Recently, several letters passed over my desk concerning turbo sizing, and they got me thinking. One guy, Mr. X, was contemplating a turbo conversion. Another, Mr. Y, was complaining about the driveability of a kit he bought used online and the third guy, Mr. Z, had just scored a used Turbonetics T66 Q-trim for his street-driven 240SX. Mr. X is on the right track, researching before jumping in. The other two guys got killer deals but one is relying on 1990s tuning schemes and the other has way too much turbo for his intended usage.
There are tried-and-true combinations that deliver the goods, but like many things each car make has its own go-to turbo.
Take the Garrett Disco Potato (GT28-RS) that is the most popular destination for SR20DE/SR20DET boost-heads. It caught on because it is sized and trimmed to complement 2.0- to 2.5-liter engines and is reasonably priced ($1,100 range). Tuners embraced the Potato and, as a result, the combination has been fine-tuned to the point that it's a plug-and-play proposition for a multitude of Nissan engines (including the 240SX) and more recently the Subaru EJ20. This is a prime turbo, prime tuning scenario.
Honda pilots turn to the T3/T4 hybrid. The T3/T4 has probably boosted more B-series engines than any other hairdryer. From DRAG, Rev Hard and Turbonetics turbo kits back in the day, the concept was to use the smaller T3 family turbine and bigger T4 family compressor.
The T3 hot side was small enough to provide response while the T4 compressor was capable of providing the volume needed to create the ungodly power that has put the fear of death in domestic V8s since the early '90s.
The key to success here is getting the right combination of housing sizes and wheel trims to generate the proper/desired power curve. The T3/T4 turbo can be configured to generate anywhere from 220 to 500 hp. It's all about how much power you want and where in the powerband you want it. Here it's a pick-the-right-turbo-specs-and-get-Y2K- tuning scenario.
The Buick GN has the T3/T4 60-1. Diamond Stars look to the Mitsubishi TD05-20G as the quick fix for bigger boost. It is critical that you know how you are going to drive your car and where your engine makes the bulk of its horsepower and torque. Then work with a turbo design expert to select the right housing A/R and wheel trims for your application.
When it comes to fueling the passion, it is tuning that determines success or failure. We have seen engines with smaller turbos outspool and outpower engines with bigger turbos because the tuning strategy on the smaller-turbo engine was far superior.
If you're considering going turbo with a street car, look into a tried-and-true combo for your make and model. Then find shops with the tuning prowess to maximize the potential of said combo. Research like Mr. X; don't drop the ball like Mr. Y and Mr. Z who focused on the "deal" when they should have been getting the best parts at the fairest price. Until next month, stay spooled.