Cobb AccessPORT Discussion
03-05-2009, 08:00 PM
#5353
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getting back to basics.... The more I think about things the more complicated it seems
Reported MAF - What exactly is this? Looking at my logs it seems to me that the reported maf isn't the raw mass airflow reading but actually a humidity/temp/baro corrected mass air flow. I have logs when its 90 deg F and logs when its 20 deg F outside and i get ~220 g/s of max flow in either condition. So it seems to me this is actually a compensated MAF being reported....
Reported LOAD - This one i'm still a bit confused about as well. I graphed the calculated LOAD vs the load I figured out by dividing the MAF by the theoretical airflow of the engine. It doesn't match and its not off by a constant percentage either. I then graphed the reported LOAD vs MAF/theoretical airflow/Mazda's VE numbers. This came closer to a match then the first attempt... so i'm thinking the load being shown is the (actual VE / theoretical VE) which is not what i had expected
Reported MAF - What exactly is this? Looking at my logs it seems to me that the reported maf isn't the raw mass airflow reading but actually a humidity/temp/baro corrected mass air flow. I have logs when its 90 deg F and logs when its 20 deg F outside and i get ~220 g/s of max flow in either condition. So it seems to me this is actually a compensated MAF being reported....
Reported LOAD - This one i'm still a bit confused about as well. I graphed the calculated LOAD vs the load I figured out by dividing the MAF by the theoretical airflow of the engine. It doesn't match and its not off by a constant percentage either. I then graphed the reported LOAD vs MAF/theoretical airflow/Mazda's VE numbers. This came closer to a match then the first attempt... so i'm thinking the load being shown is the (actual VE / theoretical VE) which is not what i had expected
03-06-2009, 09:57 AM
#5357
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If you are tuning with the AP, I would just work on getting the fuel mixtures and timing the way you want them. I didn't get my tune the way I wanted it untill I just left the MAF alone and focused my attention elsewhere.
-Yambo
-Yambo
03-06-2009, 02:46 PM
#5358
Any of you guys played with injector scalings for different sized injectors?
Cheers,
Hymee.
03-06-2009, 03:00 PM
#5360
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is it ghey to play with OTHER people's injectors?
got your email: I like the color coding.
got your email: I like the color coding.
03-06-2009, 03:16 PM
#5362
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keep fighting the fight! 
- excellent answer on the injector question.
(insert Kane's evil hamster)
- excellent answer on the injector question.
(insert Kane's evil hamster)
03-06-2009, 04:08 PM
#5366
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I have a video of MM being tortured AND consuming alcohol.
(think Vegas meet last year...Jeff knows what I'm referring to)
(think Vegas meet last year...Jeff knows what I'm referring to)
03-06-2009, 05:15 PM
#5369
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Good advice! Unless the MAF is actually calibrated wrongly, best to leave it alone. It is a critical piece of the equation in that PCM working out so many things. What the PCM thinks the LOAD is - is the basis for just about every decision it makes.
Any of you guys played with injector scalings for different sized injectors?
Cheers,
Hymee.
Any of you guys played with injector scalings for different sized injectors?
Cheers,
Hymee.
03-06-2009, 05:30 PM
#5370
In simplistic terms: Volumetric Efficiency.
The ratio of the theoretical mass flow of the engine at that RPM based on it's displacement in naturally aspirated form, compared to the actual mass flow.
So if the engine takes 300 g/s at 6000 RPM, and you are seeing 150 g/s, then the engine is being held back by the throttle. In this case it would be at 50% load.
If you had a compressor in the loop, and it was pumping 600 g/s at an RPM when then engine would theoretically only displace 300 g/s, then you would be at 200% load. At that point, the pressure in the manifold would be about 2 bar (2 atmospheres) or 14.7lbs boost.
Here is the OBDII (SAE J1979) definition of Load (Absolute):
The absolute load value has some different characteristics than the LOAD_PCT defined in PID 04 This definition, although restrictive, will standardise the calculation. LOAD_ABS is the normalised value of air mass per intake stroke displayed as a percent.
LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / intake stroke) * cylinder displacement in litres]
Derivation:
Characteristics of LOAD_ABS are:
NOTE See PID $04 for an additional definition of engine LOAD.
Cheers,
Hymee.
The ratio of the theoretical mass flow of the engine at that RPM based on it's displacement in naturally aspirated form, compared to the actual mass flow.
So if the engine takes 300 g/s at 6000 RPM, and you are seeing 150 g/s, then the engine is being held back by the throttle. In this case it would be at 50% load.
If you had a compressor in the loop, and it was pumping 600 g/s at an RPM when then engine would theoretically only displace 300 g/s, then you would be at 200% load. At that point, the pressure in the manifold would be about 2 bar (2 atmospheres) or 14.7lbs boost.
Here is the OBDII (SAE J1979) definition of Load (Absolute):
The absolute load value has some different characteristics than the LOAD_PCT defined in PID 04 This definition, although restrictive, will standardise the calculation. LOAD_ABS is the normalised value of air mass per intake stroke displayed as a percent.
LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / intake stroke) * cylinder displacement in litres]
Derivation:
- air mass (g / intake stroke) = [total engine air mass (g/sec)] / [rpm (revs/min)* (1 min / 60 sec) * (1/2 # of cylinders (strokes / rev)],
- LOAD_ABS = [air mass (g)/intake stroke] / [maximum air mass (g)/intake stroke at WOT@STP at 100% volumetric efficiency] * 100%.
- STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg (101.3 kPa) BARO, WOT = wide open throttle.
Characteristics of LOAD_ABS are:
- Ranges from 0 to approximately 0.95 for naturally aspirated engines, 0 – 4 for boosted engines,
- Linearly correlated with engine indicated and brake torque,
- Often used to schedule spark and EGR rates,
- Peak value of LOAD_ABS correlates with volumetric efficiency at WOT.,
- Indicates the pumping efficiency of the engine for diagnostic purposes.
NOTE See PID $04 for an additional definition of engine LOAD.
Hymee.
03-06-2009, 06:11 PM
#5371
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That is why I think it is so important to figure out just how much the throttle body is actually opening. When tuning with the ATR software, you can set it to open however much you want. I currently have mine set at 90% max. However, the datalogs(as well as live data) only show it opening to a max of 67-68%. I have asked the question here and on the COBB forums and no one can answer why this is.
-Yambo
-Yambo
03-06-2009, 06:51 PM
#5372
1) Look at the TB when you command it to WOT. You will be surprised at what the opening angle is at a 68% duty cycle.
2) I'd recommend upgrading the P2 injectors to 730cc. This gives you a total fuel flow of 2800cc, which is enough for about 450 crank HP.
3) For PCM injector scaling, just figure out the % increase in flow and multiply the scaling number by that amount. Just realize that the number is not quite linear and that the injector scaling can be off by as much as 5%+ right from the OEM.
2) I'd recommend upgrading the P2 injectors to 730cc. This gives you a total fuel flow of 2800cc, which is enough for about 450 crank HP.
3) For PCM injector scaling, just figure out the % increase in flow and multiply the scaling number by that amount. Just realize that the number is not quite linear and that the injector scaling can be off by as much as 5%+ right from the OEM.
03-06-2009, 07:05 PM
#5373
I'm wondering if the specs of the injectors isn't correct.
Cheers,
Hymee.
BTW - Yambo - I wouldn't be concerned about the TPS so much - if it is at 84% or whatever it maxes out at, then it will be WOT. The MAF is what matters the most as far as the PCM is concerned.
03-06-2009, 07:15 PM
#5374
The latency is probably wrong.
You can try adding 1/2 of the LTFT correction back into the injector scaling.
Is the LTFT correction everywhere or just at idle?
Its more important to get the open-loop scaling right at mid-RPM and then take care of the trim at idle with the MAF.
You can try adding 1/2 of the LTFT correction back into the injector scaling.
Is the LTFT correction everywhere or just at idle?
Its more important to get the open-loop scaling right at mid-RPM and then take care of the trim at idle with the MAF.
03-06-2009, 11:14 PM
#5375
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Why is the open-loop scaling at mid-rpm important? And if you make changes there, does that mean you need to scale the rest of the MAF accordingly, since otherwise it would a "wiggly" curve instead of a smooth one?
Please excuse my ultra-scientific terminology
Please excuse my ultra-scientific terminology