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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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  #1  
Old 12th April 2005
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Default Modifying standard mufflers for better flow and sound

I don't like having loud pipes on my bike.
But I also don't like the chuff chuff sound the standard mufflers make.

A lot of people drill the baffle plug out of the standard mufflers but I have read this can create tuning issues due to "wave reversion" problems (dunno what that is though. Crim, Shu and Stevo know heaps about this stuff)

OE mufflers are also quite restrictive so I removed the baffles with a 44mm (1 3/4") hole saw and enlarged the holes in them to 6mm (1/4") and also added a cuppla extra rows on the outlet side of the baffle plug.

The baffle plug must be left intact.

Doin' this helps to increase the gas flow and allow a more fuller and deeper sound without bein' too loud but is unlikely to give much in the way of performance increase. Although my bike feels slightly stronger at low to midrange revs which is where I spend most of my time riding anyway.

I then have the outlet end flared (I had to have flares made that welded on the end of the baffle tube) so it fits snug back in the the hole made by the hole saw.

Then weld them in taking care not to blue the chrome.

It helps to wrap a wet towel around the area to be welded to keep the chrome cooler.

This was done for me by the local exhaust shop.

Hole saw and home made guide


The top baffle is standard


Welded back in. note: they don't need to be welded the whole way round. A cuppla short welds will do.

Last edited by gronk62; 1st July 2007 at 05:54..
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  #2  
Old 6th May 2006
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Smile A few links discussing the gronk mod

Here's a few link to threads discussing the Gronk mod and variations of it..

Gronk's Mod Complete - Thanks Gronk!

Home-brewed CS tapereds <--This thread shows a great home made high flow baffle design.

How Mattbastard modifies stock cans (now with video goodness)<---another great original baffle mod with pics

Performance: Gronk's Mod vs. Screaming Eagles

New exhaust for power = quiet?!?!

2004/06 stock muffler mods from stargateops

Just did Gronk's muffler mod

Another "Gronk mod" testimonial

Last edited by gronk62; 13th July 2006 at 05:01..
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  #3  
Old 3rd September 2011
cartoonguy2002 cartoonguy2002 is offline
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Just took the hole saw and drilled out the inner baffle. Then just put the muffler back on. On 883, it's not too bad. We'll see.
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  #4  
Old 3rd September 2011
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This thread must be getting old....it has shrunk drastically since the last time i read it.
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The water-logged OEM starter/system relay on 2007-2009 Sportsters is a OMRON G8H-UA-007401, but this can be crossed over to some automotive apps: Borg Warner R3154, Gp Sorenson 41-5154, Niehoff RL 35381 are examples. Good luck!
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  #5  
Old 3rd September 2011
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Quote:
Originally Posted by cartoonguy2002 View Post
Just took the hole saw and drilled out the inner baffle. Then just put the muffler back on. On 883, it's not too bad. We'll see.
I have done the cutting out of the baffle plug with a 1 1/4 inch hole saw for a friend and have seen a couple of other bikes with it and everyone (all rubbermounts) with the baffle plugs cut out had a whistling/chirping sound at idle. Otherwise the mod sounds good with still considerable volume but without the harsh metallic sound of many aftermarket exhausts. I also drilled a 1/2 inch hole through the center of my own baffle plugs (which didn't cause a whistle/chirp at idle) but finally settled on the Gronk Mod for the best combination of moderate sound and performance. The Gronks aren't excessively loud at idle but they do make a pleasant deep bass sound when you get on the throttle.
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  #6  
Old 10th September 2011
cartoonguy2002 cartoonguy2002 is offline
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I'm having great success with louder pipes. People in SUV's don't swipe me and run me off the road any more. They may not see me, but they sure can hear me now! Thanks Gronk!
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Old 11th September 2011
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Quote:
Originally Posted by cartoonguy2002 View Post
Thanks Gronk!
Cheers
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  #8  
Old 25th June 2012
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I had the stocker, then the screamin eagle II, but they hurt my ears.

I decided to change the stock exhaust but I made 5/16 holes instead of 1/4. I realized only after i finished.

Can it make it much lowder or make it lose power?

Last edited by Freud; 25th June 2012 at 17:35..
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  #9  
Old 26th June 2012
hugie03flhr hugie03flhr is offline
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I did 5/16 holes also. It sounded good but still a little too quiet
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  #10  
Old 27th June 2012
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I like the sound of the standard Gronk Mod but if the Gronk Mod with the 5/8th inch holes in the baffle walls is still too quiet for you, you can still drill a hole through the center of the baffle plug as well. Start with a small hole and work your way up until you have the size hole that makes the sound that you like.
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