master class series POWERFLOW
What goes in must go out — it seems simple, right? But when it comes to extracting the spent gases from your cylinder heads there is power to be gained if the process is executed correctly. It’s not just about making the system roar. While that might be some people’s main driving force for getting an exhaust system in the first place, unlocking some hidden ponies is never going to hurt, right? This is done through what is known as scavenging, whereby the spent gases are actually pulled from the combustion chamber.
Simply welding some pipes together to direct fumes will not achieve this, and more likely will cost you power and drivability. However, apply some design best practice — which we’ll outline below — and you can unlock that beast within. We sat down with some local leaders in the field to understand how you can go about creating a complete system for your project that not only sounds great but is optimised for your engine package, unlocking a few extra ponies in the process. From headers to mufflers, we’ll cover it all in this Master Class.
EXTRACTION
All good exhaust systems start at the heads. Known as headers, or as extractors, this collection of primary pipes has a huge role to play in the system. This is where the exhaust gases travel inside individual tubes running from each exhaust port and are brought together before being sent through the exhaust.
The two main design considerations to take into account are the length and diameter of the primary tubes. When it comes to the length of these pipes, this refers to the measurement from flange to flange. Most typically you will be faced with choosing a ‘shorty’ or long runner style of headers, but there are also mid-length offerings out there. Why is this important? The length will affect the performance, as XForce’s chief operating officer, Tim McMurray explains. “Header pipe length will determine power and torque peak value and also delivery — e.g. where in the rpm range the power is delivered best from the engine.”
A short-length header is
