MOTORMAN — SUPERCHARGED!
IS THERE STILL A PLACE FOR SUPERCHARGERS IN A WORLD OF TURBOS? DONN ANDERSON RECALLS THE HISTORY OF AND HIS EXPERIENCES WITH ‘BLOWN’ ROAD CARS
Taming the energy of the twinsupercharged, aluminiumbodied Aston Martin Vantage was almost too much. Arriving at a British roundabout at rather more pace than I intended, I had reason to be thankful for the superb brakes that restrained the almost two tonnes of machinery and allowed me to give way to a grumpy-looking bloke in a repmobile. He seemed sure my Aston would be unable to stop, but happily he was wrong.
It was the mid ’90s and far from my first experience of engine supercharging, although this drive was certainly something special. At the time the Vantage was the most powerful production engine in the world, alongside Bugatti’s twin-turbo V12 EB110, and blessed with seemingly endless amounts of performance. Just a few months earlier, I had been motoring in the Scottish Highlands with a supercharged Jaguar XJR four-door saloon.
Today, when turbocharging is so prevalent, supercharging is a less-trodden route, yet several fine cars have chosen this path to performance. Over the past three decades, General Motors, Mercedes-benz, Volkswagen, Porsche, Volvo, Mini, and Range Rover have offered supercharged engines. Toyota even offered a blown version of the first-generation MR2 and Nissan did likewise with the odd-looking Note DIG-S.
Fifty-seven years ago, my older brother Rodger decided his early Kiwi-assembled 848cc Mini required more power to match the car’s polished handling, and managed to squeeze a supercharger into an already crowded engine bay. The installation was hardly professional, and there were struggles to achieve real gains.
Not long after, however, he fitted a blower to a Mk1 MG Midget, which, in standard trim, boasted a modest 1098cc, 42kw version of the A-series engine. This time the supercharging results were impressive. The little MG did well in Auckland area car club speed events, and notched up a third place in a modified production sports car race at
Pukekohe in April 1966, behind a Morgan 4/4 and Daimler Dart.
Long history
There is nothing new about supercharging. In a quest to improve thermal efficiency, two-stroke engine pioneer Sir Dugald Clerk tried a pump to force extra air into a largecapacity, slow-running engine in 1901, and ended up with an increase in power. The Roots Eaton M90 superchargers fitted to the ’90s Vantage and Jaguar XJR were based on a design patented by Francis Marion Roots in Victorian times.
In 1907, Lee Chadwick in the US adapted a centrifugal-type supercharger to a six-cylinder motor, running it at nine times engine speed. It was a success, Chadwick piloting his early machine to just over 100mph (161kph). It was believed to be the first car to top the magic ‘ton’ while also winning a hill climb. JT Nicholls used belt-driven centrifugal blowers with success, including a three-stage blower for the cars that competed in the
Vanderbilt Cup and Savannah Grand Prize race of 1908.
Worried by what was perceived to be an unfair advantage, motor sport authorities banned blowers in competition until 1921. Years later, superchargers were allowed but the engine capacity was limited and blown engines had to compete in the higher capacity normally aspirated class. Thus, an unblown engine capacity class limit of 4.5 litres would also allow supercharged engines but only up to a capacity of 1.5 litres.
In the latter stages of World War I, the Germans experimented with aeroplaneengine output, finding that superchargers were compensating for thinner highaltitude air. Fiat, Mercedes, and Maybach were also working on blowers. In the
’20s and ’30s came the ‘Blower Bentleys’, with a Roots Villiers supercharger driven from the front of the crankshaft; the sixcylinder MG K3 Magnette, ERA, and Mercedes SSK; and the incredible Grand Prix (GP) cars from Mercedes-benz and
Auto Union. World War II saw the age of supercharged aeroplane engines, including the all-conquering centrifugally blown Rolls-royce Merlin.
Supercharged BRM raced here
The formidable 1.5-litre supercharged V16 BRM unveiled in 1951 was dogged with problems but three years later appeared sorted when it arrived in Auckland for the first New Zealand GP at Ardmore. Favourite to start the lengthy 338km race, Englishman Ken Wharton led from the start, with the BRM often more than a lap ahead of the field, until the British car slowed with brake problems in the second half. Wharton drove on the gearbox to finish second, and was third in the Lady Wigram Trophy at Christchurch a few days later. New Zealand was the only country in the Southern Hemisphere to witness the extraordinary-sounding BRM, which had a pair of two-stage centrifugal blowers delivering huge boost pressure. This
engine developed more than 296kw in a narrow powerband, which made the BRM extremely difficult to drive and the project was shelved.
Supercharging in GP racing was again banned until 1966 when few Formula 1 (F1) teams showed any interest, but in North America, Indy cars long used supercharging. When it came to road cars, Paxton centrifugal blowers were employed on the Ford Thunderbird, Shelby Mustang, and Studebaker Avanti. In 1983, Lancia introduced the Beta Volumex with a Roots supercharger that had improved torque, but it was uneconomical and disappeared after two years. Rated as having two-litre performance, Volkswagen’s 1987 1.3-litre Polo G40 was a limited-production model that sold out rapidly.
Types of superchargers
There are two types of centrifugal superchargers; one is driven from exhaust gases using an impeller to draw air in, while the other is driven directly by the engine via a belt drive. The positive-displacementpump Roots, twin-screw, and Eaton blowers use different meshing blades so the main differences between these and the centrifugal type is how they move air to the intake manifold.
The Roots blower is effectively an air pump and does not compress the air inside the supercharger. Compression of the inlet charge takes place in the cylinders and manifold. A Shorrock vane-type blower has paddles on an eccentric shaft, scooping air in and compressing it into a small space.
The mechanically driven Roots blower is the most popular and was fitted to the XJR Jaguar, providing a generous 240kw that gave a wide powerband and seamless performance.
During my rural drive, the Eaton M90 blower linked to the four-litre straight-sixcylinder motor provided immediate response, achieving high boost levels at low to mid engine speeds. On testing Scottish roads, the XJR turned steepish climbs into flat surfaces and seemed to have an inexhaustible amount of power. Equipped with the Getrag fivespeed manual gearbox, the Jaguar trickled along at 50kph in top with barely 1000 revs on the dial, yet even at this modest engine speed the Jaguar pulled away strongly.
Aston Martin announced an order bank of 50 Vantage coupés when the model was unveiled in 1993, and that took care of the first year of production. In total, 1050 were produced before the model ended in 2000. All examples had the six-speed ZF manual transmission from the Corvette ZR-1, a noisy and slow gearbox with a tricky left-biased spring. I soon found the 5.3-litre, 410kw, twin-supercharged engine would deliver 100kph spinning happily at a mere 1500rpm in sixth gear.
The all-alloy, four valves per cylinder V8 came with two Eaton blowers with water intercoolers, a Ford EEC enginemanagement system, and fuel injection.
Running on a compression ratio of 8.2:1, the Aston’s engine produced a solid 745Nm of torque at 4000rpm — more than any other production car at the time. The superchargers kicked in down low and the broad spread of power spelt flexibility and response, even if the car was difficult to get off the line in a hurry. Not enough revs and the motor bogged down; too much throttle and the rear wheels spun uselessly.
Driving the Vantage required high concentration and effort for smoothness but the performance was crushing, with a 300kph top speed and a mere 4.6 seconds needed to race from a standstill to 100kph. In 1993 the Vantage was the third most powerful production car in the world, behind only the Mclaren F1 and Bugatti EB110.
Volkswagen’s unique approach
At a more modest level, Volkswagen adopted a unique engine-boosting approach in 2005 with the Mk5 Golf TSI that was the first engine to combine turbocharging, supercharging, and direct injection. In spite of the 1.4-litre capacity, the TSI produced 125kw and 240Nm of torque, effectively providing the output of a 2.5-litre engine.
The Roots supercharger feeds in low rev boost with 200Nm of torque from 1250 revs before the turbo spools up and takes over. By 3500rpm the supercharger disconnects. VW engineers claimed the dreaded turbo lag had been banished to the past.
Superchargers run directly on engine power, so they work immediately, but the disadvantage is that they constantly soak up some engine power, so they aren’t all that efficient. What’s worse is that this extra load from the supercharger increases as the car builds up speed. VW reckoned on combining the advantages of both blower and turbo and achieving strong performance as well as good fuel economy. In service, however, the TSI engine gave a few problems. It was essential to use 98-octane petrol since any octane lower than that caused pinging and ultimately cracked pistons.
Mercedes was well known for its Kompressors, and the R170 SLK range produced between 1996 and 2003 had no
fewer than five models with superchargers. These ranged in power from a 120kw two-litre, four-cylinder SLK 200 to a hearty 258kw three-litre V6 SLK 32 AMG. Larger AMG S55 Mercedes models had blowers with Teflon-coated rotors but were phased out in 2006.
A likely classic?
In 2002 Jaguar introduced a 4.2-litre, 292kw blown V8 in the S-type R saloon, and the same year BMW’S first-generation modern Mini arrived in the R53 Cooper S model with a mechanically driven Roots supercharged and intercooler version of the 1.6-litre Pentagon engine made by Tritec Motors in Brazil. This single-over-headcam power plant came with an old-school cast-iron block and metal timing chain and produced 125kw. This was an impressive 47 per cent increase in power over the same normally aspirated engine found in a standard Mini Cooper. At the same time, torque surged from 150Nm to 220Nm, an increase of 34 per cent.
As is usual with supercharging, the Mini’s compression ratio lowered from 10.6:1 down to 8.3:1. The conversion was not simply a matter of bolting on the blower. Increased thermal and mechanical loads demanded by the supercharger meant stronger con rods, crankshaft, pistons, engine bearings, and valves. Also fitted was a heat exchanger for engine oil and water, and splash oil cooling for the pistons. A bonnet scoop fed air directly into the intercooler.
There was so little room in the engine bay that the battery on a standard Cooper was repositioned in the car’s boot, and the exhaust system was reworked. The results were impressive, carving two seconds off the zero to 100kph time and greatly improving midrange response.
There are clear signs the supercharged R53 Cooper S built between 2002 and 2006 will be the favourite modern-day Mini to have as a classic, with the last few years of production ranked the best examples to own. When BMW unveiled the second-generation R56 Mini Cooper S late in 2006, supercharging was dispensed with in favour of a twin-scroll turbocharged, double-overhead-cam Prince engine shared with PSA Peugeot Citroën. This is of similar capacity to the Pentagon engine, with only slightly more power but 18 per cent higher torque and superior fuel efficiency.
Power-leading Chev Camaro ZL1
Four supercharged engines — the 280kw and 294kw three-litre V6, and the 405kw and 423kw five-litre V8 — have been
There are clear signs the supercharged R53 Cooper S built between 2002 and 2006 will be the favourite modernday Mini to have as a classic
used in Jaguar F-type and F-pace models and Range Rovers. Jaguar says the Roots twin-vortex blower has sophisticated boost control and a secondary throttle valve. This ensures torque curves rise steeply over a broad range of engine speeds to provide linear power delivery. In both V8 engines, the supercharger is fed by two intercoolers featuring their own water cooling to reduce the temperature of the pressurized air, meaning more air can reach the engine, optimizing combustion and therefore power output.
Volvo’s XC90 came with a two-litre, supercharged four-cylinder, and in 2008 Lotus offered the Elise with a 160kw engine using a Roots-type supercharger.
The Americans were not left behind: the 2017 Chev Camaro ZL1 was launched with a stonking 6.2 litre, 650bhp (480kw) supercharged V8, a power plant also found in the Cadillac CTS.
So, which way for supercharging?
Mercedes decided to drop blowers in 2004 in favour of turbocharging as it believed turbos were superior in terms of noise and cost. Juergen Frey, head of engine development for the A-class, said, “When we introduced supercharged engines it was the right decision. Turbocharging has greatly improved in the meantime and we have virtually no turbo lag any more.”
While superchargers are not generally regarded as ideal for good fuel economy, other engineers counter that they still have a role to play in the quest for performance.
Meanwhile, I could almost forgive the bulky Vantage for being a handful on narrow Oxfordshire lanes 25 years ago — the driveline shunt at slower speeds, the lack of cruise control in such a grand touring car, and the poor visibility — because the power from the twin-supercharged, hand-built engine was utterly sensational.