Edited by The Batman, 06 December 2016 - 07:57 PM.
Big Power Vxt Project
#3541
Posted 06 December 2016 - 07:57 PM
#3542
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
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
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
Posted 06 December 2016 - 10:57 PM
#3546
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
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
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
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
Posted 07 December 2016 - 12:07 PM
#3551
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
Posted 07 December 2016 - 12:24 PM
#3553
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
Posted 07 December 2016 - 12:58 PM
#3555
Posted 07 December 2016 - 01:09 PM
#3556
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.
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
Posted 08 December 2016 - 05:13 AM
#3558
Posted 08 December 2016 - 02:09 PM
#3559
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
Posted 08 December 2016 - 05:37 PM
do you have a clean air supply for breathing when you are welding?
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