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Hi =)
I recently purchased a good condition Blitz Nür Spec cat back, but like most of them, its pretty flown out in the muffling department. Having read online, i see that they don't really last for long.
So i am thinking about repacking it. I know its not made to be repackable, but with a grinder and some welding, i think it can be done. I love trying out new stuff, and this seems doable and interesting to learn.
I found this worklog on the Lotus Elan forums that i think looks reasonable to follow: LINK
So i have done some research and tried to identify common problems, and so far what i am left with is the following main issues:
- Heat - Most packing materials cant handle the rotary exhaust temps.
- Durability - Most packing material end up blowing out of the exhaust due to low binding strength.
So my research lead me to a material used in forges and other industrial high temp applications. Its called Fiberfrax Durablanket, and can take temps up to 1250C / 2282F.
It is made from long ceramic fibers, and the sales pitch is "long fibers" and "high strength", suggesting it would be a good choice for the outer muffler material. Problem is to find a place that sells it in DIY sizes, and not a 25" roll
For the inner part, closest to the center pipe, i see people are using stainless steel wool/scrubble. I have looked at Burns Stainless, since they both manufacture exhausts, and offer "Scrubble" in their webstore for muffler repacks.
So my question is if this seems doable? Have anyone made custom mufflers for the rotary and tried to keep the sound down (not racecar loud)?
I think it would be very doable. I would cut along the rear seam of the muffler and re-weld it there, if the weld is a little sloppy you won't see it on the car.
That said the Nur Spec is a REALLY damn loud exhaust in general. Changing packing may change that. I'm not sure how much impact the packing material, amount of material, etc. changes the exhaust note.
I don't know much about muffler packing but have heard in the past that fiberglass packing is the one that REALLY dies a quick death on a rotary. That's typically only in super cheap mufflers though.
I repacked a RE-Amemiya Dolphin using Acousta Fil.
I cut a large square on the top side through both skins and put it to one side, then wrapped the centre pipe in Acousta Fil and used safety wire to keep it in place. I then took it to a proper welder to close up as my MIG skills are terrible. It's now much, much quieter than it was when I got it. Just to note Acousta FIl is designed to expand and fill a space so don't go packing it in super tight, with sound proofing it's actually the tiny air pockets formed by the material that provide most of the absorption.
^ that acousta fil is good stuff. Used it on my motorbike. Packing a muffler tight and then getting it all back in is a struggle at the best of times so the expanding thing is great. I used sello tape. melts away after the first run. Bike sounds magic.
I repacked a RE-Amemiya Dolphin using Acousta Fil.
I cut a large square on the top side through both skins and put it to one side, then wrapped the centre pipe in Acousta Fil and used safety wire to keep it in place. I then took it to a proper welder to close up as my MIG skills are terrible. It's now much, much quieter than it was when I got it. Just to note Acousta FIl is designed to expand and fill a space so don't go packing it in super tight, with sound proofing it's actually the tiny air pockets formed by the material that provide most of the absorption.
How well does it last? I suspected it would burn/blow out pretty fast?
With Rockwool HQ not too far away from you, you might find better luck buying small quantities of that locally, last time I was given some blanket like foundry insulation material free, can't remember the name! Should still be a write up on Ausrotary using rockwool and stainless steel wool from about 13 or 14 years back, but expect pictures have died long ago,
Last thing done here was an old oval Ansa that had a seam lengthwise for an old Italian supercar POS. Used a fine blade in the angle grinder rather than a hacksaw. Main thing is getting the stainless wool and the outer high temp material bound tight to the perforated tube and fully occupy the canister otherwise it will blow out more easily.....they will still fail at some point in my experience.
I decided to give it a try. Found a nice seam at the back where i could get a clean cut. Was filled with "scrubble" and giberglass. Fiberglass was as you can see partially burned out, and the metal stuff was not much to brag about.
Next up is to order some ceramic fiber and new scrubble packing.
Did you follow through with repacking the muffler?
Any pictures? What material did you use?
I did, but as i tend to get excited and forget to take pictures i dont have any from the repack process.
Materials:
Scrubble from burnsstainless.com
Acousta-Fil® ZT1 from textiletechnologies.co.uk
Did a layer of scrubble, and then wrapped that loosely in the Accoustafil. Its rated to 850C so should handle hot rotary exhaust.
So far it works pretty good, but its loud af still x)
I repacked a RE-Amemiya Dolphin using Acousta Fil.
I cut a large square on the top side through both skins and put it to one side, then wrapped the centre pipe in Acousta Fil and used safety wire to keep it in place. I then took it to a proper welder to close up as my MIG skills are terrible. It's now much, much quieter than it was when I got it. Just to note Acousta FIl is designed to expand and fill a space so don't go packing it in super tight, with sound proofing it's actually the tiny air pockets formed by the material that provide most of the absorption.
Hi Jack_am, I have RE as well and looks like they blew the exhaust during tuning. I love the look of the exhaust but don't want to spend another 1k to have it blow later. do you have pics on how you did it? how did the Acousta hold up?
05-30-18, 02:45 AM
