Manifolds (Naturally Aspirated and Turbo)

Custom manifolds are generally made from 1 of 2 materials, mild steel or stainless steel. If fabricated from stainless steel then all materials (including the weld filler wire) should be of a suitable grade of stainless steel to prevent corrosion, for instance if the manifold is fabricated in 316 stainless steel then the filler wire used should also be 316 stainless steel.

When designing naturally aspirated manifolds the design is of great importance. The length, diameter and position of the runners plays a significant role in ensure not only smooth exhaust gas flow, but also of providing a scavanging effect to gain the most HP and torque possible from the engine. Naturally aspirated manifolds can be made from thinner walled materials than that of a turbo manifold, with 1.6mm being an ideal wall thickness.

When fabricating a turbo manifold it is vital that thick wall material is used, and preferably stainless steel. This is to ensure that the manifold has sufficient material to prevent cracking during heating and cooling, stainless steel is preferred material due to mild steel quickly forming rust when heated and cooled repeatedly. The manifold is also under considerable stress when a turbo is sitting on top and it should be fully support by brackets to prevent stress cracks from engine vibrations and the weight of the turbo.

It is also recommended that manifolds are fully ceramic coated to prevent damage to surrounding items in the engine bay, this is especially important with turbo manifolds, not only because of the higher heat generated by turbocharged engines, but also to keep the heat inside the manifold which will reduce lag and increase performance. Ceramic coating is the ultimate in heat protection. In the past heat wrap was used but this degrades over time and the colour changes.

All manifolds should be fabricated to the correct port sizes with free flowing collectors, and where possible equal length/volume primaries. Ideally the primaries should match to the cylinder head or at the very least provide a smooth transition. The secondaries (after the collector) should match to the turbine inlet (on turbo manifolds) or the exhaust system diameter (on naturally aspirated manifolds).

Station MotorSport Ltd can advise on all aspects of the manifold design prior to commencing the work. Most manifolds are built on the car to suit the turbo / wastegate (if fitted externally) locations and space available in the engine bay.

With more complex manifolds they are designed in a 3D CAD software to create fully dimensioned drawings and a 3D model for you to agree to prior to beginning fabrication.