let me get this right.. lol torque converters

[racin66coupe]

so, if you have a higher stall on a torque converter, say like a 2500RPM converter, that means the transmission wont "engage" until aruond 2500RPM? so it would act like being in neutral until 2500?

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[blue66mustang]

No not at all. What that RPM range means is where the converter stops "slipping" and for all intents and purpouses it is locked. A higher stall converter allows an engine to get further into its power band if it has a radical cam. This way it wont seem to bog down before taking off.

[Gun Jam]

Yes and I believe that would also be the rpm that would cause the engine to stall if nothing were moving as in a power brake situation as the converter would be locked and the wheels are not spinning so it would stop the engine from spinning as well....I think thats accurate.

-Gun

[jcoby]

Originally Posted by Gun Jam

Yes and I believe that would also be the rpm that would cause the engine to stall if nothing were moving as in a power brake situation as the converter would be locked and the wheels are not spinning so it would stop the engine from spinning as well....I think thats accurate.

-Gun

yeah, you can pretty much mash the brakes and the gas and it'll sit there at 2500rpm.

driving a high-stall torque converter is interesting. everybody should do it at least once in their life. it's a totally different experience from a normal transmission. everything feels .. sort of loose.

[kalli]

Originally Posted by jcoby

yeah, you can pretty much mash the brakes and the gas and it'll sit there at 2500rpm.

driving a high-stall torque converter is interesting. everybody should do it at least once in their life. it's a totally different experience from a normal transmission. everything feels .. sort of loose.

ya. push the brakes, slowly get the revs up. at 2500 rpm the engine will stall as it's locked up. but that doesn't mean the car wouldn't move below this rpm, it does that typical auto gearbox slipping ... anyway. don't have an auto, but that's how I understand it

[Gun Jam]

that said if a lot of your driving is city....the 2500 will generate more heat than a 1500.. as heat is generated whenever the converter is not fully locked....Its not bad for it if you can keep it cool. I drove around with a 2700 in my c4 for a long time...an auxiliary trans cooler couldn't hurt a trans temp gauge isnt too bad an idea either..

-Gun

[JMD]

Originally Posted by Gun Jam

that said if a lot of your driving is city....the 2500 will generate more heat than a 1500.. as heat is generated whenever the converter is not fully locked....Its not bad for it if you can keep it cool. I drove around with a 2700 in my c4 for a long time...an auxiliary trans cooler couldn't hurt a trans temp gauge isnt too bad an idea either..

-Gun

An OFTEN overlooked but IMPORTANT point.

Slippage = heat....

[4reboy]

I used to wonder this question too but never asked... I just assumed it still worked under 2500 otherwise it'd be near impossibly to drive on the street. Nice to read some of the more technical explanations though

[cprstreetmachines]

Yeah, there are tight stalls and loose as well. N/A stalls tend to be a little on the loose side. Let it slip to get the RPM's up, where say the same 3500 stall for boost, is tight, to keep the converter from slipping like crazy. I would say for most cars with 3.7's and up, a 3k stall pretty much drives like a stocker. My old N/A 3500 you could tell had a stall. It would go up to about 1000 rpm before it moved. Now my turbo converter was a 3600, left form a dead stop like a TOTALLY stock conveter. hit the throttle when moving and the rpm's didn't jump much because it was very tight. Meant to push against a transbrake with 600 hp at 3500, and not go higher. Hope this didn't confuse you more.

[THUMPIN455]

Depending on a a few different things, a converter will feel and drive differently even with the same stall speed. The blade angle of the impeller (connected to the converter case and always turning at engine speed) and turbine (connected to the input shaft of the transmission and driven by fluid from the impeller) and the stators shape and angle all contribute to how efficient a converter is, and where the stall speed range will be. That is how you get the loose and tight that CPRS was referring to.

Even with a very loose converter the car will still move, but it will feel like the trans is slipping until you get enough RPM to make the converter work. Under 3000rpm most of them drive normal, over that generally they start to slip a lot and make more heat. If you have a modern trans with a lock up converter, you can get around with a much higher stall, and once the trans locks it doesnt slip. Kinda nice really, you dont have a huge heat problem and you arent wasting fuel because its slipping. It will unlock when you open the throttle, and if you are below the stall speed, it will allow the engine to wind up and when it stalls you will feel like you were shot from a slingshot.

How much torque your engine makes, what gear ratio you have behind it, and how heavy the car is all contribute to stall speed. Stall speed is when the stator is freewheeling and the turbine and impeller are at nearly the same speed. Stall speed is also where the max torque multiplication is present, after that speed the multiplication diminishes, under that rpm it is rising. A light car with a small engine, think T bucket with a 302 on it, will have a lower stall and the converter will not slip as much, less mass to move, not enough torque to slip the converter. Compare that with a 71 Mustang with a 460 that is around 3800lbs and makes 600ftlbs of torque at the flywheel. That thing is going to work the converter much harder, since it has more than double the mass and triple the torque. The Mustang will stall higher than the T bucket will, and the same converter wont work well for both of them.

I have a 3600 from B&M that is a POS behind my 400s and 455s, it does little more than slip and it cant handle the torque my big engines make. Behind a 350 sbc it would probably work pretty well. The off the shelf B&M 3000 seemed to run much better, didnt slip nearly as much and can actually hold the power, but the engine I have it behind really needs a 4500 tight converter.

I like a 2000 to 2400 stall for my street cars, it keeps them from wanting to push through stop lights and makes it easier to drive with the slightly larger cams I like to run. They dont slip much but I still run a cooler because the factory coolers are barely capable of keeping up with a stock trans and engine, and heat is what kills a transmission. You dont always need a 4000 stall or even a 3000, it depends on where your engine makes its power.