Honda's VTEC engines.
Created | Updated Dec 13, 2004
Turbos and Superchargers
Honda is unusual amongst car manufacturers in that it has never launched a forced induction petrol vehicle.1
(Forced induction is the addition of a turbo or supercharger to a car to pressurise the air intake. More air means more fuel can be burnt, hence more power.)
However, turbos and superchargers have problems with reliability - most turbos and superchargers will need rebuilding once or twice during the life of the car, and such rebuilds are not cheap. Adding a charger also complicates the car (and so increases the cost of manufacturing and maintaining it). For these and perhaps other reasons Honda decided to look into other ways of getting more power from a 'normal' engine, that could offer the benefits of a turbo/supercharger but without the associated problems.
More Airflow by other means?
As mentioned, how much power an engine develops is related to how much air gets into the engine. Some people think more fuel is the key, and they do have a point - you do need more fuel for more power. Getting extra fuel into an engine is quite easy though, virtually all engines will already be supplied with fuel via a fuel pump, so using a higher pressure pump would push more fuel in, but without the air to burn it in, the fuel isn't much use.
Honda attacked the problems of increasing airflow in several ways
Firstly they raised the revolutions per minute (rpm) at which the engine could reliably operate. An engine turning at 8,000rpm will be drawing in more air per minute than one operating at 6,000rpm. Raising the rpm for an engine is no easy task though, if reliability is to be maintained.
Secondly they spent time and money designing air intake systems and exhaust manifolds that would allow decent airflow. The standard intakes and manifold on Honda cars can be improved on, but often not by very much. Many other manufacturers fit quite restrictive systems, even to their sportier models. People who 'tune' (or modify) cars often say Honda's are hard to modify for extra performance, this is true it is hard to squeeze extra power from a Honda engine because they are already quite well tuned from the factory.
The science bit
Finally Honda invented the VTEC2
system to try and overcome one of the basic problems with petrol engines - the economy / performance compromise. To explain without diagrams is not easy, but here goes.:
Virtually everyone will understand the basic principle of the petrol engine in that a spark ignites the fuel, which 'explodes' 3 pushing the piston down. For this to happen, above the piston is an arrangement of valves which open and close in a set sequence to allow fuel/air mixture in, and then exhaust gasses out.
The sequence and timing of the valves operation affects how much air goes into the engine. The valves sit on springs and are opened by a camshaft, this is a thick metal rod with 'pear'4 shaped pieces moulded onto it. As the camshaft turns the neck of the pear passes the valve, pushing it open. When the pear's neck has passed, the spring pushes the valve back closed. In general a valve that stays open longer will allow more fuel / air in, thus giving better performance. So by changing the shape of the 'pear' (to a slimmer or wider 'neck') you can alter how long the valve stays open for
However holding the valves open for a long time will use up more fuel, so there is always a fight between economy and performance. A highly tuned performance engine will produce terrible miles per gallon (and won’t run smoothly at low revs), an engine tuned for economy will never be very powerful. Ideally you would have two engines, an economy version for the boring commute to work, and a sports version for blasting around country lanes at the weekend, plus a nice mechanic with a few hours spare to do the swap each time.
What the VTEC system does is put two 'pears' on the camshaft for each valve. At low rpms the valves follow the shape of the economy pear, at a set rpm the system switches over to the performance 'pears'. This allowed Honda to tune the car to be both very economincal AND very powerful. A bit like having two engines, except the VTEC system only takes a fraction of a second to engage.
Mass production
Its first incarnation was the B16a1 engine, first fitted to the Mk 4 Civics’ of the late 1980's. Even by today's standards it is a remarkable engine. Despite only being 1600cc it developed 150bhp, and will rev to 8,500rpm but still return very reasonable fuel economy.
Arguably the best version of the engine is the B16B, which was only fitted to a few cars and never exported outside Japan, it remained at 1600cc unit but developed 185bhp!! (from a 1600cc engine!), with no gain in weight or reliability problems. All the 'B' series engines have proven to be very reliable and 250,000 miles on an engine is not unusual, quite an achievement considering how much power is being extracted from a small unit
The sincerest form of flattery?
The system has proven so successful that most other car manufacturers now offer some form of variable valve timing engine in their range, however not all manufacturers seem able to match Honda's reliability with the system.
For out and out power, VTEC will never compete with a turbo/supercharged system, but for the masses who want performance, economy and reliability in equal measures, it has proven itself very well.
1If we are being strictly honest, Honda did make a very short production run car that was produced with a turbo, but this was done by the founder's son to show that he could modify the smallest car in the company's range into a performance vehicle. The son has since left and formed a very successful tuning company.
2Valve Timing Electronic Control3it doesn't explode, it just burns quickly, but so as to not confuse things further, we'll stick to explode for the purposes of this article4the technical term for the 'pears' is 'lobes'
2Valve Timing Electronic Control3it doesn't explode, it just burns quickly, but so as to not confuse things further, we'll stick to explode for the purposes of this article4the technical term for the 'pears' is 'lobes'
