Data logging MAF settings with Cobb AccessPort

Denny McLain

As usual, I'm a bit lost.

Someone pointed out the Cobb MAF air flow output goes flat right around 6200 rpm with right around 269 grams per second and stays there till 8000 rpm. Did a bit of logging today and that is consistent on every log I have including ones today. My question is does anyone think there is some type of flow restrictor or do you think it's the software? Even with a flow constrictor, my thinking is the GPS should increase, just not as much as w/o one. Anyone have a Grams per second/ Cubic feet per minute conversion?

Also, the thing is pulling out timing with 185 degree water temps, 90 degree air intake temps and 190 degree oil temps. Why it's doing this is still a mystery to me but my current train of thought obviously is that with the temps listed it has nothing to do with any of them.

Hi-TecDesigns

Gram is a measure of weight and cubic foot is a measure of volume... tough to do a conversion between the two.

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Denny McLain

Understand they are apples and oranges, but in this case they are the same thing as they measure airflow. I'll do a bit of homework myself but unfortunately at this point it may be a moot point. Don't believe the readings are accurate as things just don't add up coming straight out of the book of common sense.

Actual CFM
Is the flow rate of fresh air into the engine measured in cubic feet per minute (CFM). This is measured at the entrance of the air cleaner or if no air cleaner is present, the throttle body(s).

Actual CFM should correlate closely to actual dyno measurements. For example, a small block Chevy making about 334 hp @ 5500 rpm (close to what our engines are suppose to make) dropping to 320 hp at 6000 rpm using Performance Trends Race software computations will flow the following:

Rpm 2000 2500 3000 3500 4000 4500 5000 5500 6000
CFM 171 220 273 330 394 459 521 578 612
HP 118 154 188 225 263 298 322 334 319

This is pretty hardcore science which the MAF readings I'm getting do not match. Even if the hp drops some, the cfm will increase with rpm unless it's a drastic drop in hp. As mentioned from 6200 and up.....zero change in grams per second when logged.

So far I'm basically getting nothing but grief trying to figure things out as what I've learned over literally decades of doing this is going out with the baby and the bath water.

Throwing a set of 4.08 gears in the car and leaving the AccessPort in the drawer until something changes. My intentions were to throw a set of 305x30 tires on the back, lightened the car by about 100 lbs and use a few drag strip tricks in cool weather to get the car in the 12's. Putting everything on hold untill something changes as I realy do not like not being able to control things.

t-ray

When I converted to CFM, I borrowed the equation as defined in a thread on another forum. Thread is here: Grams per second-cfm?IAM of 15? - NASIOC

I understand as well that it is apples/oranges, but it's the best I could come up with.

Have you been able to determine if the value being logged for MAF is just one of the MAF's, or some kind of aggregate of the two MAF's?

Denny McLain

No, not at all if the Grams per Second reading is just one or both.

There is MAF GPS, MAF B1 volts and MAF B2 volts. I'll do the GPS/CFM conversation and play with it a bit as it should be at least ballpark. There is too much legit automotive science out there that tells you what an engine needs regarding cfm to make a certain amount of power so it might be easier than I think.

But at 6200 rpm where the Grams Per Second levels off, the volts keeps climbing on both B1 and B2. Making a pretty safe guess it's left and right MAF and at 6200 rpm the output is about 4.0 volts each. At 7900 rpm the output (they vary slightly) it is about 4.30 volts which makes more sense to me as the voltage does continue to increase.

It's got to be a bug in the logging program is what comes to me right now. One of the issues is fine fuel/air tuning with the program relies upon accurate MAF readings to correlate at what rpm to tweak the MAF settings. Need to dig a little deeper as that may not be an issue and it might be based upon voltage instead of grams per second.

Upon first noticing it, my initial concern was is there something preventing the engine from getting enough air. Throttle bodies to small, not opening up, issues with the Gen 3 intake, something purposely induced by Nissan, etc. Another concern is traction control. Even though the traction control is turned off, is it still retarding timing or even closing the throttle body?

Everything will eventually come out in the wash, in the interim this thing is driving me nuts trying to figure out exactly what is going on and what to do about it.

t-ray

It's nice to know that you have access to the actual MAF voltage values. And as long as those are increasing, you're good to go. I agree that the observed ceiling for MAF GPS is a bug at this point.

Kastley85891

They (COBB) probably scaled the MAF to give flat fueling up top, can you post up your MAF scale/s and fuel targets for Open loop?

Denny McLain

Does the Nissan ECU automatically go into open loop at WOT? Guessing it does but we'll see how the log posts but this is a log file from one of my last dyno session runs. Do you want to see the tuning fuel tables?

Seconds (sec) Coolant Temp ( F) Intake Air Temp ( F) Ign Advance () RPM (RPM) Mass Airflow (g/s) Mass Airflow B1 (V) Mass Airflow B2 (V) Air Fuel Ratio (AFR)
18.67 172.4 66.2 14 2800 109.33 3.04 3.04 13.8
18.71 172.4 66.2 16 2712 108.72 3.05 3.01 13.03
18.82 172.4 66.2 15 2750 109.44 3.02 3 13.37
18.89 172.4 66.2 15 2750 107.16 2.99 3 13.11
18.95 172.4 66.2 15 2812 109.98 3.05 3.04 13.24
19.03 172.4 66.2 15 2812 110.71 3.04 3.02 13.3
19.1 172.4 66.2 16 2825 111.23 3.09 3.02 13.17
19.15 172.4 66.2 19 2850 113.46 3.07 3.04 13.21
19.25 172.4 66.2 21 2875 112.81 3.1 3.03 13.19
19.33 172.4 66.2 22 2900 113.25 3.09 3.02 13.13
19.36 172.4 66.2 22 2912 115.06 3.06 3.05 13.01
19.44 172.4 66.2 22 2937 112.55 3.1 3.04 13.06
19.49 172.4 66.2 22 2950 116.52 3.14 3.07 13.21
19.55 172.4 66.2 22 2975 116.71 3.13 3.09 13.26
19.66 172.4 66.2 22 2987 117.85 3.13 3.08 13.12
19.74 172.4 66.2 23 3025 119.82 3.14 3.11 13.29
19.82 172.4 66.2 23 3050 118.94 3.13 3.12 13.27
19.89 172.4 66.2 23 3075 123.08 3.15 3.11 13.31
19.93 172.4 66.2 23 3087 122.86 3.18 3.06 13.26
19.98 172.4 66.2 23 3100 122.92 3.18 3.12 13.37
20.07 172.4 66.2 23 3112 123.76 3.15 3.1 13.37
20.16 172.4 66.2 24 3150 125.67 3.17 3.15 13.36
20.23 172.4 66.2 23 3175 127.13 3.17 3.15 13.3
20.33 172.4 66.2 23 3187 125.34 3.17 3.16 13.32
20.41 172.4 64.4 24 3225 127.46 3.22 3.17 13.21
20.44 172.4 64.4 24 3237 128.35 3.19 3.14 13.23
20.52 172.4 64.4 23 3250 130.04 3.2 3.16 13.12
20.57 172.4 64.4 23 3275 132.22 3.22 3.17 13.23
20.61 174.2 64.4 23 3300 131.05 3.22 3.14 13.28
20.72 174.2 64.4 23 3312 133.44 3.23 3.19 13.26
20.8 174.2 64.4 23 3337 132.13 3.2 3.19 13.19
20.85 174.2 64.4 23 3362 137.1 3.25 3.18 13.15
20.89 174.2 64.4 23 3375 138.14 3.25 3.23 13.2
20.98 174.2 64.4 23 3400 137.17 3.29 3.24 13.14
21.06 174.2 64.4 23 3412 137.25 3.28 3.21 13.09
21.15 174.2 64.4 23 3450 139.23 3.28 3.23 13.12
21.23 174.2 64.4 23 3462 141.58 3.28 3.25 13.12
21.31 174.2 64.4 24 3500 141.66 3.3 3.29 13.12
21.33 174.2 64.4 25 3512 143.52 3.32 3.25 13.06
21.42 174.2 64.4 25 3525 144.24 3.32 3.27 13.06
21.5 174.2 64.4 24 3550 147.01 3.31 3.31 12.96
21.58 174.2 64.4 24 3575 145.01 3.32 3.31 12.88
21.67 174.2 64.4 23 3600 150.49 3.37 3.33 12.95
21.72 174.2 64.4 23 3625 151.97 3.36 3.28 12.99
21.81 174.2 64.4 22 3637 148.93 3.37 3.3 12.87
21.9 176 64.4 23 3662 151.42 3.34 3.31 12.89
21.97 176 64.4 23 3700 153.64 3.38 3.32 12.89
22.03 176 64.4 22 3712 155.33 3.38 3.37 12.85
22.08 176 64.4 23 3737 155.94 3.38 3.34 12.87
22.16 176 64.4 23 3750 153.57 3.39 3.33 12.81
22.23 176 64.4 22 3775 158.67 3.38 3.34 12.76
22.29 176 64.4 23 3787 156.46 3.4 3.34 12.74
22.38 176 64.4 21 3812 160.28 3.41 3.35 12.75
22.45 176 64.4 21 3837 162.43 3.37 3.39 12.7
22.47 176 64.4 22 3862 161.77 3.39 3.38 12.77
22.58 176 64.4 21 3875 162.13 3.41 3.4 12.77
22.66 176 64.4 21 3900 162.72 3.41 3.4 12.74
22.71 176 64.4 22 3925 168.11 3.44 3.4 12.77
22.77 176 64.4 21 3937 167.26 3.44 3.4 12.69
22.88 176 64.4 21 3962 166.85 3.44 3.41 12.69
22.95 177.8 64.4 21 3987 164.91 3.43 3.41 12.69
23.01 177.8 64.4 21 4012 169.78 3.47 3.39 12.72
23.06 177.8 64.4 22 4025 172.2 3.51 3.44 12.66
23.12 177.8 64.4 22 4050 172.61 3.5 3.45 12.71
23.23 177.8 64.4 21 4062 174.04 3.48 3.44 12.64
23.31 177.8 64.4 21 4100 177.8 3.5 3.41 12.55
23.39 177.8 64.4 22 4125 177.48 3.5 3.46 12.5
23.46 177.8 64.4 22 4150 178.49 3.54 3.5 12.56
23.5 177.8 64.4 22 4175 178.75 3.56 3.46 12.5
23.54 177.8 64.4 22 4175 178.83 3.54 3.49 12.51
23.63 177.8 64.4 22 4200 178.77 3.53 3.49 12.44
23.7 177.8 64.4 22 4225 181.78 3.53 3.45 12.44
23.76 177.8 64.4 22 4250 184.81 3.54 3.49 12.38
23.84 177.8 64.4 22 4262 184.52 3.54 3.52 12.35
23.92 177.8 64.4 22 4287 184.94 3.59 3.51 12.22
23.95 177.8 64.4 22 4312 186.88 3.54 3.53 12.24
24.03 177.8 64.4 22 4325 188.29 3.54 3.51 12.32
24.11 177.8 64.4 22 4337 188.54 3.55 3.53 12.32
24.18 177.8 64.4 22 4375 188.33 3.6 3.52 12.35
24.23 177.8 64.4 22 4400 191.22 3.59 3.55 12.3
24.3 177.8 64.4 22 4412 190.7 3.6 3.52 12.31
24.38 177.8 64.4 22 4437 192.7 3.6 3.56 12.36
24.42 177.8 64.4 22 4450 194.76 3.6 3.57 12.44
24.49 177.8 64.4 22 4462 195.82 3.61 3.57 12.38
24.57 177.8 64.4 22 4487 193.88 3.62 3.55 12.35
24.66 177.8 64.4 22 4512 195.44 3.63 3.59 12.34
24.74 179.6 64.4 22 4537 198.63 3.66 3.58 12.29
24.81 179.6 64.4 22 4562 198.85 3.67 3.56 12.19
24.85 179.6 64.4 22 4587 203.02 3.66 3.62 12.16
24.9 179.6 64.4 22 4587 200.11 3.68 3.57 12.14
24.97 179.6 64.4 21 4612 199.86 3.66 3.59 12.17
25.06 179.6 64.4 21 4625 201.15 3.66 3.6 12.21
25.15 179.6 64.4 21 4662 204.33 3.68 3.59 12.13
25.2 179.6 64.4 21 4687 204.91 3.7 3.62 12.18
25.24 179.6 64.4 21 4700 207.57 3.73 3.66 12.12
25.33 179.6 64.4 21 4712 206.71 3.71 3.61 12.21
25.41 179.6 64.4 22 4737 205.81 3.7 3.63 12.01
25.51 179.6 64.4 22 4762 210.93 3.7 3.63 12.1
25.6 179.6 64.4 22 4800 214.01 3.72 3.7 12.08
25.65 179.6 64.4 22 4825 213.4 3.7 3.64 12.14
25.7 179.6 64.4 21 4837 215.25 3.73 3.63 12.1
25.77 179.6 64.4 21 4850 212.92 3.71 3.64 12.17
25.81 181.4 64.4 21 4875 212.23 3.74 3.66 12.16
25.88 181.4 64.4 21 4875 216.11 3.75 3.71 12.18
25.98 181.4 64.4 21 4912 217.73 3.73 3.68 12.15
26.01 181.4 64.4 21 4925 220.03 3.77 3.72 12.22
26.13 181.4 64.4 21 4937 220.58 3.77 3.73 12.28
26.17 181.4 64.4 21 4975 221.11 3.78 3.74 12.04
26.24 181.4 64.4 21 5000 223 3.8 3.73 12.19
26.32 181.4 64.4 20 5012 225.51 3.78 3.76 12.2
26.41 181.4 64.4 20 5037 223.78 3.79 3.74 12.13
26.48 181.4 64.4 20 5062 226.71 3.79 3.75 12.29
26.54 181.4 64.4 20 5087 230.33 3.8 3.78 12.15
26.63 181.4 64.4 20 5100 230.1 3.81 3.79 12.21
26.7 181.4 64.4 19 5125 231.2 3.83 3.75 12.2
26.8 181.4 64.4 19 5150 232.62 3.86 3.81 12.21
26.87 181.4 64.4 19 5175 233.25 3.82 3.75 12.12
26.94 181.4 64.4 19 5212 236.61 3.83 3.77 12.25
27.02 181.4 64.4 19 5225 234.15 3.82 3.79 12.2
27.05 181.4 64.4 19 5237 236.09 3.84 3.81 12.24
27.14 181.4 64.4 19 5262 236.81 3.86 3.86 12.17
27.22 181.4 64.4 19 5287 234.19 3.8 3.79 12.13
27.32 181.4 64.4 19 5300 240.35 3.83 3.82 12.12
27.41 181.4 64.4 19 5325 239.9 3.87 3.81 12.12
27.46 181.4 64.4 20 5350 240.09 3.89 3.82 12.2
27.5 181.4 64.4 20 5375 240.37 3.86 3.83 12.16
27.59 181.4 64.4 20 5387 243.05 3.91 3.87 12.17
27.66 181.4 64.4 21 5425 245.08 3.82 3.84 12.08
27.74 181.4 64.4 20 5437 241.51 3.88 3.85 12.17
27.82 181.4 64.4 19 5450 245.47 3.86 3.86 12.16
27.89 181.4 64.4 20 5475 246.17 3.92 3.86 12.14
27.95 181.4 64.4 20 5500 243.71 3.88 3.88 12.09
28.04 181.4 64.4 20 5512 245.13 3.89 3.86 12.06
28.12 181.4 64.4 20 5550 243.55 3.84 3.92 12.08
28.21 181.4 64.4 20 5575 248.93 3.85 3.88 12.13
28.26 181.4 64.4 20 5587 248.27 3.92 3.91 12.14
28.3 181.4 64.4 20 5600 250.78 3.88 3.91 12.05
28.42 181.4 64.4 20 5625 249.03 3.88 3.86 12.2
28.52 181.4 64.4 20 5650 249.23 3.87 3.93 12.03
28.6 181.4 64.4 20 5675 247.85 3.85 3.95 12.21
28.63 181.4 64.4 21 5712 255.58 3.86 3.91 12.21
28.71 181.4 64.4 21 5712 255.23 3.87 3.92 12.14
28.75 181.4 64.4 21 5737 258.6 3.86 3.96 12.3
28.84 179.6 64.4 21 5750 260.72 3.9 3.94 12.22
28.91 179.6 64.4 21 5775 261.2 3.89 4 12.27
28.97 179.6 64.4 21 5775 251.93 3.91 3.88 12.08
29.05 179.6 64.4 21 5812 256.89 3.9 3.91 12.22
29.13 179.6 64.4 21 5825 259.35 3.88 3.98 12.33
29.16 177.8 64.4 21 5850 261.63 3.98 3.94 12.32
29.24 177.8 64.4 21 5862 259.85 3.89 4 12.32
29.28 177.8 64.4 22 5887 265.17 3.95 3.98 12.41
29.35 177.8 64.4 22 5900 262.47 3.91 4.01 12.23
29.44 177.8 64.4 22 5912 266.45 4.02 3.97 12.25
29.52 176 64.4 22 5937 267.42 3.92 4.01 12.21
29.6 176 64.4 23 5975 268.79 3.95 4.02 12.09
29.7 176 64.4 23 5987 268.63 3.96 4.03 12.17
29.75 176 64.4 24 6012 266.27 4.01 3.94 12.19
29.79 176 64.4 24 6037 268.7 3.96 4.01 12.38
29.88 176 64.4 24 6050 268.79 3.98 4.05 12.54
29.97 176 64.4 24 6075 268.37 3.98 4.01 12.52
30.02 176 64.4 24 6100 268.79 3.97 4.05 12.42
30.06 176 64.4 24 6112 268.79 4.05 3.99 12.43
30.15 176 64.4 24 6125 268.79 4.05 4.02 12.43
30.22 176 64.4 24 6150 268.79 4.02 4.01 12.29
30.32 176 64.4 24 6175 268.79 4.03 4.01 12.37
30.35 174.2 64.4 24 6200 268.79 4.03 4.03 12.45
30.47 174.2 64.4 24 6212 268.79 4.03 4.02 12.46
30.51 174.2 64.4 25 6250 268.79 4.07 4.03 12.24
30.58 174.2 64.4 25 6262 268.79 4.05 4.05 12.22
30.66 174.2 64.4 25 6275 268.79 4.08 4.03 12.3
30.77 174.2 64.4 25 6300 268.79 4.08 4.07 12.34
30.86 174.2 64.4 25 6325 268.79 4.04 4.08 12.37
30.93 174.2 64.4 25 6350 268.79 4.09 4.03 12.31
30.96 174.2 64.4 25 6362 268.79 4.05 4.11 12.52
31 174.2 64.4 25 6375 268.79 4.14 4.01 12.52
31.05 174.2 64.4 24 6387 268.79 4.06 4.08 12.44
31.12 174.2 64.4 24 6400 268.79 4.14 3.99 12.35
31.18 174.2 64.4 24 6425 268.79 4.14 4.03 12.38
31.25 174.2 64.4 24 6437 268.79 4.15 4.05 12.46
31.31 174.2 64.4 25 6475 268.79 4.1 4.03 12.3
31.38 174.2 64.4 25 6475 268.79 4.19 4.02 12.21
31.44 174.2 64.4 25 6512 268.79 4.11 4.08 12.3
31.51 174.2 64.4 25 6512 268.79 4.18 4.02 12.5
31.57 174.2 64.4 26 6537 268.79 4.14 4.11 12.34
31.64 174.2 64.4 26 6550 268.79 4.12 4.07 12.49
31.67 174.2 64.4 26 6562 268.79 4.16 4.06 12.44
31.74 174.2 64.4 26 6587 268.79 4.19 4.05 12.44
31.85 174.2 64.4 25 6600 268.79 4.18 4.11 12.52
31.93 174.2 64.4 26 6625 268.79 4.18 4.11 12.46
32.01 174.2 64.4 26 6662 268.79 4.2 4.08 12.42
32.05 174.2 64.4 26 6662 268.79 4.24 4.05 12.54
32.15 174.2 64.4 26 6687 268.79 4.24 4.05 12.35
32.21 174.2 64.4 26 6725 268.79 4.18 4.16 12.58
32.29 174.2 64.4 26 6737 268.79 4.2 4.11 12.59
32.37 174.2 64.4 26 6762 268.79 4.21 4.15 12.31
32.45 174.2 64.4 26 6775 268.79 4.24 4.11 12.44
32.49 174.2 64.4 26 6800 268.79 4.24 4.09 12.44
32.56 174.2 64.4 26 6812 268.79 4.28 4.09 12.23
32.6 174.2 64.4 26 6837 268.79 4.19 4.17 12.46
32.67 174.2 64.4 26 6837 268.79 4.17 4.15 12.4
32.75 174.2 64.4 26 6862 268.79 4.2 4.17 12.42
32.78 174.2 64.4 26 6875 268.79 4.19 4.19 12.3
32.87 174.2 64.4 26 6887 268.79 4.28 4.12 12.22
32.94 174.2 64.4 25 6912 268.79 4.25 4.17 12.54
33 174.2 64.4 26 6950 268.79 4.26 4.11 12.35
33.05 174.2 64.4 25 6950 268.79 4.24 4.22 12.34
33.13 174.2 64.4 25 6975 268.79 4.3 4.17 12.38
33.21 174.2 64.4 25 6975 268.79 4.21 4.21 12.4
33.25 174.2 64.4 25 7012 268.79 4.24 4.24 12.45
33.32 174.2 64.4 25 7012 268.79 4.26 4.12 12.55
33.41 174.2 64.4 26 7037 268.79 4.32 4.12 12.68
33.5 174.2 64.4 26 7050 268.79 4.32 4.14 12.63
33.58 174.2 64.4 26 7100 268.79 4.28 4.19 12.52
33.65 174.2 64.4 26 7100 268.79 4.32 4.17 12.58
33.71 174.2 64.4 26 7125 268.79 4.31 4.19 12.46
33.76 174.2 64.4 26 7150 268.79 4.26 4.26 12.46
33.85 174.2 64.4 27 7150 268.79 4.29 4.2 12.35
33.93 174.2 64.4 27 7175 268.79 4.32 4.18 12.56
34 174.2 64.4 28 7200 268.79 4.32 4.19 12.58
34.06 174.2 64.4 28 7225 268.79 4.28 4.24 12.39
34.14 174.2 64.4 28 7250 268.79 4.29 4.21 12.33
34.18 174.2 64.4 28 7250 268.79 4.29 4.24 12.46
34.26 174.2 64.4 28 7262 268.79 4.36 4.18 12.44
34.34 174.2 64.4 28 7287 268.79 4.36 4.2 12.32
34.44 174.2 64.4 28 7312 268.79 4.34 4.19 12.41
34.53 174.2 64.4 28 7325 268.79 4.26 4.26 12.4
34.58 174.2 64.4 28 7350 268.79 4.31 4.22 12.42
34.62 174.2 64.4 28 7375 268.79 4.27 4.26 12.39
34.73 174.2 64.4 28 7387 268.79 4.34 4.19 12.42
34.81 174.2 64.4 28 7412 268.79 4.32 4.2 12.5
34.86 176 64.4 27 7425 268.79 4.32 4.24 12.47
34.95 176 64.4 27 7437 268.79 4.34 4.21 12.42
35.03 176 64.4 27 7475 268.79 4.29 4.25 12.37
35.11 176 64.4 27 7475 268.79 4.33 4.22 12.46
35.15 176 64.4 27 7500 268.79 4.37 4.24 12.57
35.25 176 64.4 27 7512 268.79 4.35 4.19 12.45
35.28 176 64.4 27 7537 268.79 4.34 4.18 12.38
35.4 176 64.4 27 7537 268.79 4.3 4.28 12.49
35.44 176 64.4 27 7575 268.79 4.33 4.22 12.51
35.51 176 64.4 27 7575 268.79 4.34 4.19 12.4
35.61 176 64.4 27 7600 268.79 4.3 4.26 12.41
35.7 177.8 64.4 27 7625 268.79 4.33 4.3 12.46
35.78 177.8 64.4 27 7637 268.79 4.32 4.29 12.23

Kastley85891

Denny M
The AFR target will have a set point to go to OL fueling, can you post a screen shot of the MAF scale from the rom itself and the fueling target tables? be interested to see the timing base/advance tables to, I can pull it for my self shortly..lol well when I can squeeze the next 'mod' cash past the Wife! but interested to see.
Cheers