Spark Exhaust dB Killer Grid-O 45 mm Open Universal G9988

Forty-five millimetres through a fifty-one and a half millimetre body. There is barely a wall left — which is exactly the point of this article.

Key Features

• dB killer for Spark Grid-O silencers.
• Ø 51.5 mm outer, 45 mm internal bore.
• Open type, no perforation.
• The widest and least restrictive of Spark's four Grid-O inserts.
• Stainless steel, removable.
• Spark part number G9988, made in Mantova, Italy.

Three Millimetres of Wall

Forty-five inside a fifty-one and a half body leaves about three millimetres all round. That is as little restriction as an insert can offer while still being an insert, and it is why this one costs sixty euro: a thin section in stainless takes more care to make than a thick one.

Who Needs the Widest One

Large-capacity machines, and venues whose limits are generous. On a big four or a large V-twin the narrower Grid-O inserts cost real mid-range, and if the machine only needs two or three decibels shaved off, the 45 does it without the penalty.

It is also the sensible first purchase if you do not yet know how far over the limit you are. Start wide, measure, go narrower if you must.

The Family Ladder

32, 38, 40, 45. Four bores, one body, one silencer family. Owners who run the same machine at different circuits sometimes carry two of the four; the swap takes minutes and needs a screwdriver.

Why All Four Are Open

Because the Grid-O ends in a woven titanium mesh across the whole outlet, and the mesh is already doing acoustic work. A perforated insert behind it would restrict without adding much attenuation, so Spark builds all four as plain bores.

Sixty Euro, and Why

The most expensive of the four Grid-O inserts, because it is the hardest to make. A three-millimetre wall in stainless has to be machined and finished without distorting, and there is less material to hold while that happens.

Ordering

One per silencer. If the case came to you without an insert, send us the exhaust's article number rather than guessing — the four look identical from outside and only the bore separates them.

Approval

Unaffected. A racing Grid-O stays a racing article with any insert fitted, and a homologated exhaust belongs in the configuration Spark tested it in.