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Yea, I would be interested in seeing some FSI big bore MAF flow numbers vs Stock MAF flow numbers also......thanks for taking the time to collect these...
I just loaded a new map. Gonna let it learn for a few miles and then do some 3rd gear pulls. Hopefully just a few days.
Yes the Wallace Racing Calculators is the best collection of Automotive Performance Calculators you will find anywhere on the net...and have been around for decades...
I finally got out to collect this data.
2004 C4S, 104k miles
I actually bought, just out of interest, a 997.1 3.8 airbox, so I did 2 runs with my old stock 3.6 airbox, and 2 runs with the new 3.8 airbox.
Both have pretty new filters (3.6 is about 2k miles old), (3.8 is brand new). I had to use the 3.6 snout on the 3.8 airbox in order to clear the SAI pump.
I used the same MAF in both, I just transfered it over.
These runs were back to back all within about an hour. I'm reporting here the better of each of the 2 runs.
My car is stock, except for Top Gear 200 Cell Cats.
For both runs:
Ambient (F): 60
Humidity (%): 31
Barometric Pressure (inhg): 30.19
Altitude (ft): 715
Atmospheric correction: 1.037
"HP" comparison point is calculated as: [MAF(g/s) / 0.75] * (MSA Correction Factor)
Read footnote (2): This is a purely calculated value, and should NOT be mistaken for actually measured WHP. (even if the result from delirium45 is really close!!)
Has anybody actually measured the cross-section of the 3.6 air box compared to the 3.8 air box ??
IF they are "exactly " then same cross-section then yes....
IF the 3.8 air box has a slightly larger cross-section, then it will "report" a lower mass air flow, when in fact the "actual " mass air flow being the same...
IF it reports a lower mass air flow, then it will also reduce injector time leaning out the AFR a bit also...( and looks like the injector time IS reduced)
Has anybody actually measured the cross-section of the 3.6 air box compared to the 3.8 air box ??
IF they are "exactly " then same cross-section then yes....
IF the 3.8 air box has a slightly larger cross-section, then it will "report" a lower mass air flow, when in fact the "actual " mass air flow being the same...
IF it reports a lower mass air flow, then it will also reduce injector time leaning out the AFR a bit also...( and looks like the injector time IS reduced)
I did measure the 3.8 before installing it. I'll post the numbers later after I can go find them.
I have not precisely measured the 3.6 box after removing it. I was interested in that too.
I did measure the 3.8 before installing it. I'll post the numbers later after I can go find them.
I have not precisely measured the 3.6 box after removing it. I was interested in that too.
Yea, a precision measurement at the MAF mounting point is a "must have" to relate the data to........
Interior opening, measured in two perpendicular directions:
3.6: 85mm
3.8: 85mm
Depth from MAF opening:
3.6: 101.5 mm
3.8: 102.0 mm I may pull the 3.8 and remeasure these at the same time to get a better feeling for any real difference versus just error between these two measurements.
I took the measurements more precisely than shown in these pictures. These pictures were just taken to show which directions I was measuring.
Has anybody actually measured the cross-section of the 3.6 air box compared to the 3.8 air box ??
IF they are "exactly " then same cross-section then yes....
IF the 3.8 air box has a slightly larger cross-section, then it will "report" a lower mass air flow, when in fact the "actual " mass air flow being the same...
IF it reports a lower mass air flow, then it will also reduce injector time leaning out the AFR a bit also...( and looks like the injector time IS reduced)
Based on my measurements, I think they are the same size, but do I understand correctly that if the 3.8 was larger, then it would be reporting lower mass air flow than actual (as you say), then the engine would be run lean.
However, over time, if that were the case, I should see my fuel trim readings start to drift up to correct the AFR. Is this correct?
Based on my measurements, I think they are the same size, but do I understand correctly that if the 3.8 was larger, then it would be reporting lower mass air flow than actual (as you say), then the engine would be run lean.
However, over time, if that were the case, I should see my fuel trim readings start to drift up to correct the AFR. Is this correct?
Well, we are actually talking about two different things that are closely related and even intermingled at times..
I'm just going to skim over a few things giving facts but in a broader more general way as to not get too deep in a never ending rabbit hole ,that may sound like contradicting if not taken literally and knowing that some things will overlap.. But if you need more clarification, or if I sound contradicting, just ask for more detail..
I was refereeing to the injector times in milliseconds at WOT,( open loop) and you are talking about fuel trims to correct AFR ( closed loop)..
Our cars have narrow band 02 Sensors ( wide band Sensors were not yet invented) . Narrow band 02 Sensors are very accurate at 14-16 AFR and are tuned to 14.7 AFR ( also known as Stoichiometric or Lamda 1 ) which is the best ratio for the cats..and they switch high/low at ~.5v ..( whereas wide band 02 Sensors can read from 10-19 AFR)
So, our cars under full throttle are in "Open loop" and ignore the 02 Sensors, but under idle or cruise loads they are in "closed loop" and use the 02 Sensors to adjust fuel trims to 14.7 AFR ( Stoichiometric/Lamda1)
14.7 AFR is the best ratio for the cats/emissions, and ~12.5-13 AFR is for power
Most all MFG's tune their cars on the rich side under WOT as a safety margin..ours is no exception..This is done in the "fuel table' of the DME program.
The fuel trim values are used to modify the fuel table by adding or extracting from the fuel table to get to Lamda 1 ( Stoich) ...or 14.7 AFR..
Now, under WOT the fuel trims are not used to modify the fuel table unless the fuel trim a positive value, if the fuel trim is a negative value a zero is used so that the AFR cannot be leaned out ( safety factor) ...
So , to answer your question, if you are at a 0 fuel trim now and after driving it goes to a positive number , that number will be used to modify the fuel table, but if you are already at a negative number on the fuel trim and after driving for a while it becomes a less negative number fuel trim,, then a zero will be used and no change to the fuel table will be made for WOT..
Last edited by Porschetech3; 11-11-2023 at 12:13 AM.
A variation on the zirconia sensor, called the "wideband" sensor, was introduced by NTK in 1992[5] and has been widely used for car engine management systems in order to meet the ever-increasing demands for better fuel economy, lower emissions and better engine performance at the same time.[6] It is based on a planar zirconia element, but also incorporates an electrochemical gas pump. An electronic circuit containing a feedback loop controls the gas-pump current to keep the output of the electrochemical cell constant, so that the pump current directly indicates the oxygen content of the exhaust gas. This sensor eliminates the lean–rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry this sensor is also called a UEGO (universal exhaust-gas oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air–fuel display equipment. The wideband zirconia sensor is used in stratified fuel injection systems and can now also be used in diesel engines to satisfy the upcoming EURO and ULEV emission limits.
Ok correction ,,, wideband just had been " introduced by NTK" but "Bosch " had not yet supplied them to Porsche for the M96 996....24 years ago.....lol...
So, again, our cars use the narrow band 02 Sensors.....
Last edited by Porschetech3; 11-11-2023 at 07:10 AM.
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I was refereeing to the injector times in milliseconds at WOT,( open loop) and you are talking about fuel trims to correct AFR ( closed loop).
...
...
So, our cars under full throttle are in "Open loop" and ignore the 02 Sensors, but under idle or cruise loads they are in "closed loop" and use the 02 Sensors to adjust fuel trims to 14.7 AFR (Stoichiometric/ Lamda1)
Now, under WOT the fuel trims are not used to modify the fuel table unless the fuel trim a positive value, if the fuel trim is a negative value a zero is used so that the AFR cannot be leaned out ( safety factor)
...
...
So , to answer your question, if you are at a 0 fuel trim now and after driving it goes to a positive number , that number will be used to modify the fuel table, but if you are already at a negative number on the fuel trim and after driving for a while it becomes a less negative number fuel trim,, then a zero will be used and no change to the fuel table will be made for WOT..
So yes, I was aware of wideband vs narrow band, and that I know wideband has been around a while, I believe especially used on turbocharged cars.
But I appreciate the reminder that at WOT, the cars run open loop; I didn't know that they will use the fuel trim only if positive.
My injectors are new, replaced about 2-3k miles ago, but if the numbers above (97%) are correct, it seems to mean that even if I got more air flow, and sought out a tune to take advantage of that, that I'm pretty much already injector limited at the top end. I might get more at lower RPMs, but shouldn't expect anything much at peak.
I have no plans to do any of that, just thinking it through.
...but if the numbers above (97%) are correct, it seems to mean that even if I got more air flow, and sought out a tune to take advantage of that, that I'm pretty much already injector limited at the top end. I might get more at lower RPMs, but shouldn't expect anything much at peak.
Yea, but your 3.8 box had you below 95% ... gives you a little more room to grow
10-19-2023, 06:19 PM
