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pulley change, down on boost, and reading logs questions, belt slip?

andrewtac

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Paxton kit, ran the 3.6 while getting everything dialed in. Changed to a 3.48 pulley, went for a dyno run. It ended up at about the same power, which kind of through me for a loop was expecting more. Looking at the weather it was probably the most humid and hottest day of the year, in addition density altitude was up; likely that was the issue after looking at the logs.

I went home, decided to put on the 3.375 pulley (tuner gave me the thumbs up) and make a couple logs. They felt strong, but at this point I doubt I can tell any difference, still getting used to the car. Looking at the logs and comparing MAP, the 3.48 pulley was up over the 3.6 3-4psi over the RPM range, and was climbing at a very similar rate as the 3.6 pulley. The 3.375 had less MAP over the range than the the 3.48 pulley and it slowed way down increasing PSIT about 5800-7000 (actually went backwards a little at the end). Also, the rate of climb seemed to die off over the RPM range. This was with the same belt as the 3.48 pulley and the tension pulley in the same location (o o x o). Figured this was slip for sure, then went to one size smaller belt. It would not fit, so I moved the pulley over one (o o o x) and the tension seemed about the same as bigger belt and other pulley location. Ran this belt and very similar results.

I guess first question is MAP a good indicator of boost? If so looking at the data below, am do I possibly have belt slip with the smaller pulley? Or am I chasing a problem that doesn't exist?


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andrewtac

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Where are you getting the map reading from?
The log file. Tuner replied this morning from last night's log and said map was inferred, which is what I thought. He also said no indication of belt slip or drop off, so I think I am chasing a problem that doesn't exist.

Going to set up a camera to record the mechanical gauge on the next run.
 

engineermike

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The inferred map is only as good as the speed-density model in the pcm. My confidence in these being accurate in boost is very low, especially when trying to distinguish small changes. Atmospheric conditions will also affect the reading. I would recommend adding a gauge or pressure sensor and logging device if you want to know.

That said, I would log “load” or maf and use those for before/after comparison. Load, rather than boost, is used in the pcm anyway for all the calculations.
 
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andrewtac

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The inferred map is only as good as the speed-density model in the pcm. My confidence in these being accurate in boost is very low, especially when trying to distinguish small changes. Atmospheric conditions will also affect the reading. I would recommend adding a gauge or pressure sensor and logging device if you want to know.

That said, I would log “load” or maf and use those for before/after comparison. Load, rather than boost, is used in the pcm anyway for all the calculations.
I see "desired load" and "air load" in the logs, is that the load you are referring to?
 

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engineermike

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Yes, log air load with each pulley. It will change with rpm.

Air load is the amount of air trapped in the cylinder divided by the same volume of air at standard temp and pressure. So, on a nice 68 deg day at sea level if your engine has 100% VE then your air load will be 1.0. Boost makes it go up; heat makes it go down. The Ford pcm’s don't distinguish between boost and vacuum, as it doesn’t really matter if you know how much air is in the cylinder. Air load is calculated by dividing the maf flow by the rpm, then dividing by 4 (cylinders per revolution).
 
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andrewtac

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Yes, log air load with each pulley. It will change with rpm.

Air load is the amount of air trapped in the cylinder divided by the same volume of air at standard temp and pressure. So, on a nice 68 deg day at sea level if your engine has 100% VE then your air load will be 1.0. Boost makes it go up; heat makes it go down. The Ford pcm’s don't distinguish between boost and vacuum, as it doesn’t really matter if you know how much air is in the cylinder. Air load is calculated by dividing the maf flow by the rpm, then dividing by 4 (cylinders per revolution).
Thanks for your help, appreciate the explanation. Trying to educate myself on log reading and maybe someday how to tune as well. Engineering background as well, but don't really practice in the traditional sense.
 
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andrewtac

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Upon further review, the airload is lower for the 3.375 pulley versus the 3.48 pulley at similar RPMs. It ain't the belt, got it on super tight now (tensioner has a small amount of give). Looking at acceleration rates on the log the 3.375 is the fastest. Maybe there is no problem.

I did take videos this time, was getting about 10psi on the mech gauge with the 3.375 pulley.
 

engineermike

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Is ambient temp any different? If so it will skew the data. I’m running 2 psi more boost in hot weather and getting the same air load.
 
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andrewtac

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looks like that isn't being logged. IAT is though, starting/finish IATs 3.6-81/101; 3.48-106/114, 3.375-93/123; the temps were rather stable prior to the hit.
 

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andrewtac

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Was it dynoed with inlet of and now it’s on?
We did a run on, power was way down then off. Previous run was filter off. Power was the same with a reduction in pulley (3.6 to 3.48). Temp was about 20 degrees cooler, density altitude was lower, and humidity much lower with the 3.6. Will start making better records.
 

Cory S

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We did a run on, power was way down then off. Previous run was filter off. Power was the same with a reduction in pulley (3.6 to 3.48). Temp was about 20 degrees cooler, density altitude was lower, and humidity much lower with the 3.6. Will start making better records.
This is what correction factors are used for. Disregard air temp and DA when using STD/SAE dyno correction. Look at your MAF lb/min @ RPM. There, you can see intake volume, and compare it to your pulley changes etc. Watch spark advance above 5500rpm, to make sure its the same on all three pullies as well, in order to keep everything the same by comparison.
 

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BOV problem?
 
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andrewtac

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