The best way to boost your daily commute is to ask the experts. First you need to know the specs of the engine-stock or built-we're talking internals and head work. Know what you want in performance-street or strip-and have an idea of how fuel enrichment will be handled. A turbo specialist will be able to provide you with a few options and the understanding to make an educated selection.
If you own a car that has been figured out like a Supra, Z car, Eclipse, Honda or Turbo Buick, selecting a turbo is much easier. Those that have come before have had the trial by fire and you can now reap the benefits without the risk. For our Project Boneyard Buick, we contacted John Craig of Limit Engineering.
Craig has concocted a complete line-up of turbos designed for use on a variety of Buick applications. From stock to an 8-second, 4.1-liter Stage II engine, Limit can provide the best in boost. With a moderately modified engine with ported heads and a built transmission with a high-stall converter, we outlined our intention to run the car on the street. Responsiveness was key, crazy, top-end flow was not as important. The engine is set up to be smog legal, so we wanted a stock-appearing turbo. Craig said that we described his TA60V turbocharger. Designed for intercooled Turbo Regals, the TA60V incorporates a Garrett T04B compressor side with a 60-1 trim 60mm compressor wheel in a .60 A/R housing. The hot side runs a newer 71mm Garrett turbine wheel that has 10 blades, which is less than comparable to T04 turbine wheels, which have 11 blades. The reduction of blades means there is less backpressure.
Backpressure is bad for three reasons. First, backpressure can hinder turbo spool-up. The second reason is pumping losses-a loss of power due to the engine having to "work" to move or pump exhaust gases through the system. The third is extra heat at the exhaust valves. This heat can damage the valves or the valve seals. The TA60V turbo utilizes a dynamic type oil seal on the compressor side, which causes less drag than a conventional carbon seal and less drag means quicker spool-up. Peak efficiency for this turbo is between 16 and 23 psi; the turbo can support up to 575-600 hp. Craig has it down to where the type of downpipe on the engine is figured into the mix. Since we are running a Terry Houston pipe, Craig honed out the wastegate signal port to 1-inch in order to increase performance. If a stock elbow were to be used, the signal port would have been enlarged to .930 inches. Once ported, Craig contoured the inside of the port for increased flow.
The car's godfather, Lou Czarnota of Lou's Auto Service, played with the boost, but due to an ailing radiator and a hot-running engine, we are leaving boost at 15 psi. When a 130,000-mile engine is rebuilt and making more power, more fuel is being burned and consequently more heat is being generated than before the rebuild.
We wanted to leave boost at 15 psi anyway to illustrate another myth-more boost means more power. Because of sizing and efficiency issues, two turbos running identical boost can create different levels of power. It is a dilemma of pressure vs. volume. When a greater volume of air is introduced to the engine, no matter the psi, more power will be made (as long as there is proper fuel on hand). Since the TA60V will pump more volume, it should make more power than the stock T3 at the same boost level. How much more? What will the car turn in the quarter mile? Will we turn up the boost? See the answers to those exciting questions and more in the next episode of Project Boneyard Buick.