At the same time, the VTEC design is made more compact - so reducing its inertia - by integrating the sliding pin used to operate the cam profile switch into the roller structure. As a further benefit, oil injection is now unnecessary and the simplified oil path leading to the camshaft journal now passes through the new hollow camshaft.


World-first metal injection moulding

In a world-first, an advanced production method is used to produce the lightweight, yet very strong rocker arms. Instead of conventional casting or forging processes which require complex machining afterwards, the components are formed in a single step using metal injection moulding which provides the higher precision finish required by the roller-type co-axial design. Heat treatment of the hollow rocker arms provides additional strengthening.

The valve springs are notably light and use materials developed especially for Honda's CART ChampCar race programme. Each high strength spring is formed from conventional round-section wire, further reducing inertial weight.


Compact scissors gear

High engine speeds call for a high degree of precision and a chain with automatic tensioner, rather than the more usual belt, drives the camshafts via a scissors gear. Using a scissors gear helps to reduce engine length, while keeping the gear diameter to a minimum allows a narrower camshaft spacing and a valve angle similar to that of an ordinary SOHC design, as well as a shallower rocker cover, a critical advantage in keeping the bonnet line low. The small pitch chain makes for quiet operation.

Engine dimensions are also kept to a minimum through the neat installation of the alternator, water and air conditioning pumps which are driven, in a single plane, by a serpentine belt driven off the crankshaft. And since the steering is electrically-assisted there is no power steering pump. To withstand high engine speeds, the belt core is in aramid to reduce elongation.

To ensure a hot, stable spark at high revs, an individual coil sits atop each iridium-tipped spark plug in the cylinder head which also makes for a more compact engine through the elimination of a conventional distributor.


Deep breathing

The intake and exhaust manifolds together with valve timing and overlap have all been tuned to reduce manifold back pressure and improve breathing efficiency. As befits a pure sports engine, the intake manifold features a simple, straight-through design with a large-bore, low-restriction inlet. Intake air is drawn directly from the front of the car and passes through a conical filter for reduced intake back pressure.

Similarly, each element of the exhaust system is designed to reduce back pressure and take advantage of exhaust gas energy and features include large diameter pipes, high-efficiency dual silencers with a two-stage pre-chamber, and a U-turn pipe.

An exceptionally high, racing engine-like 11:1 compression ratio further boosts output. A contributory factor in achieving this outstanding figure are the chain drive and scissors gear which have allowed the camshafts to be brought closer for a narrower valve angle to give a more compact combustion chamber. Furthermore, optimised water flow around the cylinders and the good heat dispersion properties of the Fibre Reinforced Metal (FRM) cylinder liners help to prevent engine knock despite the very high compression ratio.

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