Spark Exhaust Bent Tube 30° Ø 35 × 1.0 mm Stainless Steel Universal G9129

Thirty-five millimetres through thirty degrees. A shallow bend in the diameter that suits the small twins Spark builds its Force silencers for.

Key Features

• Mandrel-formed 30° bend, AISI 304 stainless steel.
• Ø 35 mm outside, 1.0 mm wall thickness.
• Straight tangents at both ends.
• Matches Spark's 35 mm straight tube, article G9011.
• Spark part number G9129, made in Mantova, Italy.

Wall Thinning

The outside of any bend stretches. On a mandrel bend at a sensible radius the wall loses perhaps ten per cent on the outer heel; on a tight bend made badly it can lose a third.

That matters because the outer heel is also where the gas scours hardest and where a system usually fails first. Buying the bend rather than making it is the cheapest way to keep the wall where it should be.

The Diameter and Its Silencers

Thirty-five is the internal bore of Spark's Force db killer for the Yamaha R3 and Kawasaki Ninja 400, and of its Moto GP inserts. It is a small-twin diameter, and a 30° bend in it usually appears in the run between a header and a mid-mounted silencer.

Shallow Bends and Flow

Every change of direction costs something. A thirty degree bend at a generous radius costs very little — far less than a ninety at the same radius, and less than two forty-fives that add up to the same angle.

If a run can be made with shallow bends instead of sharp ones, it should be. The parts cost the same and the engine notices.

Clocking the Bend

A bend has a plane, and rotating it about the tube axis before tacking swings the far end through an arc. On a build with two or three bends in series, that rotation is the whole adjustment — get the clocking right with tape and clamps before any heat goes near it.

Cutting a Bend Shorter

A 30° bend trims down to twenty or fifteen degrees easily, and doing so is normal rather than a compromise. Cut through the curve rather than through the straight tangent: that way the offcut keeps a usable straight end too, which on a build with several corrections is a second bend for free.

Ordering

One bend per article. Available in 30°, 45° and 90° at this diameter.