Audi · B9 · Mod guide

Audi B9 S4, S5 and SQ5 Mod Guide

The B9 S4, S5 and SQ5 share Audi's 3.0T EA839 V6, with a single twin-scroll turbo tucked inside the V, an 8-speed ZF automatic and quattro. That shared hardware makes them some of the most rewarding cars to modify: software alone unlocks a big jump in power, and the right supporting parts keep it consistent lap after lap. This guide covers the order we recommend, what each step does, and what to check before you start.

Covers: Audi S4 (B9/9.5), Audi S5 (B9/9.5), Audi SQ5 (B9/9.5)

Chassis
B9
Years
2018 to 2025
Engine
3.0L turbocharged V6 (EA839)
Transmission
8-speed Dual-Clutch
Drivetrain
quattro all-wheel drive
Stock power
349-354 hp / 369 lb-ft

Before you buy

  • Check your transmission software first

    Some 2021+ cars, and most 2023+ cars, leave the factory with a locked transmission control unit (TCU). The engine tune still works, but a TCU tune may need an unlock first. Check with us by VIN or model year before you order.

  • Know which suspension your car has

    Cars with Audi's adaptive dampers need coilovers built for adaptive suspension, or a cancellation kit, to avoid warning lights. Check your build sheet or ask us before choosing suspension.

  • SQ5 owners: confirm fitment

    Engine and transmission software, intercoolers and fuel parts usually cover the SQ5 too. Many intakes, downpipes, sway bars and wheels are S4/S5 only. Check the fitment on every product page.

  • Sort out maintenance before adding power

    A tune makes existing problems worse. Fix any coolant leaks, worn spark plugs or coils and overdue services first, and check the water pump (see Known issues below).

Start here

  1. Step 1

    Tune the EA839

    Engine software is the biggest single upgrade on the 3.0T. Tuners claim a Stage 1 tune adds roughly 100 hp and well over 150 lb-ft on 91-93 octane, with no hardware changes. It's the foundation every other step builds on. A transmission (TCU) tune is optional at Stage 1, but it sharpens shifts and raises the gearbox's torque limits.

  2. Step 2

    Control intake temperatures

    Once the car is tuned, the factory intercooler heat-soaks quickly and the engine pulls timing to protect itself, so power fades on hot days and back-to-back pulls. An upgraded front-mount intercooler keeps power consistent. Metal charge pipes replace the plastic factory pipes, which can crack under higher boost.

  3. Step 3

    Upgrade the intake and exhaust

    A high-flow intake and turbo inlet add a modest gain on a tuned car, and a lot more turbo sound. On this engine a cat-back exhaust is mostly about sound, so choose the resonated or non-resonated version based on how loud you want it. Downpipes pair with Stage 2 software and bigger turbos, and are sold for off-road use only.

  4. Step 4

    Upgrade fuel and ignition

    Higher-output tunes, ethanol blends and bigger turbos need more fuel than the factory high-pressure fuel pump can deliver, so an upgraded pump or pump internals come first. Fresh, colder spark plugs and upgraded ignition coils keep the spark strong at higher boost.

  5. Step 5

    Dial in the suspension

    Coilovers lower the car and tighten up body control, and stiffer sway bars cut body roll without making the ride harsh. If your car has Audi's adaptive dampers, choose coilovers built for adaptive suspension or add a damping cancellation kit to avoid warning lights.

  6. Step 6

    Upgrade brakes and wheels

    More power needs more stopping. Performance pads and stainless brake lines, with fresh high-temperature fluid, are the first upgrade for spirited driving and track days. B9 cars use a 5x112 bolt pattern, and wheel spacers are an easy way to fill the arches for a flush stance.

Known issues

  • Water pump coolant leaks

    The EA839's vacuum-operated water pump can leak coolant internally. Watch for coolant loss, low-coolant warnings, a boost-related fault code (P0299) or coolant residue on the cylinder head. Audi offers an updated pump, and it's worth checking yours before you tune.

  • Carbon buildup on the intake valves

    US-market B9 cars use direct injection only, so carbon slowly builds up on the intake valves and can cause a rough idle and lost power. Walnut blasting every 40,000 to 60,000 miles is commonly recommended.

  • Oil consumption from the PCV valve

    A torn PCV diaphragm in the valve cover is a commonly reported cause of oil consumption and rough running as these cars add miles.

  • Front-end clunks

    Worn front control arm bushings can cause clunks over bumps or a vague, wandering feel at higher mileage. Fresh arms make a lowered car feel noticeably tighter.

  • Transmission fluid service

    Audi calls the ZF 8-speed fluid a lifetime fill, but a fluid and filter service every 40,000 to 50,000 miles is cheap insurance, especially on a tuned car.

Supporting mods

  • Bigger turbos (Stage 3)

    Once the stock turbo runs out of headroom, hybrid and larger turbos such as the PURE750 or APR DTR8868 take these cars well past 500 hp, according to tuner claims. They need the intake, turbo inlet, downpipe, intercooler and fuel upgrades above, plus matching engine and transmission software.

  • Gauges and monitoring

    A digital gauge shows boost, intake temperatures and timing corrections in real time. It's the easiest way to spot a problem early on a modified car.

  • Fluids and maintenance

    Shorter oil change intervals with a quality European-spec oil, fresh brake fluid and regular coolant checks keep a modified B9 reliable.

FAQ

Do I need a transmission (TCU) tune?

Not for Stage 1, since the engine tune alone makes full power. A TCU tune adds faster shifts and higher torque limits, and it's required for bigger turbos. Some 2021+ cars, and most 2023+ cars, need their TCU unlocked first.

Will a tune void my warranty?

In the US, a manufacturer can't void your whole warranty just because you installed aftermarket parts, but it can deny a claim if it shows a part caused the failure. Expect engine and transmission claims on a tuned car to get a closer look.

Which fuel should I run?

Most tunes come in 91 and 93 octane versions, and 93 makes a little more power. Ethanol blends make the most power but usually need an upgraded high-pressure fuel pump.

Is a tune safe on the stock turbo?

Stage 1 and Stage 2 tunes are designed around the stock turbo and fuel system, and they're widely run on these cars. Keep up with maintenance and add an intercooler to keep temperatures in check.

Does the SQ5 use the same parts as the S4?

Engine and transmission software, intercoolers and fuel parts are usually shared. Intakes, downpipes, exhausts, suspension and wheels are often different, so always check fitment.

Do S5 parts fit the S4?

Most engine, suspension and brake parts are shared between the S4 and S5. Body parts differ, and some products are listed for one body style only, so check the fitment notes.

What order should I do mods in?

Tune first, then the intercooler and charge pipes, then intake and exhaust. Add fuel upgrades before bigger turbos, and upgrade brakes and suspension as your power and driving demand it.

Shop all Audi S4 (B9/9.5) parts Shop all Audi S5 (B9/9.5) parts Shop all Audi SQ5 (B9/9.5) parts

Last reviewed October 29, 2026