I think a lot of people go a little overboard on stall converters, I did some searches on the internet for reasons and actual information from anywhere other than people that sell them or from people that think they know them. I see people all the time wanting to put a stall converter behind a moderately built engine and they dont need it. Example: A person has a 350/350hp engine, rpm peaks at 5500rpm, Peak Tq is 2600RPM (probally less) (You should actually put your vehicle on a dyno and find exactly where it is) According to the information below and several other sights I would want to use a Stall Converter 300-500rpm less than peak Tourque that puts me in the 2100 - 2300 stall range. Stock factory converters are usually between 1800-2000RPM and depending how much tuorque is applied they might stall as high as 3000RPM. So do you really need one? Your buddy will say yes, the salesman at Jegs, Summit, etc will 98% of the time will say yes. To really determine if you need one.
1. Get on the Dyno, You think it's to expensive? Usually $50 for a couple of runs and minor tuning, this will tell you exactly where your peak TQ is and if this guy is experienced with tuning and racing he will be able to tell you if you need a stall converter. It's far cheaper than wasting $250 on the wrong Tourque Converter that will only hurt your performance as well as getting even worse fuel econmy.
2. Can you smoke the tires real easy without reving it up and dropping it in gear? You dont need one, perhaps you have an open differential and only one tire spins, get a posi (better money spent) If you can spin the tires easily with road tires think about a set of DOT drag radials. If the vehicle is a combo street/strip and more for strret use then generally if your overall very happy with street performance you probally don't need one.
3. If the vehicle is a dog from a dead stop and doesnt really pickup untill your hitting the higher RPM's, you need a stall converter, or if the vehicle is overlly lazy through the entire range your gearing may be too high or maybe you just don't have the overall power you think you have.
My best advise is #1, I have a friend that owns a dyno shop, everytime I see him he tells me about people that bring their vehicles in after having them adding all these goodies to the engine (cams, headers, carbs, free flowing exhaust, etc. etc, etc.) and they think there putting out 450HP and after they dyno run their only putting out around 250HP at the rear wheels. If you are going to stay running street tires and you have no problem smoking the tires just off idle to having a stall of 2500 sittng at the lights reving your motor at 3000+RPM and then punching it, the tires are just going to sit there smoke.
http://www.kennedysdynotune.com/Torq...ter%20Tech.htm
Stall Speed and the "K" Factor
Stall refers to the maximum speed a the motor can achieve against the converter when the turbine is locked and prevented from rotating. The rpm achieved (stall speed) will be a function of the engine torque and the converter design. In general, the higher the stall, the less efficient the converter is at high speed. So why would you want a high stall converter? To allow the engine to get into the meat of the power band quicker. A converter optimized for drag racing will have a stall speed much higher than a street converter. Allowing the engine to get into the power band quickly more than compensates for the disadvantage of lower efficiency. On a street car, the penalty in gas mileage and heat generated by a high stall converter favors a lower stall. Also, a high stall can be annoying to drive on the street because it degrades throttle response. When you stab the gas, there is a delay while the engine revs before the car starts to accelerate. To illustrate how this works, there can be up to 0.5sec or more improvement in 1/4 miles times by switching to a high stall converter. The improvement all comes in the first part of the run, and interestingly, trap speeds may decrease due to the inefficiency of the higher stall converter at high speeds.
For a street/strip car, converter stall is a compromise. For example, a given combo may need a 4,500-5,000rpm stall for the best 1/4 mile times but be annoying on the street due to excessive "slippage" but a converter which stalls at 3,000-3,500 will allow tolerable street driving without too much effect on the 1/4 mile performance. Stock converters typically stall in the 1,500-2,000rpm range. Of course, what is tolerable to one person may not be to another and vice versa. To get a converter that stalls at the right speed for your application, you need to speak to the converter manufacturer. For best drag strip results, we like to see a converter that stalls ~300-500rpm below peak torque.
Labeling a converter as having a specific stall without reference to the motor it is behind is misleading and naive. That stock converter, which stalls at ~1,500rpm behind a stock motor, might stall at 3,000rpm or more behind a blown big block, if it didn't blow up first! To elaborate a bit: stall speed is not just a function of the converter. It is also a function of engine torque. This can be relatively easily described by defining the "K" factor. K is simply the constant in the equation K = rpm/sqrt{torque}. The equation describes the observed behavior of the converter behind a specific engine. What this allows us to do is determine what the stall speed of a given converter will be if we put it behind a different engine.
For example, if a motor has 400 ft-lbs. of torque and stalls a particular converter at 3,000rpm, K = 3,000/sqrt{400} = 150. Since we know K = 150, we can predict the new stall speed if torque is increased to say 500 ft-lbs by rearranging the equation to rpm = K*sqrt{torque}. In this case, the new stall would be rpm = 150*sqrt{500} = 3350. This formula isn't perfect. It won't work if the engines have wildly different torque curve, for example. And it won't tell if a particular converter will hold together under markedly increased torque. But it gives a decent ballpark estimate and serves to illustrate a basic aspect of torque converter function. For most street and street/strip, you probably want a stall in the 2,500-3,500rpm range. But do not buy an off the shelf converter thinking it will give you the advertised stall unless it has been proven to do so on an identical setup. Speak to the manufacturer first to be sure you are getting what you need for your particular combo.