Spark Exhaust Bent Tube 30° Ø 28 × 1.5 mm Stainless Steel Universal G9117

Thirty degrees at twenty-eight millimetres. The smallest bend in Spark's range, and the only one below seventy millimetres with a wall thicker than one millimetre.

Key Features

• Mandrel-formed 30° bend, AISI 304 stainless steel.
• Ø 28 mm outside, 1.5 mm wall thickness.
• The smallest diameter Spark bends.
• Straight tangent sections at both ends for cutting and welding.
• Spark part number G9117, made in Mantova, Italy.

Thirty Degrees Is a Correction

Nobody designs a system around a thirty degree bend. What it does is fix the problem that appears once the main runs are tacked and the silencer does not quite line up with where it has to sit.

A pair of them, opposed, gives a shallow offset that shifts a run sideways without changing its direction — the standard way of dodging a shock mount or a frame rail without redrawing the whole exhaust.

Small Bore, Thick Wall

At twenty-eight millimetres a one millimetre wall would collapse on the inside of the radius under any bender. A millimetre and a half survives it, which is why this diameter carries the heavier wall through the whole tube and bend range.

The trade is weight, and at this size the weight is trivial.

What Uses 28 mm

Balance pipes between headers, link sections on 125s and small singles, and the short connecting runs a one-off system needs around the main gas path. On anything above 250 cc it is plumbing rather than exhaust.

Mandrel, Not Crush

A mandrel bender supports the tube from the inside as it forms, so the section stays round and the bore stays constant. A crush bender does not: the tube flattens on the radius and the flow area drops where the gas is already having to turn.

Every bend Spark sells is mandrel-formed. That is the difference between a bought bend and one made in a shed with a hydraulic press.

Cutting It Down

A 30° bend can be cut back to fifteen or twenty degrees, and often is. Cut through the curve, not through the straight tangent, and you keep a usable straight end on the piece you are throwing away as well as the one you are keeping.

Where It Gets Supported

Even at this size a bend is where a system flexes and where it eventually cracks: the weld at the tangent is a stress concentration. Put a mounting point within a hand's width of any bend carrying weight, and make at least one mount in the system rubber-isolated.

Ordering

One bend per article. Spark supplies this diameter as a 30°, 45° and 90° bend and as a 500 mm straight length under article G9010.