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Thread: Fullsac 1.75" Baffles vs. Stock CVO Cores "Drilled Out" on 4" Mufflers

  1. #1
    HCG Technical HCG TechnicalSenior Member JD's Avatar
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    Fullsac 1.75" Baffles vs. Stock CVO Cores "Drilled Out" on 4" Mufflers

    This is a pickup from this thread:

    http://www.harleychatgroup.com/forum...uring-Mufflers

    I've been running these "de-plugged" (otherwise stock) 4" CVO mufflers for the past few years on a early TC88 touring bike with the stock (catless) header and Andrews TW26 camshafts. The previous mufflers I had were too loud and "aggressive" sounding at speed. I really like the way these CVO mufflers look and would like to take advantage of the performance potential of a larger volume muffler.

    These CVO muffers have "the" tone for my ear. It is deep and throaty and not at all "tinny". However, with the great sound, they carried a couple of issues for my setup. First, they just seemed to have too little backpressure, especially with the cam change. At low RPMs the power I previously had was just not there (seat of the pants dyno doesn't lie). On the interstate when in the sweet spot of the cams, they did fine, but lower speeds there was a noticeable power loss. Second, at interstate speed, they were just too loud. Loud enough to overcome the road, wind, and engine noise. Without earplugs, after a day of riding, my ears were ringing. Last, I developed a popping noise between high rpm shifts that I could not resolve with new exhaust seals or carb tuning:

    http://www.harleychatgroup.com/forum...Between-Shifts

    I ordered up a set of the Fullsac 1.75" "power core" baffles with the mesh screens and packing:

    http://fullsac.com/product/2006-2017-cvo-power-core/

    The install was fairly straight forward. I took the advice of using a die grinder with carbide bit to knock off the welds holding the original baffles to the housings. This took all of 10 minutes (taking my time to ensure I didn't burn through the wall of the muffler body). The old baffles needed to be knocked out with a pipe and the new baffles needed to be knocked back in with a small sledge and block of wood. I didn't want to drill new holes in the mufflers to fasten the new baffles (to avoid rust) so I had the bright idea to JB Weld them in as it is good to 600F. Those muffler ends couldn't possibly get that hot, right? Wrong! First blast on the highway that epoxy burned off and vanished without a trace. So apparently they get hotter than 600F. No big deal, though, as the tight fit didn't allow them to move even 1mm and it doesn't appear that they ever will. If they do, the end caps will prevent them from shooting out and I can always pop in a little 1/8" stainless rivet to secure them.

    After riding for a couple hundred miles today I have a few first impressions. The tone is a bit more crisp than the CVO baffles. Very similar to stock 1-piece mufflers actually. Definitely not as loud as the modified CVO baffles. Easy now to hear the engine and tires along with the exhaust. Don't get me wrong, they aren't quiet or wimpy sounding, and certainly too much volume for someone to tailgate on the insterstate, but just not quite as loud. Probably louder than stock 1-piece muffler, which is exactly what I was after. They do have this annoying little high-pitched "chirp" overtone at certain speeds though. I'm hoping as they break in that will go away. That low rpm power associated with the CVO baffles is noticeably improved (why the 1.75" and not 2.0"+ ID Fullsac core size was selected). Best part, though, is no matter what I did I could not get it to pop in between shifts (and believe me I tried). In hindsight, I think the CVO baffle works more like a drag pipe whereas the Fullsac baffle works more like a performance baffle taking more advantage of the muffler body volume.

    Bottom line, for a catless header and all-day riding where too much volume level is a concern, the Fullsac baffles work well. If you need some additional flow (i.e. bigger engine and/or cat. header) and are ok with a higher volume level, the modified CVOs are as good as I've heard.

  2. #2
    HCG Technical HCG TechnicalSenior Member JD's Avatar
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    Here is a dyno graph from Fullsac of the 1.75" (blue) vs. 2.0" (green) vs. 2.25" (red) ID baffles. Test was done back-to-back-to-back on a 2009 Twin Cam (header without cat.). Clearly the red graph illustrates this low rpm power loss (~10%) when the baffle is "oversized". That can certainly be felt. I think this is exactly what was happening to me with the modified CVO baffles and what ultimately led me to try the 1.75" Fullsac baffles.
    Attached Images Attached Images

  3. #3
    HCG Technical HCG TechnicalSenior Member JD's Avatar
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    Well it turns out that the JB Weld isn't good to 600F and a WOT at 80mph generated enough pressure to push the right side baffle out, and as expected, travel was limited by the end cap mounting hardware. I tapped the baffle back into its position and used a different, high-temp epoxy to secure it. If that doesn't work I guess I'll have to drill the housing a and install either a bolt or rivet.

  4. #4
    HCG Technical HCG TechnicalSenior Member JD's Avatar
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    The high temp epoxy putty seems to be working well as hoped. I also put it on a bit thicker this time for added strength. Once the end cap is installed the epoxy isn't visible. Much better solution than drilling a hole in the housing for a bolt as that will quickly rust.

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