Technical Torque Converter Stall Speed?

Just a quick question. If you have a 2500 stall speed converter behind a 283, then you install a higher horsepower and torque 383, what happens to the stall speed? I'm not doing this, just curious.

 

In my opinion, it'll be easier for the engine to hit the 2500rpm. The more torque and heavier the car, the more likely it is to achieve the max stall speed. Right?

 

I remember reading articles on this topic years ago. It’s a worthy discussion. In short, with the same weight of vehicle, but more torque, that same converter will react differently. Might need a higher stall speed, but lots of factors involved. Testing is probably best before you buy a new one.

 

For a given torque convertor, the higher the power so goes the stall speed. There are some variations depending on size/design that will change the percentage of stall speed increase, but you will get an increase.

 

If the converter is rated 2500 then you might get 2200 with the 283 and 2400 with the 383

 

Why is stall speed important.? Does one want higher or lower?

Ben

 

Your rear end gear and cam have a lot to do with selecting a stall speed, many variables but 2500 is a little high but it depends on other things gets the engine into the torque of the cam quickly but that converter is going to do a lot of slipping anytime you are below stall speed, heating up that fluid and running the radiator temp up, unless it is a lockup type I know the lockup feature went out on my OT truck and cruising on highway*****ed

 

Not really a benefit on a stock setup, but if you're hot rodding and your engines power is from 3000 to 6500rpm, it'll get you up in that power range off the line.

 

By definition, stall speed indicates when the engine will stall if you stand on the brake and gas at the same time.
If you have 'x' stall speed that simply means how much slippage occurs before engaging and stopping the engine. Also, keep in mind that the same 'slippage' occurs at elevated speeds so stall speed needs to be considered if/when calculating gears, tire diameter and cruise speed, etc....

 

Choice of stall speed is somewhat dependent on what your intentions are for the use of the car. Drag car, higher, cruiser around town, lower.

 

It depends.... LOL. If you're going racing, getting into the powerband quicker is a plus. Or if you have a lumpy cam that doesn't idle all that well, a higher stall speed can allow it to idle faster without excessive 'creep'. But the higher stall speed can come with a cost... mushy off-idle performance at low throttle openings, higher transmission temps and poorer fuel economy if it's not a lock-up type trans. A Smooth, lower idle speed will like a lower stall speed for best low-speed performance. Too high of a stall speed can mean that the convertor won't reach lockup at all in slow town driving.

There are two basic parameters that controls stall speed and convertor lock-up; convertor diameter and number of vanes/angle of vanes in the impeller/turbine/stator. Playing with the vanes will determine if the convertor is 'loose' or 'tight' which can affect the rate of slippage before lock-up is reached.

Diameter will also affect stall speed. Generally speaking, the smaller the diameter the higher the stall speed for a given power input. Back when Powerglides first started getting popular in racing circles, it was discovered that using a small 8" OEM convertor from a 4-cylinder Vega would net a high stall speed at low cost behind a V8. Problem was that hydraulic pressure got so high in the convertor that they would 'balloon' and fail. A much more robust outer shell was needed. The smaller convertors can be run 'tighter' for a given stall speed at the same power level compared to larger ones, but need to be designed for the power level.

A lot of trade-offs involved in convertor design, talking to a pro about your particular combination can pay dividends.

 

Just going through this exercise myself so will follow along.

 

Thanks all. I think I will stay with three pedals.

Ben

 

That's my choice too... LOLOL

 

Having the correct “ stall” speed converter is very important on the drivability of your vehicle. Having a slightly higher stall speed will let your car “ launch” quicker from the stop sign, on most mild engines, by letting the rpm go up slightly to make more horsepower. But it would be easy to “ too” much stall in a converter and make your vehicle a****** to drive!
My friend just bough a Chevy pick up that had a mild 350 and some kind of huge “ stall” torque converter and it drove terribly!
A converter matched to your driving and engine and vehicle, will make all the difference it the world! Bones said that!




Bones

 

I’ve read @squirrel s posts about using a switch pitch converter from a Buick? I think, anyways, since we’re on the topic of stall converters, are aftermarket switch pitch converters available? Not sure if the ones that came OEM are easy to find.

Seems like a good thing.

 

Is there any markings to show what the stall speed is on a torq converter.
I bought a 700r4******* several years ago and it came with a torq conveter and I don't know the stall speed. It came out of a 3/4 ton 2 wd truck with a 350 ci engine.

 

Kenne-Bell used to market their switch-pitch converters a lot in the eighties. Looks like a great idea to me. I don’t know what is currently on the market.

 

My 27 T with a 496 flashes around 4500-5000rpm. A little loose for the street but works ok on a 2500lb car with a .714 lift cam.

 

First of all you have to understand, or remember, that there are at least 2 different things both called "Stall Speed". Technically the stall speed is the max rpm the engine will reach when in gear without the rear tires turning. If the brakes are strong enough and will hold the car in gear at full throttle that will give you the true stall speed. But there is also a "flash stall speed" which is the rpm the engine will reach when you accelerate under full throttle before the convertor impellor and turbine (i.e. the input and output) equalize. The 2 different stall speeds are not the same.

To answer the OP's question, the stall speed will increase under those conditions.

Someone else asked why this is important. A higher stall speed allows an engine to get up into the rpm range where the power band is strongest; this allows significant increase in acceleration; this is true both for initial acceleration from a stop as well as when the transmission upshifts into the next range; but as others, such as @Boneyard51 posted there are potential downsides to drivability on the street. One other potential disadvantage to a higher stall speed, especially for highway driving, is if the stall speed is equal to or higher than rpms at cruising speed the convertor will remain slipping while cruising, which creates a lot of heat. The shearing of the oil that takes place when the input and output speeds of the converter are not equal generates a lot of heat; so additional trans oil cooling is usually a good idea, or required even depending on the circumstances.

 

Three pedal's is sometime's referred to as... "Variable" stall. LOL!!!

 

Something I've been reading about lately, which I'm sure I'm way behind most others, but it's something called a Dump Valve, which reduces oil flow to the convertor allowing a higher stall speed. You can set this dump valve up to be operated automatically on an electronically controlled car; or manually with a switch that allows the driver to engage the valve for staging at the strip and for leaving the line for a harder launch, then disengage it for improved efficiency for a higher top end. That sounds intriguing for those with transmissions with no availability of a switch pitch convertor.

 

3 pedals must disable the car though, cause nobody with that many pedals drives em

 

I've got over 500 mile's on my**************, with 3 pedal's, since it got done. Been shaking down and tuning, and driving the dog piss out of it this year!!! Dingus... LOL!!!

 

Stall speed with a traditional 39 transmission is whatever the tach was reading when you dropped the clutch and pressed as hard as you could on the brakes. Somewhere around 1960 there were people going fast fast with an automatic but three pedals were still the king. I'm amazed at the number of "traditional hot rods" of pre-1964 vintage that are running automatics. I'm into my eighties and although I no longer have much in the way of mental recognizance I still know how to use my left foot to operate a traditional hot rod transmission. Screw them automatics, even if they are faster.

 

Stall is directly related to TQ output. The last street car I mullered around with in that dept had a 468 RHS crate motor. I ordered up a 2200 stall convertor for the 400 and the 3500 lb car (with driver) had a 3.73 gear. No issues. None. No excess heat in either the trans or radiator even after screwing around all night cruising and street racing. In fact it was surprisingly efficient in the MPG dept too.

"Yeah so what, what's the point?" Packaging. I could manually "flash" that convertor to 2400 by staging it up at 1200 with 9x28 slicks and a hard stab. A little more if I was good with the juice, closer to 2600. Driveability was actually pleasant with the 3.73 and the mild cam BBC. More than enough of everything everywhere. Another point closer to the question, depending on the 383 low end ability, or lack of, just the extra cubes I think would make it "feel" looser by a small measure but not sure it would create issues. If it was monster fire breather then yes, loose almost like a blown trans, and unless it was an actual performance convertor it might not live long. Directly related to TQ output. And remember stall ratings are not "zero until..." and always connect the crank to the trans at all speeds.

Oh yeah, stick vs auto debate? My ultimate dream Vette (L-88) would have it's monster 34 element 400 auto. Yeah, I said it, an automatic. And if I was to build an ultimate hoodlum racer again, automatic with a brake. 3 pedals are comfy toys and I love em like that but...

 

Over 20,000 on mine. 15,000 plus after "souping up " the engine. Planning a 4000 mi plus trip in July. Wish me God speed.

Ben

 

Damn you're sensitive

 

More power makes more stall that's why the old Vega converters were so popular, when behind a V8 instead of the 4 banger instantly higher stall.
On the opposite side of the coin I took my buddy's B&M holeshot 2000 stall out of his 56 chevy with a 427 bbc and put it in my t-bucket with a sbc, it doesn't stall at all.
Motor is a little hot and won't idle under a thousand, no stall makes it have a lot of creep through the 4 wheel drums at the stoplights.

 

I guess I'll jump in here.
As the cam duration goes up, so does the torque curve.
Yes, the weight of the vehicle does have an effect on the stall speed when the vehicle is moving.
While static flashing or checking the stall, the engine won't know the difference.
What I'm getting at here is, a rumpity-rump cam in a 283 powered T bucket with a stock converter will be no fun at all at a light or when driving around town. Some type of raised stall converter would be necessary.
Talk to the converter man , with card in hand ;-)
Probably best to leave the mutha thumpa cams for the stick shift guys.
As stated, a lock up , higher stall converter in a later model trans would be another option.

On the switch pitch deal...I have never heard of anyone manufacturing any of the part parts for one.
The units I knew of being sold were just re-worked factory 11 or 12" cores.