Could someone explain to me what the differences in diameter of a torque converter means when it comes to driving the car? Do the smaller 8" converters launch harder than 12" ones, ect?

Thanks

 

In general, smaller diameter -> higher stall.

Higher stall, when properly matched to the engine, allows the engine to spin up into its power band at launch. My cars, for instance, "come on" at 3000 RPMs (purely a coincidence that they act the same), so the '57 has a little too much stall with a 10" converter (for the time being), and the Camaro has too little with a 12". Higher stall makes launch and shifts feel a little more "mushy", but 60' times are certainly improved with proper stall.

Actual stall speed is a function of the combination of diameter, stator angle, and engine torque. The 10" was advertised as 2800-3200, but the mild cam in the 396 makes it produce a little more torque so it stalls a little high. A fellow racer has the same converter behind a slightly more "built" 454 and it stalls right at 3200 for him. The Camaro converter is a "restalled" stock unit done by a local company, he said they typically stall at 1800-2000 - when I told him it stalls at 2300, his response was, "You must be putting out some serious power."

 

I thought stall speed was determined by the internal fins not by diameter of the converter? A smaller diameter converter will weigh less than a larger version, which is better for obvious reasons. More power will make a converter stall higher than what its rated at, or in a different car w/ more power, yes.

EDIT:We are both right. I took a second to look somethings up. To my knowledge, the smaller diameter can acheive the same stall speed w/o having the fins as shallow, because you have less fluid friction due to the smaller size...

Whereas the bigger converter is going to have to have the fins bent back a lot more because of so much more surface area, making it a lot less efficient.

 

I said "stator angle", but fin angle would probably be more accurate (not just the stator fins).

 

The internal fins(or how much fluid they can pump) directly affects the stall speed. So a smaller converter with small fins needs to reach a higher speed to get the same amount of fluid to be pumped.