Project Grand Caddy received Doug Thorley's ceramic-coated Tri-Y headers and cat-back exhaust system. The exhaust system without question increased the engine's horsepower and torque. The bolt-on system (welding optional) is 50-state smog-compliant. All systems utilize factory hangers.
One of the most tried and true methods of increasing your vehicle's engine power is replacing the factory exhaust with well-designed header and exhaust systems that properly and efficiently increase flow. The simplest way to prove this is to put your hand over your mouth and try to exhale. It's a little difficult, isn't it? That's what your factory exhaust system is doing to your vehicle. The hard part about squeezing additional horsepower from your engine is selecting the right exhaust system.
The exhaust ports cannot just be opened up to gain power, proper flow must be present, especially in modern engines. Though some techies may question the theory that exhaust systems must maintain proper and slight backpressure to retain low-end torque and power, it's a generally accepted rule. The exhaust systems on older, carbureted engines aren't as complicated because they don't have the sensitive electronics of modern vehicles, but they still need accurate attention and proper, unrestricted flow. One cannot simply bolt on the largest exhaust pipe available without taking these things into consideration.
The factory intake and exhaust systems on some vehicles are so restrictive that it's hard to understand why they're designed in such a manner. Actually, it's a matter of manufacturing economics. A factory exhaust manifold simply collects all the gases from the engine heads' exhausts ports and jams them into one tube and hopes they flow smoothly out the end of the tailpipe. When it comes to this design, "hope" is the key word. Why does this cause a loss of power? Because your engine has to work harder to expel the burnt air/fuel mixtures. A header helps the gases flow out of the engine much more smoothly and efficiently. With a little extra effort and a few more manufacturing cents, an increase in engine power, performance, efficiency, mileage, and consumer appeal would be easy. The manufacturers' neglect of performance design is a windfall for aftermarket companies like Doug Thorley Headers that take great pride in producing high-quality exhaust systems.
Project Grand Caddy was chassis dyno-tested before and after the Doug Thorley header and exhaust systems were installed. A definite increase in power was recorded on the second run after installation. | 
You can see in the factory design of the exhaust manifold that escaping gases will actually collide rather than flow smoothly away from the engine. This causes the engine to work harder dispersing exhaust, hence a loss of power. | 
The header and exhaust systems are relatively easy to install for an enthusiast with moderate mechanical abilities. Doug Thorley's expert technicians had our full system installed in just a few hours. In some newer vehicles, restrictive engine-compartment space isn't always accommodating to headers, yet these slipped in with ease. |