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  #1  
Old 10th June 2006
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650brad 650brad is offline
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Smile Home-brewed CS tapereds

I tried the Gronk mod on my GF's Street Bob and it wasn't loud enough for her. It got me thinking that if you can get the old baffle out, why couldn't you put in a different one? I've seen re-cored mufflers on e-bay before that used spiral baffles. I tried to find the spiral cut material. No luck. So, instead I made my own CS style baffles. If you have access to the tools to do Gronk's mod you should be able to pull this off. Here's how I did it.
I noticed that one end of the stock baffle is expanded to fit over a spigot inside the muffler. Turns out, the diameter of this part is 1 3/4", the same as the hole saw used to cut the old baffle out. The length of the stock baffles is 18" so, I went and got two 18" chunks of 1 3/4" exhaust tubing from my local auto parts place. To make the slash in the baffle I used my hacksaw to cut 1/2 way through the pipe 4" from one end and used a small press to push the slash into the pipe until it took up 2/3 of the inside of the pipe. When I put the SEII's on my Sportster I noticed that the slash took up about that much of the pipe so, that's what I went with. The pipe distorted a little so, some some hammering and tweaking was required to get it through the hole in the muffler and to give the slash a nicer contour. Next, I drilled 4 rows of 1/4" holes spaced 90 degress apart, 8 per row. I deburred the holes as good as I could and put them in. They fit tight enough that I didn't have to tack them in to fire up the bike for a listen. WOW, what a difference. Loud, but not obnoxious, with a nice deep rumble. The GF could hear it inside the house over her hairdryer. She likes how it sounds but, it's been raining for 2 days and we couldn't road test it. I'm hoping tommorow is nicer. The only real screw up that I made was that I never thought of taking any pics until after I tacked the baffles in. Sorry, maybe I'll take one out just so you all can see. All in all, it was pretty easy and cheap. The two peices of pipe cost me $14, the hole saw $7 and some welding gas and wire. It took about 3.5 hours. Doesn't get any better than that. The big plus is that the GF is happy and you know what that means.

P.S. Thanks to Gronk for his work in this area. Without it, I might not have thought of this.
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  #2  
Old 10th June 2006
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Thats awesome. I did somthin similar to a set. I took the 1 3/4 pipe and made some slots at the the end and hammered in some brass washers in a staggered pattern then brazed 'em in place (brass to steel) then pounded the pipes in. Ya can hear the exhaust gases "slappin" against the washers a bit but I have the perfect mix between exhaust sound, carburetor sound and gear whine. One thing I noticed is small changes in the throttle can be felt on the highway (HSR42). I might try the same thing w/ some 2 1/4 pipe and wrap the 1 3/4 w/ fiber glass. I was gonna use one washer in a 1 1/2 to
1 5/8 peice in the center. Then it will look like straight pipes plus a little less weight.
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  #3  
Old 10th June 2006
jbrews jbrews is offline
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Congrats on a job, well done.
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  #4  
Old 10th June 2006
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I MUST see pics of this.

please?
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  #5  
Old 10th June 2006
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I could only download 2 pics. Here they are.


One thing you will notice is that the outlet end is expanded for another 1 3/4" pipe to fit inside. That's how I bought them. To overcome this I had to remove some material from the muffler body with my die grinder and a carbide burr. If you get a straight piece of pipe you won't have that problem. Use a wet rag to cool the muffler as you tack them so the chrome doesn't blue. Also, these are for Dyna mufflers. My stock 06 Sportster muffs are a little shorter so if you buy 18'' of pipe you will have to trim it to fit. Crude but effective.

Last edited by 650brad; 10th June 2006 at 19:43..
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  #6  
Old 11th June 2006
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And you should be able to vary the loudness and backpressure by messing with the depth of the slash and/or the # of holes in the baffle.
Plus, if you only use a couple of tack welds, you can easily grind them off and remove the baffle for mods. Or drill a 1/4" hole in the muff and baffle on the bottom backside where it won't be too conspicuous and bolt them in, making it even easier to play with them, if that's what you're into.
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  #7  
Old 11th June 2006
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Great job Brad!!

What you have done is exactly the kind of messin' around I did back in 96 when I first came up with the gronk mod.

I just tried different baffles and mods till I arrived at the one that suited my needs.

Your mod can be done to the standard Sporty mufflers as a louder and better flowing version of the gronk mod.

I'm gunna link this thread from the gronk mod thread so please keep your picture available so others can see what you have done.

Cheers
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  #8  
Old 11th June 2006
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Brad, that rocks. It's like you've earned your Gronk Master Degree.
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  #9  
Old 12th June 2006
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Thanks guys. What I like about this whole "Gronk mod" thing is how easy and cost effective it is. I'm always looking for a cheaper and easier way to do things. Aren't we all? I wish I had thought of it before I bought my SEII's. Now, if anyone else has pics of their home-brewed baffles, I would love to see them. I think it would be great to see other peoples ideas and have as many options as possible.
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Old 29th October 2006
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hi all
just acquired a new 07 Sportster and was wondering if i can apply the Gronk mod on this baby of mine . any one have some idea ? can't have too much noise with our strict noise emission laws down here in Singapore. whatever little help will be much appreciated. thanks in advance.

3 cheers to all the DIY guys
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