Straight Pipes for Honda CRX EH

Straight pipe is the raw material of a fabricated exhaust, cut to length and joined with bends, flanges and silencers. Tube comes in stainless steel, mild steel and aluminium, in 0.5 m and 1 m lengths. The section also holds vehicle-specific race pipes and mid-sections that replace part of an original system.

Pipe diameter sets the speed of the gas and the back pressure. Too small a pipe chokes the engine at high revs, while too large a pipe slows the gas, which can blunt response lower down on a naturally aspirated engine. After a turbo, lower back pressure generally helps the turbine, so turbo systems tend to run larger pipe.

Tube is sized by its outside diameter, and the bore is that figure minus twice the wall thickness. A thicker wall is more forgiving to weld and stands up better to dents and vibration, while a thinner one saves weight. Austenitic stainless such as 304 also expands more with heat than mild steel, so long stainless runs need room to move.

Choose tube by these details:

• Diameter: from 38 mm (1.5″) to 127 mm (5″), in inch-based and metric sizes such as 42, 54 and 60.3 mm.
• Wall thickness: the 304 stainless tube lists its wall as 1.5, 1.6 or 2 mm, as in 76 × 1.6 mm.
• Length: 0.5 m (50 cm) or 1 m.
• Material: stainless steel for long life, or mild steel for easy welding and repair. Aluminium tube, from 45 to 102 mm, is for the cold side, such as intake and charge-air pipes.
• Ready-made sections: race pipes and mid-sections are made for the car named in the title, and the mid-sections come with gaskets and fixings. A race pipe swaps part of the original system for plain tube, so the car gets louder. Without road approval it is for competition use where the rules allow, and circuit noise limits still apply.

Cut tube square with a pipe cutter or a saw in a guide, then deburr the inside. Clean the ends back to bright metal before welding. Keep stainless joined to stainless where possible, because welding it to mild steel needs a suitable filler.

Support long runs with enough hangers that no weld carries the weight, and keep the pipe clear of fuel and brake lines. Check welds and hangers after the first runs, since a crack often starts at a weld next to a stiff mount.