Typically, where does the power range lay.....

3" is low end, as they get bigger the range goes higher?

 

Roger that, jt. Think of slipons much like you would cams....you can't have your cake and eat it too. The smaller the diameter, the more back pressure your engine gets, which equates to more torque. That said, you lose HP on the top end. The bigger you go, the less torque you have, but the more HP you gain on the top end, up to "that point of diminishing returns", wherever that may be based on your set up.

Based on our conversation earlier today, you're happy with your cams which are mid range to top end cams. If you want to maximize those cams, you'll choose slipons that are 4" to 4.5", most likely. You'll have a 103" that'll easily do 120 MPH, and still be making solid power when you roll on the throttle cruising at 85-90 MPH, and likely even higher. If you want to balance those cams out a tad, you might go with 3.5" slipons that are going to increase your torque range a touch, give you excellent mid range, and respectable top end (HP). But the top end with 3.5" won't be the same as it would be if you went with a larger diameter slipon. If on the other hand you wanted "off the line, hold on for a good time" bottom end torque, you're current cams would not be the right choice for that. You would want to choose a cam that makes power in the low RPM range, AND couple that with 3.5" slipons.

For whatever it's worth to you, I don't think that the 103" puts out enough power to really support a 4.5" slipon IF torque is the goal. I ran a set for three years until I dropped down to a 3.5" last weekend. The difference in torque is remarkable with the 3.5" slipons. BUT......before changing to 3.5" slipons, I could roll the throttle at 90-100 MPH, and the power that my motor was still making at that speed and RPM level was astonishing (118+ MPH was no problem, and I don't have a top end cam in my bike with the TW-222's). I just decided that that was not where I wanted my power band to be. Stuff can go very wrong very fast at those speeds, so I would rarely go there for that reason.

Comes down to what you want, but they can be viewed through the same lens (essentially) that you view cams through: you can have one or the other (or something right in the middle), but you can't have both or all three at the same time.

 

A little more food for thought -

Slip-ons are better for a softail because the cats are in the mufflers. The cats are in the head pipe on an FL.

And with the stock touring 2-1-2 exhaust, about 70% of the exhaust goes out the right side.

 

I dont think this is true for recent softails, 10-up, I think.

 

You might be right, I should have posted more details. I had a '13 Deluxe and the cats were definitely in the mufflers, slip-ons made a good improvement. My current bike us a '14 RK and the cats are in the head pipes. In the near future I am going to go with a complete new exhaust, no slip-ons.

 

I really dont think the cats were in the mufflers on the 13 softails...

I could be wrong tho, its happened before, remarkable as it may seem...

 

Softtails have cats in the mufflers like the Street Bob and Super Glide Dynas. Slipons are a easy upgrade on these bikes.

 

Gipper, you're thinking 4" is a good compromise? I took a peek at those supertrapp stouts.

Right now owning the h.d. screaming eagles....I think their 3.5"

 

I run Screaming eagle night sticks and like the idea of tunable exhaust.Supertrapp makes a great product.I don't have your engine build but a great thought.Ill never run another muffler.

 

The size of the can isn't going to affect the hp/tq as much as the baffle size and style. There are quite a few baffles available for the 3 1/2" SE cans, I have 4 myself.