Choosing a stall converter
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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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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 | 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, then do a gentle drive afterward. Assuming you didn't just shred the tires, that was your "foot-brake | seconds, then do a gentle drive afterward. Assuming you didn't just shred the tires, that was your "foot-brake | ||
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The converter was an 1800-stall. I could, occasionally, chirp a tire from a dead stop. But i soon got curious | The converter was an 1800-stall. I could, occasionally, chirp a tire from a dead stop. But i soon got curious | ||
about the [b]converter slippage[/b]: 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. | about the [b]converter slippage[/b]: 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 | |
| − | 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? I lifted off. Yes, a total slip at WOT of 400 RPM. Again, fairly typical it turns out. | of slippage? I lifted off. Yes, a total slip at WOT of 400 RPM. Again, fairly typical it turns out. | ||
| − | + | 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. | + | |
Combo 2: '78 Camaro LG3 ( 145-HP 305 ) TH350, swapped stock 1200-stall for B&M TorkMaster 2000 converter, 3.08:1 | Combo 2: '78 Camaro LG3 ( 145-HP 305 ) TH350, swapped stock 1200-stall for B&M TorkMaster 2000 converter, 3.08:1 | ||
axle, 235/70R15 tires. | axle, 235/70R15 tires. | ||
| − | |||
I know this converter was stock, I know it was 1200 RPM flash stall, I know the slippage was the same as my 'bird | I know this converter was stock, I know 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. | already described above, and I know it drove fine for granny. But I decided to swap it. | ||
The B&M gave my combo a 1700 RPM flash stall, [b]the launch[/b] felt much better. 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. | The B&M gave my combo a 1700 RPM flash stall, [b]the launch[/b] felt much better. 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. | ||
| − | + | But I was in for another surprise. I finally stopped playing in traffic and got on the highway. I was so stunned | |
| − | 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 | 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. | 350, for a total of 400. | ||
| − | + | I didn't bother to check my MPG, this carb was also leaky, and I always did 17 MPG, same as with the 2.41:1 axle | |
| − | I didn't bother to check my MPG, this carb was also leaky, and I always did 17 MPG, same as with the 2.41:1 axle | + | |
it had before. But that aside, I know it would help MPG. After all, my previous '78 / LG3 / TH350 / 1200 / 2.41:1 | it had before. But that aside, I know it would help MPG. After all, my previous '78 / LG3 / TH350 / 1200 / 2.41:1 | ||
/ 205-75R14 Camaro did 23 MPG with a best of 26. | / 205-75R14 Camaro did 23 MPG with a best of 26. | ||
| − | + | 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. | |
| − | 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. | + | |
Combo 3 was a friend's '65 Mustang. It had an 8.3:1 302 with Roush 200 heads, a Comp Magnum 292 cam, headers, | Combo 3 was a friend's '65 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 | + | |
street radials for drag tires. Then we went out to the exact center of nowhere, did up the 5-point race harnesses, | street radials for drag tires. Then we went out to the exact center of nowhere, did up the 5-point race harnesses, | ||
and he let it fly. | and he let it fly. | ||
| − | + | If you've ever felt a jet plane on takeoff, this puts them all to shame. Nothing you've ever experienced at any | |
| − | If you've ever felt a jet plane on takeoff, this puts them all to shame. Nothing you've ever experienced at any | + | |
amusement park even comes close, either. This was like God's own pillow-covered sledgehammer to the heiney. | amusement park even comes close, either. This was like God's own pillow-covered sledgehammer to the heiney. | ||
| − | + | First experiences are always more vivid than follow-ups, and that's the case here. This wasn't to be my last | |
| − | First experiences are always more vivid than follow-ups, and that's the case here. This wasn't to be my last | + | |
experience with race converters, but it was an eye-opener. | experience with race converters, but it was an eye-opener. | ||
Following that, I was playing with an '85 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: | Following that, I was playing with an '85 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: | ||
No traction in first gear, very very fun! | 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 | Driveability? Not annoying, not irritating, not aggravating. Snow? no clue. Rain? easy to drive, but stomp the fun | ||
pedal, and no traction in first or second gears. | pedal, and no traction in first or second gears. | ||
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Great tragedy I never tried it in any snow, in either car. | Great tragedy I never tried it in any snow, in either car. | ||
So, the combo is everything. | So, the combo is everything. | ||
| + | |||
If you're studying the COMP CAMS catalog, for example, you'll note that once you look past the smallest cams, they | 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. | 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. |
| + | |||
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 | ||
| − | raise that to 4500. | + | raise that to 4500. |
| + | |||
Choosing converters is also about [b]size[/b]. Stock SBC converters are about 300 MM, which is nearly 12". They're | Choosing converters is also about [b]size[/b]. Stock SBC converters are about 300 MM, which is nearly 12". They're | ||
referring to the outer diameter of the whole converter. | referring to the outer diameter of the whole converter. | ||
Why it matters? | Why it matters? | ||
My TM2400, above, was a loose 12". That looseness is most of why it was able to slip 1200 RPM all the time. Had it | My TM2400, above, was a loose 12". That looseness is most of why it was able to slip 1200 RPM all the time. Had it | ||
| − | been a tight 10.5", still 2400 flash stall, it would have been much less slip, and much less irritating. | + | been a tight 10.5", still 2400 flash stall, it would have been much less slip, and much less irritating. |
| − | So, this bit about | + | |
| + | So, this bit about loose or tight: | ||
Loose converters are great when your static compression is way low, or way high. Way high, a loose converter helps | Loose converters are great when your static compression is way low, or way high. Way high, a loose converter helps | ||
reduce detonation. Way low, it covers the soggy off-idle. And a cam that's way too big is the same soggy feel as | reduce detonation. Way low, it covers the soggy off-idle. And a cam that's way too big is the same soggy feel as | ||
| − | way low compression. | + | way low compression. |
| − | + | ||
| + | Efficiency: This is difficult to discuss. Look back at my '78 Camaro. The TM2k was much more efficient than | ||
the stock converter it replaced, and was also more efficient than what was in my '79 Firebird. | the stock converter it replaced, and was also more efficient than what was in my '79 Firebird. | ||
But how to tell, the reduced slip at cruise? Partly. That it had that plus the better launch? Mostly. | But how to tell, the reduced slip at cruise? Partly. That it had that plus the better launch? Mostly. | ||
| − | So my TM2400 wasn't efficient? Correct. | + | So my TM2400 wasn't efficient? Correct. |
| − | Are all converters | + | |
| + | Are all converters rated by the same standards? NO! | ||
Watch some vids on You-Tube where guys have recorded their gauges while driving around. I watched mostly LS1 F-car | Watch some vids on You-Tube where guys have recorded their gauges while driving around. I watched mostly LS1 F-car | ||
guys' vids, but that's enough to illustrate the point. Yes, their results are combination-dependant, but I watched | guys' vids, but that's enough to illustrate the point. Yes, their results are combination-dependant, but I watched | ||
| − | 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. |
| − | + | ||
| + | Gas mileage: My 2400 most definitely did hurt my LT1's MPG, in town and on the highway. But would that 2000 | ||
have helped my '78 in town, had I fixed the carb, and acted mature when lights went green? Probably. | have helped my '78 in town, had I fixed the carb, and acted mature when lights went green? Probably. | ||
It's not as simple as less stall = more MPG. | It's not as simple as less stall = more MPG. | ||
Engines can lug to the point it's un-mistakeable, but like detonation, there are lesser levels where the driver | Engines can lug to the point it's un-mistakeable, but like detonation, there are lesser levels where the driver | ||
| − | really can't tell. And if your converter is too tight, it will hurt your MPG. | + | really can't tell. And if your converter is too tight, it will hurt your MPG. |
| − | + | ||
| + | Performance: Is it all in the launch? Nope. The instant after an upshift is called the shift recovery. And | ||
with an automatic, how much the RPM drops from the upshift isn't controlled by gear ratios alone. Yep, we're back | with an automatic, how much the RPM drops from the upshift isn't controlled by gear ratios alone. Yep, we're back | ||
to the converter. And it's effect on performance after the upshift is more pronounced with a wide-ratio 700R-4 | to the converter. And it's effect on performance after the upshift is more pronounced with a wide-ratio 700R-4 | ||
than with a close-ratio TH350. With the TH350, the launch is what the converter helps most. | than with a close-ratio TH350. With the TH350, the launch is what the converter helps most. | ||
But with more gear, you need more stall. | But with more gear, you need more stall. | ||
| − | Torque converters are much more sensitive to | + | Torque converters are much more sensitive to load than to engine torque. |
More gear reduces the load that the converter feels. Same with taking weight out of the car. But not only that, | 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, helping it survive stoplight antics. | having more gear also takes load off the transmission, helping it survive stoplight antics. | ||
| − | + | When to buy what? | |
Should this be an early mod? Or later, after everything else? | Should this be an early mod? Or later, after everything else? | ||
The first mod in the drivetrain should be making sure you're not running a 2.73:1 axle ratio with 26" tires. With | The first mod in the drivetrain should be making sure you're not running a 2.73:1 axle ratio with 26" tires. With | ||
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