identifying torque converter

[Bain]

I need a little help identifying/understanding my torque converter. I'm going to get a new one to match other new components and I have found some that match stall speed wise but for my th350 there are three different kinds. This is the list of them if someone could help explain these to me I would appriciate it.

1. dual bolt pattern (except variable pitch)
2. small bolt pattern (except lockup, high stall)
3. large bolt pattern (except lockup and variable pitch)

Thanks for any info you can give me.

Also if it helps any it's for an 81' z28 I'm replacing the stock converter due to a complete engine rebuild for drag car conversion.

[curtis73]

Its a little tough to decipher their things because there are other factors. You are also at a fun year since about 81-83, GM started switching their TH 350s to lockup converters.

The variable pitch is an easy one... avoid it. The switch pitch is an uncommon TH400 configuration from the late 60's/early 70's. Since some converters are identical between the 350/400 depending on input shaft configuration, they are advertised that way.

If you are building a drag car, make sure you get the pre-lockup 350 converter. I'm pretty sure your tranny is a non-lockup anyway, but the lockup feature was prone to failures in the 350.

Can't help you on the large and small bolt patterns. I know that trucks often used a six-bolt pattern, but you can use a three-bolt converter by just omitting the other three bolts. Not sure about large and small though.