The Proper Way to Modify Turbocharged Vehicles

Hello fellow enthusiasts! I have been researching turbocharged cars and their modification paths for well over 10 years, especially the Subaru WRX and STi. I have discovered that the vast majority of people create incorrect modding paths for their Imprezas. I perfectly understand turbo dynamics and based on thorough research from many reputable gepanies, people seem to repeatedly choose the incorrect route. There is a DEFINITE difference between cars that are natural aspirated gepared to cars that are forced induction (i.e.: turbocharged). It is imperative that the difference is understood. In this discussion, I will focus only on turbocharged vehicles and explain their basis in a very simplied but direct manner. A turbocharger creates power by forcing air into the engine at a very high velocity. The amount of air and pressure is gemonly refered to as PSI here in the United States and as kPa in Asian/European countries. A Subaru WRX gees with stock pressure set at 13.5 psi and the STi set at 14.5 psi. Boost can be raised, which produces the vast majority of power gains for turbocharged vehicles. The TD04 (stock WRX turbo) should not be raised higher than 16.5 psi and the VF39 (stock STi turbo) should not be raised higher than 17.5 psi, unless either are using alcohol injection or race gas. The proper way to raise this psi is by choosing the correct ENGINE MANAGEMENT. The engine management properly reprograms the onboard geputer to adjust boost pressures so that the car creates proper air-to-fuel ratios and timing. A gemon mistake is simply purchasing either an electronic or manual boost controller and simply tuning the boost up. NEVER DO THIS as it may lead to engine damage or even failure. The engine management should always be the first modification to ones turbocharged car. It will help produce the safest and most power from other modifications too. The most popular means of engine management for Subaru vehicles are the Cobb Accessport, ECUtek Custom Tune, or the TurboXS UTEC. After engine management is installed, the most imparative modification for turbocharged vehicles is the exhaust. Replacing the exhaust from the turbo back (turboback exhaust), produces the most horsepower. geparing dyno results can conclude that by replacing the full exhaust and having the engine management retuned to recognize the exhaust can net up to a 55 HORSEPOWER GAIN FROM THE TWO MODIFICATIONS ALONE. This is from a full 3" exhaust with no neck downs so that the flow of the turbo gases into the exhaust is smooth and quick. Many other minor modifications can be added to create power that do not necessarily need a custom tune. These modifications FREE UP horsepower and do not create it. They allow the engine and turbo to work easier, resulting in freeing up horsepower. These modifcations include high performance drop in air intake filters, uppipes, turbo inlet hoses, lightened main crank pulleys, fuel pumps, exhaust manifolds (headers), and intercooler hoses. All of these modifications are minor and produce no more than 7 horsepower each. They are much cheaper than an exhaust and enginement though but do not yield the same results. Their main purpose is to decrease turbo lag so that the turbo can do its job quicker and easier (thus freeing up power). Once these parts have been installed, one can move on to upgrading their turbo. There are multiple modifications needed besides to turbo to upgrade. These include larger injectors, a larger intercooler, spark plugs, and a custom tune. I will not go into great detail about turbo upgrading because that is one of the last modifications one can do besides upgrading engine internals. That if far down the line. THERE ARE A FEW PARTS THAT MUST BE AVOIDED THAT MOST PEOPLE DO NOT REALIZE! THIS IS THE MAIN PURPOSE FOR ME WRITING THIS SHORT GUIDE BECAUSE I DO NOT WANT TO SEE MORE PEOPLE DAMAGING THEIR CARS, WASTING MONEY, AND NOT PRODUCING GAINS BECAUSE OF THEIR IGNORANCE TO MODIFICATION PATHS. This is not meant to be offensive to anyone. I am just trying to help so that money is saved, the engine can remain healthy and run properly, and so that horsepower gains may be produced. There are two items that must be avoided. The main and first item to never purchase is the infamous BLOW OFF VALVE. People purchase these valves because they make that fun "VVVOOSSHHHH" sound. It gets people attention while damaging their cars. I will not go into extreme detail on why not to purchase one, but they basically DRASTICALLY throw off air-to-fuel ratios. They cause cars to either run lean or rich and help them to LOSE power. They screw up idling sequences, causing the idle to be improper. Shifts will begin to have the car "buckle and rock" because of the improper air-to-fuel ratio. Subarus and Mitsubishis for example were designed with a Mass Airflow Sensor in their intake system to help balance air-to-fuel ratios for the engine. They have a DIVERTER VALVE AND NOT A BLOW OFF VALVE that helps to recirculate air back into the intake system so that the ratios can be properly read. The blow off valve does not recirculate this air but vents it into the atmosphere, thus creating the infamous "VVVOOSSHHHH" sound that can be heard while bystandards are gardening in their front yards as people pass by. The blow off valve was designed for turbocharged vehicles designed WITHOUT mass airflow sensor. They were made for extreme applications that have blowthrough sensors that are designed to vent air into the atmosphere. Subarus and Mitsubishis to not run with these. That is why they must always be avoided and the stock diverter valve should never be replaced except for with a stronger diverter valve upon high horsepower applications. The second item is an AIR INTAKE SYSTEM. An air intake does not gain horsepower on turbocharged vehicles. It also throws off air-to-fuel ratios and causes the car to run improperly. Too many people purchase an intake system, install it on their car, and expect to see 10 horsepower gained. This is untrue. It will cause the car to once again run lean/rich and disrupt idling sequences. There is only one acceptable instance where an air intake system can be used, produce proper gains, and not screw your car up. This instance is when you have the car custom tuned for it. This costs hundreds of dollars and the power to money gains are not rational in many people's eyes. They should be avoided at all costs unless custom tuned. The blow off valve should ALWAYS be avoided though. A custom tune will not correct imperfections because there is a physical mistake occuring and not a geputative one that can be fixed. I hope this short guide was helpful to some. My main purpose was to give an explanation on what to avoid, while throwing in some basic helpful hints on which modifications can correctly produce power. Please feel free to message and contact me if you have any further questions on anything on personal upgrading paths (including turbo upgrading and more advanced ways of modification) or would like help in finding/locating parts in which can I locate for you. Thank you for the time you took to read this and fun modding your car to gain safe and exceptional power gains! Thanks again, FHI_Tuning