' Piston to valve synchronization '
" Our product dramatically improves horsepower and torque with an amazing sound - the ultimate rock band of exhaust sound . Customers have compared the deep note we achieve to V8 hot rods or to the
blowdown to remove exhaust gases , pumping losses are reduced because fewer gases remain for the piston to physically dispel from the cylinder . If header diameter is too large , exhaust gas velocity will be low , thereby weakening the scavenging wave and reducing its effect during valve overlap . As such , it is important to note that as blowdown pressure declines , there is an increased dependency on the exhaust system to scavenge cylinders of spent exhaust gases . Ideally , you want a balance between back pressure and velocity . Headers made of 1-3 / 4-inch pipe work well with stock and mildly modified V-twin engines . To maintain the proper back pressure / velocity balance with a street engine , it is suggested not to use 2-inch diameter or larger header pipes unless your engine is at least 100 cubic inches and preferably larger . But be aware that even in the case of a large engine there are trade-offs , because a 2- inch pipe will bleed off some bottom-end torque for top-end horsepower . To optimize high-rpm power with a 100 ci-130 ci engine , you should use a 3-step header design .
Header Pipe Length
Pipe length is determined by the engine ' s application and the most important rpm range . Pipe length is important for perfecting inertia and wave tuning , which determine the effect scavenging has on power production . Scavenging refers to the process of where a column of fast-moving exhaust gases ( inertia scavenging ) supersonic energy pulse ( wave scavenging ) aids the removal of combustion residue from the cylinder while assisting the intake charge into the cylinder . Because pressure waves can only be timed to help exhaust scavenging over a narrow rpm band , the engine ' s most critical rpm range must be first
determined so pipe length can be matched to the rpm band . A longer pipe length optimizes power at low rpm . Conversely , a shorter pipe length improves upper-end rpm performance , because as the pipe becomes shorter , the tuning effect has less time to enhance slow-speed engines ' operation .
Stepped Header Pipes
Various exhaust systems are designed with a stepped header pipe . A stepped header includes the placement of pipe diameter differentials in the pipe . The differentials are referred to as steps . Stepped headers are divided into two or more pipe sections . Stepped headers are most beneficial when used on large displacement and / or high rpm engines to achieve maximum performance . A cam with a long overlap can benefit from a pipe design that produces a wide exhaust-scavenging wave because a greater portion of the overlap period is effectively covered . A stepped header is an excellent design for this application .
Mufflers
Most stock Harley mufflers are small for aesthetic reasons and include a healthy dose of internal baffling to satisfy EPA noise limitations . As a result , airflow is restricted and so is power . Large touring model Harleys ship with large volume mufflers and a crossover pipe . This large , interconnected design produces a few extra ponies over the Dyna / Softail models with smaller volume mufflers . Adequate muffler volume for the engine displacement is important for keeping exhaust back pressure low at high rpm . Muffler volume should be ten times the cylinder volume to make good high rpm power . However , horsepower is also a factor because the more horsepower an engine makes , the more exhaust flow it generates . In other words , as engine airflow increases , exhaust gas volume also increases . With increased exhaust gas volume , muffler airflow and volume must also be increased . Large engines need a muffler with a large main body , free-flowing baffle and unobstructed exit . Since large mufflers do not look aesthetically pleasing on a V-twin , it is difficult to make a pipe for a large displacement engine that satisfies both aesthetics and performance . The easiest and least costly method for improving
3-STEP DESIGN
Three-step design delivers " incredible horsepower as well as great sound ". It reduces the DB level even without baffles and is " comparable to most leading aftermarket exhaust systems ".
exhaust system performance is to change the system . Most 2-into-2 systems are tuneable by changing the internal baffles . Modifying baffles , especially those used in small-volume mufflers , can improve power . Increasing the number and / or size of holes in the baffles or shortening the baffles reduces back pressure and helps top-end power . However , remember that increasing flow too
AFTERMARKET MOTO DESIGN - OCTOBER 2021 33