Torque converter size

[dancinwulf]

Have a 1970 Duster 340 727 am looking to replace my TC is there a benefit to the size of TC such as an advantage to the 9.5, 10, or 11 inch if so what would it be. This is a street car but it was going pretty well but the TC took a dump and it was not stock so I am not sure what would be the best replacement. It was about a 3600 or somewhere near there.

 

[Hellrats]

As the diameter of a torque converter decreases, the stall speed (RPM) goes up. Most of the factory torque converters are 12-13 inch diameter and have a stall speed around 16-1800 RPM. This promotes excellent fuel economy and drive ability because they are specifically designed for these purposes.
The problems arise when the modifications are done to the fuel system, camshaft or other engine control systems. Smaller diameter torque converters are needed to provide more slip at idle. This allows engines with a lot of camshaft to idle better. As the torque converter and
horsepower range is moved higher through the RPM range, the smaller torque converters with their higher stall speeds provide maximum torque multiplication where needed. Also the same torque converter will react differently when used behind different engines. So in short you need to match your torque converter to the engine / camshaft and gear ratio. If your TC did "take a dump" you'll need to to at least disassemble the transmission and inspect it. I'm sure you will find burnt clutch plates. Make sure you at least flush out the cooler as well. If it was a 3600 as you stated it would be way more than a street car needed. You could run that but you'll have to add a cooler. As a side note, the factory convertor would have been about a 2400 stall.

 

[Jimacuda]

Call Edge converters...Andre will ask you lots of questions and build the correct sized converter to match your setup and needs.

 

[roccodart440]

You definitely at least want to do a flush, but better yet an inspection.

I've run a 3500 convertor in my car and a 4000 convertor in my last car for 20 years without issue with a ton of street and even daily driving miles. IF you have a quality convertor it's not an issue.

More on a quality converter... you are better off with a smaller tighter convertor than a looser larger one. I.e. a 10" that stalls at 3000 vs. a 10.5 or 11 that stalls at the same is desirable. really you shouldn't even have to choose. Call and give them your specs and usage and they should set you up with what you need. Dynamic once gave me a choice on a a 9.5" or 10" that stalled the same. THe smaller one cost a little more but had some added features.

 

[transman]

Get a converter that is built for YOUR APPLICATION by a quality builder of performance converters. These builders will ask you a lot of questions to ensure that your get what is best for your combination. If you go to any of their websites, you typically will see an information sheet they want you to fill out. Any mis-information you give them will not be to your benefit. Also, just because the converter in my car is doing what it was intended to do, doesn't mean it would perform worth a damn in yours.
Don't let price be your only guide as you will only get what you pay for. Buy directly from the converter builder. Auto parts outlets that sell performance converters have staff that mean well, but usually lack the knowledge to get you the right converter. Avoid used converters.