or something to adjust/account for the ported ends) to reduce their intake restrictions as much as possible and still give good gps readings to the PCM.

Injuneer could explain this much better than myself and in much more detail but I think the above is an average Joe way to explain it. LOL!

cmotorsports.com

It's very possible to tune for ported ends, it just ends up being such a pain that it's not worth the trade off. Hand ported MAF's each have their own little quirks, from the finish sanding roll used, to the i.d. of the housing itself due to the porting, the shape of the finished taper, etc. It generally takes me about 5 hours to TRULY tune for a ported MAF, and by truly tuning it means that the car drives just like stock with BLM's or LT's in the 128/0 range in all cells. It just involves a LOT of data logging and calculations, not hard, just very time consuming. Now, that's not to say that you can't tune a ported MAF quickly, it's just not going to be perfect. The reason descreened MAF's are so much easier to tune than a ported MAF is that it's a constant. Everbody that removes their screen has just changed the PCM's calculations by XXX%, whereas with a ported MAF, there are just too many variables.

Seth

MentalCaseOne

Question for you guys. Mar car has a stock air intake. from ducting to heads. everything is stock.

In My scan report it Idles at 650RPMs, MAP reads 1.25volst (20Hg), and the sensors are within especs execpt for the MAF that reads 6gr/sec at idle.

per your post:
Sounds as if my stock MAF is reading low. At WOT it reads 228 grms/sec at 5450 RPMs.

My question. On a totally Stock 95 A4 Z28. What would be the normal grms/sec readings? I know many of you are anything but stock so I cant just take your readings for the same reason.
but does anyone know what should I be reading at idle?

My scanner reported 14* knock retard when I was going up a hill with the AC on and 60 percent throttle somewhere between 2200 and 2400 RPMs. My BLMs are showing 114 at idle yet the car acts lean under load. Fuel pressure checks out ok.

Does anyone have the original readings before their car was updated?

Marvin

fredmr39

so what does this mean for those of us who did not have this brilliant thread to rely upon? mines ported polished and cleaned.....thought i was doing good since the website I got the info from reported stroger top ends in their 4 tehy ported...

so here are my options: leave as is (ported)
replace with stock
purchase an aftermarket MAF

what would you guys do? my car is lightly modded, but i have noticed pretty poor gas mileage lately, do you think thats because the car is running lean and that the computer is adding the most amount of fuel it can to compensate, or just because my car has 68K and needs a good tune-up?

Brent94Z

IMO, there are enough people out there who have done this (like TONS) and have not had "problems" that, since you are lightly modded, I would not worry too much about it. Like has been mentioned above, a stock or lightly modded car will usually see gains from this. You'll just want to keep this thread in mind if you do a heads/cam package or slap on a blower or nitrous. If it bothers you a lot, then just keep your eyes open for a good deal factory MAF or a good deal Granatelli. If you have access to a stock MAF then you might want to do a little testing on your own and see if you notice any difference when switching back. Just some ideas.

If your gas mileage just recently decreased and you ported it a while ago, it is most likely unrelated.

InjectedSS

While I agree with Brent for the most part, I would have to say go back to the STOCK ends and just leave it descreened... Only REAL WAY to find out is to put the car on a wideband and see..

But from my experiences and tuning many cars, I have seen the MAF screw the a/f ratio on a car that has exhaust, headers, intake, pretty basic mods, and it threw the A/F off QUITE A BIT

I can't say anything about the granatelli or the other aftermarket ones cause I still haven't tested them YET. BUT I have a granatelli and another guy who is going to send me his ZO6 MAF for some testing

I will let you guys know how it turns out

Injuneer

You really need to keep your posts all in one thread.... we've been all through the 1.25V = 20"Hg MAP.... and I thought you understood that 1.25V is approx. 10"Hg MAP = 20"Hg vacuum, which is totally NORMAL for your car. Apparently you didn't believe my earlier explanation.

And... 6gps for a stock idle on an A4 is totally normal.... it's explained in my online ScanMaster writeup, and I have explained it to you in another thread as well. Your 228gps at 5,450rpm sounds reasonable as well. Is there some particular reason you don't accept these explanations? Just curious, because we appear to have some sort of communications gap here, and I would rather try and help people who put some degree of credibility in my advice.

Let me know, please.

Injuneer

Brent.....

Your explanation overlooks one of the key issues in miscalibration... the fact the the sensor ASSUMES that the small sample of air that cools the wires is representative of the flow velocity across the entire open area of the meter. That is the purpose of the screen, and of the dividing wing. They are there to promote a uniform flow velocity over the meter, from the edges of the housing to the center where the wires are.

And, this uniformity of flow must exist over a wide range of flow conditions, from laminar flow at idle to turbulent flow at WOT/max rpm.

When you remove the screen and the wing, you increase the possibility that the velocity passing the wires is not representative of the true average velocity across the open area. At very low (laminar) air flows, you will likely see a "bell-shaped" velocity profile, with a higher velocity at the center, and slower velocities the closer you get to the walls of the housing. In that case, the descreened, or ported MAF may show idle gps flow slightly higher than actual. I have seen this result in many of the dozens of data logs that people have sent me for analysis of performance problems. I can generally tell them if they have a ported MAF.

At WOT/max rpm (turbulent flow), it is likely you will see a more uniform distribution of velocities over the open area of the meter. Now your explanation is valid.... the larger area results in a lower average velocity across the meter face, and the wires in the center "see" this reduction and under-report air flow, leaning out the mixture. That's what people see when they port their MAF.... about 15HP from leaning out the A/F ratio. The arguable point is whether the PCM will eventually negate this gain, as Cell 15 (high rpm/high load) long term fuel corrections start to compensate for the under-reporting of air mass flow.

Point is, they developed a calibration curve (frequency vs. gps) based on the testing they did to see how well the "stock" meter represents the air flow.... with the screen, and with dividing wing, and in the specific air inlet configuration the car has. Once you alter any part, you alter the calibration, and my contention is that this "alteration" is not predicatable. Hence, many "tuners" don't like to see ported MAF sensors.

Just an opinion.

97FormulaWS-6

I've said this same thing since I 1st saw the ported MAF discussion back when I joined in '00.... no one ever listened to me...

Brent94Z

As usual, Fred...



I have a slight grasp of this stuff but not nearly like you or some of the others here.

While I do agree 100% with the porting of the housings and removing of the wing messing up the calibration of the sensor, I really haven't seen myself where removing the screen (ONLY the screen) has any negative affects. The screen is there to promote "even and predictable" air flow over the sensor, but with the crude testing I've done with scan tools on a couple of my cars, I haven't seen any difference in the way the sensor behaves with removing just the screen. I always try to watch all your posts closely about this but I don't recall seeing you post about JUST the removal of the screen being a "bad thing". I know we have both seen on here people who can get repeatable negative results by removing the screen but those are just a handful of people and usually we never can come up with a reason So, I think we are on basically the same page about porting and the wing (with me being on a lower lever. hahaha) but just not sure about the screen removal only? I know the GM engineers put it there for a reason... just doesn't seem that reason comes into play very often. Similar to the coolant going through the throttle body... why is that provision there... I can honestly say I have never heard of anybody (even in sub zero temps) ever saying that doing the throttle body bypass had negative affects

I've got so many ideas/theories that I'd like to test to prove/disprove but I just can't get the time to do it. ARRGGHH!!! I'd love to be able to test all this stuff more precisely (something other than scan tools) but I work too damn much. Heck, I've had the 48,52,58, and mono blade throttle bodies and a stock, high hp N/A and supercharged car to test them on... been going to do that for the last year or two and so far they still just set on the shelf. LOL!

Anyway, thanks for the EXCELLENT reply. I'll be saving this one to refer to