Downpipes

A downpipe carries the exhaust from the turbine outlet to the rest of the system, and on many modern turbo cars it also holds the main catalytic converter. This section has turbo downpipes with a sport catalyst, decat versions for competition use, and downpipes for some older models, each made for the car and engine in the title.

A turbine is driven by the drop in pressure and temperature across it. Lowering the pressure after the turbine lets the same exhaust flow do more work, so the turbo can build boost sooner and the engine pumps against less resistance. Factory downpipes often carry a dense ceramic converter close to the turbo, so that it reaches working temperature quickly, and that converter is a large part of the restriction.

Sport downpipes generally replace it with a lower-density catalyst or with plain pipe. The engine management then sees different pressures and sensor signals, so a downpipe usually goes with a matching engine calibration.

Check these details in the title:

• Car and engine: each downpipe is listed for a model and engine, often with the power output, engine code or date range. Some exclude the four-wheel-drive versions of a car.
• Particulate filter: versions differ for cars with and without a particulate filter, so check which applies to yours.
• Catalyst: catalysed downpipes give the cell density, at 100, 200 or 300 cpsi. A higher density converts more of the pollutants, while a lower one flows more freely.
• Decat: these have no catalyst at all, so they are competition parts and not legal on public roads in Europe.
• Material: some downpipes for classic models are made from aluminised steel.

Fit a downpipe with a new gasket or clamp at the turbo, and move the lambda sensors across with sensor-safe anti-seize on the threads only. Check the clearance to the driveshaft, subframe and steering parts, and refit every heat shield.

After fitting, run the engine and look for leaks and stored fault codes. Any downpipe without type approval is for competition use where the rules allow. On a road car it can affect type approval, inspection and insurance, so check that the downpipe and the calibration meet the rules where the car is registered.