Dunno if this has been discussed, and I was chatting with a few friends about it, and I wanted to see what the .org had to say.

How should you dyno an automatic car?! I went to two dyno places. Both couldn't seem to get the tranny to stay in 3rd. It would always downshift when the guy went WOT at 40.

 

I believe the trick is to put the car in drive and bring the rpms up to around 3500-3800rpms and mash the gas. The higher rpms in drive keep the tranny from downshifting. This is why you see most automatic dynos starting at a higher rpm (to avoid the downshift).


Dave

 

That's because the auto shift mapping still allows a 3-2 downshift at that point. On a an automatic without a "manual mode" you need to get the car up to the speed where it will no longer allow a 3-2 downshift. I think on a 4th gen that's about 65 mph, so you were going too slow.

 

I had the same problem and its not great for trying to tune with a wideband either, thats why I plan on doing it on the street or track now.

I even had to do part throttle nitrous activation to get it up so it wouldn't downshift. Don't try this though without a wideband, could be disastrous.

 

Does anybody know the rpm bands for each gear in the automatic, and at what point does the ecu decide to downshift or not?

 

They don't show the rpm just the speed.

 

3rd gear (OD/OFF) on automatic pulls the hardest, therefore you will be dyno on third gear. first you'll drive normally with OD/OFF (3rd gear) until you hit 3,500rpm on 3rd gear, which should put you around 70mph, then you will floor it till redline (around 122mph). the computer will start to record your WHP from 3,500rpm-redline.

if you floor before 3,500rpm you will most likely shift back to 2nd gear automatically.

 

Third gear doesn't pull the hardest. First gear does.

They dyno in third because it's the closest to a 1:1 ratio.

 

okay sorry for bringing up old thread but I needed this info.

 

The squiggly part is where the auto will shift if you floor it.

Put it into D w/ O/D off, roll it up to almost 70mph and then floor it. Translates into about 3500rpm on the tach and you should be good. They might still drop it a gear. I've done it about 15 times now and I still screw it up occasionally.