Turbo

It is quite possibly the single mechanical part that gave the Japanese auto industry, power to compete against all other automotive industries during the early 1980's. Cars normally producing a maximum of 300HP, could achieve numbers as high as 800HP reliably (well somewhat), with boost. So what is this “snail” hanging off our exhaust manifolds? Well, the turbocharger of course! A turbo is nothing more than a complex fan that feeds air into the engine. Most turbocharged engines have a single turbo, while there are some that have two and again, others like certain exotic cars have up to four turbochargers! One of the most important aspects of a well-tuned turbo engine is “turbo selection”. Too big and the turbo will take too long to wind up (called spooling) that the car's powerband will not be smooth, as such not being pleasant to drive. Too small and your top end power will taper off although the car will feel more powerfull in the mid-range!

There are many ways to increase turbo output, without infact changing the turbine itself. You can raise the work done by the compressor or increase the efficiency of the air pushed by the turbo. Raising the work, means raising the amount of air the turbo pushes, in turn raising pressure in the system. A turbocharger's work is controlled by pressure, stock usually being between 7-12psi. Most turbo engines have room for some pressure increase, even on the stock turbo. A general rule of thumb is, 1psi = 10 flywheel HP. To raise pressure you can use a boost controller, you can read more about them in the Electronic Section . The 2nd way to increase output without infact changing the turbo itself, is to increase efficency. Cooler air is denser than hot air. In other words, the colder the air, the more power you have. If you have ever driven a turbo car in the winter weather, you know what we're talking about. A local tuning shop tested a lightly modified WRX in the winter resulting in 35ft lbs. higher torque, just from cold weather! So how do you make the air cold? Only drive in winter? Well, turbochargers do blow air, but in the process of compressing air they also heat it up a great deal. Through the turbo piping, there is an intercooler, which is basically an air-air cooler or an air-water cooler. Cold air also helps engine reliability dramatically, decreasing the chances of detonation. You can read more about intercoolers in the Intake Air section.

So if you're a quick thinker, you've probably found a major problem with the turbo system. If the turbo spins up (spools), and forces pressurized air through the engine, wouldn't that pressurized air go through the turbo on its way out, making the turbo work harder, and harder, until it blows up? Well, to control this problem we have a wastegate. This is what controls turbo output, and system pressure. There are 2 types of wastegates , internal (like most stock turbo engine systems) and an external type (used mainly for racing). The wastegate is a door before the turbo, in the exhaust manifold, that directs air around the turbo, back into the exhaust system after the turbo. When the pressure gets to a set limit, say 7psi on a stock SR20DET, the wastegate actuator pushes the door open, and allows enough air to flow around the turbo to hold the pressure at 7psi.

Now that you know how the turbine system works, you can begin to decide what size of a turbine would be best for you, and in which way you should mount it.

As you can see the spool RPM goes very very high as HP increase, especially for the smaller 2.0 litre engines. Note that this table is just a rough guide and does not include MANY factors such as camshafts, engine work, intake, exhaust, intercooler, tuning.

If you are planning on building a high HP engine, please feel free to contact us for advice on which turbine would be best for your application. We would love to help you construct a kit and make your car a Domestic killer!

Below is a diagram showing the turbo system: