Spark Exhaust dB Killer Force 40 mm Open 70 mm Universal G9954

Forty millimetres of bore over seventy of length. The wider Force insert, for the larger engines the family gets fitted to.

Key Features

• dB killer for Spark Force silencers.
• 40 mm internal bore, 70 mm long.
• Open type, no perforation.
• Stainless steel, removable.
• Spark part number G9954, made in Mantova, Italy.

Which of the Two

Spark builds the Force insert at 35 mm and at 40. The smaller one goes on the small twins — R3, Ninja 400 — and this one on everything above them. The rule is simple: match the insert to the engine, not to the silencer, because the case is the same in both instances.

If you fit the 35 to a large twin you will feel it in the mid-range. If you fit the 40 to a 400 you will not hear any difference at all.

Seventy Millimetres

Short, as open inserts go. Spark relies on the Force case's own internal volume for most of the work and uses the insert to trim rather than to transform.

That also makes it easy to fit: seventy millimetres needs very little clear length behind the outlet.

A Replacement Part in Practice

Most Force silencers leave Spark with an insert already in them. The reason to buy this article is that one went missing — during a rebuild, in a previous owner's garage, or on the road, because an insert that was refitted carelessly can work its way out.

Fifty euro against a silencer that is otherwise unusable on a road ride is not a difficult calculation.

Fitting It Properly

The retaining screw does the work. It should be tightened properly and checked after the first heat cycle, because an insert that vibrates loose in a titanium case will mark the bore on its way out.

Forty Millimetres of Bore

On a Force case fitted to anything from a middleweight upward, forty is the figure that leaves the engine alone. It narrows the exit enough to take the top off the note and not enough to show up anywhere on a dyno chart.

Approval

Unaffected. Where the Force silencer is homologated, the supplied insert is part of the approved configuration; where it is a racing article, no plug changes that.