Spark Exhaust Stainless Steel Tube Ø 42 × 1.0 mm 500 mm Universal G9008

Forty-two. The size nobody plans around and quite a few builds turn out to need — when forty is measurably tight and forty-five loses too much gas speed.

Key Features

• Straight exhaust tube, AISI 304 stainless steel.
• Ø 42 mm outside, 1.0 mm wall thickness.
• 500 mm long.
• Fabrication stock.
• Spark part number G9008, made in Mantova, Italy.

The Value of an Odd Size

Most suppliers stock 40 and 45 and nothing between. Spark stocks 42 as well, and the reason is that original-equipment exhausts do not confine themselves to round numbers. A factory system measured at forty-two is not unusual, and matching it exactly is easier than adapting to a size that is close.

Two millimetres of diameter is about ten per cent of flow area. On an engine already breathing at its limit that is not nothing.

Sleeving Over a 40

Forty-two outside with a one millimetre wall gives forty inside. That means a 40 mm tube slides straight into it — no expanding, no swaging, no machining.

It is the neatest slip joint available in Spark's range and it is the reason to keep a length of 42 in the rack even on a project built around 40 mm tube. One article turns a butt weld into a serviceable joint.

Clamp or Spring

A slip joint needs holding. A band clamp is quicker; a pair of springs is what Spark uses on its own systems, because a sprung joint allows the thermal movement that a rigid clamp fights. Spark sells the springs and the hooks separately.

Two Millimetres of Difference

Between 40 and 42 there is about ten per cent more flow area. That is enough to matter on an engine at its limit and not enough to notice on one that is not — which is why 42 is a size you choose deliberately after measuring, rather than one you reach for by default.

Springs and Hooks

Spark sells the springs that hold a slip joint together and the hooks that fit them: articles MOLLA01 and MOLLA02 in two lengths, with or without rubber, and SGATT068 or SGATT037 for the hook. Two springs per joint at opposing sides is the arrangement Spark uses on its own systems.

Half a Metre

One 500 mm length per article. For sleeve work you need very little of it, so a single length usually covers several joints.