The C8 RS6 Avant, RS7 Sportback, and RSQ8 SUV all share the same 4.0L twin-turbo V8 — BMW M5 / E63 AMG territory in a quattro driveline. Stock these cars make 591 HP and run mid-3-second 0-60 times. With a tune and downpipes you are past 800 wheel HP. Built engines push 1,000+ wheel HP and put the C8 RS platform on the short list of sub-$200K cars that genuinely outrun a McLaren 720S. This guide walks the full Stage 1 to Stage 3 path for the EA825 4.0T.

What is the Audi C8 4.0T?

The EA825 4.0L twin-turbo V8 launched in the C8 RS6 / RS7 / RSQ8 in 2020. It is a 90-degree V8 with twin turbos mounted in the valley (hot-V layout), direct injection, and a 48V mild-hybrid system. The engine shares architecture with the Lamborghini Urus and Porsche Cayenne Turbo S V8. Factory output is 591 HP and 590 lb-ft. With Performance Package it climbs to 621 HP. The 8-speed ZF Tiptronic is the only transmission offered.

Cars that use the C8 4.0T

C8 RS6 Avant (2020+)
C8 RS7 Sportback (2020+)
RSQ8 SUV (2020+)
Lamborghini Urus (variant)
Porsche Cayenne Turbo S (variant)
Bentley Bentayga V8 (variant)

Stage 1: Tune Only (700-760 HP)

Stage 1 on the C8 RS is the biggest single power gain you will ever buy. The factory tune leaves enormous headroom on the table. On 93 octane premium, expect:

RS6 / RS7 base tune: 700-730 wheel HP
RS6 / RS7 Performance Package: 720-760 wheel HP
RSQ8 (slightly higher transmission delta): 690-720 wheel HP

On E30+ ethanol mix, Stage 1 routinely hits 770-810 wheel HP without bolting on a single piece of hardware. The factory turbos and fueling support this on a tune alone.

Best tuner for C8 RS in 2026

APR Stage 1: The 4.0T community standard. Largest dealer network, most refined drivability.
034 Motorsport Dynamic+ Stage 1: Strong alternative. More aggressive on E30+ mixes.
JHM: Highly respected on the V8 platforms. Smaller dealer footprint.

All three flash via OBD2 and reflash back to stock for warranty visits.

The TCU tune (don't skip it)

The factory ZF8 transmission calibration is conservative. A TCU tune (APR sells one) holds gears longer, slams faster shifts, and unlocks higher torque limits. Combine with ECU Stage 1 for a step change in driveability.

Stage 2: Bolt-Ons (820-880 HP)

Stage 2 = downpipes plus updated tune. C8 RS has twin downpipes (one per turbo) with primary cats and secondary cats. Aftermarket downpipes drop massive backpressure. Build order:

Downpipes (catless or 200-cell catted): Single biggest bolt-on. The hot-V layout puts the turbos at the top of the engine, so EGTs are critical and aftermarket downpipes drop them significantly. ARM Motorsports, IRL Performance, CTS Turbo, and 034 Motorsport make direct-fit C8 4.0T downpipes. See the ARM Motorsports C8 downpipes.
Midpipes: Drop the secondary cats. ARM Motorsports and IRL midpipes are direct-fit. Real-world Stage 2 gain on the midpipes alone is 15-25 wheel HP.
Intake: Factory C8 airbox is well-designed. Aftermarket intakes from Eventuri and ARM Motorsports give 5-12 wheel HP at Stage 2+.
Inlets: The C8 has restrictive factory intake inlets. ARM Motorsports C8 inlets are a 15-25 wheel HP gain at Stage 2 and mandatory at Stage 2+.

With Stage 2 bolt-ons (downpipes + midpipes + inlets) and an updated tune, expect 820-870 wheel HP on pump gas, 880-940 wheel HP on E30+.

Stage 2+: E60-E85 (900-980 HP)

Factory C8 fueling supports up to about 900 wheel HP on E60+. The factory port injection helps here — unlike the B9 3.0T (DI only), the C8 4.0T benefits from factory PI for ethanol mixes. Above 900 wheel HP, you need:

Larger intercooler (CSF, CTS Turbo, Wagner Tuning C8 race-spec)
Auxiliary low-pressure fuel pump for E85 use
HPFP upgrade at 950+ wheel HP
Aggressive cooling — oil cooler, transmission cooler, charge cooling

Stage 3: Turbo Upgrade (1,000+ HP)

Above 950 wheel HP, the stock C8 turbos run out of breath. Upgraded turbo options in 2026:

Pure Turbos PURE800 C8: Drop-in upgraded twin turbos. Supports 1,000 wheel HP.
Doc Race / VTT custom builds: For 1,100+ wheel HP targets.

At Stage 3, you also need: forged rods (factory rods bend around 950-1000 HP at sustained pulls), upgraded HPFP plus auxiliary pumps, race-spec intercooler, ZF8 transmission service every 5,000 miles.

Supporting Mods That Save Your Engine

Transmission cooler

The ZF8 in the C8 RS handles factory power easily. At Stage 2 (800+ wheel HP) you need an auxiliary transmission cooler. At Stage 3 (1,000+ HP) you need a high-capacity cooler plus more frequent fluid service intervals.

Oil cooler upgrade

Factory C8 oil cooler is sized for stock power. CSF and CTS Turbo make direct-fit upgrades. Mandatory for any RSQ8 SUV doing track work (higher mass = more thermal load).

Differential

The C8 quattro driveline can take 900-950 wheel HP. Past that point, upgraded differential bushings and a rear-diff brace become important. 034 Motorsport sells street-density bushing kits.

Brakes

Stock factory carbon-ceramic brakes are excellent. If your car has the steel brake option, EBC Yellow Stuff pads are the standard upgrade for spirited driving without a full big-brake kit.

C8 4.0T known issues to watch

Turbo wastegate rattle (cold start): Common on early production cars. Aftermarket downpipes mask it but the underlying issue is mechanical. Not a reliability concern unless it gets noticeably louder over time.
Primary cat substrate breakdown: Stock cat substrates can break down at sustained high-load driving. Aftermarket downpipes remove this risk entirely.
HPFP failures (early production): Some 2020-2021 cars had HPFP failures. Audi extended warranty coverage. Verify your VIN.
48V mild-hybrid system errors: The 48V system can throw codes after extensive Stage 2+ driving with the start-stop active. Disable start-stop permanently via tune.

What chassis are you working with?

FAQ

What is the safe Stage 1 HP for the C8 RS6 / RS7?

On 93 octane premium, 700-730 wheel HP is safely sustainable from a stock C8 RS6 or RS7. With Performance Package factory option, the safe Stage 1 envelope climbs to 720-760 wheel HP. E30 mix moves the envelope to 770-810 wheel HP.

Do I really need the TCU tune?

Yes, if you want to feel the Stage 1 power. The factory TCU limits torque to protect the transmission, holds gears too long, and shifts slowly under boost. A TCU tune unlocks the ECU work and is one of the highest gain-per-dollar mods on the C8 platform.

How much HP can the stock C8 4.0T turbos make?

The factory twin turbos top out around 950-980 wheel HP with full bolt-ons and E60+ fueling. Past 950 HP, response falls off and you need upgraded turbos.

Will Stage 1 affect my warranty?

Any aftermarket flash gives the Audi dealer grounds to deny powertrain warranty claims if they detect it. Stage 1 reflashes back to stock cleanly but leaves a trace in the DME (and TCU if you tune the transmission).

Where do I buy C8 RS parts in Canada?

KORE SPEED is Vancouver's Audi RS specialist. We stock APR, 034 Motorsport, JHM, ARM Motorsports, IRL Performance, Eventuri, Akrapovic, and Brembo for the C8 platform in-stock for same business day shipping across Canada. See the C8 RS6 catalog, RS7 catalog, or browse all tuning options.

Audi C8 RS6 / RS7 4.0T Tuning Guide: Stage 1 vs Stage 2 vs Stage 3 (2026)