Spark Exhaust dB Killer Classic and Sinfonia 32 mm Open Universal G9939

The insert that turns Spark's two long vintage cases from open pipes into something a neighbour will tolerate. Forty-seven millimetres across the body, thirty-two through the middle, a hundred long.

Key Features

• dB killer for Spark Classic and Sinfonia silencers.
• Ø 47.3 mm outer, 32 mm internal bore, 100 mm long.
• Open type — a straight-through restriction with no perforated section.
• Removable with the silencer in place.
• Stainless steel.
• Does not change the approval status of any silencer.
• Spark part number G9939, made in Mantova, Italy.

Open, and What That Means

Spark builds db killers in two kinds. Perforated ones move the gas through a wall of small holes; open ones simply narrow the exit. This is the second sort: a tube inside a tube, no holes, thirty-two millimetres of bore where the silencer would otherwise give you the full outlet.

An open insert is the gentler of the two on back pressure and the less effective of the two on noise. For a long vintage case that already has volume on its side, that is usually the right balance.

Two Silencers, One Insert

The Classic and the Sinfonia share this part. They are different shapes — one has a rolled mouth, the other is a plain even cone — but the outlet section is common to both, which is why Spark lists one article number for the pair.

If you have one of each on a twin, you need two of these.

A Hundred Millimetres

Length matters as much as bore. A hundred millimetres of restriction gives the gas column something to work against over a distance rather than at a single point, which is quieter and less abrupt than a short plug of the same diameter.

What It Will Not Do

It will not make an unapproved silencer legal. Spark's vintage universal cases carry no homologation and no insert changes that: approval describes a complete system on a named motorcycle, and a piece of tube fitted into an outlet is not part of any such description.

What it does is change what a meter reads at a circuit gate. That is a real and useful thing and it is the whole reason the article exists.

Fitting and Removing

Hand tools, silencer in place. The insert is retained at the outlet and comes out without disturbing the mounting or the link pipe — which is what makes it practical to run quiet on the way to a circuit and open once you are there.