What converter depends on the gear ratio and idle speed of the 572. Need to figure out what it will idle at, and also the rpm of the engine in it's usual cruise speed.
The higher the rpm, the more heat, and that's because it is only delivering full pressure to the clutches at the set stall speed. So if you cruise with the engine rpm at 2800, then any higher stall speed will be creating heat, and the higher above your cruise speed the more heat.
For all out race engines that are constantly running near peak rpm, the higher stall doesn't mean much for heat, since they're almost always above and never doing much low rpm running.
I would determine what your usual cruise speed and rpm will be, and get a converter that's just below that speed.

 

Hi, thanks for your explanation. The engine builder suggested a 3000 RPM torque converter but he told me as well that if I need a lower RPM torque converter, he needs to change the cam shaft accordingly. What do you think of a 3000 RPM torque converter?

The gear ratio you are referring to is for the TH400 or the rear axle? If it's for the TH400, I do not where to start but for the rear axle will be 3.55

Engine idle speed is stated to be 1000 RPM.

Engine rpm in it's usual cruise speed - this is difficult to determine perhaps our island is small and the roads are not long. But on my 85 camaro, the RPM would read 2500-3000 rpm normal cruise speed for approx 3 minutes on the longest road we have. Other than that, the engine RPM will be all the way from idle up to 5500 having fun with the car.

The more I read on stall speed and torque converters, the more complicated it gets to me. Can you please explain this again? So if you cruise with the engine rpm at 2800, then any higher stall speed will be creating heat, and the higher above your cruise speed the more heat.

So if my cruise speed is 2500-3000 what will be the correct converter for me?
Thanks for all your help and time

 

The ratio you're concerned with is the output of the trans you choose, plus the rearend ratio. The TH400 is a one to one ratio, so the output is the same as the engine at cruise speed. In this situation you're only concerned with rearend ratio and tire diameter. If you run 3.55 rear gears, with a 27" tire, then your rpm at 65 mph will be around 2875 rpm, and at 35mhp it will be 1550 rpm. So you'll probably be in 2nd most the time around town.
The heat that's developed is when your engine is running slower than the converter's stall speed. Once you go past that speed there's no excess heat as it's reached full pressure. I'd stick with what your engine builder suggests for a stall speed, but just be aware that it might be higher than most of your driving, and will always build a little excess heat if you can't run fast enough to reach stall speed in your cruising. Also make sure you run a good sized trans cooler that's separate from the radiator, and will help the life of your transmission.

 

Hello. With the above calculations if I go for a 2500 RPM torque converter will it be streetable?

Questions:-

1) So the engine RPM needs to reach 2500 until the transmission clutches are fully engaged and will be no slip and no extra heat?

2) Below the 2500 engine rpm (say 2000) the transmission will not be fully engaged and clutch will slip?

3) Above the 2500 engine rpm (say 4000) the transmission will be fully engaged and no clutch slip but will be torque converter slip internally. As well this will cause heat?

Thank you

 

1, 2, 3....No, not at all.
The "slip" is happening inside the torque converter, not the transmission. The converter has a pair of "vanes" (think of it as fan blades or a water wheel) that are only connected by fluid friction. The converter engages itself at a certain rpm (stall). Until then, it's slipping and that slipping causes extra friction and more internal heat of the torque converter. That heat (hot fluid) is pumped through the transmission and raises the temperature of everything. Even past the stall point of the converter, it slips a little bit naturally. A locking converter on the other hand, has a clutch that mechanically locks the converter completely once in overdrive.
I think I may have a bookmark on the workings of a torque converter, I'll look.

 

How Torque Converters Work

 

Yes, every torque converter has some slippage internally, except the lockup converters Camaro69 mentioned. None are 100% efficient, but that's not a problem. I'd not worry too much about it, and stay with whatever your engine builder recommends.
All standard type torque converters will still pull slightly at idle, but you don't want a stall speed that isn't high enough for your engine, or your brakes wont hold the car at stoplights. Use what the engine builder says, and a good cooler. It's not a daily driver you're building, so it wont ever be like one.

 

Thank you camaro69 and every one who helps me in making good decisions and understanding a good build.

 

Yes 1971BB427, I will stay with the engine builder recommendation. The builder told me 3000 rpm or lower is possible as well. So if I stay with 2500 - 2800 torque convertor with my setup you think will be ok?

 

I would have a converter built for your car. They arent that much more than an off the shelf item. Also it helps to think of a converter as a fan blowing directly at another fan. Here is an example.
Performance Torque Converters of Texas - drag racing
To determine your engine’s peak torque and match the stall speed ratio with the engine’s horsepower, we will need to know the engine size, vehicle weight, cam specs, rear end ratio and transmission type.

I personally have only bought three or so in my life. One was a mild Hughes, a used unknown one that was said to stall at 4500, and finally I got one from Coan. The one from Coan was the best. I drove down to Coan with a buddy to get a Powerglide from them. While there they went over my combination with me and told me I needed a 5500 stall for the car I had at the time. That turned out to be the single best upgrade to the car. Between the trans and the converter I dropped 4 tenths off my time. My car never felt so good either. Here is a link to Coan's site.CoanRacing.Com | Turbo Hydramatic 350 & 400 Converters They stand by their work too.