is this what a torque converter replaces or can i get a ultralight flywheel. What kind of added performance can i expect?

 

first let me explain what a flywheels purpose is.

a flywheel is supposed to give the engine momentum to continue spinning. if you look at some really old engines they have huge flywheels, because they ran at really low RPM, and they had to have mass to store the energy created to keep the engine spinning until it had another combustion stroke.

on an automatic transmission the torque converter weighs a lot, and it is bolted dirrectly to the engine via a flexplate, that has the teeth for the starter on it, and it weighs about 1lb.

so in a car with an automatic transmission, the torque converter acts as the flywheel, continuing the momentum that the combustion stroke started.

hope I helped.

 

then can you get lighter torque converters?

 

No point in a lighter torque converter, it's filled with fluid anyhow, so the weight gain is neglible.

However, they do make high performance torque converters which would be worth your time.