THE SHOP

July '16

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66 THE SHOP JULY 2016 PERFORMANCE favor low-end and mid-range torque. Shorty headers, as the name implies, fea- ture relatively short primary tubes. Shorties are popular for many hard-to-fit applica- tions with regard to available under-hood space and often help with installation ease. Short primary tubes will tend to favor the upper rpm range, but as a compromise for a street vehicle where space is an issue, they remain popular. Lakester styles are so-named because of their use in early dry lake racing. This style features short primary tubes that imme- diately enter a long straight megaphone (tapered) style secondary pipe. Lakesters usually feature a cut-out plate, allowing you to run through a pipe/muffler system, or open, bypassing the rest of the system. This style remains popular for nostalgia/ old-school hot rod buffs. Tri-Y headers are "regular" headers that feature two of the primary pipes merging into adjacent primary pipes (creating a "Y" intersection). The bank of four primary pipes are relatively short, connecting to a pair of larger-diameter primary pipes, ending with the two larger primary pipes merging into a common collector. The idea behind a Tri-Y design is to create a port separation by pairing the cyl- inders that are firing 180-degrees apart. By merging the primaries and transitioning into a larger-diameter pipe helps to increase exhaust scavenging. Pulling exhaust gasses out quicker promotes increased air intake, speeding up the combustion process and theoretically producing more power. PRIMARY TUBE DIMENSIONS When we consider header primary tube diameter, many variables come into play including engine displacement, camshaft profile and the intended vehicle use. (Does the driver demand more bottom-end torque or power at higher engine speed?) In a way, we can relate exhaust tube diameter to liquid plumbing pipe diameter. At the same input pressure, a smaller-diam- eter tube will create higher water pressure, while a larger tube will result in lower water pressure output. Similar to the selection of carburetors, fuel injectors, tires, wheels, etc., bigger is not always better. Generally speaking, smaller-diameter primary tubes tend to promote low-end torque, but if the tube diameter is too small, backpressure can increase to a detri- mental condition (loss of power and burnt exhaust valves). Many leading header manufacturers store thousands of initial header patterns, categorized by engine and/or vehicle application. Each set is recorded with all fitment data, such as vehicle make, model and year, engine size, accommodation for accessories such as A/C, power steer- ing, etc. In each case, the initial pattern was developed for finalized fitment. If an issue arises in the future with a customer's application, the manufacturer can refer to the initial pattern to determine if the customer's vehicle features an irregularity that poses a fit or clearance issue. Long-tube headers feature longer primary tubes prior to joining at a collector, to provide in- creased torque at lower rpm. Performance-wise, this is the preferred approach where bottom- end power is desired—providing the long-tube style will fit the vehicle, of course. Getting Ahead on Getting Ahead on HEADERS

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