You must have noticed that so many OEM performance exhaust system manufacturers offer dual exhaust systems that are connected by ‘X pipe’ or ‘H Pipe’ sections. This can leave you a little bit confused because on the face of it, two separate pipes or ‘true duals’ as mechanics call them are supposed to offer better performance. Strangely, that is not the case at all once you look at the intrigues and finer details of how a typical internal combustion engine of a Porsche model works.
H and X Pipes
X and H pipe exhaust sections greatly benefit V8 and V6 types of engines mostly because they connect separate pipes that come from two separate exhaust banks found in V8 and V6 engines. This cannot happen in inline engines where there’s just one exhaust bank and are all cylinders are in a row. Note that H and x pipes are so effective that automotive experts use them on specific high performance models like Porsche. These sections also make it easy for one to add an existing dual system with little to no modification.
Exhaust flow experts all seem to unanimously agree that V8 engines benefit from X and H pipe sections mounted on dual exhaust systems. Other experts are of the view that X pipes are more ideal to free revving overhead cam V8s and V6s. They assert that H pipes are a natural fit for all high torque big block Porsche V8 engines that make their power low on the rotations rpms scale.
Pulses And H Pipes
Hold your hand behind the tailpipe for a minute. You will notice the exhaust flow feels like a continuous stream. That’s mostly because of a series of pulses. Each pulse is created each time an exhaust valve of a cylinder opens in the firing order. On any Porsche V8 engine, a cylinder on each bank is designed to fire within 90 seconds after a crankshaft rotation of another cylinder that is on the same bank. The resulting exhaust pulses stand very close together as they move through the exhaust system. That explains why so models create a pop like sound. H pipe sections come in to solve the problem by quieting the noise. When two close firing cylinders exhaust on one bank, nothing happens in the other bank. This means connecting both pipes will enlarge the exhaust system and allow the exhaust pipes to exit through both sides of the system. With the addition of the H pipe you increase power and at the same time, reduce noise by as much as 2 decibels.
An X Pipe section means that the two sides of a Porsche exhaust system are not just connected but merged together. This design allows the exhaust from all exhaust banks to flow with ease into both exhaust pipes. The exhaust pressure is then equalized on both banks as power increased with speed. Note that just like it is the case with H pipes, X pipes can also reduce noise. It is important to note though that many have described the exhaust note from X pipe systems as smoother and higher pitched than noise from H pipe systems.