EDIT: no point bumping this with a reply so I'll just add today 13th dec that I ended up speaking to the local Harley tech dept and they recommended the muffler with the larger diameter hole, which is good because it's the lighter one by 220gms.

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OK, I just scored a pair of 2015 Dynas rail mounts, that are not like the usual rail mount dynas as they are made for Australia and designed to work with an emission control device on one  the result of this is that they  have different back pressures.

And as a bonus they already have a heat shield built in which is going to save me having to deal with that part, so I'm pretty chuffed with that.

You can see the EMD with a red square around it. This is what the larger diameter hole would be for.

I am hoping to get some advice on whether to go for more back pressure/small hole, or less back pressure/larger hole.

I have so far checked the idle mix because it was easy as there was no dome plug fitted, started at 1 1/2 turns out, turned it in 1/2 and engine started to die, turned it all the way out to 3 and there was no change from 1 1/2 so I'll be ordering a larger pilot jet. I also tried the roll on at full throttle from 50-60kph for a few seconds then backed of 1/8th and there was no surging that I could notice but I'll go up a size on that anyway.

I haven't checked the plugs yet as I'm still waiting for the special motion pro bent feeler gauge to arrive. I will not be putting these on till January so I'm looking for opinions on which one of these two dynas I should fit, more back pressure or less.

The Dyna with the smaller hole is 220gm heavier.