imported post
As mentioned, the OEM resonator allows for expansion of the exhaust as well as allowing the outlet pressures to be shared across both exhaust pipes. Since the 1500 is a very even-firing engine, this allows the exhaust velocity in each pipe to be slower and more stable (again, as mentioned above, you can completely close off one of the exhaust pipes and notice that all your exhaust will flow from the other side at 2X volume and increased velocity).
I've not been able to confirm this in research, but I would suspect that the Honda Engineering team worked the design of the OEM chamber to work as a Helmholtz resonator, which would actually help evacuate the headers more efficiently than venting direct to atmosphere.
While discussing the TorqMonster pipes, it's been mentioned that they do not provide a cross-over connection. The competitive pipe-set, "Xtractor" from MBL Innovation does provide this cross over and also includes an over-all longer exhaust path. I don't have a dyno, time, or the cash required to graph and compare these two systems on equal footing, but I can say that there are Dyno graphs that show the Xtractor producing better low-end torque than the TorqueMonster pipe-set, which, (as noted above) is what is found commonly in the automotive Hot Rod after market where cross-overs are more common place and used as an aid for low-end torque.
From personal experience (having installed both on a few bikes), I prefer the Xtractor for the sound quality (I'm assuming from the reduced exhaust velocity in the crossed-over system); the TorqMonster set seems a bit more "harsh" in tone (more high frequency that is not attenuated). Also, I believe (seat of the pants only) that the Xtractor does provide a little more "oomph" near the top of the tach... having run a newly installed TorqMonster'd 1500 side-by-side up the hills with a 1500 fitted with the Xtractor (in fairness, I couldn't tell you much about the differences in maintenance and tuning on either bike, so this could have just been clean plugs and airfliters talking)...
Fitting the short pipe from the OP is doable; the bends are uncomfortable to form without cutting and welding. You will see the doubled (or more) velocity outta the pipes, so expect higher pitch and more heat in the mufflers themselves. Totally my opinion here, but I believe that the shorter pipe will not act to add any poiwer, and you may find reduced torque and reduced higher RPM performance as the bike acts to push exhaust through the GL's fairly restrictive pipes (when taken singly - this is prolly why these manufacturers advocate the use of their pipes, which should flow more freely)
To install these pipe without cutting the OEM resonator, you will want to have 3 of the header-to-head exhaust gaskets on hand. Removing the right side's header pipe from the head will be required (should be covered in the instructions for both of the aftermarket pipe-sets mentioned as well as in the FSM for resonator removal for the 1500)
