Last year, I swapped out the jet-a-way in my 1966 cutlass, and installed a TH400 out of a 1979 Buick Electra instead...
I didn't really care about the torque converter and just installed the one, the transmission came with.
Now I just wondered, which convertor you would choose for my application!
Engine is the original 330, 2.78 rear gears...I know it's not a race car, but I feel something keeps it from being faster, could that be caused by a wrong convertor?
Any help will be greatly appreciated, hope to learn something about this topic!
Thanks for looking

 

I'm no tranny expert but I'd say the torque conv is probably fine for your setup. If you feel a lack of power it's probably due to the 47 year old engine that's likely putting out well under 200 hp

 

Two summers ago I swapped out my Jet-a-Way for a TH400 Switch Pitch and a 12 bolt with 4.10 gears. I know it's not an apples to apples comparison but it did make a huge difference. I have the same engine you have in yours currently and also had the 2.78's before the swap.
That being said I don't recommend the 4.10's, lol. I'd prefer something in the mid 3.00's range. 3.42's? That would really wake up the 330.
Since you have a standard TH400 I would go with something with a little higher stall. I think those stock converters are in the 1500-1800 range. I would go with something in the 2200-2500 range. You'll hardly notice the difference accept when you step on it. Right off the bat you're going to notice a difference between the two transmissions because of the first gear ratios. ST-300, Jet-a-Way, have a 1.77 first gear ratio and TH400 have a 2.48 first gear ratio. The ST-300 is almost like starting off in second gear with the TH400 as far as gear ratio goes.
Hope this helps.

 

Dan be aware that while a THM-400 is a very robust transmission, it eats more horsepower then the old 2-speed Jetaway. But the 400 also has a lower 1st gear for a quicker takeoff, but at the same time the Jetaway may have had a switch pitch converter which would have made it close to the 400 for breakaway off the line. You could get a looser converter for the 400 at the expense of more heat and less mileage on the open road or, better still, try and find a pre 1967 switch pitch pump and torque converter to retrofit into your present 400.

 

Agree with Trip - the gear would be more help!

 

As noted, the problem is a 3700 lb car with 2.78 gears and a stock (and likely tired) 330.

 

Hey guys,
Thanks for all the helpful answers and suggestions!!
To summarize it, the torque converter is the last thing I should pay attention to...
The ideal solution would be changing the rear gears to something like 3.42's, converting my TH 400 to a switch pitch TH400 and then freshening up the engine or swapping it for something bigger.
I don't have any comparison, so I don't know if my engine is tired or healthy, but it sure doesn't have the factory 320 hp (I'm totally aware that these numbers were extremely optimistic), when I step on it off the line it lays down a short stripe of rubber though

Is there any possibility to change the rear gears to something higher, without swapping the whole rear end?

Thanks

 

Just to give you an example Dancutlass. Like yours my 330 would barely lay down a strip before the swap. Now it can bake the tires from a standing start through first and into second effortlessly. For what I consider a heavy weight 66 convertible I think that's a big accomplishment. Of course the rear end gear change is probably most responsible for that but the fact that the engine is farther into it's torque band contributes also due to the higher stall of the switch pitch. My switch pitch is approximately 1800/3200 but that is behind a big block as witnessed through my tach when I had the transmission in my 70 Cutlass. What it flashes to in the 66 behind the 330 is anyone's guess as I don't have a tach in it. I have to be careful with the 4.10's because it revs so fast I could easily over rev it if not careful. 4.10's were nice at the track but I don't like them on the street.

Just be aware that if you do change the TH400 to a S/P it can use the same converter as the Jet-a-Way. Don't get rid of it.

 

Really sounds like a great improvement, Trip! Even though as you said the difference would not be as big with lower gears than you have, but definately noticeable.
Are you going to go with lower gears, when swapping in your 496?

Good to know thank you very much! What else do I need to convert it to a switch pitch then? Only the switch pitch pump?

 

I've never done the swap, my trans came that way when I bought it so I don't know exactly what's needed. I do know you need the front pump, converter, solenoid (does this mean different valve body?) and a two prong plug on the side of the case (probably use the ST300 one).
No the 496 will never see that kind of rpm. 3.42-3.55 is tops for rear gears for me.