Slip-ons are probably the best mod that you can do to your motorcycle. For a few hundred bucks, a slip-on will seriously upgrade the looks of your motorcycle, completely change the way the exhaust sounds, and make it significantly louder. What’s not to love?
However, since slip-ons are considered a performance part – won’t they upset the air-to-fuel ratio? Do you need a tuner with slip-on exhausts?
Does a Slip-on Exhaust Increase Horsepower?
Before we go any further, let’s first get this out of the way: in most cases, slip-ons do not increase horsepower, and when they do – it’s only a few HP at best. A lot of people think that they do improve performance, but it’s mostly a placebo from the motorcycle being louder.
It all comes down to how restrictive the piping prior to the muffler is and the OEM muffler itself. If the headers and the rest of the piping are smaller than the diameter of a slip-on exhaust, then you most likely won’t see a difference in performance even on a dyno. The exhaust gases can only travel as fast as the narrowest and most restrictive part allows them to. In order to increase HP, you have to address that first.
What if the OEM Muffler Is the Most Restrictive section of the Exhaust?
Most OEM motorcycle mufflers use a straight-through design. This allows exhaust gases to flow relatively freely through the perforated pipe inside the muffler, which means that most OEM mufflers are well-designed and not restrictive in the first place.
On the other hand, some motorcycle manufacturers go overboard with the number of baffles in order to reduce sound. Baffles trap sound waves inside acoustic chambers, which cancels most of them out. However, this means that the exhaust gases are forced to change direction quite often and therefore slow down. This is good for sound deadening but bad for performance – you want them out of the exhaust as quickly as possible in order to make room for fresh air to flow into the combustion chamber.
Again, most OEM mufflers are quite good and do not restrict flow all that much. However, if your motorcycle has a relatively restrictive OEM exhaust, then you are likely to feel a difference with a slip-on.
Do You Need a Tuner With a Slip-on Exhaust?
Assuming that a slip-on will not increase HP in most cases, and assuming that it’s the only performance mod you’ve got, then you probably don’t need a Power Commander or any other tuner. You would only need a tuner if the slip-on increased exhaust flow and in turn upset the air-to-fuel mixture.
For example, If you already have performance-enhancing mods on your motorcycle, like a bigger and better-flowing air intake, then it’s a good idea to get a tuner in order to compensate for the increased airflow.
There are exceptions to that, however. If the OEM muffler, which you are replacing with a slip-on, is badly designed and restrictive, then getting rid of it will increase exhaust flow and upset the air-to-fuel mixture. There really is no other way to know if your OEM muffler is restrictive, other than removing it and seeing if the bike runs differently without it.
If no other performance mods are present, then the ECU is more than capable of compensating for the slightly increased exhaust flow on its own.
With that being said, getting a tuner won’t do any harm – it’s just not necessary and quite expensive.
Do You Have to Rejet With a Slip-on Exhaust?
Motorcycles with carburetors are finicky machines and sometimes it seems that just looking at them the wrong way is enough to throw the air-to-fuel mixture off. Because of that, it’s difficult to say for certain whether your specific motorcycle will need new jets.
However, in most cases, a slip-on shouldn’t cause any problems assuming that the OEM muffler wasn’t significantly more restrictive.
Final Thoughts
Slip-on mufflers are great. They’re inexpensive and will drastically change the way your motorcycle sounds, but they won’t add performance in most cases. Because they don’t add horsepower – you don’t need a Power Commander or any other tuner if you’ve just got a slip-on.
However, if you got other performance-enhancing mods on your motorcycle, or you expect that your OEM muffler is way too restrictive, then getting a tuner might be a good idea.
Jake is the site’s primary contributor.
Motorcycles and automotive repair have been a big part of his family for generations, therefore it’s only natural that he decided to become a heavy-duty diesel tech.
Outside of work, you’ll find Jake restoring and riding rare street bikes and ATVs.