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A head above the rest

What makes some engines more explosive than others? Put it down to heads and blocks

india Updated: Aug 27, 2009 16:03 IST
Grease Monkey

Your engine is made up of a million different bits that work in harmony and are supervised by the Engine Control Unit (ECU) to convert as much of the hard-earned money you spent at the pump as possible to useful work. The main parts of the engine are the head and block, also called the ‘cylinder head’ and ‘cylinder block’.

Thanks to the block
The block is the bottom of the engine. It contains ducts for the coolant which regulates temperature, and for lubricants like oil. It has to be strong enough to withstand the controlled explosions that take place in the cylinders. Cast iron blocks were common until recently because of their strength. Some engines earned a cult following because of the amount of power they could handle without serious modification.

The 4G63 from the Mitsubishi Lancer, the 2JZ-GTE from the Toyota Supra and the RB26DETT from the R34

Nissan Skyline GT-R were worshipped at the altar of performance modifications. The Lancer’s old block is present in the Cedia sold in India, which makes 115bhp.

The Lancer Evolution Vlll FQ-400 makes almost four times as much power, and it still manages a factory warranty of the same time and mileage as any other car!
The Supra and Skyline engines were rated at 280bhp on paper, but made above 300bhp in the real world, and the necessary modifications saw them put out a reliable 600bhp without modification to the block!

The last of the R34s, the GT-R Z-Tune, made 500bhp and would’ve made more if it wasn’t for emission requirements. We’re now seeing a shift to all-aluminum engines like Maruti’s KB-series, which will debut on the A-Star. Aluminum was avoided for a long time by automobile manufacturers because of the difficult and costly processes needed to recycle it, unlike iron or steel.

Current requirements of reduced weight, yet stronger cars, has ensured that it is now the metal of choice for auto manufacturers.

Starts with a spark
The cylinder head too is a complex bit of the engine. It houses the spark plug (more than one plug, in some cases), valves, and the inlet for fuel into the cylinder.

The simplest cylinder heads will contain two valves — one inlet, one exhaust, and the spark plug. The complex ones can contain up to five valves, two spark plugs and more than one inlet for fuel, as in the case of multi-point fuel injection — MPFI to the layman. The top of the combustion chamber is scientifically designed to aid airflow.

Those who know their engines really well might swap just the head — Honda enthusiasts will agree that a VTEC head with the same cylinder dimensions fitted on to another Honda engine helps performance.

This can be done with the Honda City’s engines, although the cost involved will be prohibitive. Civic enthusiasts in the USA used to swap the head of the B16A engine and fit a B16C head to it, because it offered better airflow.

The shape of things
The shape of the top of the combustion chamber can also affect combustion. A hemispherical top with the spark plug in the centre ensures that the flame (when the spark fires and the fuel burns) moves outwards at the same speed in every direction.

This is what gave Dodge’s famous ‘Hemi’ engines their name.

Today’s engines have a plastic cover, so you might not be able to see the head bolted onto the block. However, don’t let that stop you from asking your neighborhood mechanic to show you around your engine!