Manual Transmission Torque Ratings
Engine torque is something most car guys think they understand, but those published transmission torque ratings only serve to preemptively answer the top question a typical customer might ask.
Truth is whether a transmission lives or dies is more complicated than just engine torque. For the typical street/strip application, the torque that actually gets applied to the input shaft varies depending on the rate that the engine's rotating assy is either absorbing energy (gaining rpm) or releasing energy (losing rpm). Huge torque spikes can result if a clutch draws energy out too quickly. Here's a graph showing some calculated/averaged input shaft torque numbers from a 425ftlb engine making a pass in a 3100lb car. Upper red trace is engine rpm, lower trace is averaged torque applied to the transmission's input shaft...
Note how input shaft torque is affected by the engine's acceleration rate. Only 204ftlbs of that 425ftlbs actually reaches the input shaft while climbing to the shift point in 1st gear, the remaining 225ftlbs are being absorbed by the engine's rotating assy due to the quick acceleration rate! Also note that 1583ftlb spike to the input shaft during the drawdown into 3rd, a prime example of how too much clutch draw can easily kill a transmission.
Here's the same pass, but this time the torque numbers are multiplied by the transmission ratios to get torque applied to the transmission's output and driveshaft...
Grant
Engine torque is something most car guys think they understand, but those published transmission torque ratings only serve to preemptively answer the top question a typical customer might ask.
Truth is whether a transmission lives or dies is more complicated than just engine torque. For the typical street/strip application, the torque that actually gets applied to the input shaft varies depending on the rate that the engine's rotating assy is either absorbing energy (gaining rpm) or releasing energy (losing rpm). Huge torque spikes can result if a clutch draws energy out too quickly. Here's a graph showing some calculated/averaged input shaft torque numbers from a 425ftlb engine making a pass in a 3100lb car. Upper red trace is engine rpm, lower trace is averaged torque applied to the transmission's input shaft...
Note how input shaft torque is affected by the engine's acceleration rate. Only 204ftlbs of that 425ftlbs actually reaches the input shaft while climbing to the shift point in 1st gear, the remaining 225ftlbs are being absorbed by the engine's rotating assy due to the quick acceleration rate! Also note that 1583ftlb spike to the input shaft during the drawdown into 3rd, a prime example of how too much clutch draw can easily kill a transmission.
Here's the same pass, but this time the torque numbers are multiplied by the transmission ratios to get torque applied to the transmission's output and driveshaft...
Grant