Many companies will say that their slip-ons make "this HP", or "that HP", and this only goes to show how little these supposed "performance"
companies know about horsepower. Horsepower is created in the relationship between the intake, engine and primary / collector / connecting pipe exhaust sections of the powerplant, and the mufflers are just that, mufflers.
Yes, there are more restrictive and less restrictive mufflers, so how much they flow is relative to how much horsepower you can get. But assuming that you are looking at good companies (yes there are companies who can even screw-up a slip-on!), we are all able to create a 2.25" hole in a canister, so the restriction is almost zero.
Your motor cannot tell the difference between one 2.25" hole and another 2.25" hole, so the name badge on the outside means very little to the purchasing decision as it relates to the slip-on performance or HP output. (Unless of course you find one of those companies who can't even get a slip-on right!)
Yes, you need to make sure the canister is not restictive, and some companies do still run 2" cores on modern motors, as maybe they cannot afford or do not want to alter their product line for better performance. These smaller cores are more restrictive then our designs (although some smaller or less HP motors work fine with the 2" core but these are usually older machines) and will not give you the same power increases. But the end result of equal sized "holes" is that your horsepower gains will be whatever your stock pieces are able to create, as we have not altered any of the parts which make up this equation. All we have done is allow them to flow as efficiently as possible.
Quality of construction, design, materials used, re-buildability, finish and sound are are the major purchasing criteria you should be
concerned with when buying a slip-on, as you have to live with the product long after it is all shinny and new at the parts counter...
The biggest change with a slip on is in sound, then weight reduction, and then a few HP for very little effort! Micron slip-ons are designed to be as non-restrictive as possible, while still maintaining the rich / deep tone and sound that we are known worldwide for. Our construction and materials are second to none, we offer the finest in appearance & sound, and our re-buildability is un-matched by anyone in North America.
So the best part of a Micron slip-on is that since you are not altering the headpipe design, you will have a "stock" power curve, improved across the range due to the removal of restrictions, with the wonderful deep sound and looks your machine deserves!