Dunstall Replica Glass packs

whynot2 · Posted: July 11, 2005, 7:35 am Post subject: Dunstall Replica Glass packs

Just something I wanted to share. I had to replace my 27 1/2 inch reverse cone mufflers on '81H. i had been thinking about the Dunstall replicas currently on sale in the JCW catalog, but somewhere there was a comment about them being too loud. So I emailed EMGO about the effect on performance if I repacked the mufffler full of glass packing. I got a favorable reply from EMGO so I went ahead, ordered and installed and tried the mufflers without repacking them. Performance was better than I had with the old mufflers, but the sound, although pleasant at idle was way too loud. I pulled the baffles out and the original packing was shot. I repacked with a big sheet in each, same page of the JCW catalog, and last night went for a 99 mile sunset ride. The sound was mellow and quite pleasant when the sun wnet down and the humidity went up. But the best part was the performance. It is even better. This bike has never run better. If you choose to try the repackable glass pack Dunstall replicas I suggest ordering 2 packs of the muffler repack stuff and do it before installing them on your bike. Good luck, WN2

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

All man ,you completely ruined a set of perfectly sounding mufflers Mr. Green

Did you rember to remove the the center piece in the baffle? If not you'll eventually burn the sides out cuz my friend did the exact same thing and the mufflers lived a short life...........Jack

whynot2 · Posted: August 10, 2005, 6:31 am Post subject: Re: Dunstall Replica Glass packs

So Jack,
Just how short was it? What exactly burned up? How was the bike jetted? Rich? Lean? Run long and hard? We all have different tastes and tolerance for noise. I used to like the sound of a Harley with aftermarket pipes until I went to Americade last year. By the time I left I felt there should be a bounty on bikers with loud pipes. Greg

grizld1 · Posted: August 10, 2005, 10:18 am Post subject: Re: Dunstall Replica Glass packs

We think along the same lines, Greg. Some guys think the noise of loud pipes is a safety feature ('course these are the same guys who won't be seen wearing a helmet wherever it's legal to take it off). After 40 years of riding, I've come to the conclusion that loud pipes just give ticked-off drivers a target. But hey--the Harley boys have to do something to compensate for being slow! We use to say "If it won't go, paint it." Now it seems to be, "If it won't go, make it louder."

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

So Whynot2.............. It appears you overlooked my smilely and my objective was to merely pass along a tip and not pass judgement on whether or not you want your motor to breath or choke,it's your money,your mufflers and motor. The Dunstall are designed to flow gases a certain way and that's what the diffuser with the small holes in the center of the baffle does.it redirects the gases and that along with the construction of the muffler gives that distinctive classic Dunstall rumble. Now with you completely rapping the baffle with fiberglass to deaden the highs and with the diffuser still in place, how are the gases gonna counter react when they hit this diffuser or deflector.... Look down that muffler,and imagine yourself as gases and how you would want to flow after adding fiberglass........ That's the point...Jack

Tomterrific · Posted: August 11, 2005, 8:46 am Post subject: Re: Dunstall Replica Glass packs

I had real Dunstalls on my old Norton in the 70s and I have had a set of repop Dunstalls on my T140 Triumph since the 80s. Great sound that is made better with new packing. A good tip is to wrap the packing with tape to compress the fluffy glass so it can slip fit into the muffler. You get a larger quantity of glass inside that way. The tape relaxes as soon as it gets warm.

Tom Graham
Columbus, Ohio

whynot2 · Posted: August 11, 2005, 2:49 pm Post subject: Re: Dunstall Replica Glass packs

Jack,
I know I sounded more sarcastic than I needed to be. SBT. But I really was looking for information about the longevity of your friends mufflers, and other conditions that might have caused the mufflers to burn out. I thought the disc with the holes in it, the diffuser, was really just to keep the Officer from finding out the pipes are straight through. No offense intended.
and If I may,
Tom,
Thanks for the positive feed back, and the tip on the tape. By the time I was HALF way through I wished I had used tape. Greg

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Greg..........My friend had the Dunstall replicas on a Motto Guzzi and he too completely rapped the baffle and what happens is instead of the exhaust gases being directed throught the baffles preforated holes and forced towards the rear,all the exhaust pressure were held staitionary behind the diffuser with and effect of building excessive backpressure,while that particular end of the muffler recieved an adverse amount of heat build up and eventually fatigued the metal at the section and feel off. What you could do is either,enlarge the holes or removed them but if your satisfied with the performance,just keep an eye on the frontal section of extreme discolortion,then make adjustments.

I'm going with the Dunstalls myself but am transforming them into Super Trapps for experimentation cuz I like the overall look...........Jack

Tomterrific · Posted: August 11, 2005, 8:21 pm Post subject: Re: Dunstall Replica Glass packs

Hi Jack,

What happens is the tape wrapping the glass loosens up as soon as the glass gets hot. The tape bond fails right away and the exhaust passes through like it always does. The glass doesn't last long as it is pushed to the ends and gets battered pretty good by the exhaust pulses. But that's what is supposed to happen and the glass absorbs the sound, mostly highs. Get used to packing the Dunstalls because they sound great with new glass. The more glass the better.

Tom

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Tom.........I knew there had to be a catch somewhere. As to why my friends fail is beyound me but he was pissed. But anyway,the sound of Dunstall is music to my hears Mr. Green

. Awhile back,I took my Super Trapps from the R/90s and made my own Dunstall inserts with a preforated baffle of about 14" long rolled in fiberglass tightly wound and in the inlet side welded in a 3 1/2 wire mesh disfuser,then drilled holes till I achieved the proper backpressure.. This R/90s had a distinquished bark of it's own,seperating it from the rest of the BMW pack and I would get compliments on it's sound with the S/Ts in disguise. AS for mufflers for the XS,well they're limited to say the least,unless you use your magination..............Jack

RCHER

Can you get Dunstall replicas that are not fiberglass packed? I like the look, but I don't want the hassle of the fiberglass burning out.

xs650mike

RCHER wrote:

Can you get Dunstall replicas that are not fiberglass packed? I like the look, but I don't want the hassle of the fiberglass burning out.

Emgo has 2 types of Dunstall replicas, the wide mouth kind which are glass packed and loud www.denniskirk.com/jsp...amp;mmyId=
and the reverse cone style which has metal baffles and has a more mellow sound.
www.denniskirk.com/jsp...amp;mmyId=
I've been told that the metal baffled ones are better for performance but I have no personal knowledge to back that up. I suppose it depends a lot on what stage of tune the engine is in, header diameter and length and of course the all important jetting.

whynot2

Hi Rcher,
I had the Reverse Cone Emgo's on the '81 before I changed to the Glass Packs. The bike ran very poorly (RLS) with stock jetting, stock air filters etc. I knew someone used these before on an '81 so I called him and learned that he had to drill six holes in the ends of the mufflers to let the bike breathe. I had the same problem and ended up with 6 half inch holes. The bike ran well but not great. I changed the jetting more times than I care to admit, finally getting rid of a stumble at 5000 rmp in 5th gear. So when the muffflers fell off I decided to try the glass packs even though I had, and still have, a brand new set of Reverse cone mufflers in my shed. Having said all that my friend put a pair of R.C. on his '75 with NOS '75 header pipes. However he coated the pipes with some thick junk to keep them from turning color. I believe the added restriction in the pipes may be why the darn things work so well for him with NO jetting adjustments.
Which do I prefer? Changing the packing is a small price for me to pay to get the performance that I have now. I'll take the glass packs. I'd even swap the RC's that I have for a pair of glass packs. BTW By the time I got the bike to run well with the RC's it was too loud for me. It was ok with an open face helmet, but in a closed face helmet, low humidity, up hill, it was painfully loud. Greg

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