EVOIII Airflow?

[WhiteCloud]

Great info here. Makes me want to go out and log mine

So for those of us running stock MAF and an AFC, we multiply the logged airflow by the correction factor, then add that to the logged airflow amount if it the correction factor is negative, or subtract if it is positive?

 

[spyderturbo007]

Actually, that won't work. The number seen on the logger already includes the correction factor. The calculation would be as follows:

Logged airflow / (1 - correction factor) = Actual airflow

For example:

Airflow on logger = 20 lbs/min
Correction factor at rpm where airflow reaches 20 lbs/min = -33%

Actual airflow = 20 lbs/min / (1 - 0.33) = 29.85 lbs/min

If you multiply by (correction factor + 1) you will get 26.6 lbs/min, which is 3.15 lbs/min low.

Enjoy!

 

[98spydert]

Just starting to tune again after a head swap and adding FP2 cams. I'm logging 31lbs/min (via DSMLink) at 14.9psi (via GM3bar). I'll be up to 24psi again in no time

 

[Kevin Jewer]

Maybe this was already said and I missed it, but any boost leak after the MAF/MAS will appear as a higher than actual airflow reading. The air that is escaping to the atmosphere has been measured. Two things happen, one is obviously that the ECU will inject too much fuel causing you to run richer than your target AFR, and that change will be proportional to airflow lost to the leak/total airflow. The other effect it has is that to maintain a given pressure on a given setup, the turbo will have to move more air, which will be taken care of by the closed loop boost control provided by the wastegate actuator.

I'm not sure what is meant by "the ecu wont know about the leak." I know that looking at the same data the ECU sees I can tell immediately if I have a boost leak. One sign is airflow being higher than it normally is. A more reliable way though is when WBO2 data goes richer than DSMlink calculated AFR. As soon as I see this I know I have a leak, since my WBO2 and DSMlink are always in perfect agreement.

Shape's 44 lbs/min was logged on a stock 2g MAS, which has always been very accurate in my experience. Any readings taken after a MAFT would be skewed, as has already been said. It was by attempting to calibrate the MAFt to the stock 2g MAS that I initially found the baro signal problem with the MAFt units. Don't trust any info from any sensor on your car until you have verified and validated it to the best of your knowledge and ability.

 

[98spydert]

That's what I was trying to get across, thanks Kevin. What's this baro signal problem? I haven't read about this. Is it taken care of when using DSMLink to "ignore baro/intake temp"?

 

[Kevin Jewer]

Some people were having trouble with the baro output from the MAFT, reading around 3.2 volts or 24" instead of 3.9 volts/30". The units tested fine on the bench IIRC, but in particular cars the voltage would be off leaning things out about 25%. There was a resitor that you could clip to fix the problem, that info is in other threads. There is a ton of info on how the problem was found in the DSMlink forums. It was a nice group effort. Selecting ingnore IAT/Baro does in fact fix the problem, and the values in dSMlink and what the MAFt is supposed to put out are almost identical.

At any rate, calibrating the MAFt to work like a stock sensor is a worthwhile venture. In my case all the knobs ended up on zero except the WOT knob at plus or minus 5%, I forget which, after fixing the baro issue. So it was pretty close. I did it with both sensors installed switching between the two, but you can also use boost or WBO2, or a combination of all 3. You can tune around any airflow discrepancies, but it's nice to have a trustworthy number that can be compared to other poeple's numbers.

 

[90AWDTalon]

Some people were having trouble with the baro output from the MAFT, reading around 3.2 volts or 24" instead of 3.9 volts/30". The units tested fine on the bench IIRC, but in particular cars the voltage would be off leaning things out about 25%.

I just logged the raw value of the barometer and got 205 which converts to 4.018 volts. Is this off enough to cause the high airflow readings I'm getting, or are there other things that can cause the calibration to be off? I'm logging 11.1:1 afr and the target afr at the grev and rpm I'm logging is 9.3:1. I'm just using an eprom, you guys are talking about dsmlink, I don't know if this compares between the two or not?

There was a resitor that you could clip to fix the problem, that info is in other threads.

I tried searching for this but I suck at search engines and couldn't find it. If you know how to find it with out too much trouble could you post a link?

 

[Kevin Jewer]

Thats only off by ~2.5%, shouldnt be enough to cause much of a problem. I just searched "baro" and by my username to find that thread. But you do not seem to be having the same problem, so I wouldnt recomend clipping that resistor.

 

[nanokpsi]

MAFT is zero'd out, I'm doing all the tunning with my eprom.

It doesn't matter. There is no way to insure it reads accurately unless you use dsmlink. 46lb/min is completely inaccurate at you boost level

 

[90AWDTalon]

It doesn't matter. There is no way to insure it reads accurately unless you use dsmlink. 46lb/min is completely inaccurate at you boost level

We already determined that a long time ago.

 

[90AWDTalon]

I think Monday I'm going to start trying to calibrate my GM maf. I was waiting until I went to the 1/8th mile drags again last night, ran a 7.51, and then I have autoX tomorrow, I didn't want to mess with the tune with those two events coming up.

Any ways, here's what I was thinking, you guys that have calibrated yours let me know if I have the right idea.

I'm going to start by making a +5% change to the global setting in the maft, and then reduce the injector compensation on my eprom by 5%. I will keep this up until my wideband o2 matches the target AFR for the airflow I'm at in my fuel map. After I get it calibrated I'll retune the eprom.

Does this sound right?

 

[rightaway]

any new numbers on pump gas?i'm stuck at 35 lb/min. would increased timing add any air flow?or should i just try to turn up the boost? i'm afraid to turn up the boost to much more with with just the greddy small fmic. and my coolant temp(213-216) are already way to high. going to try to make some ducting or something to help cool things down.

 

[truwarrior]

My EvoIII was flowing about 36.8 today. Intake temps....25 degrees

To bad I'm still knocking up top (6000+) and pulling 2 degrees of timing, I wonder if I replace my SBR bridge ported stock 2G O2 housing with a real O2 housing if that will help combat some of that.

A/F is in the 10.5:1 range. Stock timing.