Spark Exhaust Bent Tube 45° Ø 38 × 1.0 mm Stainless Steel Universal G9136

Thirty-eight millimetres at forty-five degrees. The angle most systems are built from, in the diameter a middleweight twin breathes through.

Key Features

• Mandrel-formed 45° bend, AISI 304 stainless steel.
• Ø 38 mm outside, 1.0 mm wall thickness.
• Straight tangents at both ends for cutting and welding.
• Matches Spark's 38 mm straight tube, article G9007.
• Spark part number G9136, made in Mantova, Italy.

Around the Shock

On most modern middleweights the single rear shock and its reservoir sit exactly where an exhaust would like to run. Getting past them is the routing problem the system is designed around, and forty-five degrees is the angle that does it: enough to step out and back, not so much that the run doubles its own length.

Measure the clearance hot, not cold. A shock body that clears by ten millimetres on the bench will clear by less once the exhaust has expanded and the suspension has compressed.

Why This Angle Dominates a Rack

Because it is the only one that is useful on its own and useful in pairs. A single 45 turns a corner. Two of them opposed make an S. Two of them facing the same way make a right angle with an offset. Three make a full U in stages.

A fabricator buying one angle in quantity buys this one, and a fabricator buying three buys more of this one than the other two put together.

The Middleweight Diameter

Thirty-eight is a common header size on parallel twins from 650 to 900 cc, and the internal bore of the Grid-O insert Spark supplies with its MT-07 and XSR700 systems. Building around that platform means building in this diameter.

Tacking a Bend to a Straight

Four tacks at ninety degrees to each other, then stop and check. Thin-wall stainless pulls as it cools and a joint tacked at two points will not be straight afterwards. Run the finished bead in opposing quarters for the same reason.

Back-Purging Past a Bend

A curved run holds gas differently from a straight one, and a bend can trap a pocket of air at its high point. Give the purge longer than seems necessary before striking an arc — a sugared root inside a bend is invisible until the joint cracks a season later.

Ordering

One bend per article. Spark builds 30°, 45° and 90° at this diameter, plus a 500 mm straight.