Spark Exhaust Stainless Steel Tube Ø 38 × 1.0 mm 500 mm Universal G9007

Thirty-eight millimetres. The size at which a link pipe stops being small-bore plumbing and starts carrying the whole output of a middleweight engine.

Key Features

• Straight exhaust tube, AISI 304 stainless steel.
• Ø 38 mm outside, 1.0 mm wall thickness.
• 500 mm long.
• Fabrication stock.
• Spark part number G9007, made in Mantova, Italy.

The Middleweight Size

Thirty-eight is a common header diameter on parallel twins between 650 and 900 cc, and a frequent link size behind a collector on a middleweight four. It is also the internal bore of the Grid-O db killer that Spark supplies with its MT-07 and XSR700 systems, which is a fair indication of the gas volume it is sized for.

Measuring Before You Buy

Exhaust tube is specified by outside diameter, and the number stamped on an original part is often the inside. Thirty-eight outside with a one millimetre wall gives thirty-six inside — so a system described as thirty-six is very likely this tube.

Measure across the outside with a vernier and compare that figure, not a nominal one from a workshop manual.

Sleeving a Joint

To slip one 38 mm tube into another you need an intermediate: a short piece of the next size up, expanded or as-supplied depending on the fit, welded to one end. Spark's own systems use slip joints throughout, held by springs, and they come apart for maintenance because of it.

Two butt-welded tubes never come apart again. That is worth thinking about before the torch comes out.

Support, Not Suspension

A half-metre run of thin-wall stainless weighs almost nothing and will still crack at a weld if it is hung from one point. Two mounts, at least one of them rubber-isolated, is the rule that keeps a fabricated system alive through a season.

Where the Silencer Goes

Thirty-eight is a link diameter rather than a silencer inlet. Spark's universal cases take sixty; getting from one to the other means either a cone — article SGMA14 makes the 60 to 40 step — or a stepped transition of your own. Plan that part of the run before cutting the straight sections.

Half a Metre

Spark supplies one length per article. On most builds two or three lengths of the same diameter is the realistic order — cutting, mitring and getting a bend wrong all consume material.