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Big Power Vxt Project


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#3541 The Batman

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Posted 06 December 2016 - 07:57 PM

:yeahthat: That's how the repackable silencers are done However like you say maybe a thicker metal.. not sure how much 0.3mm makes :unsure:

Edited by The Batman, 06 December 2016 - 07:57 PM.


#3542 Nev

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Posted 06 December 2016 - 08:23 PM

I'll have a look at it tomorrow and have a head scratch as to what is best.



#3543 jules_s

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Posted 06 December 2016 - 08:58 PM

Might be a pita/daft but I'd consider bending the rod the the profile of the box and then weld it around?



#3544 Nev

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Posted 06 December 2016 - 09:35 PM

Might be a pita/daft but I'd consider bending the rod the the profile of the box and then weld it around?

 

That's a really good idea too, if the rod was underneath and then bent up it would hold the weight from underneath (rather than hanging the box from the top).

 

You've just won yourself another "joy ride" ! LOL  



#3545 oakmere

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Posted 06 December 2016 - 10:57 PM

Nev just looking at your design do the exhaust gasses have to pass through the glass fibre fill to exit the exhaust? If so isn't this a major restriction? Shouldn't this just be used to absorb sound around the perforated tube as the gas passes along the tube?

#3546 Nev

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Posted 06 December 2016 - 11:09 PM

Nev just looking at your design do the exhaust gasses have to pass through the glass fibre fill to exit the exhaust? If so isn't this a major restriction? Shouldn't this just be used to absorb sound around the perforated tube as the gas passes along the tube?

 

Yep, all my gas has to pass through 2 lots of glass fibre (where as only some of the gas does that in a normal straight through absorption exhaust). It shouldn't be much of a restriction really, as the surface area of the perforations and glass-fibre is huge (7 times the open surface area of the 3.5" pipe that feeds to it). I agree the g/f + perf pipe usage of this design is quite radical really, but that's what happens when you're a bold maverick!

 

The G/F is rather necessary though (and an easy/cheap win), as it really kills high and mid frequency noise - it knocked off a massive 5 dB off my A-filter reading (but only 3 dB off my C-filter reading as that is more bass biased).

 

I am a little nervous of the back pressure, inevitably there will be more than the old silencer which was doing next to nothing. Maybe I will lose 20 to 40 HP, but I can just change the boost on the map by 1 PSI, en richen the mixture and get that power back with 5 minutes of laptop time :)

 

At the end of the day I wanted this thing to actually bring the noise down to an acceptable level for the neighbours and track testers, and some increased back-pressure is inevitable really.


Edited by Nev, 06 December 2016 - 11:31 PM.


#3547 Nev

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Posted 06 December 2016 - 11:30 PM

I have to say I am itching to actually drive it now, it's been off the road for 2 weeks and I'm missing my fix!

 

Maybe, just maybe (if I pull my finger out tomorrow), it will be ready for a test drive.

 


Edited by Nev, 06 December 2016 - 11:34 PM.


#3548 vocky

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Posted 07 December 2016 - 08:54 AM

that Glass Fibre wrap will come away from the pipe, you need to pack the entire silencer with the stuff, plus add some wire wool between it and the perf pipe.

 

I have stripped a couple of silencers and repacked them, so have seen what happens.



#3549 Nev

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Posted 07 December 2016 - 10:03 AM

that Glass Fibre wrap will come away from the pipe, you need to pack the entire silencer with the stuff, plus add some wire wool between it and the perf pipe.

 

I have stripped a couple of silencers and repacked them, so have seen what happens.

 

Yep, I have another box of glassfibre yet to stuff in there, once it's welded up. A key reason to put the vertical wall in was to divide the silencer into 2 halves that would help retain the stuffing.  


Edited by Nev, 07 December 2016 - 10:11 AM.


#3550 oakmere

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Posted 07 December 2016 - 12:07 PM

I think the GF will be destroyed in a very short time in this application. The gasses will find a weak spot and blow a hole in it. I think it's great you are trying somthing new and I could well be wrong. I would chamber the box like the N/A box with some chambers filled with glass fibre. May be the 3.5" pipe in and 2 x 2.5" out of a chamber will kill certain frequencies?

#3551 Nev

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Posted 07 December 2016 - 12:11 PM

Yea, I don't hold much faith in the glass wrap surviving if I pedal hard. This is why I put the central wall in (partly as a wadding retainer) and have one end cap easily removable so I can simply shove more wadding in there easily. I reckon to repack it would be only be an hours work, as the end cap should be removable whilst the exhaust is still on the car. That will be far easier and quicker than the Tullet or 2ubular solution which requires the owner to completely take the silencer out of the car to repack it. When I repacked a Tullet it took 2 of us about 5 hours to do on a friends VX220.


Edited by Nev, 07 December 2016 - 12:21 PM.


#3552 The Batman

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Posted 07 December 2016 - 12:24 PM

What Glass wrap did you buy?

#3553 Nev

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Posted 07 December 2016 - 12:27 PM

What Glass wrap did you buy?

 

e-glass.

 

I thought of getting more expensive stuff but I don't think any of it will survive TBH no matter what price you pay, or what the marketing bollox says. At the end of the day it is glass strands and it will simply become brittle with heat and get shot out of the rear. I suspect the thing that will determine it's longevity is the weave interlocking (to keep it bigger clumps) and the thickness of the strands (to reduce melting).

 

I might pop along to B&Q and buy a huge bag of loft insulation as it will be about 5 times cheaper.

 

The key to the wadding usage in my design is fast easy repacking :)

 

Even with no packing the silencer only registered 102 dB, which though not perfect is still nearly 2 times quieter than my old silencer, so I can afford for it to become a bit noisier.

 


Edited by Nev, 07 December 2016 - 12:37 PM.


#3554 Mopeytitan

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Posted 07 December 2016 - 12:58 PM

The exhaust stuff is specifically designed for the high temperatures it will see. Your best bet would be Acoustafil ZX1 or whatever it is. That's good for really high temps

#3555 The Batman

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Posted 07 December 2016 - 01:09 PM

Having tried a few types of wadding the expensive stuff does last longer.. depends how often you want to change monthly or daily :lol:

#3556 Nev

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Posted 07 December 2016 - 10:56 PM

Welded the whole thing up today. In the end I couldn't face drilling upteen holes for the removable end, so I just micro tacked the "removable" end cap to make it mostly leak free. This will mean my idea of not having to take the exhaust off for a re-pack is fubared, as I will need to dremel the tacks next time to get the end cap off! If/when I repack it, I will then drill the holes so it becomes easier to re-pack next time.

 

The 1.2mm skin warped and twisted a hell of a lot, also the 3.5" round stubs warped as well, but I can "fix" them with a hammer and a die tomorrow. My welding isn't pretty, but hopefully it will all hang together, some of the welds are still semi tacked and I can improve them tomorrow.

 

The whole structure got a lot more rigid with the tack welded central wall and the end caps properly installed. It is almost rattle free.

 

Posted Image

 

 

All I need to do tomorrow is add some more rods for strengthening the hangers, cut and weld the shortened flexi-pipe and fit a tail pipe.

 

I might make 2 tail pipes (if I can fit them which is not 100% certain yet):

  1/ a twin exit tail pipe for the road

  2/ a single exit with 90 degree bend pointing downward for the sound testers at Castle Coombe.

 

I will try and remember to weigh it tomorrow. Then it's test drive time *gulp*


Edited by Nev, 07 December 2016 - 11:19 PM.


#3557 Dan r

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Posted 08 December 2016 - 05:13 AM

Suitably impressed, good luck for the test drive!

#3558 FLD

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Posted 08 December 2016 - 02:09 PM

Get a metal punch for your holes Nev. Makes short work of it. To keep distortion down weld an inch, stop, weld an inch elsewhere etc. Too much heat in one place is a pain. It's what killed my manifold project. Sent from my iPhone using Tapatalk

#3559 Nev

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Posted 08 December 2016 - 05:31 PM

Wowzers, I'm tired, another full day of bashing, welding, cutting and struggling under the car.

 

But, it's finally finished, installed and tested at idle. It had a couple of whisper leaks in a couple of places, but nothing to worry about. Am gonna take for a gentle drive tomorrow to give it a few proper heat cycles.

 

At the last minute I was going to weld in a lambda bung for the dashboard AFR gauge, and then realised that I didn't have a 20mm drill bit, so this is something I will have to re-visit in a few days time, but it won't stop me being able to drive it in the meantime.

 

After the final assembly the noise seemed to have gone up a dB, but it overall way quieter than the old silencer. I could walk round the rear of the car and I my ears weren't ringing. Thankfully it didn't seem to rattle (yet).

 

I've learnt a lot from this mini project, as usual it has been humbling to actually struggle to build something rather than pay for someone else and not have a clue to the effort involved. My welding (key man skill !) is certainly better, particularly my tacking.

 

Will take some pics of the tailpipe (just a single 3.5" exit) tomorrow as it was dark when I finished 15 mins ago.

 

 


Edited by Nev, 08 December 2016 - 05:42 PM.


#3560 siztenboots

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Posted 08 December 2016 - 05:37 PM

do you have a clean air supply for breathing when you are welding?






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