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Digital Subscriptions > Fast Bikes > Issue 334 > TURBOS VERSUS SUPERCHARGERS

TURBOS VERSUS SUPERCHARGERS

You can’t fit a quart into a pint pot, or so the old proverb goes. But one of the coolest things in bike tuning revolves around exactly that. Well, kind of…

TECH

Both turbocharging (as seen on the GSX-R1000 we caned on p52) and supercharging (as embodied in Kawasaki’s incredible H2) are based on squeezing an extra dose of power and torque out of a certain engine capacity. Riding one of those bikes is like riding with a much bigger engine – the H2 in particular is like a tuned ZZR1400 motor in a litre-bike chassis. But how do their builders make a small motor feel like a big one?

Well, simply put – they use a megapowerful fan that blows more air into the engine than the engine would normally take. Imagine one of the 250cc cylinders which sit inside a GSX-R1000 or a ZX-10R. When it turns over on the starter, the inlet valves open as the piston is moving down, and the descending piston sucks air in through the valves. At normal pressure and temperature, 250cc of air weighs about 0.3g. So we have a third of a gram of air inside our cylinder, as the valves close. Of course, it’s actually a bit less, because we squirted some petrol in as well, but if we stick with 0.3g of air then there’ll be an ideal amount of fuel to burn with that. The Kawasaki is very clever, so it’s worked out the correct amount, and the ECU has squirted that dose of gas in. Next, we compress the whole mix, light it up with a spark, then the resulting inferno heats up the air, and pushes the piston down, turning the crank and moving the bike.

Now, let’s fit our fan to the intake manifold, so that it’s blowing lots of air into the engine, at high pressure. Say it’s able to blow air at a measured 15psi – that’s on top of the normal atmospheric pressure. Now, when our inlet valves open, we’re blowing air in there at 15psi more than we did before. The air pressure was about 15psi (normal atmospheric pressure) last time, so by adding another 15psi, we’ve doubled the pressure. And that means we’ve doubled the amount of air inside the cylinder: we now have about 0.6 grams of air. Guess how much more fuel we can burn now? Yep – twice as much. That means a bigger burn, more heat, and so more pressure on the piston and a stronger turning force (torque) at the crankshaft. That’s the science behind the ‘charging’ part of the supercharger and turbocharger equation. The other half comes down to how we power our fan.

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About Fast Bikes

In this month's issue of Fast Bikes... - New Models for the new season, 2018 starts here! - 7 Naked middleweights shoot-out - Triumph Street Triple RS - Ducati Monster 821 - Suzuki GSX-S750 - Kawasaki Z900 - Yamaha MT-07 - KTM 690 Duke - WK 650NK - Blow & go 492BHP Turbo Gixer vs Kawasaki H2 plus: - KTM 950SM, Know your aid filters, turbos versus superchargers, TT treat: WK's Lightweight 650 , Battlefield Blitzing
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