Selecting a turbocharger is an exercise in compromise.
First, a larger turbo can force more air into the engine, and so can produce higher peak horsepower. Also, it can make full power all the way to the top of the rpm range.
But a big compressor wheel takes much longer to spin up to speed. The result is the infamous "turbo lag," which is the time between when you first press on the throttle and when the turbo spins up to its efficient speed.
The early (89-94) DSM cars had a moderate-sized Mitsubishi 14B turbo. It exhibits some turbo lag, but can produce high boost levels up to around 5500 rpm.
Later (95+) cars were equipped with the smaller Garrett T25 turbo, which reduced turbo lag to almost zero, but also limited boost levels.
Pre-95 automatic transmission cars also received a smaller turbo, since turbo lag plus automatic tranny lag can make for an unpleasant driving experience.
The Buschur Racing Sport Turbo upgrade uses a Mitsubishi 16G turbo, which is a moderate shift from the stock turbos in terms of lag and peak power. Lag on a 16G is more than a stock turbo (particularly the low-lag T25), but is still not unbearable. On the other hand, the 16G can maintain over 20psi of turbo boost all the way to redline.
The Race Turbo upgrade uses the same turbine housing as the Sport Turbo, but the compressor side is enlarged even further. The result is a turbo that still has a liveable amount of lag, but can force huge amounts of air into the engine. The large compressor wheel needs a lot of exhaust flow to keep it moving, so the turbo works best under high-rev race conditions.
The 20G turbo creates so much flow through the engine that the stock wastegate can no longer relieve all the pressure, so an external wastegate is a must. Also, the factory fuel system cannot cope with that much air flow, so injectors and fuel pump have to be upsized.
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