How to create a quiet exhaust/silencer??
Discussion
How can I create or buy a quiet exhaust, I understand that there are two methods to reduce noise with an exhaust, packing the box with fibreglass and some other method of reflecting back the noise waves. Oh also there's a thing you can bolt to the end of the exhaust that opens past a certain boost/airflow level.
I want my 95 STi Impreza with a 2.5 STi engine, to be somewhat 'stealthy'. It's front mounted intercooler should mean that I can do away with the scoop but, the previous owner put a Mongoose 3 inch (but urgh, 5 inch past the silencer) 'drainpipe' exhaust on the car. Everyone and I mean everyone seems to want to race the car and I frankly don't enjoy the attention - especially as I'm running in new pistons and don't venture above 3000 rpm!
Does anyone have any expertise in this? Internet searching ain't that fruitful, there not seeming to be any 'specialists' in this area..
I want my 95 STi Impreza with a 2.5 STi engine, to be somewhat 'stealthy'. It's front mounted intercooler should mean that I can do away with the scoop but, the previous owner put a Mongoose 3 inch (but urgh, 5 inch past the silencer) 'drainpipe' exhaust on the car. Everyone and I mean everyone seems to want to race the car and I frankly don't enjoy the attention - especially as I'm running in new pistons and don't venture above 3000 rpm!
Does anyone have any expertise in this? Internet searching ain't that fruitful, there not seeming to be any 'specialists' in this area..
Powerflow, Hayward & Scott... can't think of any others. They'll make you a custom exhaust to whatever spec you want. Powerflow are franchised and the quality of their work varies from place to place. Also they don't (in most outlets) use mandrel bending - they crush bend instead so the diameter of the pipe decreases in the bends.
I have a mongoose on my Rover and it's fairly quiet at sensbile speeds. It's a 2.5" with 3 silencer boxes and a 3" outlet. A friend had a Mongoose on his 200SX and it was stupidly loud and had a 5" outlet.
How many boxes does yours have? Mongoose are quality built items so in your case I'd look into getting Powerflow or similar to add in an extra box or two and change the tailpipe. Saves you getting an entire new system and you get to keep the existing nice mongoose pipework and boxes.
I have a mongoose on my Rover and it's fairly quiet at sensbile speeds. It's a 2.5" with 3 silencer boxes and a 3" outlet. A friend had a Mongoose on his 200SX and it was stupidly loud and had a 5" outlet.
How many boxes does yours have? Mongoose are quality built items so in your case I'd look into getting Powerflow or similar to add in an extra box or two and change the tailpipe. Saves you getting an entire new system and you get to keep the existing nice mongoose pipework and boxes.
As Leo says, adding extra boxes will quieten things down.
A mate used to run a Cossie sprint car and with just one silencer box it was marginal for noise levels. We stuck a small straight through silencer in the run alongside the propshaft and it knocked over 5db off.
We got that from Jetex who sell all the bits you need to mod your own exhaust.
Or you could try Custom Chrome who custom make Cherry Bomb silencers in whatever bore, outside diameter and length you want.
A mate used to run a Cossie sprint car and with just one silencer box it was marginal for noise levels. We stuck a small straight through silencer in the run alongside the propshaft and it knocked over 5db off.
We got that from Jetex who sell all the bits you need to mod your own exhaust.
Or you could try Custom Chrome who custom make Cherry Bomb silencers in whatever bore, outside diameter and length you want.
A rare breed indeed It was from a company called 'JT', they had a good rep in Saab circles.
There website seems to be : http://www.jt-tuning.se/
This is what I had fitted on my 9-5, you can work out the sizing of the boxes from the 3" tubing.
There website seems to be : http://www.jt-tuning.se/
This is what I had fitted on my 9-5, you can work out the sizing of the boxes from the 3" tubing.
Our Celica GT4 has a Blitz Nur Spec exhaust that has a removable muffler for such instances.
Long journeys are hellish with a loud exhaust. It's essentially a bolted in tube that tapers and you bolt it in half way to the exhaust. Works a treat.
I can't see why a decent custom exhaust place couldn't do you something similar.
Long journeys are hellish with a loud exhaust. It's essentially a bolted in tube that tapers and you bolt it in half way to the exhaust. Works a treat.
I can't see why a decent custom exhaust place couldn't do you something similar.
Absorption silencers will tend to target high frequencies, a 2 or 3 pass silencer will tend to target low frequencies more and an absorption silencer will perforations will target somewhere in between, with more perfs tending more toward low frequencies. It is more of an analytical and quantitative science then most realise. OEM companies like Tenneco, Gillette or Arvin (guys who did the exhuats system on the E46 M3) know this science well.
Most other after market place don't know what they're on about and just use trial and error.
The wadding you use can be varied to reduce noice levels. Another way to reduce overall sound level is to reduce your exhaust pipe diameter- this raises back pressure and back pressure is a cheap way of silencing- but I suspect this solution wouldn't be ideal for you.
General rule of thumb to meet the current 74 db drive by regs is target a total silencer volume of 10 to 12 times the engine capacity. If you're using very big diameter pipes and want a very unrestrictive system 16 times the engine capacity could be used. I think however because you're engine is turbo charged so much silencer volume will probably not be needed- as Turbos act as a damper for the noise anyway.
Most other after market place don't know what they're on about and just use trial and error.
The wadding you use can be varied to reduce noice levels. Another way to reduce overall sound level is to reduce your exhaust pipe diameter- this raises back pressure and back pressure is a cheap way of silencing- but I suspect this solution wouldn't be ideal for you.
General rule of thumb to meet the current 74 db drive by regs is target a total silencer volume of 10 to 12 times the engine capacity. If you're using very big diameter pipes and want a very unrestrictive system 16 times the engine capacity could be used. I think however because you're engine is turbo charged so much silencer volume will probably not be needed- as Turbos act as a damper for the noise anyway.
Thanks all. The quiet exhaust is as much for long distance cruising comfort as it is for 'beneath the radar' use of a fun and tactile performance car. I've driven long distances with wax earplugs for years, it's quite staggering how less tiring a journey is when your brain doesn't have to process useless noise, the radio/music versus background noise ratio is better with earplugs. In a perfect world though they'd be unnecessary - and they don't prevent the 'look at me' effect of noise leaving the car.
It seems to me that a good compromise bearing in mind that with even some sound dampening (what's there now couldn't be considered as noise reduction really) is going to make a big difference. I'm happy to fit as large a silencer into the space under the car as I can, assuming it doesn't protrude too far down and restrict the under car airflow too much. There are so many truly scientific factors to consider:
Baffler pipe holes, which are the best compromise?
What about a boost controlled (or switch) bypass that switches exhaust flow to the open air/a less restictive second exhaust, I've seen the switching devices in the US.
Will several small silencers nearer the turbo end (plus the main silencer) have a significant sound reducing/performance reducing effect?
How does the noise reach the passenger cell, can sound dissipation work when applied to the exhaust surround/the car body?
What about having several layers to the exhaust, seperate skins with seperate sounds reducing materials.
Call me a geek but these are all interesting questions to someone who enjoys a car far more if having the 'sporty' noise is an optional extra.
It seems to me that a good compromise bearing in mind that with even some sound dampening (what's there now couldn't be considered as noise reduction really) is going to make a big difference. I'm happy to fit as large a silencer into the space under the car as I can, assuming it doesn't protrude too far down and restrict the under car airflow too much. There are so many truly scientific factors to consider:
Baffler pipe holes, which are the best compromise?
What about a boost controlled (or switch) bypass that switches exhaust flow to the open air/a less restictive second exhaust, I've seen the switching devices in the US.
Will several small silencers nearer the turbo end (plus the main silencer) have a significant sound reducing/performance reducing effect?
How does the noise reach the passenger cell, can sound dissipation work when applied to the exhaust surround/the car body?
What about having several layers to the exhaust, seperate skins with seperate sounds reducing materials.
Call me a geek but these are all interesting questions to someone who enjoys a car far more if having the 'sporty' noise is an optional extra.
There's definetely a market for a bespoke exhaust manufacturer who applies some science to producing minimally restrictive super quiet exhausts..
I'm interested in the equal length manifold idea although I don't fully understand what that means practically, i.e. would one have to be made etc.
I'm interested in the equal length manifold idea although I don't fully understand what that means practically, i.e. would one have to be made etc.
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