Power FC HP Calculations from Datalogit logs
07-15-03 | 11:20 AM
#26
Banned. I got OWNED!!!
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From: Bannished
Originally posted by books
Ok, I thought I’d give this horsepower calculation another shot. I used the logs from the dyno shop. I averaged a 10 mph range around peak horsepower (also a flat part of the curve). Then I converted the acceleration for that range into g’s, plugged it into the equations and came within a few horsepower of what was measured by the dyno.(provided my car weighs 3000 lbs; touring model, owners manual states 3210). I also checked another log from a different shop and came up with similar results. However when I used Datalogs of the dyno runs the calculated horsepower was off by quite a bit from the measured value.
I’ve noticed that the Datalog sampling varies depending on how much you’re monitoring, for example if you have a couple of watches, (I use AFR, and knock) on as well the map watch you get samples around .2 s, whereas if you activate just the monitor, it samples closer to .1s. I believe this variation contributes significantly to the error in calculated horsepower. In addition, the Datalogit s/w varies from one version to the next, if you use 1.07, sampling can occur in less than .05s.
So is there any benefit to any of this, who knows? What I desire is the ability to calculate horsepower using Datalogs exclusively, to that end after my last dyno session, I logged several 40-80mph 3rd gear runs, I calculated the acceleration from 40-80mph plugged it into the horsepower formula and using 110 mph the calculated figure was within a few horse of the dyno. The use of 110mph was somewhat experimental, really a fudge factor or correction factor, although coincidentally 80*1.391 is about 111mph, where 1.391 is the 3rd gear ratio. Perhaps some others, who know what their horsepower is, can perform this little experiment to either discredit or to add credence. Please remember to use version 1.07 and do not activate any additional watches.
Ok, I thought I’d give this horsepower calculation another shot. I used the logs from the dyno shop. I averaged a 10 mph range around peak horsepower (also a flat part of the curve). Then I converted the acceleration for that range into g’s, plugged it into the equations and came within a few horsepower of what was measured by the dyno.(provided my car weighs 3000 lbs; touring model, owners manual states 3210). I also checked another log from a different shop and came up with similar results. However when I used Datalogs of the dyno runs the calculated horsepower was off by quite a bit from the measured value.
I’ve noticed that the Datalog sampling varies depending on how much you’re monitoring, for example if you have a couple of watches, (I use AFR, and knock) on as well the map watch you get samples around .2 s, whereas if you activate just the monitor, it samples closer to .1s. I believe this variation contributes significantly to the error in calculated horsepower. In addition, the Datalogit s/w varies from one version to the next, if you use 1.07, sampling can occur in less than .05s.
So is there any benefit to any of this, who knows? What I desire is the ability to calculate horsepower using Datalogs exclusively, to that end after my last dyno session, I logged several 40-80mph 3rd gear runs, I calculated the acceleration from 40-80mph plugged it into the horsepower formula and using 110 mph the calculated figure was within a few horse of the dyno. The use of 110mph was somewhat experimental, really a fudge factor or correction factor, although coincidentally 80*1.391 is about 111mph, where 1.391 is the 3rd gear ratio. Perhaps some others, who know what their horsepower is, can perform this little experiment to either discredit or to add credence. Please remember to use version 1.07 and do not activate any additional watches.
Tony
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