Originally Posted by MMZ_TimeLord
Steve,
Heres the data I had from my completely stock Mustang dyno runs. NOTE: The dyno was being run in AWD mode, so both roller sets were connected.
As you can see my numbers were 249 HP and 252 Torque.
Going by these numbers for adding back in the 18% and 12%...
18% ... 82 * 1.2195 = 99.999
12% ... 88 * 1.1364 = 100.0032
18 + 12 = 30% ... 70 * 1.4286 = 100.002
Add back in the 18% drive train loss they told you to use...
249 * 1.2195 = ~303.66 HP
252 * 1.2195 = ~307.30 torque
IF the Mustang dynos typically show another 12% lower than say dynojets, then we add back in the 12%...
303.66 * 1.1364 = ~345.08 for HP
307.30 * 1.1364 = ~349.22 for torque
This looks VERY close to the numbers we had figured for the SRT6 (not advertised, but actually closer to the SLK 32 AMG)
Adding both percentages together and then doing just one step...
249 * 1.4286 = ~355.72 for HP
252 * 1.4286 = ~360.01 for torque
There IS a flaw in these calculations. My question is which is right...
Add in each percentage separately OR add the percentages together and then add back in the overall percentage???
By the way Adding 18% back in... is not the same as subtracting it! Because you are working with LESS than 100% for a starting number, you have to actually add in a higher percentage of the number to get a full 18% of the original 100%.
So, if you LOOSE 18% from say 330 from the drive line, you are loosing an actual 18%. 330 * 0.82 = 270.6 ... BUT, if you want to add back in this loss, you must add in MORE than 18% of 270.6!
270.6 * 1.2195 (21.95% added) = 329.9967
Make sense?
Jody, keep in mind the math only works if you're careful. This example may help:
Let's just say our example car has a true crank hp of 300. Assuming a drive train loss of 20%, that car would have an actual wheel hp of 240. (That's 300 * .80 = 240)
Now put that example car on a Mustang Dyno, which reads numbers 12% less. So a 240 whp car should read as 211.2 on a Mustang dyno. (240 * .88 = 211.2)
Now, I know that you're thinking that I worked that backwards, and you're right. But I did that deliberately. When you talk about losses, you need to work down from the big number (100%).
To work up from the Mustang number, the math works a bit different. In our example car it read 211.2 on the Mustang. To figure out what the actual whp would be we have to divide the 211.2 by 88, then multiply the result by 100. See how that "upsizes" the number proportionally? 211.2 / 88 = 2.4, 2.4 * 100 = 240.
Then to get the crank hp from the whp, divide the whp by 80 then multiply the result by 100. So: 240 / 80 = 3, 3 * 100 = 300. Notice how the numbers work exactly back up to the original crank hp number, showing that the math works, just the method is different dependent on which direction your calculating.
I hope that helps.
In Steve's case:
Mustang hp: 266
Adjusted WHP = 266 / 88 * 100 = 302.3
Adjusted Crank HP = 302.3 / 80 * 100 = 377.9
That's assuming 12% loss for the Mustang dyno, and 20% loss for drivetrain.
Steve: also note your dyno run only went to 5548 RPM. If you take that up to 6200 RPM your numbers should go up another 15-20 hp.