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Civic Si Downpipe
Your Civic Si
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+10–20 whp (est.)
Hard$850–$1,0003–4 hrs
Why do it
Lets the turbo breathe more freely. A real gain, but only with a matching tune.
Heads up
Only buy a catted downpipe for street use. PRL says its catted version needs no tune, but most of the power gain comes with a matching tune.
Tools you'll need
- Jack stands
- Socket set with extensions
- Penetrating oil
- O2 sensor socket
- New gaskets
Parts to buy
- PRL High Volume catted downpipe (PRL-HC10-HVDP) Includes a catalytic converter. Fits 2016–2021 Civic 1.5T including Si.Fits 2017–2020
Doesn't fit your car (0)
Always double-check fitment for your exact year, trim and transmission before buying. Prices change. ModBuddy doesn't earn money from these links.
Steps
- Soak the bolts in penetrating oil and let the exhaust cool fully.
- Raise the car on jack stands and remove the under-tray and heat shields.
- Remove the O2 sensor and unbolt the downpipe from the turbo and the exhaust.
- Install the new downpipe with new gaskets and reinstall the sensor.
- Install the matching tune before any hard driving.
Safety first
- Park on flat, solid ground, set the parking brake and chock the wheels.
- Use jack stands rated for your car. Never get under a car held up only by a jack.
- Let the engine and exhaust cool completely before touching them.
- Disconnect the negative battery terminal before unplugging sensors or electrical parts.
- Wear safety glasses, and gloves around sharp heat shields and hot fluids.
- Tighten bolts to the torque spec in your factory service manual.
- If a step doesn't match your car or you're unsure, stop and ask a shop.
These are overview steps written to help you plan the job. Always follow the instructions that come with your part and the procedures and torque specs in your factory service manual. Horsepower is an estimate; results vary.