Ok Here is another way to look at it.. the MAF wires measure Flow by cooling the wires. If the flow is fast... the heat dissapated is more... thus measuring higher flow. But It really cant measure Volume. I has no idea how BIG the air mass entering it is. Imagine putting the MAF in the middle of a big FAN. The kind they use to cool an Automotive garage. Tons of air volume is moved through it. But the maf would hardly read a drop of it. Now Shoot a blow Drier (on Cool) over the maf wires. You slam it. The MAF wires are a crappy way to measure air flow. Just because the MAF did not register the air from the big fan does not mean it does not exist.
Just like the Ported MAF ends. The flow exists.

Hope this helps :D

 

Here is a better explanation..this has been proven numerous times.

The ported MAF gives the pcm a false reading of less incoming air. The pcm, in turn calculates less load and increases engine timing (good) and lowers transmission line pressure (bad). The lower line pressure is linked to many problems...namely shortened tranny life, converter clutch lock-up problems, and trans related (DTC) codes.

I still stick by my original recommendation it is not worth the risk for a couple hp.

:confused:

 

I have an MN6... Nooooo Problem :smash: :D

 

Smoke-n-shot VERY NICE SETUP!!!! I likes it.I have heard talk at XTREME about a kit that has been dynoed and designed by Bill our newest engineer but hardly a beginer with 20+ years of doing this.I cant make any claims it is above my head but you may want to call Nate or Mike our other design engineer and get the poop on it.But if memory serves me correct they are taking a consistant dyno proven 15 pony consistent Rear wheel gain and I
believe it was done on a stock99 C5.
Its terrible to have to keep stock cars around for R&D actually I think this car had a black wing and Bassani exhaust and mabe an X-pipe.If I'm correct its low buck hi-hp product something we all want.Enjoy your weekend drive very
careful but do it very FAST!!!!.David Smilovic 480-517-4969

 

I am not 100% about the C5s but on the F-bods if you run a ported MAF with an A4 and higher stall you can eventually have shiftihng issues and prematurely worn out trans.

The problem stems from the lack of vacume signal that is sent to the trans which in turn causes a lowering of line pressure which really kills your 2-3 shift and in some cases causes you to bang off the limiter!

There are numerous posts on LS1Tech.com about this but not everyone sees this problem because in 98 the computer tuning was more agressive when it came to shift firmness and sensitivity to this vacume signal. As the years progressed they became more sensitive and less agressive to the point where the 01'-02' cars are having major issues with this.

My car had no problems when I was stock or had the Yank3000 but when I got the Yank3800 stall then later the PT-4400 and my car would'nt shift right at all for 8mo or so till I finally swapped to my stock MAF and it was instantly cured. I now have the SLP 85mm MAF (reworked LS6 MAF) and the problem is all gone and my shifts are back to normal. The only other fix is to buy a vacume module kit which does away with the electronic solenoid and uses a maunual setup that takes vacume from the power brake booster.

Agin, not everyone sees this problem but this is just a warning from those of us that have had issues and I'll tell ya they aint pretty. :)


[Modified by F8LPONY, 7:03 PM 4/27/2002]

 

yellowy2kc5 posted this way up above:

This is correct. Slower airflow means less cooling means lower frequency. What you have changed by using ported ends is the relationship between a given flow rate and reported frequency. Recall that the inverse relationship is known by the PCM.

It is not an issue of unmeasured air as has been erroneously repeated here and elsewhere many times. It's not like a turnstile where all the little molecules get counted as they go by. :) It's simply a calibration issue. The reason you see and correct for a lean condition from the feedback components (O2 and fuel trims) is that one of the feed forward components (MAF signal) is reporting lower flow rates (i.e. less load) and less fuel than actually needed was delivered.



[Modified by ToplessTexan, 1:30 PM 4/27/2002]

 

TTT

 

Lets say the maximum amount of airflow the MAF sensor can flow is 600CFM.

Given a fixed engine displacement, and fixed ability to pump air, the airflow ability of the maf will reach it's peak flow rate at a specific peak RPM. At all other lower RPMs, increasing the size of the MAF is meaningless with resect to the need to flow more air.

The only way to increase the ability of a MAF to flow more air, at and above that specific peak RPM, is to make the opening larger.

Lets assume the peak RPM is 6K where the MAF flows at capacity.

And the flow rate is 600CFM at 6K RPM.

At say 7K RPM (where we will say the engine can still make power) the flow rate is still 600CFM. The engine starves for air, and initially goes rich. The feedback controls sense the rich condition, and lowers the injector pulse rate.

Thus the engine looses power in direct relation to the MAF's inability to flow air beyond 6K RPM.

Since the maf has a fixed opening, its ability to flow (up to 600CFM), is porportional to its opening.

So "let's say" a stock diameter MAF = 3 inches:

also note that:
Velocity (LFM - Linear Feet per Minute) = Volume (CFM) / area (ft²)

1K RPM - 100CFM Velocity = 100 / .048583 = 2058 LFM
2K RPM - 200CFM Velocity = 200 / .048583 = 4116 LFM
3K RPM - 300CFM Velocity = 300 / .048583 = 6174 LFM
4K RPM - 400CFM Velocity = 400 / .048583 = 8233 LFM
5K RPM - 500CFM Velocity = 500 / .048583 = 10291 LFM
6K RPM - 600CFM Velocity = 600 / .048583 = 12349 LFM
7K RPM - 600CFM Velocity = 600 / .048583 = 12349 LFM
8K RPM - 600CFM Velocity = 600 / .048583 = 12349 LFM

Then let's say at greater than stock diameter 4 inches:

1K RPM - 100CFM Velocity = 100 / .08722 = 1146 LFM
2K RPM - 200CFM Velocity = 200 / .08722 = 2293 LFM
3K RPM - 300CFM Velocity = 300 / .08722 = 3439 LFM
4K RPM - 400CFM Velocity = 400 / .08722 = 4586 LFM
5K RPM - 500CFM Velocity = 500 / .08722 = 5732 LFM
6K RPM - 600CFM Velocity = 600 / .08722 = 6879 LFM
7K RPM - 700CFM Velocity = 700 / .08722 = 8025 LFM
8K RPM - 800CFM Velocity = 800 / .08722 = 9172 LFM

While seeing that at a given RPM the CFM doesnt change, note the difference in velocities. The PCM is programmed for stock MAF velocities, not the larger MAF velocites.

So you can see for example that when using the aftermarket maf at 7K RPM, the PCM will think its at about 4K RPM, and initially provide less fuel than needed. If the PCM was in closed loop mode (non-wot) The O2 sensors will pick this up as a lean condition, and the trims will be skewed to add to the base injector equation to provide more fuel and achieve 14.7:1 stocimetric ratio. Thus the ltrims will skew in a positive direction. Also if it was in PE mode (WOT), the same velocity descrepencies would hold true since it would be looking at MAF/RPM/TPS/IAT information.

There are other considerations, such as turbulance and laminar airflow, obstructions such as the screen, and so forth.



[Modified by kewlbrz, 4:43 PM 4/29/2002]

 

Ok now I'm really confused. I didn't think the computer adjusted based on feedback from the O2 sensors when in WOT....

 

Your right. I didnt mean to insinuate that. My syntax wasnt good on that. I have corrected it. :cheers:

 

Ok now what about those that claim to redirect airflow closer to the sensor?
Here is a quote pulled off of one

"Upgraded MAF Housing Ends includes directional airfoil. Directs all incoming charge towards the Maf electronics. The computer is able to calculate the exact amount of air coming in to give a perfect air fuel ration out the exhaust, eliminating any check engine trouble codes."

Now from my understanding the computer will basically update its tables and all is well, but at WOT it doesn't, so it is very important to get correct MAF readings. Are these accurate enough to not cause problems?
My question is how much R&D was put into these things, and are they THAT accurate even at WOT.

I want to put one on my car but I'm running N2O and have no Autotap so I'm real worried about going lean.

 

You don't actually believe advertising text do you?

I personally would not spray w/o doing some AFR analysis w/ WB 02 sensors. Something like AutoTap is an adequate measuring tool for doing your part throttle tuning but you really need better measuring tools (i.e. WB O2 sensors) if you really care about accurate WOT tuning.

 

Yes, the foils can help smooth the airflow across the wire elements, and eliminate turbulance and improper metering.

Your right, in that during WOT the PCM doesnt use any feedback from the O2's.

It looks at RPM, TPS, IAT, and the MAF. However if you were running lean before going to WOT, the PCM will add in some fuel for that when switching into PE mode.





[Modified by kewlbrz, 3:28 PM 4/29/2002]

 

This sure started a thread. I think there are too many people against it, or at least if you don't have an autotap and other tools to do fine tuning, its not worth the hassle it seems.

 

It's just that there are better tuning alternatives if it's not in fact a flow restriction. For the vast majority it's not.