Turbo Tech - All About The Turbo

Turbocharging Basics
Turbocharging is one type of what's called "forced induction." A turbo is an air pump that pushes compressed intake air into the combustion chambers. This charge is far denser than the air that would normally flow into the cylinders due to atmospheric conditions. When the denser air charge is combined with a greater-than-normal amount of fuel, it will create a more powerful burn, which exerts greater pressure on the pistons and therefore increases the engine's power output.

Inside a turbocharger is a shaft with finned wheels at each end. One wheel, called the turbine, is driven by exhaust gases leaving the engine. The exhaust flowing past the wheel causes it to spin, which in turn spins the wheel at the other end of the shaft, called the compressor. It's the compressor's job to take fresh air and pressurize it before sending it down the intake tract to be mixed with the fuel.

Turbocharging has a couple of advantages over supercharging, the other form of forced induction. Because a turbo has no mechanical link to the engine (like a supercharger's drive belt and pulleys), there is no parasitic drain in power to drive it. Additionally, freewheeling turbochargers aren't limited to or by engine rpm. Plus, turbos are designed to produce boost at higher engine speeds than a supercharger, which makes them well suited to high-revving sport compact engines.

Engine Upgrades
All our experts agreed that it's far easier to upgrade a car that came from the factory with a turbocharger than to add a turbo to a car that didn't originally have one. And that's not just because the turbo, brackets, and necessary plumbing are already in place. More importantly, the engine components that are vulnerable to damage due to high boost pressures-head gaskets, pistons, rods-should already be stouter in a car originally equipped with a turbo.

That doesn't mean a naturally aspirated engine will automatically grenade when you bolt on the turbo, though. "If you're mounting a well-designed kit, and you're keeping [it] at lower boost levels, you shouldn't need many internal upgrades," said Mike Chung of GReddy's R&D department.

The definition of "lower boost levels" depends on who you're talking to and the vehicle you're discussing. To Chung, low boost means 5 1/2 psi for an older SOHC Civic, and 7 to 7 1/2 psi for an Integra. But we also heard 10 and even 15 psi quoted as "low" and "street-oriented" boost. As with so much of this stuff, discuss your application in depth with your turbo maker of choice to determine the appropriate amount of boost for your car.

No matter how much boost you're shooting for, one mod you must make is to increase the amount of fuel going to the cylinders. If you don't add more fuel to burn with the denser compressed air charge that's coming from the turbo, not only will the engine not make more power, but it could experience detonation and possibly burn pistons. And speaking of preventing detonation, be sure to switch to premium fuel if you haven't done so already.

There are all sorts of methods of feeding more fuel to a turbocharged engine. Some are electronic, like altering the fuel map in the stock ECU or piggy-backing a fuel-control unit to the stock computer. Plumbing changes can be made, too, like adding a fuel-pressure regulator (some are boost-sensitive), high-flow fuel injectors, and more powerful fuel pumps. But no matter how you do it, "additional fuel enrichment is the key to producing safe power for any turbocharged application," according to Willie Yee of HKS.

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