So , 749 silencer now cut and open , that was fun !! Tubing ordered so whilst it’s coming a couple of questions. I am leaving the cats in the pipe/silencer , theory being it may keep some back pressure and not affect ecu fueling hopefully . And not give full loudness The plan is to use the wire wool and stranded stuff but add more to fill missing metal . Do I pack this tight or loose? Does tight quieten things or make noise anyone used acustafil packing ?
Once wrapped does anyone know any stainless steel welders in Yorkshire who could weld back together ?
When prepping to getting it welded back together. The chances are that whoever does it will be going it with a tig setup, so to make their life/job easier, get your joins as neat and close together as you can. That way they won’t be needing to weld up big gaps with filler rod. Also get all the areas to be welded as clean as you can. Makes their job nicer and will keep your cost down.
Whatever you're stuffing in there, stuff it in well. I don't know how acousta-fil goes but I'd want to minimize packing blowing out over time as it looks like it'll be a prick of a thing to repack as it's welded (unless you like cutting a re-welding). I find metal mesh (i.e. fly screen) wrapped around your perforated tube can help reduce the packing blowing out the back over time. A funny thing a friend found was when we thought we'd take a look inside the Termignoni's on his 916, the packing was wrapped in plastic! By the way, what you're going (except for having the catalytic converters in) is giving you pretty much what was the included-in-the-crate race system on my 2003 999R.... It didn't sound too bad and going to a full system down the track didn't add much in the way of power and torque.
Cheers, apparently the acoustafil doesn’t need mesh as it’s a woven mat that expands on heat , but I will pack firmly . Lead to believe the mod is similar to termis can,so we’ll see how it goes Just need to find a good welder in yorkshire
Looks like you already have good advice, but to add a little more info... The fiberglass packing is there to attenuate high frequencies. I can't remember the cut off frequency range but under a certain frequency the muffler will act like it's empty. Point being the 'glass leaves the low frequencies intact but takes out the high frequency harshness. Don't worry about packing the fiber too tightly - while theoretically there is a limit, in practice you can't get there packing it by hand. Stuff as much as you want/can without heroic efforts and you'll be fine. The margin between not enough and too much is huge. The reason OEM stuff isn't usually packed super tight is cost savings, not loss of attenuation. Metal wools - if the glassfiber is woven don't bother. It should only be used to pretoect the glass wool, keep it as thin as possible if you must use it. It's attenuation is horrible compared to glass fibers. In OEM automotive systems they use continuous fibers for durability but i'm not sure you can buy that through the aftermarket. Acoustifil sounds familiar but it's been a while since I"ve done this stuff... the description of woven and expands in use makes it sound like what I used for my 996 mufflers back in the day though. I have no idea if leaving the cats in will allow it to run well with the stock calibration, but I know having it tuned will make it run better. Having the stock set up tuned will make it run better too after all. People talk about the "Termi tax" and how you have to add an exhaust and have the bike reflashed to make it run right.. but no one has the stock system tuned to show the Termis aren't the magic in that formula. (IMHO). Wrapping the fill in plastic is common for OEM manufacturing, it makes it easy to put in place. The plastic normally goes away but so what if it doesn't, it's not doing anything after the fiber is installed anyway. I've used masking tape to help everything keep it's shape while putting all the parts together.
Thanks for that much appreciated will update as it progresses, I’ll leave the wire wool off and reuse the horse hair Ducati stuff , along with the acustafil
