Question: Can you explain why most Mercedes-Benz AMGs have so much torque? How is it possible that the E63 AMG with its new 5,5-litre, twin-turbocharged V8 beats the new BMW M5 in the torque department, while the M5 has more power? Is it only engine capacity that counts?
BOKAMOSO NTEHELANG, By e-mail
Answer: Let us look at the basics: Torque is the result of a force creating a moment around a point. If you connect a wheel spanner to a wheel nut and apply a force to the end of the spanner, it is converted to a torque moment at the nut to loosen/fasten it. Let’s assume the wheel spanner is a single bar and one metre long (no weight) and you apply 1 N (1 kg = 9,81 N) to the end. This will equate to 1 N.m at the nut.
An engine converts the combustion pressure on the pistons to a force, which in turn results in a torque moment on the crankshaft (which can be measured). Engine geometry does play a small part (crankshaft throw and conrod length), but it is mostly the force on the pistons that relates to the torque on the crankshaft. The force on a piston equals the pressure times the area of the piston. Therefore, the larger the area and the higher the pressure, the greater the force and therefore torque output. Engines with high torque outputs will generally have:
• A large capacity;
• High combustion pressures (turbo/supercharged engines will have higher pressures than normally aspirated ones). Power (kW) is a function of torque (N.m) and engine speed (r/min). Therefore, if you have less torque (like the M5 vs. the E63 AMG) but the engine revs higher (M5), it still produces more power.