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PERFORMANCE MOTORCYCLE PARTS AND KITS FOR AMERICAN V-TWINS

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How does my new SSW+ breath?

In many respects, S&S SSW+ engines are similar to Evolution style engines, but when it comes to the way they handle crankcase venting, they are a whole 'nother animal! Most S&S Evolution style and SSW+ engines have two engine breathing systems that can be used separately, or together, commonly referred to as case breathing, and head breathing. 

For case breathing, SSW+ engines still uses the venerable breather gear to regulate the engine's internal airflow, just like the Evolution style engines before it. However, the head breathing arrangement is markedly different. SSW+ engines don't use hollow breather bolts to vent excess crankcase pressure to the outside. Instead, the head breathing arrangement of a SSW+ engine consists of two hoses—a small hose on the front head, and a larger hose, equipped with a one-way check valve on the rear head. (More on the check valve in a minute). 

The front hose is routed from the front head to the intake manifold. It applies manifold vacuum to the crankcase anytime the engine is running. The rear hose is routed from the rear head to the carburetor backing plate (or other suitable location). Its purpose is to relieve excess crankcase pressure at all RPMs. Unlike the hose on the front head, the hose on the rear head doesn't do anything until pressure builds in the crankcase. Just remember, the front hose sucks, the rear hose blows. 

The rear head breather hose on an SSW+ engine performs the same function as the breather bolts on an Evo engine; that is, venting excess crankcase pressure to the outside, without allowing outside air back in. Both engines use a check valve to perform this function. 

Evo engines use a pair of umbrella valves located inside the rocker boxes, while SSW+ engines use a one-way check valve, S&S Part #50-8122. It is located outside the engine, placed in the aforementioned rear head breather hose. The one way check valve must be used with the rear head breather hose, no exceptions. (By the way, SSW+ rocker boxes will have provision for Evo style venting, but it is not functional). 

The front breather hose supplies vacuum to the crankcase as added insurance against engine blow by. In most applications it is beneficial. However, there have been a few cases of this hose pulling oil into the intake, causing the engine to smoke. Using the front hose is optional. If the front hose is causing a problem, it can be removed and the fittings capped. If the front hose is removed, a check valve is still required in the rear head hose. 

The one-way check valve is critical to the engine's operation. It must be installed in the hose so that air can flow out of the motor, but not back in. The valve is light colored on one end, and black on the other. You can blow through it to determine which end faces the motor, or, if you'd rather not wrap your lips around the thing, just remember—"black out"— the black end always faces out, or away from the engine.