ECU torque calculations impact 6AT shift speeds

[themyst]

Just wanted to share a video during torque limiter testing on Cobb.

It appears when the ECU perceives high torque, it shifts slower. When it perceives low torque, it shifts faster. It could be backwards, I'm not sure. Anyway, this is an example of how fast the 6AT is capable of shifting if induced to do so. When actual torque is high but reported torque is low, the transmission is capable of completely missing a shift.

[Eleventeen]

Damn, that's pretty quick. It actually sounds like the RPM drops faster than the tach is indicating, which means it's a fast shift.

[marv85]

Wow, you weren't kidding when you told me it sounded like a DCT

[Sticky]

Pretty good shift. Not DCT quick but quick for an auto.

[Terry@BMS]

Looks like a normal shift. Piggybacks inherently trick the DME in to thinking it's making a lot less torque during the shift. So much so that for large turbo applications I think we'll need to go the other way around. Tank advance post shift for a second or so to give the trans a chance to really lock in gear before hitting it again.

[themyst]

Looks like a normal shift. Piggybacks inherently trick the DME in to thinking it's making a lot less torque during the shift. So much so that for large turbo applications I think we'll need to go the other way around. Tank advance post shift for a second or so to give the trans a chance to really lock in gear before hitting it again.

Compare the example video to this video of hotrod's car. The difference is clear! That's how my car shifts on the off-the-shelf Cobb mapping. Only reason I posted that video is because I had it sitting around during my Torque Limiter testing for Cobb. Basically all I need to figure out is why my car flatlines on Cobb ONLY between 6000-6400 RPM. Doesn't flatline at 5900, doesn't flatline at 6600. Something is happening in that cell in some table buried deep in the ECU that even Cobb hasn't found yet which will fix my long-time issue!

[e90TiAg335i]

Have to agree with Terry. Mine shifts pretty darn fast. My tech even asked if I had a dct. He finally got to drive it fully modded after replacing the front pads and rotors under warranty. Mine does seem quicker than other pre-LCIs I've driven with JB4s. I just figured it was something with transmission programming BMW changed for the LCIs. Guess I'll need to get a video and compare to be sure.

[Sticky]

My tech even asked if I had a dct

I'd be concerned about that tech.

[e90TiAg335i]

I knew that was coming...lol He IS a pretty knowledgable guy. He knows I've done a LOT to the car. He really wouldn't be suprised if I did install a dct as I've talked about doing it in the past.

[Sticky]

I knew that was coming...lol He IS a pretty knowledgable guy. He knows I've done a LOT to the car. He really wouldn't be suprised if I did install a dct as I've talked about doing it in the past.

Haven't seen anyone do a DCT swap yet.

[e90TiAg335i]

No but anything is possible. I started to do the research but just don't have the time right now. Not to mention my wife would KILL me. Her: Whatcha doing? Me: Swapping trannies. Her: IN A TWO YEAR OLD $50K CAR? WTF!!!!!!!!! I think you get the idea...lol

[Sticky]

No but anything is possible. I started to do the research but just don't have the time right now. Not to mention my wife would KILL me. Her: Whatcha doing? Me: Swapping trannies. Her: IN A TWO YEAR OLD $50K CAR? WTF!!!!!!!!! I think you get the idea...lol

I understand what you are saying and I'm sure it's possible but nobody, even the big name tuners, has done it. They usually end up ditching the DCT for something else which tells me this is pretty damn hard to do.

[LostMarine]

its fast, but def not DCT fast. hotrods car is shifting slow though too. that looks about normal to me.

**edit, actually it does look a bit faster than usual, still not dct territory though

[themyst]

No but anything is possible. I started to do the research but just don't have the time right now. Not to mention my wife would KILL me. Her: Whatcha doing? Me: Swapping trannies. Her: IN A TWO YEAR OLD $50K CAR? WTF!!!!!!!!! I think you get the idea...lol

If you short shift at around 6000 RPM, the car shifts quick. If you let the transmission shift itself at redline it will slow down guaranteed.

The reason I picked hotrods video is because you can compare redline shifts, true apples to apples.

[Brey335i]

I feel like that video looked pretty slow. Seems right about the same speed that my AT shifts...

[George@BMS]

If you short shift at around 6000 RPM, the car shifts quick. If you let the transmission shift itself at redline it will slow down guaranteed.

The reason I picked hotrods video is because you can compare redline shifts, true apples to apples.

I made a thread about this in October. You said I was being unscientific.
It can be controlled and altered.

[e90TiAg335i]

Paid closer attention to the shifts on the way home tonight and they definetly are not quite as fast as themyst's video. I did let it run through redline also.

[klipseracer]

I mentioned swapping a DCT as well... I just don't want to have to buy a 335is to get the dct in the N54... I want an E93 DCT N54... If I could have it the way I wanted it anyway. Wonder what needs to be changed?

[Sticky]

Wonder what needs to be changed?

Knowing BMW, everything.

[themyst]

It's impossible to really appreciate what these shifts feel like in a video... Would make more sense if you were actually driving the car.

[tofu]

your shifting does appear faster than mine. i did always feel that with more power, my shifts got worse, but terry's reply leads me to believe it is just placebo.

[BavarianBullet]

need to vbox or dyno it and shift and then I think it'd be more obvious since the rpm drop could be graphed.

FWIW, my '11 335xi shifts plenty slow. Sometimes it seems to even ignore my DS mode shifts altogether.

[enrita]

On stage 3 street my shifts are VERY fast and tight.
On the race map i hit the torque limiter set an 512 ftlbs . Working with cobb finding the right spot. Very close now.

[tofu]

now if there was a way to initiate shifts faster from the paddles...

i sometimes feel like it takes a whole 0.5-0.7 seconds to respond...