I'm in the process of swapping out the tired old LG4 and 700R4 for an SP350/357 and a TH350. I'm soon going to be ready to drop it in the car but I'm having trouble choosing the proper torque converter for my application. The engine came with a 153 tooth flex plate so hopefully that will work with a TH350, but I'm confused at stall speeds, lockup and the many different sizes of converters. The guy I bought the tranny from is a well known local expert with these transmissions and he said to not buy a lockup converter? Any reason why? I would call him but I've since misplaced his number. I bought it from him last summer so I can't remember the reason why he said to go with no lockup. Also what brand should I go with? I want to make sure I'm buying a quality product. And I plan on using the car as a Sunday driver once it's done so it'll probably never see any formal "racing" other than a pull every once and a while from a red light.

The cam specs are "0.473 in. intake lift, 0.473 in. exhaust lift, 215° intake, and 223° duration"

Thanks

Trent

 

He said NO LOCKUP because a TH350 does not have the capability of using a lockup torque converter.
The 700R4 has overdrive, the TH350 does not. You are going to need a different shifter.
Your camshaft specs suggest you use a TC in the 2200-2400 rpm stall range.
What rear end gear ratio does your car have? That will influence your choice.
Brand is your personal preference.

 

Thanks for the reply, I'm planning on going with the B&M Megashifter that fits right into our cars. As for the rear end I'm fairly certain its all factory, 3.23.

 

If you want to use a lockup torque converter on a TH350. You will need the TH350C. This used a lockup torque converter.

 

Make sure thats what you want before putting that TH350 in here. Most do that swap from TH350 to 700r4 for sunday drivers. The TH350 is 3 speed transmission. The 700r4 is 4 speed + lockup. Lockup is good for MPG and controlling trans Temps. Higher stall = more heat. Im not sure thats the best swap for a sunday cruiser. But im also not a transmission expert.

 

I agree. The other thing is you're going to feel slower off the line due to the numerically lower first gear. TH350 first gear = 2.48. TH700R4 first gear = 3.06. It'd be the equivalent of taking a 3.23 axle ratio and dropping it down to a 2.54.

That aside, for the torque converter, I'd go with a 2500 rpm. It's perfect for a street cruiser. With normal driving, you don't even know you have a performance torque converter... it drives and feels 100% stock. But when you punch it, you get the benefits. The higher stall speed also helps take load off the engine in gear at idle, which helps smooth it out too.

I ended up going with a Hughes converter, but I know everyone has opinions on which company makes the best ones. Though I have nothing but good things to say about mine.

 

The reason he said "no lockup" is because the Turbo 350 doesn't support that. Only way to get it in a trans like the Turbo 350 is the 350C, which if you didn't buy that, you don't have it. And I can assure you, if you had bought it you'd KNOW, by the giant hole it would have made in your bank account.

In 2023, a Turbo 350 isn't a good choice for a street driven vehicle. Was GREAT in the 60s & 70s; not so much 50-60 yrs later. IMO buying that before researching all the consequences was not a wise decision.

There's good reasons why all transmissions for cars from the last 40 yrs have lockup. Fuel mileage, lower operating temps, reduced engine wear from lower cruising RPMs; the list goes on.

The 350C is RARE. Almost as rare as frog hair. Converters for it are the same way, maybe worse. And as we all know, rare usually = expensive, and ALWAYS = hard to maintain or replace.

I'd STRONGLY recommend sticking with the 700. Sell the 350 and work up a 700.

2500 is about the minimum converter I'd get with a 700. I'd prefer to go a bit higher, like 2800 - 3000. As said, you'll hardly even be able to tell it's there in normal driving,. but when you step on it, the engine won't get lugged by being pinned at RPMs too low for it to make power. For the 350 though the question gets a bit stickier: if the car's speed is below the point at which the engine RPMs would exceed the converter stall, then the converter will be "slipping" 100% of the time driving down the road, which is a guaranteed recipe for a severely overheated transmission. This was the main reason for short transmission life and poorer gas mileage than manuals back in the day: no lockup and terrible gears (probably 85% or more of typical American V8 cars in the 70s had 3.08 or worse gears). Nowadays transmissions tend to last ALOT longer, because they stay cooler; and they use less fuel because more of the energy from the fuel goes into moving the car instead of heating up the trans fluid. You don't say what gears you have; if you have a low ratio like 2.73, you're certain to end up in this state. If you have 3.73 or higher it's not so bad.

 

Controlling trans temps, I guess that's why my trans guy also said to use an external trans cooler other than the one in the rad, I'll continue with the TH350 install but I'll hold onto my 700R4 and probably order a new UTI 700R4 crossmember just to have and set aside if I do want to do a quick swap further down the road. I went with a 3000 stall converter after, we'll see how this turns out lol.