Clamp on silencer to meet noise limits

[aerobod - near CYYC]

After being stopped from running local autocross events ( I was 2dB over the 92.9dB limit measured 15 metres from the fastest part of the course), I decided to create a clamp-on device that only takes a minute to fit or remove.

It is created from a piece of 3/8” x 4” 6061T6 aluminium bar and a standard Supertrapp 2.5” inlet silencing disc set - 18 discs give about 118% outlet area compared with the standard R400 exhaust pipe cross section. I haven’t got an “official” noise reading at an event yet, but using an iPhone app, it drops the noise level by 7dB.

The “appendages” on the attachment have a couple of functions, the protruding angled bar at the front is a cone deflector to minimize damage to the exhaust if hitting a cone at up to 140km/h. The small plate deflects exhaust away from the wing and tyre to prevent heat damage.

The Supertrapp discs are held in place with the standard stainless steel alien bolts that they provide. The aluminium pieces are clamped together with M5 x 12mm allen bolts. I machined the recess in the main piece to fit the outer diameter on the rolled exhaust lip with a depth 1mm less than the roll width so that the half-moon clamps on the back hold it tightly in place. There is also an M4 x 3mm allen bolt threaded into the bottom of the exhaust to locate the device and stop it from rotating.

At full throttle and maximum revs I now hear the engine mechanical noise and the intake (plenum, so a lot quieter than throttle bodies). Subjectively there is a small loss in top end power, but it doesn’t scream in a manic manner, which is a subjective loss in sound quality, even if it is socially more responsible.

 

[SM25T]

Don't leave it in place on the street ... there are some lethal looking edges there !

[aerobod - near CYYC]

Nothing that the unprotected edges of the carbon fibre front wings couldn't slice up first or the burn risk to pedestrians of the exposed exhaust. Canadian specialty low volume vehicle regulations are rather more relaxed when it comes to very low probability injury to pedestrians. The sharp edges are nicely de-burred and don't pose any more hazard to a pedestrian then being hit by the edges of exposed components (such as protruding foot rest) on a motorcycle or mudguard of a Lime Bike :)