Well today was a busy day. I did a set of heads for a 95"(4" stroke/3.875" bore) Road King. Setup consists of flat top cast pistons, 203 cams, Ported OEM heads w/ 7mm valvetrain (1.900" intakes/1.610" exhausts), Rinehart TrueDual Header pipes with SE mufflers. The bike came in with this setup, aside from the headwork.
Right off the bat it made around 90TQ but only 73HP with the Screamin Eagle mufflers(not really surprised as I've ran into this before). I knew that was way below what it should make so I tried some KhromeWerks mufflers. Their HP+ 3.5" have a nice sound, make good power, and are priced pretty good. But when combined with this combo & header pipe system they had a HUGE dip in the TQ curve, right where you use it the most. They did make nice power up top at nearly 90HP.
I wasn't happy with that powerband, so I tried another KhromeWerks "Quieter chambered muffler" thinking maybe they would bring the TQ back. Still the dip, but with terrible power.
I had some junky RUSH 1.75" mufflers laying there so I stuck them on. BAM the TQ's back but the little baffle just couldn't keep up on top, yeilding only 80HP.
So by now we're kinda curious how some other mufflers would stack up on this combo.
At the end of the day I left the Rineharts on. They are a little soft off the wack, but made the best midrange TQ & held on up top. They are nice quality and sound good (kind of loud for some people).
So what does all this mean??
-Pretty much all of these mufflers make within 1-2TQ/HP on a stock engine.
-KhromeWerks mufflers seem to work nice with their header pipe. But I had seen this "TQ DIP" on other combos completely different from this one)
I do like their header-pipe a lot for most setups.
-Rinehart Mufflers seem to work on everything(until the combo gets REAL big).
-RC Components is more concerned about their endcaps (they come with a HUGE 2.5" baffle) but they did finish midpack.
-The Rush muffler with a 2" baffle would have probably done pretty well. I didn't have time to test it because I'm not real fond of the sound(they used to be a cheap alternative, now they raised their price. Still a cheap muffler though)
-I didn't try a V&H muffler but their twin slash unit would have probably done OK.
-As the combo becomes more radical (Cam Timing/Cylinder Head) the Vtwin becomes a lot more sensitive to the exhaust.
-A good 2-1 is generally a safe bet on solid performance.
sorry I snapped a pic real quick and cutoff the RPM. Imagine a 2,500 to 6000RPM window.