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Hey everyone,

I'm just curious about dynoing the 8 speed auto I have in my 2015 Challenger RT. I know when you dyno any vehicle you want to do the pull in whatever gear has a 1:1 ratio. In the 8 speed auto that gear is 6th. 6th gear is very very very tall and both shops I've been to have told me that a 6th gear pull wouldn't be possible because it would take too long. They do the pull in 5th instead and the numbers come back low as expected so I'm trying to figure out if anyone knows how true that is about not getting good data from a 6th gear pull. I have a very aggressive cam and would love to have an accurate number!
 

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Isn't the final drive for automatics, 3.09? 3.09 is not "very, very, very" tall. That's laughably stupid.

Your dyno guys are idiots.
 

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Well actually the number you would get in 5th gear would be higher than 6th because you are slightly multiplying power - no?

These cars do reach really high speeds on the dyno now with these transmissions, but that's becoming the norm and I've seen many shops dyno them without concern. There are some special fuses you need to pull to make it dyno correctly if I'm not mistaken.
 

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You can use any gear and get the same data. They use the gear they use because it is pulling about the time they like to see under full power. A short gear would pull too fast and might spin the tire and a long gear would over speed the dyno and have the engine under load for a long time.
 

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Hey everyone,

I'm just curious about dynoing the 8 speed auto I have in my 2015 Challenger RT. I know when you dyno any vehicle you want to do the pull in whatever gear has a 1:1 ratio. In the 8 speed auto that gear is 6th. 6th gear is very very very tall and both shops I've been to have told me that a 6th gear pull wouldn't be possible because it would take too long. They do the pull in 5th instead and the numbers come back low as expected so I'm trying to figure out if anyone knows how true that is about not getting good data from a 6th gear pull. I have a very aggressive cam and would love to have an accurate number!
You would need to pull in 4th gear to get an accurate number. Your dyno guys are telling you the truth. I dyno'd my car a couple summers ago and I tried in 6th because it was 1:1, but it took so damn long to get through the test window that I reached speeds of 155 or more. I also only got about 391 hp and about 402 ft-lbs of torque. Since the pull took so long my engine temps kept spiking and it felt like the car was about to fall off the dyno. We then tried to pull in 5th, which was a little better, but by then the motor was heat soaked and pulling timing. After some research on Hellcat forums and other places on the net, I found out that a 4th gear pull is actually what is required for the ZF 8-speeds. The dyno will still do all of the calculations and it will get through the test window sooner.

I also found out a bit of information concerning the Mustang dyno that I was on. I am not sure about the Dynojet version, but apparently, the Mustang dyno will add wind drag coefficients to your horsepower numbers and reduce the total output of the result. My DA for my location is almost always around 5,600 so I understand that I am on an uphill battle for dyno numbers. From what I read, Mustang dyno's begin these wind drag calculations once speeds are 100+ mph. Since 5th and 6th gear will take you well out to 155+ mph then you may see numbers that you don't agree with. When I saw 391 wheel HP from a 500hp crank motor, I was greatly disappointed. Then again the DA could have been killing it too. Since DA is a difficult variable to take into account, I guess I will just assume 391hp/402tq is what I run. I havn't been back to do a 4th gear pull since I don't feel like spending the money on an arbitrary number that really proves nothing at the end of the day. Since I prefer the circle track, much like the pic I have attached, high numbers really don't guarantee results. I have seen people show up to the track in high power cars that can't turn a lap if it was the last thing they could do in life. People spend tons of money on GT350R's and Z06 vetters, but can't drive for crap. I digress, do a 4th gear pull and take your DA into account next time. Let us know if that changes anything for you! Good luck!
 

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You will really be prone to ST KNK with a 6th gear pull as well. Tuning in 4th gear is ideal and is exactly what I do on the street.
 
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