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| | =Choosing a Stall Converter= | | =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.
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| − | 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=== | | ===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
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| − | 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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| − | raise that to 4500.
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| − | Choosing converters is also about size. Stock SBC converters are about 300 MM, which is nearly 12". They're
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| − | referring to the outer diameter of the whole converter.
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| − | Why it matters?
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| − | 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.
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| − | Loose converters are great when your static compression is way low, or way high. Way high, a loose converter helps
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| − | reduce detonation. Way low, it covers the soggy off-idle. And a cam that's way too big is the same soggy feel as
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| − | way low compression.
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| − | Efficiency: This is difficult to discuss. The TM2k was much more efficient than
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| − | the stock converter it replaced, and was also more efficient than what was in my 1979 Firebird.
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| − | But how to tell, the reduced slip at cruise? Partly. That it had that plus the better launch? Mostly.
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| − | Are all converters rated by the same standards? NO!
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| − | Watch some vids on You-Tube where guys have recorded their gauges while driving around. I watched mostly LS1 F-car
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| − | guys' vids, but that's enough to illustrate the point. Yes, their results are combination-dependant, but I watched
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| − | 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 ?
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| − | It's not as simple as less stall = more MPG.
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| − | 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.
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| − | Performance: Is it all in the launch? Nope. The instant after an upshift is called the shift recovery. With an automatic, how much the RPM drops from the upshift isn't controlled by gear ratios alone. The converter and it's effect on performance after the upshift is more pronounced with a wide-ratio 700R-4
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| − | than with a close-ratio TH350. With the TH350, the launch is what the converter helps most.
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| − | But with more gear, you need more stall.
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| − | Torque converters are much more sensitive to load than to engine torque.
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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.
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| | ===Gear ratio=== | | ===Gear ratio=== |
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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.
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| | [[Category:Transmission]] | | [[Category:Transmission]] |
| | [[Category:Undeveloped articles]] | | [[Category:Undeveloped articles]] |
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