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Tech Tuning

Why does my exhaust change color?

Often times, users can experience exhaust discoloration due to improper tuning, engine malfunction or other aftermarket modifications. It's important to keep in mind that steel exhibits different oxidation and incandescent colors depending on its temperature. 

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What Do the Colors Mean?

Below is a chart that can be used as a general guide for determining how hot your engine or exhaust system is running. Below 800°F, it will have oxidation coloration. Above 800°F, it will display incandescent (glowing) coloration.  (Not accurate to determine the header or exhaust gas temperature). Use this as an indicator to check the temperature by a more accurate method.

Why does my exhaust change color?

If your pipe is blue or bluish-grey when it is cold (the hottest oxidation colors), it may actually be much hotter when running. After the pipe cools from glowing hot, the oxidation color will remain.

A good exhaust gas temperature at the exhaust port is 1250°F (blood to cherry red). In general, glowing is acceptable for the first 6-8 inches after the exhaust port. When cool, the head pipe shouldn't be blue more than 10 inches from the exhaust port.

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Why is the Slip-On Exhaust Changing Color?

Important: No part of a slip-on exhaust system should ever be blue.  If your exhaust is displaying the above conditions, your engine is running extremely lean. You most likely need to richen your jetting/fuel map. If this does not fix your problem, you should look for an air leak after the carburetor/throttle body.

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Why is the Head Pipe Glowing?

Your head pipe is glowing because our head pipes along with many others (aftermarket or original) are made from thinner materials compared to those used in the past.  Its not that your exhaust is hotter, its that it will glow at a lower temperature due to the smaller wall thickness.  Generally speaking, it is normal to see your head pipe glow up to about 10" out of the cylinder head. Its typically seen in low light conditions, usually at idle or off idle cruise.  If glowing can be seen in daylight or further back toward the muffler your fuel tuning may not be correct.  

Users will also notice that the tubing will discolor after the engine is started and heat is applied.  This type of color change is 100% normal, and a natural property of stainless steel.  The chart below will tell you what colors are associated with what temperatures.

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Troubleshooting

If you need help with any of the information in this article, please contact our tech department at (866) HMF-PIPE.

Posted Wednesday, July 29, 2015

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