I’ve been looking how to make the exhaust on the Octavia RS quieter. I tried two things, an exhaust muffler insert and exhaust wrap. This is what they did for me.
How to make exhaust quieter – Exhaust muffler insert
The first thing I tried to make the exhaust quieter was an exhaust muffler insert (db killer) like this.
Generally the sound was noticeably quieter but not by much. At 4000rpm in neutral, volume dropped by one to two decibels. It was at 85db and with the insert it was 83-84db.
If you need something to take the edge of the exhaust noise an exhaust muffler insert will do something but not much.
The downside of the exhaust insert is the restriction it causes in the exhaust. Far from ideal.
Would I recommend fitting one?
No. The reduction is volume is too small versus the restriction in the exhaust.
Exhaust Wrap
Strange one this as honestly not something I’d thought of but I stumbled across a forum post where someone recommended it.
There was some lying around so nothing to lose.
I wrapped the centre section from the cat back to the axle and the rear exhaust muffler body.
Any difference?
The first thing I noticed was the exhaust sounded deeper, so that was a plus.
Measuring the dbs and they went from 83-84db (with the insert) to 82-83db with the wrap and insert.
Again, not a big difference.
Which made the most difference, the wrap or the db killer?
Hard to say because I didn’t use them individually but the meter says the insert and I would agree.
If you are looking for a big difference, for me at least, the wrap was not a game changer at all. But I did like the sound so I think I’ll be wrapping my exhausts from now on.
The added benefit of the wrap is that it keeps the exhaust gases hot which is supposed to maintain their speed which is supposed to be good for engine power.
Ultimate solution
If you want to maintain flow and you need close to stock sound levels, I think adding more mufflers/silencers is the only way to make a big difference. When I say big difference I mean -5db or more.
I refitted the stock exhaust in my case, you can read about it here.
The straight through mufflers with perforated tubes are good for higher frequencies. There are many advertised on ebay/Aliexpress but I doubt they are packed. It might be worth paying extra for silencers which are packed densely. And the bigger the silencer the better.
If you are running a big bore exhaust say 70mm, 76mm and bigger, I think the problem you will have is the lower frequencies, below 2-300hz.
For these frequencies a baffled muffler I think is essential. When I say baffled I mean a silencer with chambers inside, they may be packed they may be not. The internal baffles/chambers are what makes the biggest difference. Again, the bigger the better/quieter, at least 30x20x12cm.
The issue with silencers with chambers is that they can be restrictive, perhaps as much as 30% and I think all will be more than a 10% restriction.
If you are trying to maintain the same flow, choose a silencer with a bigger inlet and outlet diameter than you have now and have it so it takes up all the space available. It’s going to be a custom job most probably.
Alternatively, if the stock exhaust exits only on one side, maybe it’s possible to split the main pipe at the rear of the car and use two silencers in parallel. One in the stock position and one on the opposite side. I haven’t tried this myself but I think I will be in the near future. Run the full exhaust diameter up to the split. You can run two smaller pipes to either side of the car, the smaller the pipe the lower the noise.
This exhaust diameter calculator can help you choose the correct sizes.
Summary – How To Make An Exhaust Quieter
If you only need a small reduction in exhaust noise the first two options might be for you.
If you are looking for big reductions of 5db plus, I think adding silencers, of as big a volume of possible is the only way. And pairing straight through types with baffled mufflers will reduce sound across the spectrum.