MAF housing sizes with the 1.8t sensor

[CO AVANT]

so why would it matter how big you go in housing size if you are still using a 1.8t sensor? I was gonna do the VR6 MAF housing (3" O.D., 2.75" I.D.) but if I can go to an S4 MAF housing (3" I.D., 3.25" O.D.) then I won't have to put a silicone spacer in the inlet tube of the APR3+ TIP. The APR3+ TIP is 3.25" I.D... does the 1.8T sensor "see" the bigger housing size or does it still "max" itself out like using the stock housing?

[dougyfresh]

I don't think mine (1.8T sensor) is maxing out and it sits in a 3" housing. I think its 3" ID too. I'll check tonight. I'll have to dig up the logs (tonight).

[CO AVANT]

I don't think mine (1.8T sensor) is maxing out and it sits in a 3" housing. I think its 3" ID too. I'll check tonight. I'll have to dig up the logs (tonight).

been so long since I looked at my logs, but what does the 1.8 sensor max at, 240g/s??? What housing are you running Doug?

[dougyfresh]

I don't remember and don't have my logs with me here at work (thumb drive is at home).

I've got a custom ASP 3" billet housing. It is very similar to the one they manufacture for the S4 kits but has no taper. http://www.ecodetuning.com/shop/cart...t_detail&p=652

I also have an ITG air filter (Maxogen JC60/78) on the other end of the MAF
http://www.itgairfilters.com/airfilt...ection=maxogen

[CO AVANT]

that thing is nice as hell, but big $$$, holy shit.....just bought a B5S4 housing for $25...

[dougyfresh]

Its CNC machined out of a solid billet of aluminum. I've seen the raw stock and seen them machine 'em. Takes a while even with an optimized CNC program.

Here are some photos Chris took of his (same as mine):





As far as I know, at this point in time, its not for sale outside the GT28RS kit.

[AudiA4_20T]

Hey Jordan, I'm pretty sure as the diameter increases, the velocity on the sensor is less, so the readings are lower... If you think about blowing through a straw, the velocity is much greater then blowing through a paper towel roll

[CO AVANT]

I forgot the calculation to figure out maf diam vs. injector size, and the %'s that you can "get away with"... Anyone remember it?

[mtbrider]

I like that maf housing

[dirtybrd]

Hey Jordan, I'm pretty sure as the diameter increases, the velocity on the sensor is less, so the readings are lower... If you think about blowing through a straw, the velocity is much greater then blowing through a paper towel roll

You are correct about velocity, but the MAF doesn't measure velocity if measures flow. Reverse what you said about the straw. If you breath in as much air as you can thru it in one breath it will take a while, but a paper towel will flow the same amount of breath just in a shorter period of time. Get it. Both will only flow what is drawn thru them. With the larger MAF it will draw more air in thus increasing velocity with it. I might have contidicted myself.

[CO AVANT]

Anyone have a pic of their stock maf sensor? I was looking at mine and that little metal wire with a resistor on it that is on the outside of the sensor is not there on my 1.8t sensor but IS there on the VR6 sensor. Just want to know if the stock sensor has that wire w/resistor on the outside or not...??? there are connection nodes for it just like the vr6 sensor... don't see one in Doug's pic he posted...

[dirtybrd]

Thats the IAT sensor, it's built in on the VR6 MAFs.

[A4ringedONE8T]

Whatever increase (%) in MAF housing size needs to be increased in injector size as well (again %)

I still max out my 1.8T sensor (get a MAF upper limit exceeded stored fault, NO CEL though) but the readings are much lower (for power level) than what they were with the stock housing

[actlsub9]

You are correct about velocity, but the MAF doesn't measure velocity if measures flow. Reverse what you said about the straw. If you breath in as much air as you can thru it in one breath it will take a while, but a paper towel will flow the same amount of breath just in a shorter period of time. Get it. Both will only flow what is drawn thru them. With the larger MAF it will draw more air in thus increasing velocity with it. I might have contidicted myself.

IIRC the sensor can only measure velocity. It then uses a known diameter to calculate flow. If you use the same sensor but put it in a different diameter housing it will not be reading the correct flow. People then try to compensate for this by using a different size injector.

[dirtybrd]

I might be wrong, not sure. But if it measures less air and you'll adding fuel... sounds like it'll be pig rich. (calls, Diag, Oldguy?)

[actlsub9]

I might be wrong, not sure. But if it measures less air and you'll adding fuel... sounds like it'll be pig rich. (calls, Diag, Oldguy?)

If your have a consistent flow and you decide to use a larger housing then the MAF will be reading less flow then there really is. Therefore there is more air then the ECU thinks there is, and you use a larger injector so the ECU sends more fuel then it thinks it needs. More air and more fuel in proportion will mean the same A/F ratio.

[dirtybrd]

Got it. I don't run a MAF so I never really sat down and did the reasoning of why it works.

[old guy]

actlsub9 is correct. The MAF has a heated wire. The conductivity of the wire changes as heat is removed from the wire. The ECU measures the conductivity and alters the current as required to maintain the temperature setting. Based on the changes it calculates the amount of air passing through the MAF. If you increase the opening it will reduce the velocity for the same volume. The MAF will read it as a reduction in air flow and cut back on fuel. The calculations are based on a know flow rate for a predetermined orifice size.

[CO AVANT]

sweet, makes total sense. Thanks for the replies guys!!! That's what I thought it was, but was thinking different today after reading through the net... Side note: I am not even going to try with the S4 maf for now as I'm trying to reuse my stock air box. Just had to use a 3" hole saw to get the opening on the stock air box big enough to install. I noticed after doing this that there is not enough clearance between the vr6 maf housing and air box on one side. I had to dremel with a sanding bit and sand by hand to get enough material off the air box so I could get the vr6 maf to sit flush for screwing down in place. It's very thin plastic at that point so you need to be very careful while doing this so you don't puncture through. No way any bigger of MAF size could fit in the stock air box without REALLY cutting it up...

[A4ringedONE8T]

The stock airbox fits with the treadstone mani and 2871R or are you running something different now?

[dirtybrd]

He found an APR manifold.

[GTMRS4]

It has been a while,, but I have a 3" housing with 550cc injectors and the logs show it at 256g/s at 6300 RPMS

[A4ringedONE8T]

Stock MAF reads only up to 229 g/s so theres no way it could show more than that

[dougyfresh]

He found an APR manifold.

He's going to like that APR




Found my logs. Jordan if you want numbers instead of graphs let me know.

bone stock:


ASP GT28RS w/ 3" MAF housing (1.8T sensor) and 630cc injectors:

[dirtybrd]

He's going to like that APR

Yea, it is by far the nicest manifold out, that I'm aware of.

[A4ringedONE8T]

Too bad it sticks the turbo down next to the subframe! Top mount FTW!!

[dirtybrd]

Yeah, when you spend a grand on a turbo it's nice to see it. I really want that SPA top mount manifold.

[CO AVANT]

yeah but the apr3+ mani still sits the turbo further away than the treadstone. At least by looking at the pics and testpipe setups I've seen for the treadstone mani. Yeah I bought the APR3+ kit from Doug. Gonna be nice. Glad I will be able to reuse the stock air box. I didn't want the headache of buying all the parts and hardware to do the TIP and lines to the turbo. Also did not want to mess with a custom testpipe. after going through all this engine failure shit, I just want to get it back and install with ease... Doug, #'s would suit me much better.....can't stand graphs. Email them to me if it will be easier...

[GTMRS4]

Stock MAF reads only up to 229 g/s so theres no way it could show more than that

I don't know what to say my APR kit reads 256 g/s and I'm pretty sure they just change the housing. Here is an old post showing 254g/s at 6300

http://spreadsheets.google.com/pub?k...WfqwPG4ZckBkMA

[dougyfresh]

Doug, #'s would suit me much better.....can't stand graphs. Email them to me if it will be easier...

How did I guess?

Bone Stock:
http://spreadsheets.google.com/pub?k...zUGUYzC9o_BDGw

ASP GT28RS w/ 3" MAF housing (1.8T sensor) and 630cc injectors:
http://spreadsheets.google.com/pub?k...zUHsNveSjycUPA

Scroll to the right and you'll see a column for Mass Air Flow. Units are grams/sec

[CO AVANT]

what boost were you running on that 28rs log? maf readings seem way too low...

[986Jim]

You are correct about velocity, but the MAF doesn't measure velocity if measures flow. Reverse what you said about the straw. If you breath in as much air as you can thru it in one breath it will take a while, but a paper towel will flow the same amount of breath just in a shorter period of time. Get it. Both will only flow what is drawn thru them. With the larger MAF it will draw more air in thus increasing velocity with it. I might have contidicted myself.

Actually Velocity is exactly what it measures. Velocity and flow from the standpoint of a maf are the same, just a poor word for it really.

A hotwire maf has a heated element inside of it and it cools as air moves over, that is how the velocity and density of the air is measured.

The 1.8T Maf sensor measures velocity of the air, and density. Actual mass air flow is calculated in the ECU from this number and the ecu believes it has a stock sized housing.

If you're interested I found the calculations:

Velocity (M/)s * Area (M) = Volume/time = (Meters^3/Second)

By using a larger housing you decrease this velocity because the area is increased.

M^3/second = Velocity* Area

Area = PI*Radius^2, larger area = lower velocity at same flow.

The car will respond to the lower velocity by using a lower injector duty cycle as It thinks it's getting less air, so it needs less fuel. If the injectors open less that is less fuel going into the engine. You would need to match proportionally larger injectors to make up for this difference in velocity.

The ecu will have some adaptation and will to a point tune out using fuel trims to get an appropriate air fuel ratio, however if you increase the housing to 3" without an injector swap or ecu re-tune you will run lean. Lean conditions cause a lot of heat especially on a turbocharged car which can lead to "holeing" pistons and other pretty major problems.

Regards,

[dirtybrd]

Thanks, but I got it figured out earlier, I don't run a MAF so I never tried to figure out the reasoning behind how and why it works. Nice info though!

[dougyfresh]

what boost were you running on that 28rs log? maf readings seem way too low...

22psi

scroll all the way to the right and you'll see boost in psi

[Silence]

yeah but the apr3+ mani still sits the turbo further away than the treadstone. At least by looking at the pics and testpipe setups I've seen for the treadstone mani. Yeah I bought the APR3+ kit from Doug. Gonna be nice. Glad I will be able to reuse the stock air box. I didn't want the headache of buying all the parts and hardware to do the TIP and lines to the turbo. Also did not want to mess with a custom testpipe. after going through all this engine failure shit, I just want to get it back and install with ease... Doug, #'s would suit me much better.....can't stand graphs. Email them to me if it will be easier...

You talking bout Dgod? If so, wow, I remember selling that setup to him. Over the course of my BT ownership, which began 4 years ago, I had over 4 different setups. I even sourced the silicone inlet for that apr manifold. Haha. Those days were fun, although with the s4, the power is definitely more addicting.

[986Jim]

Thanks, but I got it figured out earlier, I don't run a MAF so I never tried to figure out the reasoning behind how and why it works. Nice info though!

I guess it's "for the record" in case anybody searches down the road.

[CO AVANT]

Thanks for the calcs, I forgot them and couldn't find them again.....till now

[dougyfresh]

The 1.8T Maf sensor measures velocity of the air, and density. Actual mass air flow is calculated in the ECU from this number and the ecu believes it has a stock sized housing.

You seem to know a bit about how the ECU operates. If I'm able to go in and tweak things (ie: custom tune) within the ECU can I change the fact that the ECU thinks it has the stock sized housing?

My gut feel is the answer is no.

[986Jim]

Problem is the ecu is not open in such a way that you can just program it yourself. You can't just go in and make changes.

Some cars have the ecu's cracked and companies make tuning systems for them (DSMLink, Hondata for example) but to my knowledge all the companies for VW/Audi keep the chip tuning secret and there is no user laptop tunable package out there.

In theory if you could tune the ecu yourself you could do that yes. All you would do is map the maf value with the stock maf housing then install the new housing, map it afterwards to see how much things have changes with all other variables being equal (say on a dyno) then tune the air/fuel, rpm, knock, egt so that it's back in the same vicinity as it used to be. It sounds easier than it really is.

I did a turbo-xs utec onto my dads Maxima with a vq35 swap in it and we ran a map and deleted the maf all together, but it was a lot of work and a lot of tuning, almost not worth it to be honest. My dad runs at the track same as I do, he's 60 and I'm 31 and we drag race in the same class haahah.

[dougyfresh]

That's what I was thinking. And thinking along the lines of what Mark@ASP could do for me with the tune we're working on. He has access to every map within the ECU.