lastray

A lot of folks been asking about this subject, and I can tell you first hand that I removed them on my 85 stock vette. Runs great, no perforomance problems at all. However I live in vegas where you have to pass a little thing called emissions. Ahh, thats when I found out the hard way that it wont pass smog without the screens in. without the screens the maf sensor doesnt read correctly and makes the car run lean. then the o2 sensor picks up on this and cant determine what to do about it. On a scanner it shows the 02 sensor fluctuating up and down from lean to rich. My point in short is if you live where there isnt any emissions your good to go. but if you do. dont do it. it wont pass. I tried running some guaranteed to pass juice threw it, still no go. It passed with no problems before i took them out. Lesson learned.

cv67

prior owner to one I owned did that (I had no idea at the time)
"thought it ran great" ; snappy responsive etc. but was lean the whole time esp at WOT eventually took the head gasket out.
Some things are just best to leave alone

Cliff Harris

The ECM uses tables to match the injector pulse width to the air flow rate. The tables will be off if you remove the MAF screens because the flow rate changes. Basically the MAF reports the wrong air flow rate. That affects the air/fuel ratio and emissions.

JrRifleCoach

Years ago there was a great debate over screen removal.
Problems stemming from screens and mixture signals were never mentioned. There were a few who experienced wire damage from debris that got past the filter. (I don't know and it really doesn't matter) So my mod choice was to remove the rear screen only.

Can't say it made a change. But it didn't hurt any inspections.

AGENT 86

The screens are there to help produce a better laminar flow, which is what is needed to get the best reading from the sensor.
They are not there to protect the sensor.
If anyone has the urge to remove them, this thread is another reason not to.

Muffin

What he said.

Aardwolf

Max power is more important than MPG on mine. The MAF is the smallest part now, I need to make a bigger housing. Removing the rear screen sounds good for a street car that isn't power limited by MAF size flow.

GREGGPENN

Plus, recently I've found a TGO post claiming our stock air boxes are a bigger restriction than (even) a screened MAF. Though stating you can bump flow quite a bit w/o screens, I haven't seen if/how you can get the stock air box near the (unscreened) 700cfm range.....at least not w/o exposure to water/road debris.

And, they don't see to make a CAI for MAF anymore.

pcolt94

And with all the other posts also. Right on tatget.

What more needs to be said.

JrRifleCoach

A good tune will rest the tables.

gunnerjuju

is the power gain from this mod really worth the trouble?

GREGGPENN

On a stock motor, there isn't any noticable power gain. Tables are used during open loop (warm-up) phase only -- so how does this matter?. Unless someone has proven the lack of laminar flow throws the tables off SO far that compensation is unattainable, I'm hesitant to believe the OP's conclusion. Are people required to test during open loop? (If so...then maybe.)

Mine is descreened (for a 383). But now it seems worthless unless I do something MAJOR to the stock airbox. I can't believe the numbers I've seen for the stock air box in comparison. Seems pretty fruitless to modify screens on a MAF after seeing this...
http://www.thirdgen.org/techboard/tp...including.html


It's not even clear if/how much a cut-lid can help. The improvement with K&N looks totally worthless as well. (Glad I never bought into that $70 overpriced snake-oil.)

Aardwolf

As I got toward 400 RWHP I modified a C5 intake, the tubing is much larger with less turns for the air to travel through as well. I run mine in open loop full time, because of the pulse width cap.

bjankuski

I doubt this is the problem, the O2 voltage is designed to switch from rich to lean as it runs, that is how it works. The voltage swings above and below 450mv to trim the fuel mixture. When the reading is above 450mv it says it is rich, and below 450mv it says it is lean. What are the block learns at? This is how you determine if you are out of correction. If the block learns are at 108 or 160 it is out of correction. Tell us what failed on the emision test and what your fuel trims are at?

GREGGPENN

Do you really NEED open loop all the time? Wouldn't PE mode (and it's auto jump into open loop) cover the cap issue?

This is what I was eluding to when I said: "Unless someone has proven the lack of laminar flow throws the tables off SO far that compensation is unattainable, I'm hesitant to believe the OP's conclusion."

Even though the ODB1 ECM's are considered "slow", samples are taken often enough that it should still be able to maintain an AFR. What the MAF doesn't "figure out", the O2 sensor is there to provide/refine measurements. IOW, if the MAF isn't "seeing" all the air, the O2 sensor will still see it.

Unless counts are at their limit, that's probably not the cause. I have to wonder if you were "on the edge" of allowable BLM's before the descreening.

Have you tried other fuels? Did you replace your O2 recently? How did it read last time? (Was it already on the lean side?) Could this be attributed to EGR? IOW, was it NOx that was too high?

blackozvet

After seeing those figures a while ago I descreened my MAF and made this cold air set up, using 3" internal silicone, I figure it must flow at least what a 3" internal MAF flows, my engine revs well to 5500 so it must work.

Cliff Harris

One other thing to watch out for is maxing out the MAF output. It can only report up to 255 gm/sec. If your mods result in more flow than that then you're giving your ECM false information. You'll go lean at WOT -- not a good time for that.

The "magic" number 255 is a built-in limitation of the microprocessor. It's an 8 bit processor and the biggest number it can handle is binary 1111 1111 = 255. There are no tuning mods that can get around that.

GREGGPENN

Unless I misunderstand your point, PE percentages can provide the extra fuel you might need and would be measured by wideband on a dyno. Kind of getting out of the scope of an OEM-config screen removal posted by the OP though.

TequilaBoy posted some good stuff on this about 2yrs ago. I reconsolidated it into another thread in an attempt to provide clarity....
http://forums.corvetteforum.com/c4-t...maf-units.html

Midnight 85

Thanks for posting this picture, I am trying to figure out a different intake for my car now that I have the 80mm throttle body I want to be sure it is not starving for air. Where did you get the 3"silicone?

GREGGPENN

And, did you have to heat/bend the elbow? I wonder if it could ever collapse?

(And, should we ask if you noticed any difference vs. the stock air box?)