4722 replies to this topic

[stu8v]

I just don't get how you've made it so loud.... Mines 98dB

[Nev]

I just don't get how you've made it so loud.... Mines 98dB

 

It is bizarre, it really is.

 

I can only think it is partly to do with the cam timing and 3.5" pipework. Though the pipes in the silencer are only 3".

 

At least the welding was rewarding, surprisingly it all went rather easily, I even guessed the current correctly first time

 

Edited by Nev, 12 November 2016 - 05:30 PM.

[Mopeytitan]

Hmmm... have you thought about trying a completely different design? Away from the VX style?... there's a lot of space in the clam to fit two back boxes and even a third where your cat would be...

[CHILL Gone DUTCH]

NOtice your exit pipe comes from middle of box nev Traditionally aftermarket boxes have 2 180 bends Does the box have baffles ?

[Mopeytitan]

Did you also know that you don't actually want back pressure?... is about finding the right size of pipe to increase the velocity of the gases while creating as little back pressure as possible. There is an equation to work out pipe diameter for power etc I'll see if I can find it for you ::

[Nev]

NOtice your exit pipe comes from middle of box nev Traditionally aftermarket boxes have 2 180 bends Does the box have baffles ?

 

My silencer is heavily baffled so the tailpipes exit from a small walled cell in the centre of the silencer. If you have the tail pipe connected to a 180 degree bend, then there is less room for the silencer, so having the tailpipes coming direct out of the silencer allows you more room for the whole assembly.

 

Most after-market silencers just use a single "free flowing" perforated pipe to allow the gases to refract. So mine is rather different to this (more like the OEM baffled box on an NA).

 

 

Edited by Nev, 12 November 2016 - 05:40 PM.

[Nev]

Hmmm... have you thought about trying a completely different design? Away from the VX style?... there's a lot of space in the clam to fit two back boxes and even a third where your cat would be...

 

I have several designs I am thinking of prototyping, and then testing with the dB meter.

 

I suppose I need to start the ball rolling and measure what sized sheet I need to roll/bend the main box from.

Edited by Nev, 12 November 2016 - 05:42 PM.

[CHILL Gone DUTCH]

How about exiting under car and creating a double diffuser

[Nev]

How about exiting under car and creating a double diffuser

 

Hmm, interesting thought...

 

I have been toying with the idea of putting my floorpan on and building a diffuser for the colder months.  

[Mopeytitan]

Do you not run an undertray?

[Mopeytitan]

Or try and make a blown diffuser now that would be a sound when coming up to roundabouts

[Nev]

Thinking about this, I think the exhaust valves must be opening whilst the cylinders still have a good deal of compression.

 

One thing I've noticed about Nipper is that the low rev noise is particularly high, though high rev dB is not that much higher (compared to other cars). This smacks of exhaust valve timing to me. I've also been told that on full chat the exhaust isn't really that loud from outside.

 

 

 

 

 

 

[Nev]

Do you not run an undertray?

 

Nope, no under-tray and and no "diffuser" for the last 6 years or so. This was for cooling purposes, though in autumn, winter, spring this isn't strictly necessary. I don't notice any adverse effects until at about 100 letpons, when I can hear a sort of buffeting resonance as air pulses in the engine bay void. This goes by about 130 leptons when smoothness returns.

[siztenboots]

look forward to your progress , I will be in the market for a new backbox , aim to be under 100db , possibly with a main cat this time.

[siztenboots]

I know your rear clam is quite different, but do you still have the boot box in place, or is it cut up for the airbox. do you still have the heat shield blanket covering all the rear silencer , also there is a odd fibreboard that sits between the boot box and the h/s blanket, did you keep that.

 

 

[Nev]

I know your rear clam is quite different, but do you still have the boot box in place, or is it cut up for the airbox. do you still have the heat shield blanket covering all the rear silencer , also there is a odd fibreboard that sits between the boot box and the h/s blanket, did you keep that.

 

 

 

My rear clam is original OEM (with bonded on wheel arches. Boot compartment is still present (though full of airbox + pipes). Yes I still have the OEM heat shield blanket around the silencer area. I removed the fibre-board insulator many years ago.

 

Currently trying to price up metal pipe + end caps for the silencer. As always, it's looking expensive, though I am considering looking at chimney flues as a silencer housing, the problem being they only have 1mm thick walls.

Edited by Nev, 14 November 2016 - 10:50 AM.

[Arno]

Perhaps a bit left-field, but as you run fairly large pipe diameters, have you ever looked into using lorry/HGV silencers?

 

Eg. http://www.ebay.co.uk/itm/182094078045

 

For them a 3" pipe diameter is probably "just getting started"

 

Of course you don't have any use for their cat/SCR/DPF units, but there are various 'plain' silencers out there too. Perhaps even from a scrapyard if you want to test some out..

 

BYe, Arno.

[Nev]

Perhaps a bit left-field, but as you run fairly large pipe diameters, have you ever looked into using lorry/HGV silencers?

 

Eg. http://www.ebay.co.uk/itm/182094078045

 

For them a 3" pipe diameter is probably "just getting started"

 

Of course you don't have any use for their cat/SCR/DPF units, but there are various 'plain' silencers out there too. Perhaps even from a scrapyard if you want to test some out..

 

BYe, Arno.

 

Thanks for the tip, on the face of it it's a good idea and I have mulled it over in the past, but discarded it really as 4 things spring to mind:

 

1. They would likely be very heavy.

2. My own design will eliminate 2 entire 180 bends (for better flow and less weight)

3. My own design will be adaptable/prototyped iteratively until it actually gets the noise down to about 100 db Static at idle.

4. My own design can be cut and welded to maximise the space in the silencer void, where as off the shelf parts won't manage this.

[Nev]

Well I've ordered up another £200 worth of metal (on top of the other £400 previously) for the silencer. Hopefully this lot will be enough to make the whole thing. I reckon I'm gonna need another £50 for gas though.

[Nev]

As this exhaust mini project is going to be quite unusual and hopefully useful to the wider community (maybe Elise's and other cars) I have decided to create my own website to log it: https://sites.google...jectives-issues

 

To summarise my design, it differs to other VX220 exhausts:

 

1. Elimination of lots of leading/trailing pipework to/from the silencer.

2. Up to 1300mm of 3.5" diameter perforated pipework inside the silencer.

3. Design can be simultaneously free flowing (straight through design) as well as refractive though 1000s of tiny holes.

4. Possible integration of an adjustable spring loaded butterfly flap, to ensure silent low revs but louder and better flow at high revs.

5. Detachable tailpipes allowing large 3.5" exit from silencer.

6. Possible deflection/turbulance tabs in the perforated inlet pipe.

 

 

 

Edited by Nev, 16 November 2016 - 04:10 PM.