My Misadventures in Back Boxes and What's this Hole?
Discussion
Before I start, let me get it out of the way, "Yes I know, silly me" 
.
Now that that's out of the way, I developed 2 leaks in my passenger side back boxes, one near the exit pipe and one on the tightening clamp to the silencer. The silencer one occurred after it got hot enough to expand slightly and that caused a leak, but the other one still needed fixing too....
....so I stupidly asked to have them replaced with straight pipes thinking that it will maybe be only very slightly louder:
BIG mistake. Whereas my car came stock with the "all silver" sports silencers, they had since been replaced with CCL sleeved ones from the Carbon Can Company when I got the car (you can get 2 versions: CCL=Loud (sleeved?) and CCQ=Quiet). I reckon the loudness was something like (at high revs):
OEM Back Boxes & OEM Sports Silencers ~105dB
OEM Back Boxes & CCC CCL Silencers ~103dB
^^^ The CCL's are marginally quieter than the TVR Sports Silencers and the car was probably just about trackable with fiddling (baffles?) but still quite loud.
...To this:
Straight Pipes & CCL Sleeved Silencers ~113dB easily (measured at 4000rpm, at 2000rpm they're nudging 108dB)
...... b******d loud and definitely too ASBO to drive (6dB is double the loudness so they ended up making it 3x louder than I was used to). It actually hurt my ears when going through a tunnel and I would definitely not be allowed anywhere near a track.
Unfortunately I had chucked my old "in need of repair" boxes away so I found ACT exhausts (East Grinstead) doing their own Back Boxes for £250 delivered and after chatting to them, ordered a pair:
Fitted as OEM with the fixings and welded in place, they are Brilliant. I measured them with my SPL meter as below 100dB A-weighted and 1m away so I can go to a track and confirm with their more accurate roadside test:
ACT Back Boxes & CCL Sleeved Silencers <100dB ?
An odd thing is that the TVR/OEM back boxes are just that, empty boxes - no baffles/perforations or anything inside them whereas the new ACT ones are boxes built around fenestrated pipes making them structurally stronger (no weak point where the entry/exit pipes are welded to the boxes - these are a pipe going through a box) and also MUCH quieter. The car is nicer to drive and doesn't appear to have any loss of power, with the bonus of me not bleeding from my lugholes after a spirited drive. It's the quietest it's ever been but also sounds deeper and more "mature" if that makes sense.
Moral of the story: DON'T remove the boxes thinking the sound will only get a tiny bit louder - have them repaired or buy some ACT ones if you want to retain your hearing (and sanity).
Holy Hole Batman.
Anyway, whilst getting all this done I noticed the following but I couldn't find any answers via google so....
What is the hole for?
The underside of the car is fairly flat with no undertray so I doubt there's much ground effect but even then I wouldn't have thought you'd want to vent lots of air underneath like this.
OTOH you wouldn't want to have an inlet here either so close to the road surface where dirt, gravel and rainwater can get sucked up. You can see trunking going up into the car - is it part of the AC system?
Just wondering and a very difficult thing to try and find on t'internet (I've tried using all sorts of phrases like "inlet under tvr", "car tvr outlet underside" etc etc - I usually only get results about the exhaust).
.Now that that's out of the way, I developed 2 leaks in my passenger side back boxes, one near the exit pipe and one on the tightening clamp to the silencer. The silencer one occurred after it got hot enough to expand slightly and that caused a leak, but the other one still needed fixing too....
....so I stupidly asked to have them replaced with straight pipes thinking that it will maybe be only very slightly louder:
BIG mistake. Whereas my car came stock with the "all silver" sports silencers, they had since been replaced with CCL sleeved ones from the Carbon Can Company when I got the car (you can get 2 versions: CCL=Loud (sleeved?) and CCQ=Quiet). I reckon the loudness was something like (at high revs):
OEM Back Boxes & OEM Sports Silencers ~105dB
OEM Back Boxes & CCC CCL Silencers ~103dB
^^^ The CCL's are marginally quieter than the TVR Sports Silencers and the car was probably just about trackable with fiddling (baffles?) but still quite loud.
...To this:
Straight Pipes & CCL Sleeved Silencers ~113dB easily (measured at 4000rpm, at 2000rpm they're nudging 108dB)
...... b******d loud and definitely too ASBO to drive (6dB is double the loudness so they ended up making it 3x louder than I was used to). It actually hurt my ears when going through a tunnel and I would definitely not be allowed anywhere near a track.
Unfortunately I had chucked my old "in need of repair" boxes away so I found ACT exhausts (East Grinstead) doing their own Back Boxes for £250 delivered and after chatting to them, ordered a pair:
Fitted as OEM with the fixings and welded in place, they are Brilliant. I measured them with my SPL meter as below 100dB A-weighted and 1m away so I can go to a track and confirm with their more accurate roadside test:
ACT Back Boxes & CCL Sleeved Silencers <100dB ?
An odd thing is that the TVR/OEM back boxes are just that, empty boxes - no baffles/perforations or anything inside them whereas the new ACT ones are boxes built around fenestrated pipes making them structurally stronger (no weak point where the entry/exit pipes are welded to the boxes - these are a pipe going through a box) and also MUCH quieter. The car is nicer to drive and doesn't appear to have any loss of power, with the bonus of me not bleeding from my lugholes after a spirited drive. It's the quietest it's ever been but also sounds deeper and more "mature" if that makes sense.
Moral of the story: DON'T remove the boxes thinking the sound will only get a tiny bit louder - have them repaired or buy some ACT ones if you want to retain your hearing (and sanity).
Holy Hole Batman.
Anyway, whilst getting all this done I noticed the following but I couldn't find any answers via google so....
What is the hole for?
The underside of the car is fairly flat with no undertray so I doubt there's much ground effect but even then I wouldn't have thought you'd want to vent lots of air underneath like this.
OTOH you wouldn't want to have an inlet here either so close to the road surface where dirt, gravel and rainwater can get sucked up. You can see trunking going up into the car - is it part of the AC system?
Just wondering and a very difficult thing to try and find on t'internet (I've tried using all sorts of phrases like "inlet under tvr", "car tvr outlet underside" etc etc - I usually only get results about the exhaust).
@ MikeE - aah thanks for that, seems obvious now you mention it - the CAI duct
@ TrotCanterGallopCharge - coming from the hi-fi side of things, as far as I understand it there is a difference between actual energy increase as compared to human (psychoacoustics) perceived loudness.
3dB is double the actual energy but 6dB is double the brain's perceived loudness (ie. what you interpret as being twice as loud)........although some sites give that second figure as 6dB and others as 10dB.
@ TrotCanterGallopCharge - coming from the hi-fi side of things, as far as I understand it there is a difference between actual energy increase as compared to human (psychoacoustics) perceived loudness.
3dB is double the actual energy but 6dB is double the brain's perceived loudness (ie. what you interpret as being twice as loud)........although some sites give that second figure as 6dB and others as 10dB.
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