MAF housing sizes and timing pull..

I though its time for a bit more technical discussion and some views from experts on the actual effects aftermarket intakes
might or DO have on the way the ECU "adapts" aftermarket software, based on its readings.

The idea is that most of the aftermarket intakes "try" to maintain an OEM MAF housing size to keep the readings as
OEM as possible, so as to assure the ECU responds well to what the performance software is asking of it.

The fact is though that even though people might not understand it, and there hasn't been any talk about it, MAF readings effect the cars performance A LOT.
One recent example is STAULKOR's who was literary tortured by -12 timing pull, without being able to find out what exactly was causing this issue.But a timing pull of that magnitude sure isn't the rule, but rather the exception.Does that mean that if you don't have -12 your car is running fine ?Well yes and no.Timing pull even in the area of -4,-6 or more might also be bad, from the point of view of power loss.Your car might not actually need to cut that much timing, but its trying to adapt to what its reading.

Differences in MAF sizes from OEM can also be monitored through the fuel trims, with the Long term trim being the most important in this case.A highly positive fuel trim might show deviations from what the ECU is expecting to see, and from my knowledge and experience, a simple increase in LTFT should be considered an increase in air flow IF it actually zeros down after the car adapts to the new intake.But a constant LTFT that just refuses to zero, possible means there is a problem.

Now most of the aftermarket intakes claim to have a MAF housing that approaches OEM dimensions, but i haven't found that to be true AT ALL.Most of the intakes run a 2.75'' or 3'' MAF housing that is in reality MUCH MUCH larger than stock.With the OEM housing being oval shaped, i did a few measurements , and figured out that for a round intake tube to have actual OEM dimensions, it should be in the 2.55'' (65mm) diameter area.That actually means OEM MAF dimensions (in a circular intake) correspond to

Circumference of :204.2
Area of:3.318

Now in an intake with a MAF housing of 70mm (2.75'') the following is true:

Circumference of :219.91
Area of :3.848

And with 76mm (3'') :

Circumference of :238.76
Area of: 4.536 !!

So in the first case there is an increase of about ~8% and in the second an increase of ~17% !!!

Now some have claimed the ECU can adapt to small changes in the measurements, but somehow i don't see 8% and 17% as being that subtle....

As for what effect these changes have on the cars performance ??Possible "theories" will be presented in the my second post sometime later...

Feel free to discuss...

Keep in mind its not only MAF size, its sensor location.

On the stock housing, the maf sits below center of the housing. In most round aftermarket housings the maf sits nearly centered. This will effect the amount of air read, which in turn will effect load, which in turn will effect everything else.....

Ever since I put my evoms intake on with BSH DV kit ive noticed my LTFT has been as high as 18%.. Ive ever throw codes in the last 2 months for running lean on bank 1.

According to others who have had the same problem they believe its the elbow that connects the intake to the noisepipe. A few people have switched from evoms to the BSH intake and their LTFT has been reduced to 0%...

pxturbo said:

Keep in mind its not only MAF size, its sensor location.

On the stock housing, the maf sits below center of the housing. In most round aftermarket housings the maf sits nearly centered. This will effect the amount of air read, which in turn will effect load, which in turn will effect everything else.....

Click to expand...

Thats quite right.I was going to mention the above in my second post (too tired to right much more now).

Many people (and i'm gonna say tuning companies also),don't realize the multitude of intakes may not actually go all that well with each and every intake.Of course it would be impossible to write code for every intake out there, but offset readings screw up what the ECU sees, and in turn what it reads from the tables.

I have to say before doing all this research, i was pretty pleased with my intake, but now i'm beginning to see, i might even be missing on some extra power and drivability.

What is really weird for me is WHY hasn't any company tried making an OVAL maf section with for example round endings (to have it connected to aftermarket intakes or DIY's.I'm pretty confident its a cost/profit thing, since a simply round pipe costs next to nothing, but a well measured oval one would have to be custom made, which means mucho dinero....

DanSan said:

Ever since I put my evoms intake on with BSH DV kit ive noticed my LTFT has been as high as 18%.. Ive ever throw codes in the last 2 months for running lean on bank 1.

According to others who have had the same problem they believe its the elbow that connects the intake to the noisepipe. A few people have switched from evoms to the BSH intake and their LTFT has been reduced to 0%...

Click to expand...

Yes this is what i mean.But you are simply refering toa turbulence issue, when in fact its not as simple as that.
Readings can be offset by turbulence yes.But the whole point of my post was to try and "correct" the timing pull and LTFT that just GOES UNNOTICED, and plainly shouldn't be there.Why miss out on a couple (or more?) horses, just cause of a few mm ?? (its really that small...)

Your calculations are a bit off. You are using OD (outside diameter for those who dont know). You must use ID (inside diameter) to take the wall thickness into consideration.

I just measured the oval on the stock intake and it's ID is 3.100"x2.100" and has a cross section ID area of 5.113in^2.

Compare that to my Neuspeed intake which has an OD of 2.80" (.05" taken up by the powder coating) and an ID of 2.62" with a cross section ID area of 5.39in^2.

There is only a 5.1% difference in area between OEM and Neuspeed. Yes, its almost as much as your 8%, but still 5.1% is 36.25% smaller than 8%.

But I digress...torture numbers and they will confess to anything.

My point is 2.75OD/2.62ID aluminum pipe is readily available and fairly inexpensive and has only a 5% deviation from stock. This 5% deviation is negligible and easily correctable and serves no real threat. If one wanted to have perfect intake pipe, it would be custom made and very expensive.

The real threat of intakes is 3" OD pipe, MAF placement, and turbulence.

--------------

And as for timing pull, it is related to the inaccurate MAF reading. The MAF only sees <----> this much air, but really there is <-------------> this much air. So it gives enough fuel for the air it sees. The problem with this is that the ECM didnt give anywhere near the correct amount of fuel for what is really there...It only knows what it's sensors report back. So it compensates for it by increasing the long term fuel trim (LTFT) to add more fuel. Eventually it cant compensate anymore (maxes out at or around 25% LTFT) and throws a CEL.

During all of this, the burns in each cylinder are not good. They are too lean and therefore too hot because the ECM simply doesnt see the actual quantity of air. The ECM compensates the high temps by pulling timing so there will not be detonation.

Fix the MAF reading, and ALL the problems go away. Its as simple as that.

This is what happened to me, loudog, and a few other people. DanSan, I think this is what is happening to you.

We spent 9 months chasing this bastard down and we nailed it on the head.

BSH DV Re-route VS. BSH Intake VS. Stock
BSH DV-Re-route on left... (14% LTFT, 30g/s lower MAF Readings, Timing Pull > -8*)




BSH DV Re-route

BSH Intake

itsagoodname, i know we talked about this before. you think it was just the elbow that was causing problems or the entire intake because of the MAF? im sick of throwing codes for being lean and its fucking killing my gas mileage. i drive the car and i can watch my gas needle move towards empty.

DanSan said:

itsagoodname, i know we talked about this before. you think it was just the elbow that was causing problems or the entire intake because of the MAF? im sick of throwing codes for being lean and its fucking killing my gas mileage. i drive the car and i can watch my gas needle move towards empty.

Click to expand...

Not sure, but i will soon find out. I have my elbow boxed up and its going back to Phil. I'll be getting a new 'good' elbow that i will test.

Obviously its something to do with the elbow because with the new BSH Intake my LTFT's are around -3%, im getting around 25-30g/s higher maf readings, and i have a bit less timing pull however the timing pull is STILL there. I may have issues on top of the intake but the intake was causing a BIG dead spot where it felt like the car hit a brick wall and didnt want to pull any harder.

Im telling you guys its MAF placement in the elbow AND turbulence.

I did some testing a while back when I found out the elbow was causing issues.

BSH Elbow + neuspeed intake = 25% fuel trims
Neuspeed intake (using coupler since it was cut in half) = 12% fuel trims
Full BSH Intake = 0.2% fuel trims

Even with the BSH elbow removed and the neuspeed intake installed (by itself doesnt cause any issues) I still had 12% LTFT. This is explained by the turbulence caused by the coupler.

DanSan, talk to Phil and get a full BSH intake and your problems will be fixed. More and more people are being found that have had the same issues as I did.

staulkor said:

Im telling you guys its MAF placement in the elbow AND turbulence.

I did some testing a while back when I found out the elbow was causing issues.

BSH Elbow + neuspeed intake = 25% fuel trims
Neuspeed intake (using coupler since it was cut in half) = 12% fuel trims
Full BSH Intake = 0.2% fuel trims

Even with the BSH elbow removed and the neuspeed intake installed (by itself doesnt cause any issues) I still had 12% LTFT. This is explained by the turbulence caused by the coupler.

DanSan, talk to Phil and get a full BSH intake and your problems will be fixed. More and more people are being found that have had the same issues as I did.

Click to expand...

Ok thanks guys.. I was trying to see what would be the most cost effecient which would just be getting a new elbow. but if the only way to fix this stupid ass issue would be grab a BSH intake ill do it i guess. may take a little bit to get the $$ but i guess ill have to

staulkor said:

Your calculations are a bit off. You are using OD (outside diameter for those who dont know). You must use ID (inside diameter) to take the wall thickness into consideration.

I just measured the oval on the stock intake and it's ID is 3.100"x2.100" and has a cross section ID area of 5.113in^2.

Compare that to my Neuspeed intake which has an OD of 2.80" (.05" taken up by the powder coating) and an ID of 2.62" with a cross section ID area of 5.39in^2.

There is only a 5.1% difference in area between OEM and Neuspeed. Yes, its almost as much as your 8%, but still 5.1% is 36.25% smaller than 8%.

But I digress...torture numbers and they will confess to anything.

My point is 2.75OD/2.62ID aluminum pipe is readily available and fairly inexpensive and has only a 5% deviation from stock. This 5% deviation is easily correctable and serves no real threat.

The real threat of intakes is 3" OD pipe, MAF placement, and turbulence.

Click to expand...

Actually i'm not using OD as you say.I used the actual screener part of the OEM housing, and even measured the inside part of that!!The numbers are used as not exact to the point of mm, and where meant to give the bigger picture.But since you wanna go into details:

The oval shape of the OEM MAF (measured at the inside of the screener) has a Major axis of 78mm and a Minor axis of 53mm approximately.Now i don't know how you got your numbers, but by using an ellipse calculator (my previous numbers came from using a circle calculator and a diameter of roughly 65mm)

http://www.1728.com/ellipse.htm

this gives you:

Circumference : 211.27
Area: 3298.66

Now talking into account the coating as you say, i'm willing to lower the circular diameter to 68mm from 70mm.These values and by using a circle calculator

http://www.csgnetwork.com/circlecalc.html

gives us

Circumference: 213.62
but an

Area of : 3631.68

That seems now to be a 10% difference (do correct me if i'm wrong, i'm just using the calculators, maybe they don't work right..)

As for the ECU corrections, yes they do work, thats why you see the difference in fuel trims.It's adjusting the FUEL
But there is no adaptation that can change from what tables the ECU reads as far as incoming air amount is concerned.And that may well take part in more than the fueling (timing for example.).I hope you understand what that means.

Subscribed!!!

I have a 3 inch ATP maf housing which tapers inside. The maf sits pretty much dead on center.

So what intakes are having this issue. Is it just the EVOMS, and if so is it the old style intake or the new style?

I am gonna go vag-com tomorrow and see how mine is running.

I used calipers to measure the major and minor axises of the ellipse along with the neuspeed intake. The only reason I said the coating explains the extra 0.05" because I know that pipe is readily available in 2.75" OD and there are tolerances involved so it wont be exactly that, but give or take. That and powder coating is quite thick.

To find area of an ellipse, you just do pi*(major/2)*(minor/2).

I said you are using OD because you said assuming 3" (76mm) pipe, you calculated the circumference to be 238.76.....76*pi = 238.76. Typical 3" pipe is only 3" OD and has a slightly less ID.

Hell, I totally forgot to calculate the circumference of the ellipse of the stock intake.

I used this calculator (http://www.csgnetwork.com/circumellipse.html) and the circumference of the stock intake is 8.3". The circumference of the neuspeed intake ID is 8.23". So there is a 0.84% deviation...completely negligible.

Again, I am sure most companies have taken this into consideration when designing intake systems. This just shows that 2.62" ID is the best to match OEM.

Now all you have to consider is fluid dynamics, but I dont know a damn thing about that. Ill leave that to the physicists :bellyroll: