Big bore engines are all about the flow, more air in and more air out, anything that slows that down, robs horsepower.
The factory M8 intake manifold does a decent job in stock form, but starts getting in the way when trapped between 124-in. and larger cylinders. The stock polymer unit is also less tolerant of the additional heat that a big bore engine can make at full noise. The solution is the new S&S high flow cast aluminum manifold and a must have for top level performance in the M8 platform. It adds 3-5 Hp with a simple bolt on install and fits most M8 models (Softail and Touring) from 2017 to 2021.
The S&S High Flow Manifold is priced at $189.95 and available through your local dealer or direct from S&S Cycle.
Link: S&S Cycle