The turbo has been around for almost as long as engines themselves. Yet turbos are not in the least outdated. The turbo works as an air compressor for the engine. At 14.5 psi the turbo has doubled the amount of air going into a normally aspirated engine. The more air you can put into an engine, the more power potential the engine has. The turbo has two sides to it, one that compresses the air and the side that the exhaust gases pass through. The exhaust must pass by a cone shaped “wheel” of blades to exit the engine. As it does this it spins the wheel very fast. The exhaust side is connected by a shaft that runs to the air inlet side. This shaft is lubricated by oil that passes between the two housings. As the exhaust side spins, it turns a similar looking “wheel” called the impeller on the intake side. This side of the turbo is called the compressor.
The air flows into the center of the compressor housing and gets thrown outward by the impeller’s blades. As it hits the outer spiral of the housing the air compresses, forcing air into the intake manifold of the engine. As the air compresses it increases greatly in heat, up to 300 degrees F. This greatly reduces the density of the compressed air. Most turbocharged cars use an intercooler. This can bring the temperature down tounder 100 degrees F. This greatly increases density and allows you to increase “boost” pressures even more. Lower temperatures allow the engine to not detonate. Detonation and lean fuel mixtures are the worst enemies of turbocharging as they melt head gaskets and pistons. Turbos can more than double an average engine’s hp. The “boost” or compressed air is usually set around 12 psi from the factory, dependant on engine setup. An engine’s compression ratio is probably the most important factor that can limit boost. For the engine to handle alot of boost it must have a much lower compression ratio. Usually a turbo engine will have a compression ratio of about 8.5 to 1. Some engines use higher ratios to make the low end torque feel better but then have to significantly reduce the gain of top end boost from the turbo.