Adding New Mufflers

[JDhog211]

I have a totally stock 2004 FLHTI Bagger, and it runs extremely well and fast.
The only thing I would like to do is add a pair of Vance and Hines Ovals the regular size not the monster ovals, just because I like their sound. 
My question is would I loose any low end torque due to lack of back pressure?
Stock air cleaner , mufflers and ECM currently on my bike. 
Which brings on another question. Do the Twin Cam models share the same stock ECM'S and Cams from 2002 to 2006 ?
THANKS IN ADVANCE!

[smoserx1]

Which brings on another question. Do the Twin Cam models share the same stock ECM'S and Cams from 2002 to 2006 ?

I don't think so.  The 2002 models show an ECM with two connectors for the input and the 2006 show an ECM with one input.  Seems to be true for either carbureted or FI models.  Remember, on FI models the ECMs also control fuel delivery.  You MIGHT be able to get by with just a muffler change if you keep the air cleaner stock.  I think this is a lot easier to get by with on carbureted models.  If you notice any performance hit at all I would suggest getting it tuned.

[truck]

Just a word about the Ovals, they do sound good but once they get 50-60,000 miles on them they get loud. That might be true of all mufflers though.