From the title, you'd think we are talking about human anatomy, but since our company recently went through sensitivity training, that subject is off-limits. The real question we are asking is does a larger diameter exhaust piping make a difference in horsepower? We are constantly surrounded by overzealous enthusiasts trying to stuff the largest diameter wheel under a fenderwell or an oversized turbo in the engine compartment, but when does it become too big. Can exhaust piping diameter affect performance? This is the question we seek to answer in this Dyno Cell article.
Aftermarket turbo kits are hot commodities. With the promise of V8 power and I-4 economy, it is easy to see why. Factor in the downfall of factory turbocharged offerings and the bloodlust of power-craving enthusiasts, and the popularity of pressure is even more clear to see. Today, turbo boosts for Civic, Integra, Prelude, Eclipse, Miata, 240SX, Accord, CRX and many more can be readily bolted on.
Our tester was a turbocharged...
Our tester was a turbocharged 1990 Acura Integra boosting only 7 psi. Stock cams and head are employed on a fully built block using JE pistons and Saenz rods. We will boost up the Integra and add a ported head and high-lift cams in the future.
Many have made the mistake of adding a forced induction kit without upgrading the exhaust system. Even though most enthusiasts will already have installed an exhaust system prior to the turbo kit, the exhaust system that was installed was probably not developed to handle the exhaust flow characteristics of a turbo engine, which means useable power is being left on the table.
It is an obvious fact that the exhaust system on a 1.5-liter Civic is considerably smaller in piping size and muffler section than a Supra twin-turbo. The most obvious reasons are displacement and the power output of the two engines. One produces an anemic 80-plus hp, while the other pumps out a staggering 320 hp. It's simple science; as horsepower output increases, more air and fuel are burned, which means more exhaust gases will be produced. This same theory can be applied to vehicles utilizing a bolt-on turbo kit. For example, a vehicle that has been modified with a turbo kit but still utilizing a normally aspirated exhaust can benefit from a purpose-built turbo exhaust system with larger diameter piping, which decreases exhaust backpressure and eliminates pumping losses. A properly sized exhaust system can produce more horsepower and increase turbo response.