I recently bought an imported 1,8-litre (ABS) Golf engine fitted with a carburettor. In South Africa, you get the same 1,8-litre (HV) engine, but I see there is a difference in power and torque (4 kW and 5 N.m more) although bore and stroke are the same. Why the difference in the power and torque outputs?
FRANKLIN JANTJIES, Grabouw
Answer: Without knowing the exact details of the two engines, but given that they have similar capacity (including bore, stroke and, we assume, compression ratio), we can offer general comments. In a naturally aspirated petrol engine, the air-fuel ratio is normally close to 14:1 (or lambda one), which is the ideal combustion ratio.
The power the engine produces comes from the chemical energy in the fuel. If both engines are equally efficient, any additional fuel that is burned will lead to more power (and torque) in that specific engine. The amount of fuel that can be burned is mostly limited to the amount of air flowing through each engine (at the 14:1 ratio, as explained).
Therefore, the engine that produces more power and torque probably “breathes better”. A possible reason is differences in intake/exhaust design, valve timing and duration (different camshaft design) or higher engine speeds. A combination of the aforementioned could also be a reason. What’s more, similar engines from manufacturers are often tuned to the specific requirements of respective markets.