Originally Posted by dineshkumar
The numbers (Eg: 200 Nm @ 4000 RPM) means the engine produces 200 Nm of torque at 4000 RPM. NOW WHAT DOES 200 NM MEANS . WHAT IS FULL FORM OF Nm. IF ENGINE PRODUCES HIGHER Nm what does it means?WHAT IS RELATIONSHIP OF 200Nm & 4000 RPM. PLEASE EXPLAIN WITH EXAMPLES?
What does cc in car engines denote. Higher cc means what more fuel consumption . Please explain how engine capacity is measured with reference to torque.
Let me start with the torque thing:
Just made a quick design in Catia and I guess it will be enough it explain it all:
Unit of force is Newton(N) and unit of distance is metre(m) and since torque is force*perpendicular distance, so the unit becomes Nm or Newton meter.
If an engine produces higher Nm that means it produces a higher torque but the numbers always say half story as its equally important to know of the engine speed/RPM the torque is being produced.
Example: 320Nm@1750-3500 rpm
This means that the engine with above rating has a torque spread of around 320 Nm all the way from 1750 to 3500 rpm.
Look at this curve(Red is power and Green is torque):
This is the curve for a turbo diesel(Cruze to be precise) with performance mods done. The curves showing lower values(of both red and green) are of stock car while the ones showing higher values are after the mods done.
Now look at the torque curve and you will understand the variation of the torque with engine RPM.
Now check the peak torque and the rpm we are getting the peak torque at and you will understand from where those ratings do come.
Higher cc means the engine can have enough power even while running under natural aspiration that it can take most of the roads and hence such engines require lesser amount of forced induction using a turbocharger or supercharger. Turbocharging means: Forced induction:
You force higher amount of air into the cylinder for more efficient burning. AFR:
Air-Fuel ratio, it is the unitary(taken into units) ratio between air and fuel. Example:
1:16 AFR means one unit of fuel is mixed with 16 units of air. HIGHER CC:
Higher displacement engines need lesser forced induction to produce more power and torque as compared to the lower displacement(cc) engines and hence they require 'smaller'(won't go deep into it) turbochargers. Lower CC:
Just opposite of what is written above. Hence there is no rule that higher displacement engine will be a fuel guzzler and lower one will be efficient. What AFR does?
Higher induction means higher pressure, which means higher amount of air per unit volume. Higher amount of air means higher amount of fuel required to maintain the right AFR and hence higher fuel consumption.
Adding to it gearbox and the ECU map also plays a vital role in the way fuel is consumed.
It's a lot to explain and will get you slept if I open it all now. I hope this was useful BTW