A1: It’s the ‘irreparable’ damage to the internal moving parts of an ICE, caused by overheating either due its Lube OR Cooling System failure.

Q2: What is Engine Life Factor (ELF)? How can it be calculated?

A2: It’s a ‘Factor’ given by the Formula ‘ALF = 100,000/Max RPM x Compression Ratio’ of an ICE. Since it’s a ‘number’ only, it’s devised to ‘compare’ the Life and Reliability amongst comparable ICEs.

Q3: A Tachometer consists of a red zone at high rpm markings. What happens actually after that limit?

A3: Upto the beginning of the ‘Red Line’, an ICE can rev safely/repeatedly without any internal damage. If revved beyond/into the Red Zone, it stands to get damaged due to inadequate Lubrication/Cooling and therefore, Mechanical/Electrical Governors are provided to prevent such a mishap.

Q4: Why ‘Multivalve’ Engines are more fuel-efficient than conventional ones?

A4: Given the basic Bore/Stroke and Compression Ratio of an ICE, its Power Output is directly proportional to the ‘weight’ of Air/Oxygen that it can draw-in to burn the matching Fuel quantity and inversely to the effort it has to make to expel the Exhaust Gases. Multi-Valve engines therefore have better ‘Volumetric’ efficiency/Specific Power Output than one-in and one-out types.

Q5: Why Automatic Transmissions are more thirsty for fuel than their Manual counterparts?

A5: An AT uses a ‘Fluid Coupling’ instead of the conventional mechanical clutch, to eliminate the need for it’s external manipulation, in order to make it fully ‘Automatic’. A Fluid Coupling basically comprises a pair of Turbine-like ‘Rotors’, one of which is coupled to the Engine which when ‘driven’ by it, develops pressure in the surrounding ‘Fluid’. This in turn ‘tends’ to ‘drive’ the other ‘Follower’ Turbine Rotor, which is coupled to the AT.

As can be visualized, such a Fluid Coupling will always have some ‘slip’ even when ‘fully coupled’ and this inevitably results in constant ‘churning’ of the ATF resulting in some Power loss – leading to higher fuel consumption – typically 5-10%.

However, with the advent of EMS-C/MPFI Engines, the ‘commands’ to the AT are now given by the EMS-C, which make sure that the Car is always in the ‘right gear’, under all possible driving conditions.

This in turn results in overcoming the lack of Driver Skills towards timely Gear Changes and therefore, today’s ATs are almost as Fuel Efficient as their Mech counterparts!

Q6: What are Gear Ratios?

A6: Due to the inherent ‘Torque vs Rpm’ Characteristic of an ICE i.e. with its Torque rising practically from nil to the max somewhere midway in the rpm range, one needs ‘suitable gearing’ to ‘match’ the road speed of the Car to the Engine rpm, to enable the Torque required by the Wheels match the one the engine can develop.

Since the Wheels’ Torque requirement varies from take-off to cruising, one needs a ‘variable’ Gear Ratio to make the transition as smooth as possible.

Hence in practice, five forward (and of course one Reverse gear) of ‘appropriate’ ratios are provided – starting from, say, I/Reverse - 3.5:1, II - 2:1, III - 1.5:1, IV - 0.9:1 and V - 0.8:1.

On top of these, there is the fixed ‘Final drive/Differential’ Ratio of say 4.5:1, which stands to be ‘multiplied’ to all the five/six above, to give the ‘Overall Wheels to Engine’ Gear Ratio, in any given position.

In short, the Ratio of any two mating gears is the Ratio of their respective number of teeth !

Q7: Why do Diesel Engines feel sluggish and feel more load on them with the AC on than their petrol cousins?

A7: The ‘Size/Power requirement’ of an Auto A/C System is dictated by the Cabin volume/initial Temp (as high as 70*C for a Car parked in the Sun) and the Rate of initial Cooling desired – amongst other factors which are common to most A/C Systems. This results in an Average Auto System to have a Rating of almost 1.5 Tons 0r 3 bhp when on!

A DE has a lower ‘specific power’ output compared to an equivalent Petrol – typical Example Accent-D (57 bhp) a/a Accent-P (94 bhp). In the mid driving range it’s ~ 50% of that. Therefore, with a more or less ‘constant’ A/C load of 3 bhp, the ‘drag’ works out to a much higher % age of Power available in a Diesel a/a Petrol.

Q8: What is ‘Torque Steer’ and what are its disadvantages?

A8: This is a phenomenon peculiar to FWD Cars – the more powerful –the worse ! What actually happens is :
Given the practical Power Train layout in FWD Cars, the Differential ends up being off-centre relative to the axis of the Car.

This in turn results in one of the drive shafts (usually the lhs) being shorter than the other – as we are all aware of.

Since the ‘Torsional Stiffness’ of the longer DS is lower than the shorter one – both being capable of transmitting the same power – under sudden Surge of High Power such as during a hard acceleration, there is a fraction of a second ‘delay’ in the 100% Torque appearing at the Wheel end of the Longer DS than the shorter one.

As can be visualized therefore, such a ‘delay’ results in the Car ‘noticeably’ pulling to the longer DS side, briefly, when accelerated very hard. In view of this, High Powered FWD Cars are now being designed with their Diff so positioned that it results in equal DS lengths on both sides.

Content generated by S. K. Gupta. - 10/’02.