4L80E conversion questions

[streetk14]

I've been doing more research on my new transmission plan. I was driving an SMG M3 today, which got me excited about the whole paddle-shift idea. I really like the idea of the 4L80E with the TCI control unit and Steve's shrifter. There are a couple things that I have been trying to figure out about the electronic transmission swap. How does the TCU get an engine RPM signal? Does it sense torque converter speed, or is it wired to the ignition system? I have a full MSD system (billet distributor, 6AL box & blaster coil) if that matters. Also, what is the best option as far as speedometers go? I have a mechanical autometer speedo right now. Should I go with an electric speedo, or use an adapter to use a mechanical speedo? Thanks,
Andy

[Steve Chryssos]

The 4L80E employs the following basic input sensors:
RPM (engine speed, obviously)
LOAD (throttle position sensor-MAP can also be configured with the PCS controller for you boosted types)
TURBINE SPEED (Torque Converter Speed)
OUTPUT SPEED (Actual Tailshaft Speed is measured and used in conjunction with tire dia and final drive gear ratio to calculate "Vehicle Speed". Hence the sensor's name is VSS.

The 4L60E does not include turbine speed. To that end the 4L80E is a more comprehensive design just by virtue of the added speed input. Engine, TC, and VSS. I would guess that the 6L80E is even more comprehensive.

For RPM (regardless of trans type), you simply tap into the white Tach signal lead on your 6AL. Auto Meter has changed their speedos numerous times over the years, but you should be okay with what you have. I chose to eliminate the mechanical variable and went all-electronic.

[streetk14]

Thanks for the info Steve. What is involved in the electronic speedometer conversion? I'm assuming that it just needs a power, ground and speed signal from either the transmission or control unit. The TCU knows the vehicle speed based on output shaft speed and tire/rear gear inputs. Pretty straight forward, right?

[Steve Chryssos]

Absolutely correct. Signal, Gnd, 12v+. Interesting note though: Even though speedo signal is output, it can confuse the controller if the speedo is not calibrated. Go figure. The PCS controller does the same thing. Trans won't shift with an uncalbrated speedo. So leave the speedo unplugged (put a male/female connector in-line). Get the trans calibatrated to your liking, then go back and calibrate the speedo.

You won't read that hot little tip anywhere in the instructions.