Change slip ons, dyno?
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Joined: Sep 2008
Posts: 14,146
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From: San Diego, CA
Yes.... but....
The word on M8 engines (I don't own, nor have I worked on one) is that they are not as lean from the factory as the Twin Cams were. Many believe you can get away with a Stage 1, higher flowing A/C and mufflers, without needing a tune..
The cats flow better than most people think... so you are affecting the heat felt off the exhaust system, more than the flow through the mufflers.
IMHO... if you are not constantly running the bike at high rpm and high load conditions, you will not hurt your engine.
Of course, anytime you change the airflow, a retune will allow the bike to run its best.....
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From: Louisiana
Stock 2022 117 Lowrider S. No still stock intake.
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Yes.... but....
The word on M8 engines (I don't own, nor have I worked on one) is that they are not as lean from the factory as the Twin Cams were. Many believe you can get away with a Stage 1, higher flowing A/C and mufflers, without needing a tune..
The cats flow better than most people think... so you are affecting the heat felt off the exhaust system, more than the flow through the mufflers.
IMHO... if you are not constantly running the bike at high rpm and high load conditions, you will not hurt your engine.
Of course, anytime you change the airflow, a retune will allow the bike to run its best.....
The word on M8 engines (I don't own, nor have I worked on one) is that they are not as lean from the factory as the Twin Cams were. Many believe you can get away with a Stage 1, higher flowing A/C and mufflers, without needing a tune..
The cats flow better than most people think... so you are affecting the heat felt off the exhaust system, more than the flow through the mufflers.
IMHO... if you are not constantly running the bike at high rpm and high load conditions, you will not hurt your engine.
Of course, anytime you change the airflow, a retune will allow the bike to run its best.....
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,146
Likes: 11,220
From: San Diego, CA
I suspect it would take more than just removing cats to cause a condition so lean, as to cause engine damage... I would suspect other factors were at play
The short version....
Part of an OEM tune uses O2 sensor feedback to adjust the tune in real time. This portion is called closed loop
Part of the OEM tune is outside the accuracy range of OEM O2 sensors, and so it does not use O2 sensor feedback. It uses algorithms based on the components of a stock engine. This portion is called open loop.
The low load and cruise areas of the tune are Closed Loop. when riding in Open Loop, immediate feedback from the O2 sensors will keep the tune safe and relatively effective.
The high rpm and high load areas of the tune are Open Loop. They will be leaner than OEM if you increase airflow through the engine. Most people don't spend a lot of riding time in these areas of the tune.
If you ride hard, at high RPM, and race around everywhere.... you should retune.
If you are a relatively sedate rider, with occasional spirited riding, I seriously doubt you will hurt your engine by just changing to non-cat, slip-on mufflers.
As always, it will run its best if anytime you increase airflow, you retune the engine.... That's what I do.
If you have any doubt, retune... it's always the best option...
I am just saying that with only a muffler change, on an otherwise OEM bike, IMHO you don't NEED to retune.
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