Spark Exhaust Bent Tube 45° Ø 35 × 1.0 mm Stainless Steel Universal G9130

Thirty-five millimetres at forty-five degrees. The working angle in the diameter Spark's small-twin silencers are built around.

Key Features

• Mandrel-formed 45° 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 G9130, made in Mantova, Italy.

Getting to the Silencer Position

On a 300 to 500 cc machine the silencer usually sits high and outboard, and the header leaves the cylinder low and central. Forty-five degrees is the angle that climbs and steps across at the same time.

One of these off the header, a straight, and a second one into the silencer covers a great many small sports bikes without anything else being needed.

Two Forty-Fives Against One Ninety

They are not equivalent. A right angle at a given radius disturbs the gas once, hard; two forty-fives with a straight between disturb it twice, gently, and let it settle in between.

At part throttle the pair usually wins. At full throttle the difference is small. What decides it in practice is space, and the pair is more adjustable.

What Runs at This Diameter

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. A bend in this size is almost always part of a small-twin build.

Marking a Curved Cut

Wrap a strip of paper round the tube, align the overlapping edges, mark along it. That gives a square line on a curve, which a rule and a marker will not. Freehand marking is why joints arrive with a gap on one side.

Support Near the Bend

The weld at a tangent is a stress concentration and a bend is where a system flexes. Put a mount within a hand's width of any bend that carries weight, and make at least one mount in the run rubber-isolated.

Wall Thinning on the Heel

The outside of every bend stretches as it forms, and loses wall thickness doing it. On a mandrel-formed piece at a sensible radius the loss is around a tenth; on a badly made bend it can be a third. The outer heel is also where the gas scours hardest, so that is where a system fails first.

Ordering

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