Bends

A moulded silicone bend takes a hose run through a fixed angle while keeping its full bore, where a straight hose forced into a curve would flatten or kink. The bends here come at 45, 90, 135 and 180 degrees, as plain and hump hose bends, alongside a T-bend and 6061 aluminium bends.

Every bend costs some pressure, because the flow is thrown to the outside of the turn and breaks away from the inner wall. A tighter radius or a larger angle costs more, so use the gentlest bend the route allows. A moulded bend at least keeps the cross-section round through the turn, which a bent straight hose cannot do.

Performance silicone hose is usually built from layers of silicone with fabric reinforcement plies between them. The plies carry the pressure and stop the bend from ballooning under boost, while the silicone keeps it flexible and resistant to engine-bay heat.

Choose by angle, bore and type:

• Angle: 45, 90, 135 or 180 degrees. Two bends joined with a short aluminium joiner can make an offset or an angle that is not listed.
• Diameter: from small lines of 5, 6.5 or 9.5 mm up to intake sizes of 102, 127 or 152 mm. Many sizes carry an inch equivalent, such as 63 mm (2.5 in) or 76 mm (3.0 in).
• Hump bends: 45° and 90° bends with a raised hump that takes up engine movement, in sizes such as 54, 76 and 102 mm.
• Special versions: a petrol- and oil-resistant 51 mm 45° bend, and a 90° T-bend of 38 mm with a 19 mm connection.
• Aluminium: 6061 bends at 45°, 90° and 135°, in sizes such as 38, 63, 76, 89 and 102 mm. They hold their shape and join to hoses with silicone couplers.
• Colour: silicone bends in black or blue, aluminium ones in silver.

Measure the pipe’s outside diameter and choose a bend with the same inside diameter. Trim the legs square and clean, because a ragged edge seals poorly and can tear. Push each leg far enough onto the pipe for the clamp to sit behind the bead, and set the bend’s angle before tightening.

Keep bends clear of exhaust parts and sharp edges, and support long runs so they cannot sag or rub. Standard silicone dislikes oil and fuel, so check bends near breathers for swelling and replace any that turn soft.