I have a 1970 dart custom that im rebuilding. I am new to rebuilding cars, as this is my first one. I bored out the engine (a 225 CI slant 6), bought forged pistons, got a header, bought a new 4 barrel carb for the car, but I am having trouble getting a new transmission for this car. Unfortunately the mechanic i had is unable to help me anymore because of medical reasons. He mentioned that the transmission I should get used to be in old taxis and police cars. Since I don't exactly know what I'm looking for, can anyone tell me what kind of transmission will work best with this engine and how to identify it?

 

You need the typical 6 cyl version of the TF 904. Rebuild your original trans.
There was a special 727 made for the 6 cyl taxi, police car. Very rare, not likely to find one.

 

If I manage to find it, how much of a difference in performance will I see?

 

NONE ! it will be faster with the 904. the taxi 727 would be more durable. The 904 is more that up to the job. It was used behind 1,000 of V-8 models. I had one behind a 360 for a while.

Make sure to put some new rod bolts in the motor, have them magnafluxed