Shift Kit and Stall Converters
09-05-2003, 11:10 AM
#1
Safety Car
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Shift Kit and Stall Converters
I have never owned an automatic performance car (the family grocery getter is another matter). I have been thnking about buying another Vette (possibly late 70's C3 or early model C4) as a daily driver and am considering an automatic.
What exactly does a shift kit do and what are these stall converters (eg 2700 Stall Converter) that I see in some of the ads.
What exactly does a shift kit do and what are these stall converters (eg 2700 Stall Converter) that I see in some of the ads.
09-05-2003, 11:42 AM
#2
Melting Slicks
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Re: Shift Kit and Stall Converters (6t9l4t6)
A shift kit changed the transmissions shift points and shift firmness( usually higher and firmer)
A stall convertor allows you to launch better at the strip. A 2700rpm stall convertor will allow you to, with your foot on the brakes, rev the engine to around 2700rpm(engine HP and vehicle weight dependent) before the car moves. They are not exactly what you would want for a daily driver. they tend to be less efficient( meaning lower fuel economy). If I'm not mistaken stock is usually around 1200-1600RPM.
A stall convertor allows you to launch better at the strip. A 2700rpm stall convertor will allow you to, with your foot on the brakes, rev the engine to around 2700rpm(engine HP and vehicle weight dependent) before the car moves. They are not exactly what you would want for a daily driver. they tend to be less efficient( meaning lower fuel economy). If I'm not mistaken stock is usually around 1200-1600RPM.
09-05-2003, 11:47 AM
#3
Race Director
Re: Shift Kit and Stall Converters (6t9l4t6)
shift-kit:
When we put the shift-kit in my Z28 20+ years ago, my buddy explained that stock transmissions are programmed to engage the next gear BEFORE releasing the previous gear (almost 'binding' itself in two gears at once), to give 'smooth' shifts for the masses. By reprogramming the fluid path via shims & check-*****, the shifts are much more crisp (stock '79 Z28 'chirped' the tires at half-throttle!!!), and transmission life 'should' be prolonged...
higher-stall converters:
To promote good fuel economy, most stock converters are 'tight', engaging at a very low RPM (drop your auto into 'D', and it 'lurches' immediately). A higher stall converter 'slips' a bit at the lower RPM (CAUTION: this DOES build heat!!!), allowing the engine to 'rev' into it's power-band.
'Generally', the smaller (in diameter) the converter, the higher the 'stall'. I'd guess that a late-'70s C3 had a 12" converter 'stock' (possibly an 11"?), with a very low 'stall-speed'. For drag-racing purposes, a 10" converter would 'stall' (or 'slip') at a higher RPM, allowing an automatic to 'leave' like side-stepping the clutch in a stick-car.
(Factors to consider calculating 'stall RPM' are vehicle weight, torque, gearing, etc. Contact a reputable converter vendor for better explaination...)
'Usually', this slippage continues though-out the RPM range, and hurts fuel-mileage, unless you get a high-stall/lock-up converter, like the THM350C/700R4/2004R models found in the early/mid '80s.
My Z28 now has an 8"/4500 RPM stall converter, STRICTLY for drag-racing; when I drop it into gear, there is no 'CLUNK', and (almost) no RPM drop, either. When I shift, there is no sensation of 'chirping' the tires; it kinda 'slimes' into the next gear.
But, going from a 10" to an 8" was worth a half-second in ET (13.30 to 12.80), after adding slicks (NO WAY it was gonna hook on street tires), and gears (to compensate for the 2"-taller slicks). MPH & trap RPM remained the same (106 MPH @ 6000 RPM), so the gearing didn't 'help'; it was a 'trade-off' for the tire height increase...
When we put the shift-kit in my Z28 20+ years ago, my buddy explained that stock transmissions are programmed to engage the next gear BEFORE releasing the previous gear (almost 'binding' itself in two gears at once), to give 'smooth' shifts for the masses. By reprogramming the fluid path via shims & check-*****, the shifts are much more crisp (stock '79 Z28 'chirped' the tires at half-throttle!!!), and transmission life 'should' be prolonged...
higher-stall converters:
To promote good fuel economy, most stock converters are 'tight', engaging at a very low RPM (drop your auto into 'D', and it 'lurches' immediately). A higher stall converter 'slips' a bit at the lower RPM (CAUTION: this DOES build heat!!!), allowing the engine to 'rev' into it's power-band.
'Generally', the smaller (in diameter) the converter, the higher the 'stall'. I'd guess that a late-'70s C3 had a 12" converter 'stock' (possibly an 11"?), with a very low 'stall-speed'. For drag-racing purposes, a 10" converter would 'stall' (or 'slip') at a higher RPM, allowing an automatic to 'leave' like side-stepping the clutch in a stick-car.
(Factors to consider calculating 'stall RPM' are vehicle weight, torque, gearing, etc. Contact a reputable converter vendor for better explaination...)
'Usually', this slippage continues though-out the RPM range, and hurts fuel-mileage, unless you get a high-stall/lock-up converter, like the THM350C/700R4/2004R models found in the early/mid '80s.
My Z28 now has an 8"/4500 RPM stall converter, STRICTLY for drag-racing; when I drop it into gear, there is no 'CLUNK', and (almost) no RPM drop, either. When I shift, there is no sensation of 'chirping' the tires; it kinda 'slimes' into the next gear.
But, going from a 10" to an 8" was worth a half-second in ET (13.30 to 12.80), after adding slicks (NO WAY it was gonna hook on street tires), and gears (to compensate for the 2"-taller slicks). MPH & trap RPM remained the same (106 MPH @ 6000 RPM), so the gearing didn't 'help'; it was a 'trade-off' for the tire height increase...
09-05-2003, 11:58 AM
#4
Team Owner
Re: Shift Kit and Stall Converters (Glensgages)
I have a Trango Shift Improver kit and it really can wake up the shifting on the car...You can also choose how firm or soft you want the shift points to be. The key to choosing the stall converter is matching it with the cam and the rear gear. I am running a 2400 TCI breakaway stall which really lets the car launch extremely hard. Don't forget to add a tranny cooler to dissipate the additional heat :cheers:
