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  #1  
Old 25th November 2008
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Default How do I modify stock 1200 mufflers?

Hello all. I own an 07 1200 Low, bone stock right now. I have heard of people who (manually) modify their mufflers/baffles (drilling holes and such) without noticeable power loss, or performance issues, and improve the sound. I was wondering if anybody could shed any light/instructions/dire warnings on how to do this...I am on a tight budget right now, but I would like to improve the sound. I mainly ride in city (Denton, TX).

BTW, great forums you guys have here! I look forward to reading responses!

Thanx,
Sly
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  #2  
Old 25th November 2008
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I see it's your first post. Hello from Pittsburgh and welcome to the XLForum.

Here's 2 different methods to modify your stock mufflers. Neither one makes much difference in power but does add some sound. A big advantage is you shouldn't need to do any tuning for these mods. The second link is free and easy. Good luck.

http://xlforum.net/forums/s...ad.php?t=16948

http://xlforum.net/forums/s...=338778&page=2
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  #3  
Old 25th November 2008
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Originally Posted by Bob F View Post
Neither one makes much difference in power but does add some sound.
I continue to say "facts still not in evidence" because your testing was too limited.

I suggest that it CAN make a decent difference, close to that of other slip ons.
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Old 25th November 2008
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I continue to say "facts still not in evidence" because your testing was too limited.
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.

The Supertrapp and PCIII made a world of difference, haven't done another Dyno yet to get the numbers. These mod were close to a grand but worth it to me.
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  #5  
Old 25th November 2008
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Quote:
Originally Posted by Bob F View Post
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.
BINGO - you changed multiple variables at the same time, possibly mismatched some components.

IF harley's claims are anywhere near correct (and they usually are) on their SE mufflers (without an AC) change, then you should see much more than 2 hp out of JUST Gronks... but without pre and post runs, there is no way to know for sure.
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  #6  
Old 25th November 2008
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Originally Posted by Kev M View Post
BINGO - you changed multiple variables at the same time, possibly mismatched some components.

IF harley's claims are anywhere near correct (and they usually are) on their SE mufflers (without an AC) change, then you should see much more than 2 hp out of JUST Gronks... but without pre and post runs, there is no way to know for sure.
Kev, Are you sure that H-D made a claim for more peak HP with the SE SP mufflers? I do know that they made a claim for more peak torque but that is at considerably less than peak rpm. I doubt that the Gronks breathe too much better than stock at high rpm, so perhaps Bob F's peak 2 HP increase with them along with the K&N filter was accurate? I wish that he could find his Dyno sheet as I'd like to look at the torque curve. I do think that the Gronks make more power in the midrange than stock just as the SE SPs do.

Correction: I just went to the H-D site and discovered that the SE SP mufflers do add 4 or 5 peak HP along with another 10 or 11 ft lb of torque at around 4,000 rpm on an EFI 1200. Despite having looked at that chart many times I had forgotten about the HP claims.

Last edited by Don Burton; 3rd December 2008 at 20:17.. Reason: Correction:
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Old 25th November 2008
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Quote:
Originally Posted by silvestre.tanenbaum View Post
Hello all. I own an 07 1200 Low, bone stock right now. I have heard of people who (manually) modify their mufflers/baffles (drilling holes and such) without noticeable power loss, or performance issues, and improve the sound. I was wondering if anybody could shed any light/instructions/dire warnings on how to do this.
Sly, In addition to the two ways to modify your stock mufflers that Bob F mentioned there are several others. (1) If you want loud and open, you can cut the baffles out of the back of the muffler with a 1 3/4 inch hole saw and leave them out. You would then want to file the edges of the saw cut smooth down to the wall of the muffler. This mod would cause you to lose some of yoru lower and midrange power just as some of the open aftermarket mufflers do. (2) The Gronk mod can be modified so that the baffle tubes do not need to welded back into the muffler. They can be expanded in place by an exhaust shop with no weld necessary. (3) You can buy or make your own baffles to fit. (4) You can cut the whole baffle plug out with a 1 1/4 inch hole saw. Some people don't like taking the whole baffle plug out as it leaves the mufflers with a slight chirping/whistling sound only at idle which sometimes goes away after 10,000 miles or so. (5) You can drill a hole from 3/8 to 1 inch through the middle of the baffle plug with no whistling sound noted. Drilling a hole through the baffle plug is the only one of these mods that can easily be reversed. All you need to reverse it is a small bolt and a couple of washers to plug up the hole. If you just drill a 3/8 inch hole in the center of each baffle plug (make sure that you keep it centered with some sort of centering device), you will have better sound and it shouldn't flow enough more to require retuning. If you then want to go louder you can do so by drilling a 1/2 inch or larger hole through the plug. The baffle plug is a sheetmetal plug approx 10 inches up inside the muffler. Personally, I like the Gronks the best as I don't like too loud.
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Old 25th November 2008
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Quote:
Originally Posted by Don Burton View Post
Kev, Are you sure that H-D made a claim for more peak HP with the SE SP mufflers? I do know that they made a claim for more peak torque but that is at considerably less than peak rpm. I doubt that the Gronks breathe too much better than stock at high rpm, so perhaps Bob F's peak 2 HP increase with them along with the K&N filter was accurate? I wish that he could find his Dyno sheet as I'd like to look at the torque curve. I do think that the Gronks make more power in the midrange than stock just as the SE SPs do.
I'd have to double-check the articles and the charts.

I remember for sure that the lionshare of the Stage I torque was now gained by SE slip-ons alone (as of 07 models).

But if memory serves me right JUST UNDER 50% of the HP gains were made by the slip-ons alone - still that was more in the neighborhood of 5-7 hp, not "2"
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  #9  
Old 25th November 2008
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Quote:
Originally Posted by Kev M View Post
I'd have to double-check the articles and the charts.

I remember for sure that the lionshare of the Stage I torque was now gained by SE slip-ons alone (as of 07 models).

But if memory serves me right JUST UNDER 50% of the HP gains were made by the slip-ons alone - still that was more in the neighborhood of 5-7 hp, not "2"
I just went to the H-D site and discovered that the SE SP mufflers do add 4 or 5 peak HP along with another 10 or 11 ft lb of torque at around 4,000 rpm on an EFI 1200. Despite having looked at that chart many times I had forgotten about the HP claims. Guess I'm getting old! If they only did one dyno run on Bob F's bike then the dyno reading wouldn't be legitimate but if they did several in the proper manner, both before and after the mod, then the readings would be legit. It sounds like they ran out of time. I suppose that it's also possible that the K&N air cleaner combined with the new exhaust may have caused the engine to go too lean, especially if the bike hadn't been run a couple of hundred miles first in order for the ECM to "learn" the new required settings.
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Old 25th November 2008
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Quote:
I wish that he could find his Dyno sheet as I'd like to look at the torque curve.
When I find it I'll post it, it won't be soon though for several reasons, sorry. The Dyno run was after many miles so the ECM had it's chance. All I asked for was a baseline pull and they slipped me in between other work.

Quote:
it's also possible that the K&N air cleaner combined with the new exhaust may have caused the engine to go too lean
The AFR will show this.
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