Choosing a stall converter

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If you have an automatic transmission, then you don't have a clutch pedal. You have a torque converter instead.
 
If you have an automatic transmission, then you don't have a clutch pedal. You have a torque converter instead.
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=Testing for stall RPM=
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===Flash stall===
  
 
Let's start with the "stall". Drive your car to a deserted road, stop, watch the tach, and stand on the gas very abruptly.  
 
Let's start with the "stall". Drive your car to a deserted road, stop, watch the tach, and stand on the gas very abruptly.  
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begins to jump forward. Or the tires go up in smoke, depending on your combo.
 
begins to jump forward. Or the tires go up in smoke, depending on your combo.
 
That is your "flash stall".
 
That is your "flash stall".
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===Brake stall===
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Now, repeat, but this time keep your left foot on the brake pedal, hard. But don't do it for more than a couple of seconds to avoid over heating the converter and transmission. Then do a gentle drive afterward to cool down the parts. That was your "foot-brake stall" unless there was tire spin.
 
Now, repeat, but this time keep your left foot on the brake pedal, hard. But don't do it for more than a couple of seconds to avoid over heating the converter and transmission. Then do a gentle drive afterward to cool down the parts. That was your "foot-brake stall" unless there was tire spin.
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You can find all sort of descriptions and explanations, but your first interest is in what your stall does for your  car.
 
You can find all sort of descriptions and explanations, but your first interest is in what your stall does for your  car.
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Converter stall speed needs mostly center on your camshaft, heads, compression, gearing, and expectations. Tuning and fuel quality are your responsibility. For this  we must assume you got the tune right and run enough octane.
 
Converter stall speed needs mostly center on your camshaft, heads, compression, gearing, and expectations. Tuning and fuel quality are your responsibility. For this  we must assume you got the tune right and run enough octane.
  
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The best way to proceed is to detail 5 different combos:
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=Examples of different applications=
  
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The first combo is a 1979 Firebird. 150-HP 301 with a slightly leaky Q-Jet hurting MPG but not driveability, backed by a T-350, a 2.73:1 axle, and on new Firestone 215/75R15 tires. I
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Details of  5 different combinations:
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bought it that way, at too high a cost because it was so cherry, and that used up all the money I was hoping to spend on performance mods. So I paid attention to what I had.  
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*Combination 1: 1979 Firebird. 150-HP 301 with a slightly leaky Q-Jet hurting MPG but not driveability, backed by a T-350, a 2.73:1 axle, and on new Firestone 215/75R15 tires.  
 
The converter was an 1800-stall. I could, occasionally, chirp a tire from a dead stop. But i soon got curious about the converter slippage: Cruising along at 55 MPH, lift off the throttle, the RPM instantly dropped 200 RPM. Ease back into it, it came back up by 200 RPM. In later years, I came to learn that this is typical of most stock GM converters, though I doubted, and still doubt, that that converter was stock.
 
The converter was an 1800-stall. I could, occasionally, chirp a tire from a dead stop. But i soon got curious about the converter slippage: Cruising along at 55 MPH, lift off the throttle, the RPM instantly dropped 200 RPM. Ease back into it, it came back up by 200 RPM. In later years, I came to learn that this is typical of most stock GM converters, though I doubted, and still doubt, that that converter was stock.
 
But then I tried it the other way: stomping the gas, RPM climbed another 200 RPM. Did that mean a total of 400 RPM of slippage?  Yes, a total slip at WOT of 400 RPM.
 
But then I tried it the other way: stomping the gas, RPM climbed another 200 RPM. Did that mean a total of 400 RPM of slippage?  Yes, a total slip at WOT of 400 RPM.
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Lesson learned: normal slip of torque converters. Also applies to lockup style when not locked.
 
Lesson learned: normal slip of torque converters. Also applies to lockup style when not locked.
  
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Combo 2: 1978 Camaro LG3 ( 145-HP 305 ) TH350, swapped stock 1200-stall for B&M TorkMaster 2000 converter, 3.08:1
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*Combination 2: 1978 Camaro LG3 ( 145-HP 305 ) TH350, swapped stock 1200-stall for B&M TorkMaster 2000 converter, 3.08:1
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axle, 235/70R15 tires. This converter was stock, it was 1200 RPM flash stall, I know the slippage was the same as my 'bird already described above, and I know it drove fine for granny. But I decided to swap it.
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axle, 235/70R15 tires. This converter was stock, it was 1200 RPM flash stall.
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The B&M converter gave my combo a 1700 RPM flash stall. It felt like I had swapped to a 350, when launching. And by launching, I mean flooring the gas the instant the light went from red to green. It pushed me into the seat noticeably more, and I loved it.  I thought I had invested wisely, and I felt I got what I paid for.
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But I was in for another surprise. I finally stopped playing in traffic and got on the highway. I was so stunned
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A change to a  B&M converter gave my combo a 1700 RPM flash stall. It felt like I had swapped to a 350, when launching. And by launching, I mean flooring the gas the instant the light went from red to green. It pushed me into the seat noticeably more, and I loved it.  But I was in for another surprise. I finally stopped playing in traffic and got on the highway. I was so stunned to discover my slippage wasn't 200 RPM. It was just 50 RPM! So I stomped the go pedal, the RPM shot up by another 350, for a total of 400. After all, my previous 1978 / LG3 / TH350 / 1200 / 2.41:1
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to discover my slippage wasn't 200 RPM. It was just 50 RPM! So I stomped the go pedal, the RPM shot up by another
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350, for a total of 400. After all, my previous 1978 / LG3 / TH350 / 1200 / 2.41:1
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/ 205-75R14 Camaro did 23 MPG with a best of 26.
 
/ 205-75R14 Camaro did 23 MPG with a best of 26.
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I can't say the 2000-stall drove better than the 1200-stall in the snow, but I can say it wasn't any worse.
 
  
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Combo 3 was a 1965 Mustang. It had an 8.3:1 302 with Roush 200 heads, a Comp Magnum 292 cam, headers,
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*Combination 3 : A 1965 Mustang. It had an 8.3:1 302 with Roush 200 heads, a Comp Magnum 292 cam, headers,
 
intake, carb, 3500-stall, C4, 3.80:1 spool. Tires were 25" diameter.
 
intake, carb, 3500-stall, C4, 3.80:1 spool. Tires were 25" diameter.
 
That thing needed 10.5:1 compression, but a full summer of tuning got it driveable. To the point that he swapped
 
That thing needed 10.5:1 compression, but a full summer of tuning got it driveable. To the point that he swapped
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First experiences are always more vivid than follow-ups, and that's the case here.  
 
First experiences are always more vivid than follow-ups, and that's the case here.  
  
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Following that, I was playing with an 1985 Camaro with a mildly modified L69, 700R-4, 3.42:1, and sticky 215/60R15s. I decided on a B&M TorkMaster 2400. It drove pretty stock, until I swapped the heads. Finally it all came together:
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*Combination 4: A 1985 Camaro with a mildly modified L69, 700R-4, 3.42:1, and sticky 215/60R15s. I decided on a B&M TorkMaster 2400. It drove pretty stock, until I swapped the heads. No traction in first gear, very very fun!
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No traction in first gear, very very fun!
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Driveability? Not annoying, not irritating, not aggravating. Snow? no clue. Rain? easy to drive, but stomp the fun
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pedal, and no traction in first or second gears.
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*Combination 5: A 1995 Camaro Z28 convertible with the LT1, 4L60E, 2.73:1, and 235/55R16s. My flash stall was now 2400, twin black stripes became effortless, from a rolling 5 MPH start, and even starting with the 4-wheel-disc-brakes applied enough to keep the car stopped, getting both tires
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But I took the car apart, saved some parts, and a year later I was putting that converter in a 1995 Z28 convertible
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with the LT1, 4L60E, 2.73:1, and 235/55R16s.  
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How to describe this? My flash stall was now 2400, twin black stripes became effortless, from a rolling 5 MPH
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start, and even starting with the 4-wheel-disc-brakes applied enough to keep the car stopped, getting both tires
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turning took like half throttle.  
 
turning took like half throttle.  
 
But the driveability? It was hell. My slippage was always 1200, maybe because someone or something had caused it
 
But the driveability? It was hell. My slippage was always 1200, maybe because someone or something had caused it
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Great converter for playing, needs some rear gear.  
 
Great converter for playing, needs some rear gear.  
  
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If you're studying the COMP CAMS catalog, for example, you'll note that once you look past the smallest cams, they begin noting stall speeds. But as with all things camshaft, these are for the popular engine.   
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=Choosing a Stall Converter=
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If you're studying the COMP Cams catalog, for example, you'll note that once you look past the smallest cams, they begin noting stall speeds. But as with all things camshaft, these are for the popular engine.   
 
If you're gonna pick a cam for a lesser-displacement version, read the notes for the next larger cam.
 
If you're gonna pick a cam for a lesser-displacement version, read the notes for the next larger cam.
 
   
 
   
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===Racing converter application===
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For racing, you want a stall about 500 RPM below the RPM at which your engine makes peak torque. For most mild
 
For racing, you want a stall about 500 RPM below the RPM at which your engine makes peak torque. For most mild
 
SBC 350s, torque peak is typically 3500 RPM. With Vortec heads and such, 4000 is more like it. AFR heads should
 
SBC 350s, torque peak is typically 3500 RPM. With Vortec heads and such, 4000 is more like it. AFR heads should
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a 4000-stall drive tighter than  my 2400 stall. And at 4000 stall, it's not just the smaller diameter.
 
a 4000-stall drive tighter than  my 2400 stall. And at 4000 stall, it's not just the smaller diameter.
 
   
 
   
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===Fuel Mileage===
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Gas mileage: A 2400 RPM stall most definitely will hurt  MPG, in town and on the highway. But would that 2000 have helped the 1978 in town, had  the carb been repaired ?
 
Gas mileage: A 2400 RPM stall most definitely will hurt  MPG, in town and on the highway. But would that 2000 have helped the 1978 in town, had  the carb been repaired ?
 
   
 
   
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More gear reduces the load that the converter feels. Same with taking weight out of the car. But not only that, having more gear also takes load off the transmission.
 
More gear reduces the load that the converter feels. Same with taking weight out of the car. But not only that, having more gear also takes load off the transmission.
  
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When to buy what?
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===Gear ratio===
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Should this be an early mod? Or later, after everything else?
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The first mod in the drivetrain should be making sure you're not running a 2.73:1 axle ratio with 26" tires. With taller tires, a bit more than 2.73 gear ratio.  
 
The first mod in the drivetrain should be making sure you're not running a 2.73:1 axle ratio with 26" tires. With taller tires, a bit more than 2.73 gear ratio.  
  

Revision as of 09:27, 1 January 2012

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