We are all aware that today’s Cars are a far cry from the good old Ambys and Fiats of the ‘70s/’80s.

Here is the second one of the ‘Q n A’ sessions spread over three ‘editions’.

Q13: Why are four cylinder engines more stable, refined and smooth in operation than a three-cylinder unit?

A13: Simply put, a Four Stroke Engine needs 2-revs to complete a 4-stroke cycle. Consequently, when one cyl is in its ‘compression/power sapping’ mode, ‘simultaneously’ there is another one undergoing its ‘power’ stroke. This results in a fair ‘power balance’ at the flywheel of the Engine.

On the other hand, in a 4-stroke/3-cyl Engine – during a period of 2-revs, only 3-cyls are firing. So there is a ‘fluctuating’ ¼ of a cycle period during which no cyls are firing (power stroke) and the other one/two are in their compression/power-sapping mode. This results in appreciable ‘Power Unbalance’ at the Flywheel, leading to unacceptable vibrations.

To overcome this inherent limitation, present day 3-cyl engines employ various techniques such as ‘balancer shafts’ etc. to smoothen out such vibrations. It may be interesting to note here that a 5-cyl engine doesn’t suffer from such an inherent limitation and was used first by Audi in the ‘60s with great success.

Q14: What is coefficient of drag? How can it be known? What are its advantages and what is its unit?

A14: A Car has a ‘profile’ – endeavoured to be as ‘aero-dynamic’ – like an Arrow – as practical – and a ‘square/rectangular cross-section’ (~ W x H).

If such a ‘cross-section/flat board’ is ‘inflicted’ with a blast of air in a Wind Tunnel corresponding to the road speed of the Car, it would experience a ‘push’ of say, 100 kgs.

On the other hand, if the actual Car is put in the place of the ‘flat board’, it would experience a push much lower than as above, coz of its ‘aero-dynamics’ – say 30 kgs.

Therefore, the ‘Coefficient of Drag’ is the ‘ratio’ of the above two i.e 0.30.

Since it’s a ‘ratio’, it has no Unit and obviously, the lower it is - the better. Present day ‘Stock Cars’ have managed to achieve a “cee-dee-alpha” (coefficient of drag) of less than 0.30 – typically 0.25.

Q15: How a ‘Distributor-less’ Ignition System is better than the conventional ones and how does it work?

A15: In a conventional Ignition System, the ‘Primary’ Circuit of the ‘Ignition Coil’ has to be continuously ‘interrupted’ by ‘electro-mechanical’ means, such as the Distributor ‘CB Points’ (M800) or the semi-electronic variants of it (Zen/Esteem).

In a DB-Less System, the on board EMS Computer performs the ‘primary coil interruption’ function totally electronically. Since it does away completely with all moving parts, it’s considered to be more stable and reliable and ‘theoretically’, having an infinite life!

Q16: How many Power Steering Systems are used presently? Which is better in all aspects, such as performance, reliability, economy, etc.? How do they work? Which types corrupt the vital engine horses more and Why?

A16: There are three basic power steering systems in use today – I) Hydraulic, ii) Electro-Hydraulic and iii) All Electric.

As they say, there are no free lunches in this world. All the three eventually derive their power input requirements ultimately from the Engine, either being directly powered off its Crankshaft OR the Car Battery/Alternator.

Of the three, The Hydraulic one is the most time-tested and Popular, as it can be applied from a Small Car to a Giant Earth Mover. By virtue of the nature of its design, it’s more maintenance prone and a little less energy-efficient.

On the other hand, an All Electric ones have their application limited to Passenger Cars – weighing, say, from 750 kgs to 1500 kgs or so. This is coz it primarily depends on the Car’s Battery to Power it, which in turn depends on the Engine driven Alternator to charge it back. Since it can be ‘Computer Assisted’, it can very easily be programmed to any desired ‘spectrum’ of ‘Assist’. Since there are fewer moving parts in it and can be virtually made ‘idle’ at straight cruise conditions, it’s more ‘direct’ and Energy Efficient.

An Electro-Hydraulic System is a ‘cross’ between the two, by way of advantages and disadvantages and don’t seem to be much popular these days, presumably from initial cost considerations.

Q17: How does a Variable Power Assisted Steering System work?

A17: The main objective is to achieve as uniform and reasonably effortless a feel of the Steering throughout the various steering conditions and Car speed. In other words, this calls for max assist during parking maneuvers and practically zero during st cruise conditions.

In a Hydraulic System, this is achieved by progressive transmission of higher and higher PS Pump pressure to the actuating mechanism, depending inversely on the engine rpm and directly on the degree of st wheel turn. The unwanted pressurised fluid returns to the Hydraulic Pump via a by-pass/relief valve.

In the case of an All Electric System, the Comp decides the degree of Assist, based on the ‘stress induced’ on the driver side of the Steering Wheel Shaft, by altering the Voltage Supply to the ‘Assist Motor’.

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