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Someone educate me on torque converters (merged)

35K views 100 replies 50 participants last post by  Jeremy77nova 
#1 ·
What is the need for different stall rpms? What does the stall mean? I feel like I should know this but I dont:eek: . Could some one please educate me on torque converters!
 
#84 · (Edited)
USMCNOVA make sure your convertor will match the 350 you plan on installing. When you go to order the convertor tell the vendor the specs for the 350 and any other info they ask for. that should help you get a convertor that Will work well with your future motor.

While the 283 is in the car since it will likely have much less torque then the 350 will the convertor will act like it has less stall then it will when you have the 350 in the car. (stall is directly related to torque) Though it would not be ideal for the 283 it will work good enough until you can get the 350 in the car. Good luck
 
#87 ·
B&M torkmaster converters are junk and not for modified engines. I had one last an hour before it sounded like a bunch of BBs in a bread pan. That was just a small cammed 350. I'd go with a TCI streetfighter, or their breakaway one at the least. If you dont get at least a 3000 stall you wont even feel it and it wont do anything for you.
 
#88 ·
torque converter

ok i'm still stressing the whole what stall to go with and i cant sleep so i thought i would post.... but anyways i'm getting the th350 installed next friday and he said he wouldnt go anything bigger than a 2200 with that cam and everyone on here recs a 2800 or a 3000 correct? and he said he had a 3000 at hs shop that i could use but he doesnt think its a good idea i know or think that the torque converter will help a lot with a 1/4 mile time how much time do you think the difference would be and what do you guys think about the idea of the 2200 -thanks
 
#89 ·
if you like the feel of a good hard shift go with the 2200, the 3000 will soften your shift kit, i had a 11" 2400 and it would only stall to 2000 in my 350 with a 222 degree @ .050 cam (2400-5400 power band) . my 10" 3000 stall only went to 2500 with a 230@.050 cam (3200-6200) so small blocks stall at the low side of a convertors range, the 3000 will make more heat with that small gear, so its a matter of taste. if it was my car i would go for the 2200 just because of the shift kit and i would get 3.55 gear with that cam.
 
#90 ·
Anything under 3000 stall will drive like stock and not even be noticable to anyone other than you because you know you put it in. When I built my first engine I ran into all those skeptics also....."thats way too big" Turns out the torkmaster i baught was junk and like stock, I went with a TCI breakaway in a cammed 350, and it was pretty good. I'll never go under 3500 again though, unless its a turbo application where things are a little different.
2200 stall would probably make no difference in the 1/4, if you want a difference get a good converter. You can run a big stall on the street and it drives normal. They dont rev like in neutral and then hit at the stall speed. You can take your foot off the gas and it will roll and you can start out slow and go normal. Its when you mash the gas is when it flashes to the stall speed.
If your cam is to 2000-6000 power band, even a 3500 stall is good, then your dead into your power when it hits. And most the time you need to get up to that to get it motivated.
If the guy is telling you a 3000 is WAY too big, I'd question if he knows the slightest of what hes talking about. If you had a big block with 500# tq then you can afford to go smaller. But you have a 350, right?
350+small or mild cam= minimum 3000 stall.
 
#92 ·
i prefer a flash higher in the power band. if your motor is making power from 2500-6000 then i would get a 3500. you want to get the rpms up in the power band for a better launch.. imo
 
#94 ·
I'd got higher than that 2200...I put a holeshot 2,000 in my '72 w/ mild 350 and was a little disappointed. I could tell the difference over stock--but a bit more would be nice.

IIRC this is mostly a street driven car (daily driver?)
If that's the case, I'd comprimise a little between best converter for acceleration vs. driveability/reduced heat of a lower stall.

A converter advertised at 3,000 will probably stall around 2,500-2,600 behind your 350 in your fairly light nova...Like in your last post, I'd say that 2,500 or so would be a great compromise for a daily driver....

I wouldn't want a true 3,000-3,2000 in my nova. I do a lot of highway/freeway driving between 2,500-3,000 and having that converter slipping for prolonged periods like that creates a LOT of heat.

Make sure you get a good (large) tranny cooler, as I've seen a lot of transmissions die because of the excessive heat of high-stall converters.
Just my opinion, YMMV.
 
#95 ·
I Had a 4800 stall in my nova drove it on the highway every day to work. If you want your tranny to last get a huge cooler regardless if you have a stall or not. And Do NOT use the cooler in the radiator, eliminate it all together, that is a heater for the tranny fluid since your radiator coolant is 180+.
Overheating is the number 1 reason for auto tranny failure.
 
#98 ·
Stall converters

I'm a little confused on stall converters. How do you determine the correct stall converter for particular application? Is it based on HP of the engine?
I'm confused and would like more info. Thanks
 
#99 ·
I'm a little confused on stall converters. How do you determine the correct stall converter for particular application? Is it based on HP of the engine?
I'm confused and would like more info. Thanks
there is lots of information out there on this - search the internet. It is not based on horsepower, rather it is based on the performance RPM range of your engine setup and where that range starts - determined largely by the cam. For example, if your cam has a performance range from like 2500 to 5500 rpm, you want a stall converter with a "stall" rating of about 2500. If you have a racing engine (high rpm most of the time) with a racing cam, and a performance rpm range of 4000 to 6500, then you need a converter with a stall rating of 4000.

also, big block engines have more torque, and therefore will engage the torque converter "earlier" than the equivalent HP small block motor would. So if you have a big block, you will want a converter with a slightly higher stall rating than a small block with the same HP.

that's my understanding anyway.

Most street performance cars have converters with stall ratings of about 2500 to 3000. Most drag racing cars have stall ratings of like 4000 and higher.

also seems like the higher the rating the more expensive it is.

Lee
 
#100 ·
Thanks for the info. My engine is the GM Performance HO 350 330 HP
Based on what you said, I would be better off with a 2500 stall. Is that correct? I do have all of the specs on the engine. They are listed on GMs web site. I also had my car dynoed last year and it is what it is:) Thanks for the help
 
#101 ·
This is from a drag racing online site,not sure which one.

Drag race torque converters: Love them or hate them, but if you select the wrong converter for your race car, you'll end up with a slug at best and an unraceable car at worst. What's the purpose of increasing the stall speed of the converter? For street-strip use or dedicated drag racing, increasing the stall speed allows the car to leave the starting line at a higher rpm, usually at a point where a modified engine is producing more torque. That translates into quicker elapsed times and increased speeds. Because of this, the most critical component in the performance mix of an automatic-transmission-equipped car is the torque converter. That should be no secret to most of you. The real secret is the way converters are rated and how the ratings affect the performance of your car.

When discussing torque-converter stall speed, two terms, and, consequently, two entirely different numbers are used: "rated stall," commonly called "footbrake stall," and "flash speed." What's the difference? Footbrake stall is just that. You load the converter by stomping one foot on the brake and the other on the gas. Watch the tach. The rpm at which the converter overpowers the brakes is footbrake stall.

Flash speed is quite different. Flash occurs the instant you release the footbrake and the rotating inertia, which is stored in the engine-flexplate-converter, is released. In many cases, this flash speed can be anywhere from 500 to 2,500 rpm higher than the footbrake stall speed. Often, a racer will stage at idle, hold the brakes, and "flash" the converter by flooring the gas pedal the instant the last yellow on the Christmas Tree comes on.

B&M points out that flash stall can be changed just by reworking the load of the converter. For instance, if a car has a 4.10 rear-axle ratio and a flash stall of 2,800 rpm on launch, a change to a 3.90 gear might increase the flash speed to 3,000 rpm. Why? B&M points out that the effective load on the converter went up. It also works the other way. If the same car used a 4.30 rear gear, the flash stall speed would go down. B&M explains this is because the converter has begun to couple up progressively as its load decreases. Thus, the combination with the 4.30 gear would make the car easier to move than the 4.10 and 3.90 combinations.

So far, so good, but herein lies the grief: Some converter manufacturers advertise the stall speed of their converters using the footbrake figure, and some use the flash-speed figure. As can be imagined, this causes no end to confusion - and it's compounded even more by the complex array of variables that contribute to converter stall speed.

Generally speaking, the larger the torque converter, the more torque and horsepower it absorbs. Because of this, a larger converter usually has less stall speed than a smaller-diameter converter. The variable is, of course, the fin angle inside the converter. Because of fin-angle changes, it is possible - in theory and in practice - to produce a converter in, for example, a nine-inch size that actually has more stall speed than an eight-inch converter. The stall-speed changes to be gained by reworking fin angles obviously are limited. The stall speed can only be increased so far before a smaller-diameter converter is necessary.

Many factors besides the converter have a direct impact on stall speed. ATI points out that engine type, engine power characteristics (and, more important, engine torque characteristics), bore, stroke, induction system, cylinder-head modifications, altitude, chassis weight, chassis modifications, tires, header tube diameter, and even body style affect stall speed. As an example, a converter that stalls at 2,500 rpm in a lightweight roadster with a small-displacement mouse engine might stall at close to 4,000 rpm in a '55 Chevy with a 454. Place one car at sea level and the other in high altitude, and a whole new range of stall speeds will result.

TCI concurs with ATI and stresses the importance of knowing complete car specifications before contacting the converter manufacturer. TCI added that nitrous-oxide, supercharged, or turbocharged applications also have a large influence on the size and type of torque converter required.

Basically, when selecting a converter, the converter stall speed should be coordinated to the engine-torque curve. It should come as no surprise that a high-revving, peaky, three-inch-stroke small-block will require a much looser converter than an oval-port, lumbering, four-inch-stroke rat engine.

Optimism, especially in the area of engine output, can be detrimental to converter selection. Turbo Action notes that inaccurate engine power and torque estimates provided by racers can seriously affect the performance of the torque converter. The same applies to optimistic dyno tests. To combat this, Turbo Action maintains that a converter manufacturer can never have enough information. It's up to you to supply it.

A-1 Automatic Transmissions agrees and notes that racers have a tendency to use torque converters with stall speeds that are too high. Said A-1's Marvin Ripes, "When recommending torque-converter stall speeds, we tend to be conservative. In order to come up with a stall speed for a given combination, we rely upon years of experience with countless different automatic-transmission combinations. There are some trends that appear in the torque-converter selection process that tend to influence the selection of stall speed. For example, a three-speed-automatic combination prefers a converter designed to work at peak engine torque. On the other hand, a Powerglide combination prefers a converter designed to work above peak engine torque." Ripes agrees with the other manufacturers with regard to information: Supply everything the manufacturer requests, and don't fudge on the specs.

As can be gathered, specifying a stall speed for any given converter is virtually impossible due to the wide array of probable engine and torque curve combinations. What about the stall-speed numbers published by converter manufacturers? Almost all manufacturers will tell you to consider these as guidelines only for stall-speed potential.

Before taking a closer look at the overall converter-selection process, one more item should be considered when dealing with high-stall-speed torque converters: efficiency. Typically, as stall speed increases, overall converter efficiency decreases - though, to some degree, this relationship has been tightened in recent years. For example, a small-diameter performance converter will almost always slip more than a large, tight OEM converter. In most cases, a typical performance converter will slip from 3 percent to 5 percent at coupling (part-throttle conditions). When a high-stall-speed converter is installed, the engine rpm increases under certain conditions, as does the ATF, or automatic transmission fluid, temperature. That's why a large, high-capacity cooler is almost mandatory in an application that experiences regular hot-lapping.

So how do you know which converter is right for your application? Frankly, it's impossible to buy a converter off the shelf and expect it to be right for your modified car. The only way to tailor the converter to your combination is to check with the experts: the converter manufacturers. ATI, for example, builds hundreds of different eight-inch race-converter combinations and has taken the time to computerize more than 7,000 vehicle combinations so that the right converter is manufactured for your car.

Hughes makes a valid point about the converter-selection process: "Be sure to spell out and understand the real application for the converter. A Super Gas or Super Comp car doesn't need a converter designed to squeeze the last tenth or mile-per-hour out of the combination. Instead, the combination needs a converter that's engineered for consistency."

The criteria for selecting the right converter are many and extremely important. Before selling a converter, ATI requires the following information; all serious aftermarket transmission and converter manufacturers will require similar information.

Chassis
Vehicle weight: The weight tells the converter manufacturer how much work is needed to reach a certain elapsed time. It affects gear ratio and helps indicate what converter flash rpm can be used in your combination.

Body style: An initial calculation of the horsepower/gear ratio will be made and may be adjusted if the car has a large frontal area. This gives the manufacturer an idea of how much air the car is pushing as it enters speed traps.

Performance
Class or bracket: The manufacturer needs to qualify your needs as accurately as possible; it might already have significant information about your type of combination on file. Additionally, converters for class or bracket racing or street-strip duty have major differences.

Average e.t., speed, 60-foot times, and rpm at the e.t. light: The manufacturer wants to know the present performance rating on your car. How efficient is your converter? How efficient is your entire combination? If you're building a new car, the manufacturer can estimate how fast the car will run and help to choose the right combination of components before mistakes (often expensive) are made.

Engine
The following information is required to evaluate the combination:


Bore and stroke
Type of cylinder heads
Cam lift, lobe centerline, and duration at .050-inch
Carburetor and manifold
Compression ratio
Primary header-tube diameter
Gear ratio
Type of transmission: Once the manufacturer knows which transmission is in your car, it knows what low-gear sets are available for your combination. Tail-housing length can help identify the transmission.

Rear-axle ratios and tire size: This information is required to calculate the actual output gear ratios (overall ratios in the respective gears), engine rpm, and vehicle mph. It is possible to have a good elapsed time and high trap speed but still have a torque converter that is all wrong for your car. Trap-speed rpm will tell you if the converter is operating efficiently when going through the traps. Typically, 100 rpm of torque-converter slippage equates to a loss of 1 1/2 mph through the traps. In essence, too much slippage means that you're throwing away usable horsepower and elapsed time.

Suspension and tires
Type of rear suspension: This information is especially helpful in diagnosing problems with your car or combination. In some cases, a loss of performance has nothing to do with the transmission or torque converter - it's in the chassis.

Tire size and code: Through extensive testing and racer feedback, racing-converter manufacturers have identified the characteristics of many tires. Tire growth, sidewall characteristics, and compounds are taken into account when selecting a torque converter. This testing has also determined which tires work and which don't with automatic-transmission combinations.

Miscellaneous
In addition, the manufacturer will request information on fuel type and ask if nitrous oxide is used. The tach type is considered, and information will be requested on motor-mount midplates, flexplate bolt circle, past performance, past equipment tested, and so on. Expect a barrage of questions before the right converter is selected.

One size doesn't fit all when it comes to torque converters. What's the bottom line? Contact manufacturers directly for an exact recommendation based on your combination. Remember to provide accurate information about your own combination. If you fudge the numbers, you'll end up with the wrong converter, and you won't be happy. That's one thing that can be guaranteed.




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