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.

Replacement & Special Order Intake Manifolds

Stock, S&S Engine or S&S Kit: To order a replacement manifold, refer to the manifold size chart for your particular engine type. Manifolds are listed for various sized carburetors and throttle bodies in the correct lengths for engines and kits offered by S&S.

Custom Engine: If the effective cylinder length is different from the standard offerings, a special manifold can be machined to your specifications. Order manifolds using the special order part numbers listed in the charts. Allow two weeks for delivery.

Specifying Manifold Length

Port-To-Port Distance: S&S Manifold Measuring Tools

• Use the S&S Manifold Measuring Tools  to measure portcenter to port-center distance on an engine or an existing manifold.
• Specify whether the measurement was from an engine or from an existing manifold. (Manifold measurements will be approximately .030” shorter than engine measurements due to clearance normally built into the manifold).

Port-To-Port Distance: Flange Method

• Assemble or mock-up the engine & install the intake flanges on heads.
• Scribe a circle around the port using the mounting flange as a template. The circle must be the same size as the I.D. of the flange. (It is recommended that front flange be installed upside down on the rear head and vice versa, to avoid inaccuracy in the circle diameter).
• Remove the flanges and measure the shortest distance between the scribed circles. See Diagram 1, below.

Effective Cylinder Length

• Measure the cylinder length from gasket-surface to gasket-surface without the head and base gaskets in place. (A precision measuring instrument, such as a dial caliper, should be used to insure accurate results).
• If all components except the cylinder are stock, the actual cylinder length and the effective cylinder length are equal. However, if base plates will be used under the cylinders or if the crankcase deck height is taller than stock, the thickness of the base plates and any extra base gaskets, or the increase in deck height must be added to the cylinder length to determine the effective cylinder length.
• If the cylinder heads have been decked to increase compression, the amount they have been shortened must be subtracted from the effective cylinder length.
• If the effective cylinder length is equal to or no more than .030” longer than the cylinder length listed for a specific manifold in a chart, that manifold will fit the engine.
• If the effective cylinder length is significantly different from any manifold that is available, the manifold must be special ordered. (When placing an order for a special manifold by effective cylinder length, you will be asked for actual dimensions of the cylinders and other components. S&S will calculate the effective cylinder length).

Manifold Size Number

Manifolds for Panhead & Knucklehead Engines