Torque Converters......... I'm dumb!!

Ok, this car I have (68) is the 1st auto I have owned or ever been around. So I’m rebuilding my 351 and warming it up just bit, nothing crazy a cam and heads. Everybody is telling me to put a torque converter in. Please school me on them!!! I have been doing a bunch of reading on them and not sure where I want it to be. The car is going to be weekend cruiser only, no racing, unless the need arises at the stop light :crazy: . Just looking for some advice on which size would work well for what I am wanting. Thanks!

Since you’ve been doing a bunch of reading, I will assume that you’ve learned that they operate based on fluid pressure. As the pressure builds they engage the gears transferring power to the input shaft on the trans. The important part is what’s called the “stall” speed. To determine what stall should be used is easy. What does the cam card say to use? It all depends on the cam specs. If the cam says to run a 2000+ stall, then that’s what you should run. If it says 2000 stall and gears, bingo, there’s your answer. What cam is it?

As far as drivability goes it won’t Change much. The cam I have in my truck said to run 1800 stall with gears. So I’m running 1800 stall with 3.55 gears (originally 2.75). Driving around town, you would never know the difference. Sitting at a street light and stomping on it? Different story. Mash it to the floor from a stop, and though it happens very fast, I can tell the trans doesn’t engage until 1800 rpm. A 91 Mustang I was a party to building about 12 years ago had a 5500 stall in it. Drove around town just fine. When racing, you could feel it not kick in until 5500… So, just do what the cam says to do. If the cam says you can run stock converter, then it will simply be a preference. If it says the stock converter is ok, then run the stock converter, no need to change something that’s working perfect…

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Just saw your other post. I see you have the 260H cam. This cam will work fine with the factory stall converter, however it is more of a truck camshaft? Why did your builder and you decide to go with this cam? Just curious…

With this cam, I would just run the stock converter. Not gaining or hurting anything to just run the stock one. Unless you’ve got gears? If you have geared the car up, then maybe running an 1800 stall would help in getting you off the line a tad quicker? Again, not going to change daily driving any…

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That’s kinda the info I’m looking for. I understand how they work, but the whole stall speed has got me scratching my head. I have done nothing with the rear gears and really have no plans to do anything with them. As for the 260H it was a debate between that and the 268H. I have a lot of faith in my builder and he seemed to think I would be happier with the 260. I really didn’t know where to start when it came to choosing a cam.

I did some searching recently for the same reasons, did not fully understand the function of the TC.

I found this, and perhaps it will help:
Excerpted from

What does a high stall converter do?

I’ll try to keep it short because it’s an involved subject. Basically “stall” means when the torque converter “locks-up” under a load. With that, if you take a car with a 2,500RPM stall converter and you hold your foot on the brake hard, and hit the gas at the same time, (as if you were going to power brake), the “general” RPM in which the tires will break loose is at “about” 2,500RPM. If the converter was a 3,500RPM stall, then it would be at approximately 3,500 RPM in which it forces the tires to break loose. Keep in mind, if you put that same converter behind a nasty big block, in a car that has serious traction or is quite heavy, the torque of the engine will drive the stall speed up to a higher RPM, and an engine with less power will have the opposite effect and won’t be able to stall the converter out as high. It’s all relative to torque, vehicle weight, traction and rear gearing. It isn’t an exact science as far as an exact stall RPM goes.

Stock cars have anywhere from 1,000 to 1,400 RPM stalls from the factory. The reason a stall converter works is simple; an engine at 1,200 RPM is only making about 80 or so horsepower (on average), but at 2,500 RPM it could be making 150 to 200HP, and obviously trying to get a car moving using 150-200HP is going to be much easier than one trying to launch at 80HP or so. Most performance engines don’t make power until 3,000 or so RPM, hence why when you have a higher horsepower engine with a big cam, you need a higher stall speed so the engine is closer to it’s “power band” when taking-off from the line, otherwise it will fall on its face and be a turd off the line.

Some people believe that “stall” means the car won’t start moving until the engine reaches that particular RPM, and that isn’t even close to being true. We build race cars with 6,000 RPM stall converters and when you put the car in gear and let it idle, it WILL roll along at 5 - 10 MPH, just like any other car will when put in gear and with the brake off.

Torque converters make a tremendous amount of heat when they are operated below the stall speed. You really should use an additional transmission cooler with a higher RPM stall converter. Where this becomes very apparent is if you have an overdrive transmission and the engine drops below stall speed when cruising in overdrive.

The 260H will give you more power lower in the rpm range, so that’s most likely what he was considering for your daily driver. Lower rpm operation, in a daily driver than a full out race engine. I hadn’t even considered mentioning the heat issue like xr7g428 did, but that’s another factor. I do have a second trans cooler on my truck, and will run one in my Cougar as well… Of course my cougar will have a 4500 stall in it…

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Geez it is almost starting to sound like I better just keep it stock. That sounds like it may be the best route since I don’t plan on racing.

Which trans do you have? A stock convertor in a C-4, C-6 and AOD are all different stalls.


They’ll all typically be between 1600-1900. Not much different. It actually depends more what engine they came off of. The factory stall in a C6 400M is 1600, but the C6 from a 460 is 1900? Typically. So, whatever the factory converter has in that trans will be just fine. Or the factory stall for the cougar itself will also be fine.

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The stock convertor from the C-4 will be good. However, if your Cougar had a C-6 and you put a factory low-stall, something that is meant to be used behind a 460 in a heavy truck, will not work too well. It’d be very sluggish off the line. Not all C-6 convertors are the same. Just about anything stock for a C-4 would suit your Cougar pretty well.

Great! Thanks guys!