Spark Exhaust Stainless Steel Tube Ø 40 × 1.0 mm 500 mm Universal G9001

Forty millimetres is the size most aftermarket link pipes turn out to be. If you are guessing at a diameter for a one-off system on a mid to large machine, this is the one to guess.

Key Features

• Straight exhaust tube, AISI 304 stainless steel.
• Ø 40 mm outside, 1.0 mm wall thickness.
• 500 mm long.
• The most commonly used diameter in Spark's straight-tube range.
• Spark part number G9001, made in Mantova, Italy.

Why This Size Turns Up Everywhere

Because it suits a wide band of engines. Forty millimetres carries the output of a large twin or a middleweight four without slowing the gas down, and it is small enough to route around a shock and a swingarm without fouling.

It is also the internal bore of several Spark db killers — the wide Force insert, the wide Moto GP one, the 40 mm Grid-O and the Force Evo and Konix Evo plug. Those parts and this tube are sized for the same class of machine.

Bending It Yourself

Forty millimetres in one millimetre wall will bend on a mandrel bender and will kink on a cheap hydraulic one. If you do not have access to a mandrel, buy Spark's ready-made bends — the 30°, 45° and 90° articles exist precisely so a builder without a bender can still make a system.

Springback is real: stainless returns four to eight degrees after the bender is released, so a 45° bend needs to be pulled past 50.

Wall Thinning

The outside of any bend stretches and thins. On a mandrel bend at a sensible radius the loss is small; on a tight bend it can take a third of the wall away. That is the argument for a factory bend on the tight radii and home fabrication on the gentle ones.

The Inside of the Cut

Deburr every cut on the inside as well as the outside. At forty millimetres a burr left on the bore sits directly in the gas path, collects carbon and stops a slip joint seating. A round file and half a minute is the whole job, and it is the step most often skipped.

Ordering

500 mm per article. A full system on a twin typically eats two to three lengths at this diameter once offcuts and mistakes are counted.