Full Size Ford Bronco Forum banner

1 - 7 of 7 Posts

·
Premium Member
Joined
·
5,415 Posts
Discussion Starter #1
Just out of personal curiosity, I've been trying to understand the performance difference between a large and small torque converter.
I understand smaller ones are generally preferred for high stall builds and larger ones for low stall builds, and that there is less rotating mass with the smaller one so shifts will be more gentle and the engine can rev a little quicker.

Let's say we're comparing a 10" and 12" both built to stall at the same RPM (say 2500 for the sake of argument)

1. Would one generate more heat than the other?

2. Would one output more torque? (more efficient conversion?)

3. Would one of them feel tighter at light load? (say normal driving vs full throttle launches)

4. Would one of them be a more direct coupling at cruising RPM higher than the stall speed? (like 3000+)
 

·
Registered
Joined
·
220 Posts
I don't have the answers but i believe the stall speed itself contributes to heat and not necessarily the case size.

Maybe one would be less efficient than the other?

My converter is a UCC that flashes around 5000 but is reasonably tight down low and is very driveable. It's a 10"

I think the higher stall speeds are where you would see the differences more pronounced.
 

·
Premium Member
Joined
·
5,415 Posts
Discussion Starter #4
I'm not looking to buy one at the moment, this question is really just for my own knowledge and understanding.

I know torque converters are more sophisticated than just a clutch or basic fluid coupling. A clutch can not put out more torque then is entering, it can only slip to convert excess RPM into heat, a torque converter can actually multiply torque.. for instance, with 2000RPM going in and 1000RPM going out, the transmission can actually be receiving more torque then the engine is putting out (or so I've heard)

So my question is really, does a 10" torque converter with a 2500rpm "stall" have a better torque conversion ratio than a 12" 2500rpm converter?
 

·
Registered
Joined
·
220 Posts

·
Premium Member
Joined
·
5,415 Posts
Discussion Starter #6
Long winded, that's putting it mildly, but it does have some pretty graphs so I may do a little reading later.

I did find the answer finally, I called a good trans builder and started asking questions, he spent an hour and a half on the phone with me and answered all my questions so I ordered a transmission from him. maybe i'll get a good one this time!


Anyway to answer my own question, in case anybody else is curious, the way to raise the stall RPM of a torque converter is either to
1. reduce its size
2. reduce the fin angles.

The negative to option #1 is that a smaller converter is generally not as strong (so needs to be built really tough to hold high horsepower)

The negative to option #2 is that as you go beyond a certain stall RPM (very little positive angle on the fins, or even negative angle) the converter begins to become less efficient... this means that instead of converting torque (which can be up to a 2.5:1 multiplier) it just makes a bunch of heat, so you're throwing away power.

In other words, if you want a flash stall at like 2500rpm or higher, a 10" will give you more torque from a standstill then a 12".

Here's an article I found with some interesting info as well
 

·
Ford Hoarder
Joined
·
6,280 Posts
Jay at Broader Performance more or less advised me the same.
 
1 - 7 of 7 Posts
Top