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Hello; I made open pipes but with trumpet/horn tips that measure 9 inches long each one and start at 1 1/2 ID to 2 3/16 max ID at the ends.
Motor is 750 Triumph and I am obtaining harsh strident sound; nothing at all like 650 s and 500 with straight pipes and deeper notes.
I am trying to restrict the pipes at minimum; however, minimum seems the infamous big washer...that no one favor but seeing some muffler s end like Supertrapp etc I see that they sell and have in some models kind of big washers with the main hole and then smaller ones all around. They suggest to check to use one or more depending the situation.
I do not know how much distance between them; also may be still not working regarding back pressure etc
Here is no any dynamometer to check some details.

All other kind of things that I see are too restrictive and may be difficult to put inside those cones?

Thanks

How about inserting a typical baffle in the pipe before mounting the megaphone? What diameter is the exhaust pipe?
https://i.ebayimg.com/images/g/cugAAOSw98RdGnYP/s-l1600.jpg

The pipes are 1 1/2 and I welded the cones; then sent to chrome.
I do not know about what is good and what is bad regarding exhaust restrictions but I thought that those baffles as you show in those photos could be more restrictive than a washer or 3 at certain distances between.

OK.
To avoid the "infamous" flat washer you could try bolting in other shapes of metal. It may be that you just need to break up the pulsations somewhat rather than restrict them. Try a 12" or so length of perforated metal tubing, flattened gradually with the inside end pinched closed. Or the perf metal could be cut and rolled into a cone shape, tack welded and pinched shut at the end.
The total square area of holes in the perf metal should at least equal the area of the exhaust pipe outlet, causing almost no restriction but breaking up the sharp blast from each pulse. This would be almost unnoticeable, and would not involve welding on your chrome pipes.
Al

Sounds good. If I understood right, do you mean to use perforated metal sheet or do the holes like those mufflers but I do not get it how I fix inside; if do not weld it. I can send it over to chrome again but I was thinking to make holes for the possible bolts, before the chroming.
-What would be the distance from the internal diameter? about 3/8?
-

You said you do not want the restriction of the washer. I was thinking of a tube of perf metal that would fit close to snug in the muffler - then notch it so it will roll into a cone shape, and have the tip inside closed - so all the exhaust must pass thru the perf metal. The cone would be inside your exhaust pipe, almost unnoticeable. I suppose you could roll a larger cone and attach it inside your megaphone but I don't think that would look good.
The square area of all the holes would have to equal or exceed the square area of the exhaust pipe diameter, otherwise there would be a restriction.

...may be closing the rear part of that mesh cone? so the gases go between the cone and the perforated tube (conic) not directly as open in both sides.

That's what I mean - except I'm picturing the narrow closed end is extending into the pipe (toward the front of cycle). Where it would attach - at the end of the straight pipe - it would barely be visible at all.