Back Boxes - Direct Fit
The exhaust manifold collects the engine output gases from each exhaust port and transfers this to one outlet pipe, which in turn feeds the intermediate pipe (B-pipe). Turbocharged engines will also have a downpipe that collects the turbine output gases and feeds it into the exhaust manifold single outlet pipe. Downpipes can be catted or catless – however, the latter is illegal in certain jurisdictions – so please do check first before committing. If the engine top-end has been modified, uprated or forged, invariably the exhaust manifold will require changing too. Equally if the turbocharger unit is altered, a new downpipe is required.
Typically made from cast iron or stainless steel, exhaust manifolds can crack under extreme heat or simply over time through wear. The exhaust manifold gaskets can perish causing the manifold to leak. Issues will manifest with either a burning smell emanating from the engine bay, an excessively noisy exhaust, and/or loss of engine power.
Retrofitting aftermarket exhaust manifolds are often made from welded tubular steel, which is stronger, lighter, rust resistant and more resilient. Better design creating a less disruptive airflow can also lead to efficiency gains. Be aware that changing one or both these components will likely alter the exhaust note. Exhaust manifolds can be creative, flamboyant works of art fit for display in an automotive gallery; capable of lighting up any engine bay. Accentuating intricate pipe work with precise tig welds in an anodised blue finished titanium is the stuff of photographers dreams.
The ‘best’ exhaust manifold depends on your goals. Stock manifolds are usually cast iron – durable, but heavy and restrictive. Aftermarket options fall into two main categories: tubular steel and stainless steel.
Tubular steel is lighter and stronger, offering better flow characteristics for increased horsepower. They're often made from TIG-welded sections for strength and precision. However, they can be more prone to rust if not properly coated.
Stainless steel manifolds offer the best of both worlds—lightweight, strong, *and* corrosion resistant. They’re typically pricier but will last a long time. For serious builds, consider manifolds designed for specific turbocharger setups or engine modifications.
The horsepower gains from a downpipe vary *hugely* depending on your car, engine setup, and whether you choose a catted or catless version. But generally, expect anywhere from 10-30 horsepower at the wheels.
On lower boost applications (stock turbo cars), it’s often more about improving spool-up time—getting that turbo spinning faster so power delivery feels snappier. On higher-boost builds, a downpipe can unlock significant gains by reducing backpressure and allowing the engine to breathe freely.
A catless downpipe will generally yield more horsepower but comes with legal implications and often triggers a check engine light. A catted version is a good compromise for street use.
No, a downpipe isn't the same as an exhaust manifold, although they’re both part of the exhaust system. They have distinct roles and locations.
The exhaust manifold collects exhaust gases from each cylinder head and directs them towards the turbocharger (or directly to the exhaust in naturally aspirated engines). It's at the beginning of the exhaust flow.
The downpipe connects *directly* to the outlet of the turbocharger, carrying those gases onward through the rest of the exhaust system. So, manifold first, then downpipe.
Downpipes are a crucial part of your car’s exhaust system, specifically in turbocharged engines. They connect directly to the turbocharger and carry those hot exhaust gases away from it.
Think of it like this: the turbo uses exhaust gas to spin its turbine and create boost. A downpipe needs to efficiently remove that spent gas so the turbo can keep spinning freely. Better flow means more power!
Downpipes often replace the restrictive factory unit, which is designed with catalytic converters in mind for emissions compliance. Aftermarket downpipes come in ‘catted’ (with a catalytic converter) and ‘catless’ (without) versions. Catless offer maximum flow but are generally illegal for street use.
