Slip-Ons That Are Internally Flared

So looking for a slip-on that will fit a 2.5” pipe and is internally flared, I only came up with three options:

1) 2”x24”x4” Megaphone, chop at the 2.5” section and weld to a slip on adaptor, use a 4” bolt in baffle.

2) Burns Stainless make a 2.5” inlet to 3.5” flared megaphone, but it’s $400+

3) Then I found the below one. $155 has a welded in baffle that flares from 2.5” to 3”.
Max Performance model.
http://www.coneeng.com/pdf/motorcycle/MC-finished-Mufflers.pdf

Does anyone have a lead on an off the shelf 2.5” inlet to 3.5” outlet that isn’t a constant diameter baffle internally? Unfortunately the options listed in best to worst for power 1-3, but for simplicity it goes 3-1 making these options less than ideal.

Thought I read somewhere that you want a constant diameter perforated baffle for best performance as it actually speeds up the velocity of the gas flow.

leatal said:

Thought I read somewhere that you want a constant diameter perforated baffle for best performance as it actually speeds up the velocity of the gas flow.

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Everything I’ve read indicates the opposite, the increasing diameter is used to increase the strength of the pulse sent back up to the valves.

With the short length of a single exhaust on the rocket the muffler is a contributing factor and will act as part of the header secondary.

1olbull said:

I like that Big Mouth 19" stainless reverse cone at $192.50 (page two).
Wonder if it would do better on the dyno with my CES than the 21" slash cut can from CES?

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I love the look of the big mouth, just wish it tapered internally like the max performance one.

I’m sure there will be some effect on the dyno, probably not a whole lot.

Why don't you just build exactly what you want ?

Funny enough, I'm actually looking at welders now to do just that I figure it's high **** time I finally do my own welding.

Claviger said:

I love the look of the big mouth, just wish it tapered internally

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As the bishop said to the actress.

Claviger: "Everything I’ve read indicates the opposite, the increasing diameter is used to increase the strength of the pulse sent back up to the valves.

With the short length of a single exhaust on the rocket the muffler is a contributing factor and will act as part of the header secondary."

That would be incorrect. The largest pulse, but at a fixed frequency, is generated by the end of a square cut tube of constant cross-section. An increasing diameter cone will send back multiple pulses of gradually decreasing strength, instead of one strong reflection. Thus megaphones are used to broaden torque curves.

A perforated tube acts like a megaphone in that the gas velocity slows down as it progresses down the length (the increasing cross section area of a megaphone does the same thing). It is true that the center of the gas stream will be faster than the flow near the boundary layer on the internal wall, but the overall effect is to slow the gross flow down and disturb wave activity in both directions breaking large waves into chaotic patterns of small waves reflecting from every hole or protrusion into the flow stream. This is how it reduces measured decibels of sound.

The muffler indeed is part of either the collector or resonance chamber. Not all mufflers are created equal.
You can buy perforated sheet and with a little skill, cut, roll and weld your own tapered internal baffle to insert into one of those shiny SS megaphones.

Now the question is: At what taper, and how long???

Thanks for the clarification. Looks like I have some more reading to do regarding taper and length. Intuitively I would expect it to act list the collector, the sharper the angle the bigger the amplitude across a narrower RPM range and the length t "rock" the shape of the torque curve using peak torque as the axis, longer being more bottom less top.

Definitely need to find some good articles on google scholar