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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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  #21  
Old 4th December 2008
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Talking questions ?

I have read the posts and have seen the pics of these mods. Has anyone just removed their baffles completely? Or possibly made their own baffles ? I am curious as to how you remove the baffle. Is drilling out the weld the only thing you do? Isnt it attached inside the muffler?? Or is it just resting snugly inside the muffler waiting to be pulled out after drilling out the weld? I have an 08 custom with stock tapered mufflers and curious to know before I mangle perfectly good mufflers.
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  #22  
Old 4th December 2008
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I have read the posts and have seen the pics of these mods. Has anyone just removed their baffles completely? Or possibly made their own baffles ? I am curious as to how you remove the baffle. Is drilling out the weld the only thing you do? Isnt it attached inside the muffler?? Or is it just resting snugly inside the muffler waiting to be pulled out after drilling out the weld? I have an 08 custom with stock tapered mufflers and curious to know before I mangle perfectly good mufflers.
Yes and yes. Just do a search for my posts and you can read all my muffler exploits over the last 2 years.

Completely removing the baffles sounds like shit, IMO. Way too much bass, headache inducing low frequencies. Plus you take a significant hit in the low-end torque.

So far, the best sounding mod to the stock muffs is to drill a 3/8" or 1/2" hole in the plug in the center of the baffle.
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  #23  
Old 4th December 2008
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I dont care about removig the muffler to drill out the baffles but if i go the route of just the hole in the end of the baffle do I need asuper long drill bit??
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  #24  
Old 4th December 2008
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I dont care about removig the muffler to drill out the baffles but if i go the route of just the hole in the end of the baffle do I need asuper long drill bit??
You either need a 12" bit, or a drill bit extension. I used an extension.

This video is a good how-to for this mod:

http://www.youtube.com/watch?v=AE1CmP57hNM
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  #25  
Old 4th December 2008
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if your mufflers have the solid plug at the front edge of the baffle, then drilling it as in the video is the way to go (1/2 inch hole would not be big enough for me).... with a long bit extension, you could do it with everything still mounted up tight......

if the front of the baffle is the scooped kind, like the CycleShacks.... remove the baffle and open up the scoop....this kind is better cuz if ya open it up too loud, pull it back out and close it up some till you get the sound you want.

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  #26  
Old 4th December 2008
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Default holy crap!!!! LOL

For the first time Ilooked in my pipes and what do I see???? One pipe is already drilled out !!!! Guess the work wont be that tough now lol
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  #27  
Old 4th December 2008
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The plug is about ten inches inside the muffler and the muffler doesn't have to be unclamped or removed from the pipe to do this unless you want to shake the muffler out or run some water through it afterward. I can't fault Gary for his method (he's a clever guy and has done a lot of work with these as well) but I had no trouble with just blowing the shavings out the back by starting the engine. If using a regular drill, it's best to loosen the rear cylinder exhaust as a full assembly just to get straight access to the front muffler, but I was able to drill the 1/2 inch hole in the front at a slight angle without even doing that. It's very important that the bit be kept centered with a washer fastened around it near the tip. If you have access to an angle drill, you won't have to loosen anything at all, even if you're using a hole saw which will require that you drill straight on and not at an angle in order to produce a round hole, unless you're cutting the whole plug out. For a pneumatic angle drill, you might try a body shop. With all of the correct tools in place it would take you five minutes to complete this mod from start to finish on both mufflers and they wouldn't charge you very much. If you want to do more you could even run some compressed air through your spark plug hole and let it blow any shavings out the exhaust. Of course the valves would have to be in the right position. Shu started a thread last spring where he tried a few different home made baffles in a pair of stock mufflers and there are several other threads around as well.
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  #28  
Old 4th December 2008
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Completely removing the baffles sounds like shit, IMO. Way too much bass, headache inducing low frequencies. Plus you take a significant hit in the low-end torque.

So far, the best sounding mod to the stock muffs is to drill a 3/8" or 1/2" hole in the plug in the center of the baffle.
Have to agree with your first statement regarding gutted stock mufflers unless one likes the harsh, metallic sound of wide open exhausts with little sound buffering. To me, they sound a lot like the standard Vance & Hines Straight Shot slip ons, which are very loud and harsh to my ears. Agree that the low and midrange power with this mod suffers as well.

I would add the Gronk Mod to your best sounding list for the stock muffler mods along with the 3/4 inch mod (but only if you like more noise for the last one). I don't believe that you've done the Gronk Mod but I'd bet that you'd like it as well. None of the sound clips do any of these mods justice and Gronk62's own mod was done on International mufflers with far fewer holes, which resulted in a different sound.
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  #29  
Old 5th December 2008
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You just need to loosen the header bolts at the head a little bit. Then unbolt the two bolts that hold the muffler to its mount and loosen the muffler clamps until they will slide off the muffler and up onto the header pipe. (There is also a bolt/clamp on the rear header pipe that bolts to the engine side cover. That has to be unbolted.) Lift up and out on the muffler enough to lift it up off the crossover port. At that point you can twist the muffler and wiggle it up and down while pulling it away from the header pipe. Keep doing that until you work it off the header pipe.

Installation is the reverse. Just don't tighten the header bolts at the head until you've got the muffler in place and the muffler bolts screwed in hand tight. Make sure you don't over-tighten the header bolts because you can strip them.
So the muffler clamp did not want to loosen; i.e.: the bolt was extremely hard to unscrew, and it does not close all the way...what do I do? As I far as I know, it is not affecting performance in any way, and I kinda managed to get it "stuck" (twisted the bolt on the clamp a little to create more pressure on the clamp) but try as I might, the bolt just WON'T tighten.......

I don't wanna give up, but...

Grrrrrrr...
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  #30  
Old 9th December 2008
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I did the Gronk Mod making the holes larger than his instruction and added a few rows. Then I opened up the AC and installed a K&N filter. When I did another baseline Dyno pull I gained 2 HP. The Dyno tech said he could have tuned some more power out of it but he wanted to schedule it for a different day. The sound was more what I wanted. I decided to save my money for upgrades so you're right, my testing was limited.

I went back and checked an old post written by Rider1951. He said he did the Gronk Mod on his 05 1200C but only drilled out some of the holes and only drilled them out to less than 1/4 inch so he didn't get all of the flow or performance of the full Gronk Modded U.S mufflers. Still, with a slightly richer than stock N65A needle, richer than stock 45 pilot jet and a leaner than stock 175 main jet in the carb for both tests, he ran 62.48 HP and 67.52 ft. lb. of torque with the stock tapered mufflers and 65.45 HP and 72.55 ft. lb of torque with his half-way Gronk Modded mufflers. I would expect that with all of the baffle tube holes drilled to 1/4 inch for a full Gronk Mod, he would pick up a couple more HP and a couple more ft. lb. of torque. That's not bad for a relatively quiet muffler that won't attract undue attention anywhere when ridden moderately, while it still sounds like a Harley. He did say that he was a little rich above 5,200 rpm and was running only 13.5:1 between 3,700 and 4,500 rpm so he could have tweaked it a little (perhaps by shimming the needle and using a little smaller main jet).

I suspect that you could have gotten more power out of your Gronk Mod if the bike had been run long enough for the EFI to adjust itself to the changes and also perhaps had the dyno operator done more runs.
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