Is the MAF the limit?

robnitro.
yes, aprox 1.3 bar, or 19 boost psi with vdo gauge. boost graph vs requested is spot on. malone stage 3.

nathan_b said:

robnitro.
yes, aprox 1.3 bar, or 19 boost psi with vdo gauge. boost graph vs requested is spot on. malone stage 3.

Click to expand...

And its 1250? What reading do you get at idle?
I'm perplexed... with an idle of 480mg/s and ideal condition, meaning no loss of VE, you should get 1104 ....

Figure this simple exercise. The cylinder at idle has very little exhaust gas left- super lean. It usually takes up 480 mg/stroke at idle, right?
If we do 2.3x the pressure (1.3 bar boost), keep the same ideal conditions (same low exhaust pressure like at idle- with minimal exhaust left and no heating of the boosted air = which would Decrease density), that would be 2.3 x 480= 1104 mg/stroke.

Sorry Jason, but no amount of porting or valves can change that. Idle is a point of highest volumetric efficiency because the ports/valves are not getting much airflow, and there is much more time for the air to flow in.

So, I don't think you are lying, it's just curious why this is happening.

no amount of calculations can predict things to a tee in a running engine. There are too many factors involved... If you could, you would be able to put EVERY tuner out of business by tuning everyone's car perfectly on the first flash.. Every car.. Every time..

Did you miss the part about the MAF not being a precisely accurate flow meter?

robnitro said:

And its 1250? What reading do you get at idle?
I'm perplexed... with an idle of 480mg/s and ideal condition, meaning no loss of VE, you should get 1104 ....

Figure this simple exercise. The cylinder at idle has very little exhaust gas left- super lean. It usually takes up 480 mg/stroke at idle, right?
If we do 2.3x the pressure (1.3 bar boost), keep the same ideal conditions (same low exhaust pressure like at idle- with minimal exhaust left and no heating of the boosted air = which would Decrease density), that would be 2.3 x 480= 1104 mg/stroke.

Sorry Jason, but no amount of porting or valves can change that. Idle is a point of highest volumetric efficiency because the ports/valves are not getting much airflow, and there is much more time for the air to flow in.

So, I don't think you are lying, it's just curious why this is happening.

Click to expand...

480mg/stroke at idle : (

dont know what to tell you.

My MAF is 3 months old with Bosch updated MAF, and full oem intake, mann cold weather intake. Still has a CAT.

Yeah...its weird...
Is that another reason why people switch to map based limiters?
I tried to see if I can do it but no luck so far. It looks straightforward on pd maps, but I cant find it on rotary damos files.

So I borrowed a friend's TDI C MAF to compare everything stock to my descreened one.
Looks like the descreening cuts the reading by 10% or so at higher rpm... that makes me wonder if it is a good way to make a maf that is saturated (like at 29 psi gauge or so) become unsaturated.

Very cool info, thanks for clearing that up robnitro

Do you intentionally have your tune set so boost/airflow drop off as you rev up?

Yes, its following the VNT17 compressor map.. I did the calculations and posted them on the "help me understand my tune" thread".
I wasn't happy with what mixed opinions people had- some said drop boost past 4k to 20 psi, some said 22, so I did the calculations.

If you check the calculations, you see that mass flow goes up, even though boost goes down... that's why HP gets flat after like 2500 on VNT17 and VNT15. My friend had an evo with cam, tune, and stock turbo. He had the stock turbo drop off boost past a point. He put down 358 hp/ 403 ft lbs, with flat HP from 3k on. On a meetup of STi vs EVOs he was beating even 400-450 hp evos and STi's on the strip, lol. They had 400-450 hp but it was in a really narrow range compared to his.

VNT17 can do 25-26 psi only in a small range, past that the turbine spins too fast, Boom LOL

I keep forgetting how small of a turbo you have LOL.. Makes sense given the compressor map..

Bhodgkiss, I recently found that the smoke map only can use values up to 1000 mg/s.

"Ok, the smoke map is listened to. BUT the ecu only does values up to 1000 mg/s lol. Need to find out if this can by bypassed... Even this latest map I did 4 last values,
900--1050--1150--1151,
40.6--47.2---51----52 In testing I always maxed out at 45, even when maf was reading 1275! 45 turns out to be where 1000mg/s is.. Same thing happened before, but the values were different. From memory the last 3 values were: 850--950--1150
37----40----52 And I was getting around 42 max, which surprise, is what 1000mg/s calcs to on that map. So 1000mg/s limit to the smoke map- doh!"

Thanks for the info.
So what can we do about it?? Loads of people must have had this issue....
Must be an easy answer???

Yeah, use the other limiters to limit fuel where the MAF can't..

no we're saying the MAF IS the limiter.....
I'm not saying I have too much fuel at high rpm, I dont have enough as the MAF maxes out at 1000mg/str in the MAF smoke limiter map. So I need to adjust this or i'll never get more fuel in.
This must be a common issue with all VE engines when boost is raised 0,5bar or more over stock?

so you set the smoke map up for max fuel at 1000mg.. problem solved..

but then as I have 1000mg/str+ of air from 2000rpm upwards, The MAF is maxed out for the entire upper rev range and whatever value of fuel is in the 1000mg/str column stays as the limit from then upwards.

So are you saying that I need to set the MAF based smoke limiter to something silly like 100mg/str fuel from 950mg/str air upwards, so that this doesnt limit the fuel and I just run off the torque limiter or driver wish instead? This should work, as the boost will have built up by then anyway so it shouldn't be hard to run a decent AFR ratio from the torque limiter and boost map?? So I wont get smoke as the MAF limiter is more for the transient response when boost is building anyway?

so then I effectively have a MAF based tune up to 1000mg/str air (decent boost) then MAP based tune above that (as I'm then just running off boost and mapping via the driver wish/torque limiter to target a decent AFR (18:1 for example) from 1000mg/str upwards.) This then still takes into account atmospheric changes via the torque limiter, so should work well in all conditions; on both hot and cold days, and at altitude. Better than a MAP based tune??

ya pretty much.. Just set the last column (950 or 1000) to 51mg since that's the highest it'll go unless you messed with the calibration..

If for some reason you're overfueling in the 2200-2400rpm range, just cut back a little on the torque limiter. It's not perfect but it'll get the job done.. You can also just use a bigger MAF housing and leave the calibration of the MAF alone and it'll report lower than actual airflow which will make it take longer to max out the MAF.. Then use your smoke limiter as you normally would...

Ok thanks
I'm requesting 60mg from driver wish and limiters are limiting to 59mg so I dont think 51mg will be enough I'll set it to 70mg so its not a limiter
(I have R520's so whatever '60mg' means with these )

Hmm, so how would one do the MAP smoke limiter? I thought it was based on a switch- one value uses MAF table, another uses MAP table.

Is that possible to run both maps? Is that why the MAP limiter is filled in with high numbers, so that it is ignored?

Also, how would we set up the MAP temperature correction map.
Let's say I am doing 2650mbar, for normal 30C density of whatever.
What would I put for the 70C column, a higher number?!?
Lower columns can run lower numbers, same air for less boost... but the higher is where I get confused... and how it ties into the IQ by MAP.

Does anyone have an example?

bhodgkiss said:

Ok thanks
I'm requesting 60mg from driver wish and limiters are limiting to 59mg so I dont think 51mg will be enough I'll set it to 70mg so its not a limiter
(I have R520's so whatever '60mg' means with these )

Click to expand...

The most the pump will report back is 51mg, so anything over that should work fine..

Sent from my DROIDX using Tapatalk 2

Ok, scoured the A4 damos in winols and found the 2 switches that turn into MAP based smoke limiter. I also found the boost correction temperature map settings... it tells the smokemap by MAP when the air is "less" due to heat or more due to cold. Those numbers you see below explain it.

Manual MAF to MAP smoke limiter
Maf setting
05AD60: 03 0C 00 00 00 01 01 00 01 01 01 00 00 00 01 01
Map setting
05AD60: 03 0C 00 00 00 01 01 00 01 01 01 01 01 00 01 01

Your address may vary.
In Vagedcsuite, open your file, Click view file in hex. Click search, click hex. Type in 01 01 00 01 01 01 00 00. You will find it 3 times (manual, auto, auto). Those last two 00's should be changed to 01 01 if you want to do MAP based smoke limiter. Do it for all 3 to be sure, unless you know exactly the offset of your maps.
Hit save on top, hit verify checksum on top of vagedcsuite.
Then edit the smoke limiter by MAP:
Manual IQ by map (VAGsuite shows it in the unknown maps.
Example, smoke map manual is address 5c9ec (279372 in decimal mode)- this is at 5cd50 (380240 in decimal) for my ECU. You will see that it is filled in with 5000 or 5500, its IQx1000 for the values... and the top is pressure, side is rpm. You can change those values.

Also the boost correction by temperature should be adjusted if you want IAT to regulate fueling (hotter air is less dense!).
You can copy my map, I got the values from a PD that used map limiter- it calculates correctly (I double checked the values with an online calc), and they use 50C as a center point. Make sure you change the temperature axis and pressure first, hit save, read, before putting in these values!

Here's my maps... it's set for around 16.5-17.5 afr, but 51 mg on my tune turns out to be more like 75 or so... so its around 1.4-1.5 x off... if you are running different nozzles, you should tune it for WOT smokefree, then scale back the other values- maybe a little less iq if you want more afr for lower end (economy).

In maf logging, I saw that with a proper functioning maf, MAF (mg/s)= 480 x (abs boost in bar). In higher rpm it drops, because its harder to push air in. If you run a less restrictive turbo, it might hold 480mg/s per bar higher up.

I think your maf readings drop up high because you're following the compressor map which pretty much requires boost (and airflow) to fall at high rpm.. I didn't see falling MAF readings when I had the 17/22, and definitely not with the 2260.. If either one of them fell off, they never reported less than 1275 up high..


I wonder if the launch control would work better with a MAP based limiter..

It's not that, I know that would drop it to 1100 or so.
It's where you do real maf divided by absBAR, to get what the cyl is filling compared to "idle". Example, at 2 bar 2500 rpm, get 980 mg/s maf reading.... so 900/2 = 490 (1 bar reading) If you go to higher rpm, same boost, 2 bar at 5000 rpm, maf would be like 900 let's say. 900/2 = 450 . Because of the harder time to push in air, and more backpressure, the "VE" is lower.

Sort of a simple way to calculate VE, run the car hard to redline, and see MAF vs Boost.

If you want, log up to redline group 03 and 11. I'm curious what your monster does... maybe we can catch a real MAF saturation (which I thought I had, but I don't).

I don't think launch control cares about map or maf. The best launch control is a smooth one, so like you do 58, then 14, then 4, then 0. When it doesnt bounce around, it doesn't smoke- and can hold boost. You can't get more fuel into the engine anyway, then it would rev up more, and so on LOL. The bouncy limiter killed my boost, because it kept changing the n75.
Check group 11 when you do launch control... the n75 is like 20%.... and req is like 2650 (for me). I get about 10 psi @ 2600, but that's cause I like my actuator set conservative.

I'll try to get a good log today.. I have to wait until it stops raining though.. 3rd will have traction problems and I don't think I can get away with running 4th out to 6000rpm.. 4th might even spin in the rain LOL..

I use the brake... in 2nd lol...
Fake brake dyno lol.
Looking forward to see what you get w your setup.
Do you have a newer style version C maf w that smaller screen in front of the element?

my MAF is a piece of 3" diameter exhaust pipe with the sensor element in the middle.. stock calibration..

I don't trust my axle shafts enough to do the fake brake dyno in 2nd LOL.. I'll try going up the hill by my house, it'll put a good heavy load on it, but it's raining pretty good here at the moment..

ok.. I tried loading a less powerful tune on so I could run out 3rd gear.. The issue I'm having is that as soon as the rpm reading on vcds hits 5355, I lose communication.. Every. Single.. Time.. Now that I think about it, it has always done that while trying to log data regardless of car or tune (my 99.5 did it as well).. If I go to the instrument cluster, it keeps communication while logging up to 6000.. it displays up to 6000 too where the engine controller will only output 5355..


Anyhow.. up to about 5000rpm it stays pegged at 1275, then tapers down to 1250 at 5300 as it loses communication.. This was with a 24psi tune and 36mg torque limiter from 3000 up to fuel cut.. I was surprised at just how strong and smooth it runs with this setup.. smoke free, EGT never tops 1400F LOL.. I'll probably use that tune for road trips and heavy towing..

Weird... id think with the bigger housing readings would be much lower...
Maybe the calibration is hosed up
You regulate by torque limiter?

with the stock housing it'll stay pegged at 1275 pretty much anytime the boost gauge is over 17psi, so it's definitely lower.. I have a V8 S4 maf housing that I want to try.. it's about 3.75"ID.. That should let me regulate throughout the entire range of airflow without hitting the end of the MAF.


I've been regulating max fuel with the torque limiter.. It makes it easier for me to tune the smoke map, and it's easier on my tires LOL.. I'm not good with the calculations so I use the rear view mirror and my EGT gauge.. I started with only 20mg max and increased boost until the smoke cleared through that range, then upped it to 30mg etc.. I'm working on the full throttle stuff now but traction is really limited with the wet roads and 100+mph isn't very safe in the rain to say the least.. Oh, and my turbo is starting to make some funky noises.. It's been slowly failing for a while so maybe now it's just giving up the ghost..