1.8 K noisy exhaust

[LesG]

Hi guys, need some advice on my exhaust please. So, I've got a repackable can on my 1.8 K, with a SLR 4-2-1 manifold (no cat), and Jenveys with Scouse air box. I measured the noise at 112db at around 4500 rpm static, which is shocking. The can is 500 mm long, 6" diameter, and has a 65mm internal perforated tube. The internal tube has wire mesh quite thickly wrapped around it, and then there is a fairly thin blanket around that.

My question is; if I were to refill it according to their recommendations, with Acousta-fil boa material, am I likely to get down to around 105db, which would be the maximum allowed at a hillclimb event, or should I be looking to purchase a bigger silencer?

TIA

[SM25T]

That is quite a small silencer. The wire mesh is to stop the fibreglass being burnt away too fast. I would have thought remove everything and fill it with new material ... maybe without the mesh ? Mine doesn't have any mesh in it and lasts a couple of years each time.

[LesG]

Yep, the overall size of the can is what concerns me most, but if it's likely to drop to 105db with new padding, then it'll do nicely, as it is gloriously lightweight!

[SM25T]

There's only one way to find out .... cheaper to try repacking it first than replacing it.

[Mankee]

That is loud! What instrument did you test it with?

[LesG]

Mankee; I'll mail you a couple of pics

[Jonathan Kay]

The wire mesh is to stop the fibreglass being burnt away too fast.

Is that what happens? How hot is it in there?

Thanks

Jonathan

[LesG]

Yep, this silencer is mostly filled with wire mesh, and then there's a thin blanket of glass fibre mat around that, so this is probably why it's so loud, as the wire mesh can't have very good sound absorbing qualities?

[metal mickey]

Highly unlikely that you'll get down to 105db with that silencer. It is basically to short and to small on diameter to be that effective. 

[Delbert]

My can is slightly larger but repacking did shed around 6 Db and I now get in the region of 98-100 depending where it tests / weather etc 

the old packing was saturated which did not help 

also I only had one wrap of wire mesh and then filled the can with blanket 

also from what I have seen noise tests anywhere other than Goodwood and Combe  are a little shall we say more relaxed 

 

[LesG]

*thumb_up*It appears that 108db is the general limit for Roadgoing hillclimb vehicles, so if I can get down to below that, then happy days. One thing is for sure, I will let you know, either way 

[Delbert]

also a decibel slayer gets circa 2 -3 db as well 

Metal Mickey is correct though a larger longer can does make life easier 

 

 

[LesG]

I do of course, bow to Mr Mickey's experience of these things (I'm still using that bonnet I collected from you btw), however, I'm curious to know what difference repacking will make now.

I do have another silencer I can use; it's a Cheesman (CSP 888/5), 700mm long, 5" diameter, and was originally for a R500 D I believe, but I repositioned the bobbin mount bracket to be able to use it on the passenger side. I just need a step-down sleeve to fit it, and I'll try that too, worth a try!

[LesG]

Ok, so to update;

the Cheesman silencer was even worse at 115db, so no good for Motorsport venues.

I repacked the titanium can with two and a half bags of Acousta-fil boa (basically about as much as I could fit in, leaving a bit of room for expansion once warm), and got down to around 108db, which is pretty good, but just on the limit for MSA hillclimb regs, for Roadgoing classes. Anyone know a trick to make my rev counter under read lol?

[Mankee]

The Emerald has a tacho multiplier function. Set it to 50%!

[LesG]

Ok, just to update this thread; back from my first hillclimb of the year, and also the dreaded sound test by MSA scrutineer...........and only 102db! So a big thumbs-up for Acousta-fil boa! 

[SM25T]

That is a huge cut from 112dB !

[LesG]

Yep, it does look like it on paper, but it does assume my little meter read accurately in the first place! To be fair; the original silencer packing was worse for wear, and there's no doubting it sounds much quieter than it did before. All in all, I'm well chuffed!

[Mankee]

Great result, Les! I need another silencer adding to my Powerspeed system.

[LesG]

Just a quick update to this thread; 3 Sisters sprint 99db; Forrestburn hillclimb 100db. It'll be a case now of monitoring how long the packing lasts.

[LesG]

Ok, time to update this thread, and let you know how I got on with this exhaust through the year after repacking with the Acoustafil. In short; brilliant! I cleared every scrutineer at the 7 hillclimb/sprint events I was able to attend, usually recording 97 or 98 db. My guess at the higher 102 db at the start of the year was maybe the packing hadn't expanded and bedded in fully? It's fine now in any case, just need to see how long it lasts, before I have to repack again.