Stroker-427
Well-known member
Revving an engine over the max power rpm, sometime make a big sense!
Remember that the acceleration is comin from the torque, so you have to analize the torque curve of the engine, not the power curve.
If I well remember the gear ratio of a TH350 is 2.52 - 1.52 - 1
The step between first and second gear is 40% so you will have 40% less torque at the wheels in second.
If the torque of the engine at full power is more than 40% lower that the torque after the shift.... you don't have to shift!
For example let analyze this engine (a tipical 383 with 450Hp)
Max power is @ 5500 rpm
Max torque is @ 4500 rpm
If you will shift (first to second) @ 5500 rpm the engine will drop to nearly 3300 rpm (40% drop).
Torque @ the driveshaft before the shift is some 1108 lbs/ft (440*2.52)
Torque @ the dirveshaft after the shift is some 700 lbs/ft (460*1.52)
Analizing again the torque curve is easy to notice that the max torque is some 480lbs/ft @4500 rpm. The theoretical best shift point should be where the engine have some 290lbs/ft of torque....... well over the max permitted rpm.
Different thing if you have to shift from second to third with a drop of ratio of 35%....
As much drop you have between gears, as much you have to rev you engine before to shift.
This is why with a close ratio gearbox your average torque at the wheels will be higher.
Hope this help....
Remember that the acceleration is comin from the torque, so you have to analize the torque curve of the engine, not the power curve.
If I well remember the gear ratio of a TH350 is 2.52 - 1.52 - 1
The step between first and second gear is 40% so you will have 40% less torque at the wheels in second.
If the torque of the engine at full power is more than 40% lower that the torque after the shift.... you don't have to shift!
For example let analyze this engine (a tipical 383 with 450Hp)
Max power is @ 5500 rpm
Max torque is @ 4500 rpm
If you will shift (first to second) @ 5500 rpm the engine will drop to nearly 3300 rpm (40% drop).
Torque @ the driveshaft before the shift is some 1108 lbs/ft (440*2.52)
Torque @ the dirveshaft after the shift is some 700 lbs/ft (460*1.52)
Analizing again the torque curve is easy to notice that the max torque is some 480lbs/ft @4500 rpm. The theoretical best shift point should be where the engine have some 290lbs/ft of torque....... well over the max permitted rpm.
Different thing if you have to shift from second to third with a drop of ratio of 35%....
As much drop you have between gears, as much you have to rev you engine before to shift.
This is why with a close ratio gearbox your average torque at the wheels will be higher.
Hope this help....
