Car Tuning Drivetrain and Transmission 4 — Questions and Answers
Question 1: What is the advantage of a carbon fiber driveshaft over a steel driveshaft in performance applications?
- Carbon fiber can operate at higher U-joint angles
- Lower rotational mass reduces parasitic drivetrain loss and raises the critical speed threshold (Correct answer)
- Carbon fiber is cheaper and easier to balance
- Carbon fiber driveshafts never need replacement
Correct answer: Lower rotational mass reduces parasitic drivetrain loss and raises the critical speed threshold
Carbon fiber's lower rotational inertia reduces power loss and allows higher rotational speeds before harmonic resonance (critical speed) occurs.
Question 2: In drag racing, what is the purpose of a 'trans-brake' in an automatic transmission?
- It locks the torque converter for better efficiency
- It simultaneously engages forward and reverse to hold the car stationary while building torque converter stall (Correct answer)
- It prevents the transmission from shifting past second gear
- It engages a line-lock on the rear brakes only
Correct answer: It simultaneously engages forward and reverse to hold the car stationary while building torque converter stall
A trans-brake engages first and reverse simultaneously, holding the car against full engine power so the driver can stall the converter before release.
Question 3: When selecting CV axles for a high-power FWD build, what specification is most critical to prevent premature failure?
- The axle's overall length
- The axle's rated torque capacity (typically expressed in ft-lbs or Nm) (Correct answer)
- The brand's country of origin
- Whether the axle uses grease or oil lubrication
Correct answer: The axle's rated torque capacity (typically expressed in ft-lbs or Nm)
CV axles have a torque rating; using axles rated below the engine's output will result in CV joint failure under hard acceleration.
Question 4: What is 'final drive torque multiplication' and how does it differ from engine torque?
- It is the engine torque reduced by friction losses
- It is the engine torque multiplied by the total gear ratio (transmission × final drive), representing actual wheel torque (Correct answer)
- It is the amount of torque the clutch can hold
- It refers to torque only at the transmission output shaft
Correct answer: It is the engine torque multiplied by the total gear ratio (transmission × final drive), representing actual wheel torque
Final drive torque multiplication equals engine torque × transmission ratio × axle ratio; this is the total torque available at the wheels.
Question 5: In a sequential gearbox conversion, what component replaces the standard H-pattern shift gate?
- A planetary gear set
- A forward/back lever with a ratchet or paddle mechanism for one-gear-at-a-time shifts (Correct answer)
- A double-clutch actuator
- A torque converter lockup switch
Correct answer: A forward/back lever with a ratchet or paddle mechanism for one-gear-at-a-time shifts
Sequential boxes use a single forward/back motion (or paddle) that moves through gears in order, with a drum-type selector instead of a sliding fork H-gate.
Question 6: Why might a high-performance build use a 'dry sump' transmission lubrication system?
- To eliminate the need for a transmission cooler
- To prevent oil starvation and aeration during high-G cornering that would drain a wet sump (Correct answer)
- To reduce transmission operating temperature by 50%
- To allow the use of heavier GL-6 gear oil
Correct answer: To prevent oil starvation and aeration during high-G cornering that would drain a wet sump
Under sustained high-G cornering, oil in a wet sump can slosh away from the pickup; a dry sump system uses a scavenge pump to maintain constant oil supply.
Question 7: A drag car experiences 60-foot times worsening despite good traction. The driveshaft is found to be at its 'critical speed.' What does this mean?
- The driveshaft is too long for the RPM range and enters harmonic resonance, causing violent vibration and power loss (Correct answer)
- The driveshaft is spinning faster than the differential can handle
- Critical speed means the driveshaft has exceeded its heat tolerance
- The driveshaft U-joints are at maximum operating angle
Correct answer: The driveshaft is too long for the RPM range and enters harmonic resonance, causing violent vibration and power loss
Critical speed is the RPM at which a driveshaft's natural frequency matches rotational speed, causing resonance vibration that wastes power and can destroy the shaft.
Car Tuning Drivetrain and Transmission 4
What is the advantage of a carbon fiber driveshaft over a steel driveshaft in performance applications?