Carolina Motorcycle Events - Questions From The Bench

Carolina Motorcycle Events - Tech Talk

Questions From The Bench

By Dennis Thurlow

Q: If I only install an exhaust on my motorcycle, what type of performance can I expect?

A: An engine is nothing more than an air pump, creating power by the flow of air and fuel in and out of the system. That's why the exhaust plays such a vital role in performance of the engine. The Screamin' Eagle baloney-cut, slip on mufflers increase air flow through the muffler by more than 16% over stock mufflers. Plus, they have a great throaty sound, too! A 16% muffler air flow increase does not necessarily translate into a 16% increase in engine power. Without a free flowing engine intake modification, carb set kit, there is very little gain with mufflers alone.

Q: Why do the pipes turn blue?

A: Since 1996, Harley-Davidson has noticed an increase in discoloration of exhaust pipes. Here are some of the reasons pipes turn Blue.

1. The wrong combination of parts. Incorrect combination of parts can change the heat and air flow of the system. Engines work like an air pump, and when the flow of air changes, the engine can run differently from how it was originally designed.

2. Fuel has changed. Today's fuel has a higher oxygen and alcohol content which causes engines to run hotter. So pipes can discolor. Changes to the carburetors, ignitions, muffler design also effect pipe discolor.

3. Improper warm-up or sitting and idling too long. The Harley-Davidson engine is an air cooled engine. If the motorcycle sits in one place running too long without air flow, exhaust can discolor the pipes.

Q: When running engines in hot climates, is it ok to mix grades of oil?

A: A motorcycle orginally serviced with Harley-Davidson 20-50 that finds itself in need of oil in an extremely hot climate could be topped off with a heavier grade of Harley-Davidson oil as needed with no ill effect. However, mixing oil grades intentionally during a service in a false attempt to adjust the viscosity will not benefit anyone. The Harley-Davidson 20-50 will provide excellent lubrication in all but the most severe high temperature situations. The heavier grades may have an effect on a given engines sound signature during high temperature operation, but the trade-off of lack of initial lubrication during cool startup is not worth it and is not recommended.