by Greg Wilson
New four-cylinder engines rival V6 engines for smoothness, power
Remember when four cylinder engines were noisy, gutless, and unrefined when they were available only in small, not-very-well-equipped import cars? Smoother, more powerful V6 engines became widely available in the 80’s, and buyers snapped them up even if they did use more gas and cost more – a trend that has continued until today.
That may be about to change: recent advances in engine technology have created a new generation of four cylinder engines that are proving to be as powerful and as smooth as many larger V6 engines without sacrificing fuel economy, say industry experts.
“Four cylinder engines have improved at a faster rate than six cylinder engines in terms of horsepower and torque between 1997 and 2002,” says Mark Stevens, Volkswagen Competitive and Market Analyst. “Since 1997 the average four cylinder engine has improved in horsepower and torque by over 8% while the average six cylinder has improved by less than 6%.”
“Four cylinder engines have gotten bigger and smoother but haven’t lost anything on the fuel economy they were getting before,” said Toyota Canada’s Product Training Manager, Doug Brooks.
While four cylinder engines found in small cars are generally between 1.5 and 2.0 litres in size, recently-introduced four cylinder engines designed for mid-size cars and compact SUV’s are now approaching 2.5 litres in size – notably Toyota’s new 2.4 litre four which is offered in the Camry sedan, Nissan’s 2.5 litre four available in the new Altima sedan, Honda’s 2.4 litre four offered in the new CR-V SUV, GM’s new 2.2 litre ‘Ecotec’ four available in the Saturn VUE SUV, LS sedans, and Pontiac Grand Am, and Ford/Mazda’s new 2.3 litre four offered in the Ranger pickup and the new Mazda6 sedan.
“The engine displacement and smoothness factor is probably one of the biggest changes – smaller engines don’t have the same off-the-line snap that a V6 would. V6 engines have been generally from 2.8 to 3.5 litres, so they’ve always had a bit of a displacement advantage which shows up in the torque and how it feels when you stick your foot into it,” says Brooks.
2002 VW Jetta 1.8T
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Add-on devices such as turbochargers and superchargers can make smaller four cylinder engines behave like larger ones though, usually at a cost of fuel economy. Volkswagen’s turbocharged 1.8 litre four cylinder engine available in the Golf, Jetta, New Beetle, and Passat is probably the best example of this. It offers five valves per cylinder, variable intake camshaft timing and a unique system for re-circulating turbo boost under deceleration that keeps the turbo spinning freely to reduce ‘turbo-lag’ on re-acceleration.
“The benefits to the customer are that variable intake camshaft timing allows the engine to perform at its optimal torque band over a wide RPM range. The re-circulation system prevents turbo lag,” says Buzz Kelley, Volkswagen Technical Training Manager. Still, VW’s turbocharged 1.8 litre engine offers poorer average fuel economy than the larger four cylinder engines mentioned above.
It’s features like continuously variable valve timing, variable air intake runners, and direct ignition that have allowed substantial increases in horsepower and torque without reducing fuel economy. Other improvements, such as all-aluminum engine designs, balance shafts, engine subframes, and chain drives have reduced the traditional noise and vibrations inherent to four cylinder engine designs.
Nissan’s new all-aluminium 2.5 litre 4 cylinder engine is a good example: it has 20 more horsepower and 24 ft-lbs more torque than its 2.4 litre iron block predecessor, yet it gets the same fuel consumption. In addition, it is 40 kilograms lighter, has 20% fewer parts, and went from LEV (low emissions vehicle) to ULEV (ultra low emissions vehicle) status.
The Nissan engine features a new more rigid block, a new silent timing chain, and new balancer shafts, which reduce engine noise by 20%. As well, the Altima’s engine and transaxle now sit on in independent subframe with vibration-reducing rubber bushings.
Perhaps the most important new development in improving four cylinder engine performance is variable valve timing, a computer controlled system that varies the amount of time the valves stay open at different engine speeds.
Toyota’s new 2.4 litre DOHC 16 valve four cylinder engine has variable valve timing on the intake camshaft. “The benefit is that it gives you cam timing to suit the occasion,” says Doug Brooks, “At low rpm when you need torque, smoother operation, and good gas consumption. And as the engine revs higher when you want more breathing, it extends the amount of time the valves stay open which gives good performance at higher rpm. In the old days, you had to pick somewhere in between – now the computer alters cam timing, fuel economy, power and emissions.”
Honda’s new I-VTEC (intelligent variable timing and electronic control) system also includes a feature which varies the amount of air coming into the engine at different engine speeds. “Variable intake volume optimises volumetric efficiency over a broader range of speed which has a direct impact on engine torque – low-end torque at low rpm, and high horsepower at higher rpm,” says Ken Dick, Honda Canada’s Manager of Service Engineering.
Many air intake manifolds are now manufactured from a lightweight composite (plastic) material instead of metal which not only reduces mass, but provides a smoother internal surface to facilitate air flow into the engine’s cylinders. “Traditional cast manifolds have coarse, pebbled interior surfaces,” says Don Reilly, GM’s Chief Engineer for 4 cylinder engines. “The smoother composite surfaces helps airflow and fuel charge.”
Balance shafts, though not a new idea, are making a comeback particularly in engine’s over 2.0 litres in size. Ford’s new family of inline four cylinder engines, which range in size from 1.8 to 2.3 litres, are up to 20% smoother than the previous 2.5 litre four cylinder powerplant, says Ford’s North American Program Manager for the new I4 engine, Joe Pratt. The new 2.3 litre four cylinder engine in the 2003 Mazda6 family sedan features balance shafts “which reduce secondary shaking forces to almost zero,” says Pratt.
2003 Ecotec 2.2 litre for Saturn VUE
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Balance shafts are also an integral part of GM’s new family of four cylinder ‘Ecotec’ engines, first seen in the 2000 Saturn L-Series sedan and soon to be offered in the Saturn VUE and certain GM compact cars. “The Ecotec has two balance shafts integrated in the cylinder block as opposed to add-on shafts driven off a gear in the oil pan,” says Don Reilly, GM’s Chief Engineer for 4 cylinder engines. Reilly says the Ecotec’s engine’s vibratory energy level has been “cut in half”, and that customers will notice how much more pleasing it is on the highway.
Like most new four cylinder engines, GM’s Ecotec has an all aluminium alloy head and block instead of an alloy head and iron block. This not only reduces engine weight – in this case by a substantial 16 to 18 kilograms – it helps the engine heat up faster which reduces emissions during startup, and warms up the coolant faster so customers can heat up the interior and defrost the windshield quicker.
Nissan’s new all aluminium 2.5 litre 4 cylinder engine features a unique dual cooling system – the head and the block are cooled separately. As the block is typically cooler than the head, Nissan’s dual cooling system improves combustion, ignition timing, emissions and horsepower. The engine also offers a unique variable capacity muffler that improves exhaust flow out of the engine.
Many new four cylinder engines have switched back to chain drives from belts for the camshafts. “We switched to belt drive in the 70’s because they were quiet running and didn’t stretch,” says Toyota’s Brooks. But timing belts need changing around the 100,000 km mark – an expensive maintenance item. Toyota, like other auto manufacturers, has switched back to a chain drive with a new, quieter design because they don’t break and don’t need to be changed for the life of the car.
Advances in noise suppression have also helped mute the four cylinder engine noise. Engine subframes mounted on rubber pads isolate the powertrain from the body, and some manufacturers are using computer controlled hydraulic engine mounts to cancel out engine vibrations. Toyota, whose cars represent the industry benchmark in quietness, use extensive asphalt sheeting on interior body panels.
From a maintenance perspective, modern four cylinder engines require far less servicing. Ford’s new four cylinder engine has recommended oil changes every 20,000 kilometres (12,500 miles) compared with typical oil change intervals of 5,000 to 10,000 kilometres (3,000-6,000 miles). GM’s Ecotec engine features a full hydraulic lash valvetrain system that requires no maintenance over the life of the engine (160,000 km advertised). Its chain-drive, which operates the camshafts, balance shafts and water pump, is maintenance-free. Other features which improve reliability include direct ignition where each spark plug has a coil on top of it which does away with traditional spark plug leads, and platinum-tipped and iridium-tipped spark plugs that don’t need to be changed for 160,000 kilometres!
Along with the improvements in four cylinder engine performance has come increased availability. Four cylinder engines were traditionally offered only in lower trim levels, but are now being offered in better-equipped models.
“If you go back five years, quite often in the four cylinder model you couldn’t get the leather interior and the full package of options,” says Brooks. “A lot of our new Camry customers have gone for the full load car, but with the four cylinder engine.” According to Brooks, 70% of 2002 Camry models are sold with a four cylinder engine.
Still, traditional perceptions about four cylinder engines are hard to change. “With the segment the RAV4 sells in, customers seem to feel a six cylinder is necessary even when a four cylinder may offer close performance with improved fuel mileage,” says Brooks. “And the segment that the 4Runner sells in will not accept a 4 cylinder engine even though current four cylinders are putting out the same power that V6’s put out a short time ago.”