Harley mufflers?

superelbert

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Hi!

Does anybody have experience running stock Harley mufflers such as those from the FXD or Sportster range?

I have a set of Dyna-glide mufflers on Mikes XS headers. It looks great and fits the bike well and the sound is very nice.

My big question is the flow capacity of these mufflers. Are they in any way restrictive or should they allow a reasonably stock engine ( mild porting and K&N filters) to perform without significant restriction?

I would assume that mufflers originaly designed for a 1340 cc engine should not be that restrictive, but then assumption is the mother of all, well you know... :)

My problem is that I replaced the rotted out stock muflers with the Harley mufflers before i got the engine sorted and carbs working properly, so I have no true base-line to compare with... :(

I still have some work to do jetting the carbs properly, but it turns out the limitation lies within the harley mufflers, I will obviously never succeed.

Again, the harley mufflers really blend in well with the rest of the bike, so I'd hate to scrap them on suspiscion alone..

Any advice and experience shared is therefore must welcome!! :)
 
You do have a baseline to compare with: the stock jetting configuration for your bike. After adding cone filters and new exhaust, if you end needing to lean out the mixture with smaller jets, the muffs are likely the culprit. I doubt that will happen.

Oh and make sure your timing and everything else is dead on before you start trying to jet it.
 
Oak,

Yes, of course, ignition timing and valve adjustment is spot on, so is synchronisation of the carbs, but good of you to mention it anyway, it would be a typical error neglecting this! :)

And as for baseline, good point.. and this takes me to the source of my doubts..
The carbs on my model have 120 jets as stock, and compared to this, 117,5 jets work better than 125 jets.

The negine is reasonably smooth and responsive up to about 5000 rpm, but it it feels i sort of have to "force it" up to the 7500 rpm redline..

I've read that an XS in good tune should be able to "zip" straight through the rev range up to the redline..

This is what got me thinking that perhaps the mufflers were restricting performance in the upper rpm range.. or perhaps they will just make the bike require "different" jetting, i.e. leaner jets and stil run OK??

This is why I was hoping to hear from someone who had tried harley mufflers vs stock muffler or some other aftermarket muffler swith "known" performance...
 
I put bologna cut Sportster mufflers on my bike, with pods. Ran fine and was pretty quiet. I put bigger main jets in to achieve a better top speed response, but it didn't really work. The bike still felt restricted with them on. Not bad, just kind of chocking. Once I put on a 30 tooth rear sprocket I got a better top speed, but it still felt sluggish. They have since been removed. I was tired of screwing with them.
bike 004.jpg
 
Littlebill,

Those bologna cut sportster mufflers, are they stock harley mufflers or aftermarket?

Anyway, very interresting what you write, could sound simmilar to my experience..

After removing the sporty mufflers, did you replace them with something else, and what was the result?
 
Hmmm... seems the harley mufflers are restrictive compared to stock XS mufflers then...

In the meantime, I have been browsing around a bit, and I came across an interresting mod for sportster dynaglide type mufflers reffered to as the "gronk-mod" :

http://xlforum.net/vbportal/forums/showthread.php?t=16948

This basically involves pulling the perforated inner tubes from the mufflers and drilling out the perforation holes to a larger diameter.

Perhaps this is an alternative to purchasing a set of new less restrictive mufflers??
 
74 650 stock jetting, airfilters and air boxes...the stock H-D mufflers have a plug half way down easy to knock out with a piece of water pipe
 
Jayel,

Thanks for your answer! :)

Yes, I've heard about that mod, and it has crossed my mind.
However, the clips you kindly posted links to, comfirms that this mod would be a bit on the loud side, at least for my taste.

But that aside, how do you find that your set-up performs?
Compared to stock mufflers and/ or harley mufflers prior to the modification you did?
 
gets noisy when you turn the loud handle it's true, no trouble turning up to 7 grand never had stock mufflers had those shortys on it when I first got it, those are loud obnoxius POS, have run the 27" dunstall reps like those too
 
well,

Seems I need to do something about my exhaust. First step will be to to the "gronk-mod".

Looking at pictures of the unmodified muggler innsrerts, I am not all too surprised if they are restrictive considering the number of holes and their diameter.

Just bought a hole-saw, so once the weather clears up I'l get at it! :)

But in case it proves unsatisfactory..

Jayel, How did you find those dunstalls compared with the sporty mufflers?
 
The weather is nice today,so i got the electric drill out, put the 44mm hole-saw on and cut the muffler inserts out. Piece of cake, only took a few minutes.

Now, with the inserts out, I looked at the number of holes and some other dimensions in order to figure out what the stock flow capacity is and where the bottle-necks are.

The internal bore diameter of the insert is 32mm, which gives a cross-sectional area of 804 mm2.

The main bottle-neck is the holes, on the engine side of the plug in the insert. These holes only add up to 254 mm2! Drilling these out to 6mm as per the "gronk-mod" increases the area to 1017 mm2, i.e. more than that of the bore of the insert.

The second, and more challenging bottleneck, is the cross sectional area between the outer diameter of the insert and the inner diameter of the muggler body it self.

The muffler body, is really a glasspack muffler. A 44mm inner dia. perforated tube with fine perforations is running down inside the lenght of the muffler body, and there is glass-fibre packing between that perforated tube and the muffler housing.

The outer diameter of the insert is 35mm and the inner dia. of the perforated tube is 44mm. This gives an annular cross sectioan of 558mm.

So no matter how much one enlarges the holes of the innsert, this is the limiting factor.

Knocking out the central plug will remove this bottleneck ,but this will only turn the muffler in to a very innefficient glass-pack muffler.

Now I know what I have to work with, now I can start to figure out a solution...

The biggest restriction is on the engine side of the central plug. the area of the holes
 
I might have tried using a 3/8 drill bit and an extention to just drill a 3/8 hole through the baffle plug. Put one hol near the top, bottom or side. Ride it and see if it helps or is too loud. If it helps try another hole. Add holes till it gets to loud or stops improving. If you go one hole to many a short screw the right size will plug the hole.
Just knocking the baffle plug out improves the flow but it's only loud when you hit the throttle hard. I did that with the stock mufflers on my 75. A bit louder but by the time you reach 35 mph the wind noise covers the exhaust noise.
Leo
 
not much difference between the sportster mufflers and the dunstall reps, I should claifiy the shorty mufflers were emgo 12 inchers the dunstalls with the removable baffle can be tuned for sound/preformance if you pack them with stainless steel wool (pot scrubbers)
 
Time to give something back here...

In a previous post, I presented some cross-seactional areas found within the flow-path of the stock harley muffler, and it was obvious that in stock form this muffler had to be restrictive.

To re-cap; even with the grunk-mod, ie boring out existing bavvle holes from 3 to 6 mm, there would still be a restriction in the annular area between the muffler body ID and the OD of the muffler tube.

The only way to further improve on this was of course to look at the muffler tube plug. Removing it alltogether would create a path of least resistance straight through the tube, meaning that very little of the exhaust would be directed in to the muffler body and out again through the holes in the tube. This would effectively turn the mufflers in to straight thru glass-packs with low damping efficiency.

I decided the best approach would be to drill SOME holes in the plug to further increase the available flow-throuhg cross section, but not so much that the greater volume of exhaust would not flow as originally intended.

I cut the muffler pipes in two nect to the plug and drilled eight 4mm holes around the circumference if the plug. then i welded in washer with 6mm holes in front of the plug with the oles offest so that you wouldn't get "line of sight " flow straihgt through.

I then welded the tubes back together and ground down the weld seam so that this would not reduce the cross sectional flow area between tube and muffler body.

Looking at the muffler tube, it struck me that the "inflow" holes were quite far upstream in the muffler, leaving a considerable length of the tube unused, i.e. the exhaust would, afte re-entry, simply travel down 20 cm or so of solid tube without any further attenuation or anything.

I then went on to perforate that final section of the tube with 2,5mm holes (quite a job) and wrap some damping arround, effectively turning that last section in to a glass-pack muffler.

Of course, there are factors like turbulence, tuned lengths and pulse reflection at work in an exhaust system. I have now way of ascerting how that works out with this mod. But what I can say is that the mufflers have now been improved in terms of flow to the point where this should not in it self be a limiting factor.

The sound?

Obviously louder than before, but not intrusive or out of proportion.
There is no puffing or whistling, I would say that there is a healthy rumble with a good grunt when the throttle is twisted, yet there is no "rasp" or harshness to the sound and the overall tone is deeper than it was with the unmodified mufflers. All in all a sound level, tone and characteristic that suits the classic sporty roadster style of my XS.

performance wise? the bike is more willing to rev now and pulls stronger. Still it doesn't quite ZIP through to the redline as I hoped it would, but I attribute that to the carburation.

And rather than trying to mess around with needles and jets, I've decided to build a fuel injection system.

I hope the pictures are self explanatory, and that this post can be of use and inspiration to others out there! :)
 

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