If you ask any avid performance enthusiast what they think is the ultimate performance mod; nine times out of 10 they would probably tell you it's turbocharging. The turbo is the weapon of choice when it comes to making large amounts of power from small-displacement engines. When it comes to making power, a V8 counterpart can rely on shear displacement to increase output. On the flip side, a four-cylinder import engine's displacement can only be increased so far before running out of room-literally. Take a look at any import block and you can clearly see there isn't much room to increase the cylinder bore for increased displacement. Even with today's custom blocks, displacement of a four-cylinder import engine is still limited to less than 3.0 liters-even with the custom sleeves and stroked crankshafts. The turbo admonishes these sins.
There are two elements that are needed to make horsepower-oxygen and fuel. Maximum power production is determined from the amount of oxygen and fuel present in the combustion chamber prior to ignition. On a normally aspirated engine, the efficiency of the intake ports and the block's displacement directly affect the amount of oxygen present in the combustion chamber. For example, when you install a free flowing air filter, more oxygen is able to reach the combustion chamber. When the air is combined with the right ratio of fuel-voila! More power.
Now the good stuff. Regular readers should be well informed about the basic workings of a turbo. In plain English, a turbocharger uses the high pressure exhaust gases to spin a turbine wheel at very high speeds. Connected to the turbine wheel, via the common center shaft, is a compressor wheel. The compressor blades induce the oxygen into the compressor housing and compress it (boost pressure). The compressed air is forced to the intake or intercooler (depending on the turbo kit) and then into the combustion chamber. Since there are more oxygen molecule present in the combustion chamber, when mixed with the right amount of fuel, more power can be made. By force feeding, the volumetric efficiency is greatly enhanced, allowing the four cylinder to ingest the same amount of air as a big-inch V8. This is where the turbo gets its "replacement for displacement" moniker.
In this segment, we will illustrate what is involved in the installation of a complete turbocharger kit with front-mount intercooler. Our tester was a 1990 Mazda Miata with 160,000 miles on the odometer. Prior to installing any kind of forced induction device ,we highly recommend having the engine checked out to see if it's ready to withstand the rigors of boost pressure. By using a compression tester, you can check if each individual cylinder is holding equal amounts of pressure. All cylinders should be no more than +/- 5-percent from each other. Second, check the leakdown percentages of each cylinder. A leakdown tester will give you an idea of how much cylinder pressure is leaking through the piston rings, intake and exhaust valves. Obviously too much leakage can not only hinder performance, but can also lead to engine failure when the turbo kit is installed. Although we would never recommend installing a forced induction kit on a high-mileage engine, our Miata engine has recently been overhauled with new Arias pistons and a rebuilt factory head.
Before starting any installation project, make sure you have all the parts necessary to complete the entire project. Most of the good turbo kits should have a complete rundown of all the parts included in the kit. If you don't have all the parts, don't start the project. With the parts in hand, look for an installation manual and thoroughly read it over. Even if you have installed a turbo kit on another vehicle, you should still read the manual as there might be certain brackets that need to be modified for proper fitting. After reading over the installation manual you can start the project.