400 Turbo Question.
 

What is the 2.75 first gear used for is for a Heavy car or light car is it better for the launch. What does it improve.

400
 

2.75 is for something really heavy or with low torque. If you put a 1000hp engine and a th400 with 2.75 first gear, in something under 2200 lbs, when you leave the lights you will either blow the tires or shake your self to death by notting up the tires?

Light cars with high power usally run powerglides, with a 1.76-1.90 first gear. These cars have enough power to launch hard from the tree with out needing the additional gearing, or a 3 speed transmission.

I hope this helps, im no pro, just my two cents...

2.75
 

I found that the 2.75 is great with a small block because of the limited torque. If you build a torquey small block or run a big block , it isn't necessary.