Has turbocharging killed the supercharger?
It's the age-old question of how best to boost power from an engine, a turbo or a supercharger? Both have their merits, but does the latest turbo tech mark the end of supercharging?
The turbocharger vs supercharger battle has been raging for as long as this technology has been available, much to the benefit of auto enthusiasts. As every classic car fan knows, superchargers were traditionally used on big V8s, while turbochargers were used on smaller engines to make them pull like V8s. An incredible amount of research has gone into optimising both systems – so which is better?
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Superchargers were always used to gain torque at lower revs. Run by a belt, they create boost at idle that significantly improves low-end torque and horsepower. The downside is as that as rpm increases, the parasitic losses spinning the supercharger exceed the gain. The advantage is packaging, as superchargers fit nicely into the ‘V’ of a V8 or V6 engine.
Early supercharged systems would begin to sap horsepower around 3000rpm, so hurting an engine’s top-end performance. Designs such as Blower Bentleys and supercharged Avantis were significant steps forward. Later designs incorporated clutches to clutch-out the compressor at high revs, but then you have to bypass the compressor blades, which adds complexity.
Unlike a supercharger, a turbocharger extracts energy from the hot exhaust and uses it to spin a compressor. The disadvantage is that at low revs there isn’t enough energy to create boost. The first generation of turbocharged cars would start their boost at 2500rpm and pull right up to the red line.
Research has focused on extracting more energy at low engine speeds. Several real breakthroughs have been made, and modern turbochargers have extremely light compressor wheels and spin up much quicker than first-generation systems. Small turbos were developed in the 1980s that used the latest turbine engine developments to spin up turbos even faster and extract the most energy possible out of the exhaust.
One of the dangers of small turbos is that the backpressure can easily overcome the boost. At higher revs the backpressure can actually stop air from entering the cylinders, so ‘waste gates’ were invented that bypass the turbo at high rpm. However, the waste gate creates its own issues, as lag is created when it opens and all the energy is dumped into the exhaust. It often takes seconds for the energy to regain its boost. The Porsche 930 Turbo is probably the perfect example of turbo lag, as its lags a bit at low revs, but when the boost kicks in you get an instant 100bhp.
An issue mutual to both turbocharging and supercharging is that compressed air is hot, which dramatically reduces the effectiveness of the total system. Intercoolers made famous by the STI vs EVO wars significantly improve the overall performance, often adding 30-50bhp to an existing supercharged or turbo set-up.
We’ve all seen turbocharged cars with giant intercoolers; it works, but adds complex routing of the compressed air to/from the unit. The largest intercooler we’ve ever seen was not on a tricked-out rice rocket, but on the Nissan GTP race car. Every Honda VTEC Turbo owner would be jealous.
Extensive research has led to advanced turbocharging systems, including the Porsche 959 and Mazda RX-7 FD sequential twin turbochargers. A turbo is optimised for low revs, and one is designed for high-rev use. This system is extremely complex, requires a computer to manage and costs a small fortune, but it works. Boost is available from 1500rpm to 13,000rpm.
Dual-scroll turbochargers have been developed that make use of pulses in the exhaust system to spin up earlier, but still work at high revs. Another breakthrough in turbo design was the 1989 Shelby Dodge Garrett Variable Nozzle Turbo or VNT. The VNT used a series of moving vanes on the hot exhaust side of the turbo to effectively change the size of the turbo. It worked, and in the Dodge Shelby boost started almost at idle and went right up to the red line. Porsche claimed it invented the technology 28 years later, when the Boxster and Cayman adopted it in 2017.
So, did the turbo guys win? Although developments in turbocharging are ahead of the game, the supercharging people haven’t given up. The advent of extremely efficient electric motors is leading to a comeback in supercharger design. No longer do you need to run them from a belt on the camshaft, as electric motors can be used to spin up the supercharger, creating boost with significantly fewer parasitic losses.
Automakers are working on hybrid systems that include motor-driven superchargers for low revs and turbochargers for high revs. Expect to see these solutions to show up more frequently in the next couple of years as car brands perfect the software and packaging.
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