B9.5 Audi S4 3.0T Maintenance & Upgrade Log

With the intake and intercooler already upgraded, we continued improving the B9/5 S4's charge-air system with CAP Aluminum Post-Throttle Valve Charge Pipes.

The factory piping was replaced with a more durable aluminum setup designed to provide a smoother, less restrictive airflow path after the throttle body. This helps complete more of the upgraded charge-air system while removing another factory plastic component from the setup.

The charge pipes pair with the other airflow upgrades already installed on the 3.0T EA839, creating a more complete intake and charge-air system.

At approximately 119,000 km, the S4 received its second documented oil change under CAP ownership.

The service included extracting the old engine oil, replacing the oil filter, refilling the 3.0T EA839 V6, and checking the final oil level.

We used a Hengst oil filter and refilled the engine with approximately 7.3 litres (7.7 quarts) of Liqui Moly Top Tec 6200 SAE 0W-20.

The first oil service under our ownership had been completed at approximately 110,000 km, putting roughly 9,000 km between the two services.

SERVICE SUMMARY

Mileage: Approximately 119,000 km
Service: Engine oil and filter change
Oil Used: Liqui Moly Top Tec 6200 SAE 0W-20
Oil Capacity: Approximately 7.3 L / 7.7 qt
Drain Method: Oil extractor
Oil Filter: Hengst filter
Engine: 3.0T EA839 V6
Oil Change During CAP Ownership: #2

As the performance side of the S4 developed, improving charge-air cooling became an important upgrade for the 3.0T EA839.

We removed the factory intercooler and installed a CAP 3.0T Intercooler.

The CAP intercooler features a bar-and-plate core, cast-aluminum end tanks, and over 135% more volume than the OEM unit. The larger core is designed to help reduce intake-air temperatures, pressure drop, and heat soak during repeated acceleration or higher-load driving.

Replacing the smaller factory intercooler gives the S4 a stronger cooling foundation while supporting increased airflow and power.

The factory intake was replaced with the CAP 8" Intake V2 for the B9/B9.5 Audi S4.

The system uses a massive 8-inch air filter and velocity stack to increase the volume of air available to the turbocharger. The intake was developed using CFD airflow analysis and 3D-scanned engine-bay data to make use of the available space while maintaining clean fitment.

One of the most noticeable changes is sound. The factory airbox suppresses much of the turbo and induction noise, while the larger open intake makes the turbo spool significantly more noticeable under throttle.

The intake can be used without tuning while also providing additional airflow capacity for higher-power setups.

The B9.5 S4's exterior received another major visual change with a set of silver forged wheels.

The brighter silver finish creates considerably more contrast against the body and exposed carbon fiber components than the previous wheel setup.

Although the wheel change was relatively straightforward compared with some of the larger exterior modifications, it made a major difference to the overall side profile and appearance of the car.

October brought some of the largest exterior changes to the S4. The hood, fenders, side skirts, diffuser, front lip, and front bumper were all upgraded, changing nearly every angle of the car.

The factory S4 bumper was replaced with a CAP RS4 Style Front Bumper, converting the front end to a more aggressive RS-inspired design.

The larger grille openings and more pronounced bumper styling significantly changed the appearance of the front of the car while retaining fitment for the B9.5 platform.

Combined with the other front-end upgrades, the RS4 style bumper became one of the most noticeable exterior changes on the S4.

We continued the exterior changes with CAP Carbon Fiber Side Skirts.

The side skirts extend the more aggressive styling along the lower sides of the car and help visually connect the front and rear exterior modifications.

Their exposed carbon construction also adds another carbon element to the side profile making the car look aggressive from all angles.

The factory hood was replaced with a CAP Pre-Preg Dry Carbon Fiber Vented Hood.

As one of the largest exterior panels on the vehicle, changing from the painted OEM hood to exposed dry carbon dramatically changed the appearance of the front end.

The hood uses the factory mounting locations and latch while incorporating integrated vents into the design.

The factory front fenders were also replaced with CAP Pre-Preg Dry Carbon Fiber Fenders.

These fenders use the factory mounting locations and feature integrated vents, adding both exposed carbon fiber and a more aggressive profile around the front wheel arches.

At the rear, the factory lower diffuser was replaced with the CAP Carbon Fiber Diffuser V3.

The V3 features a more aggressive shape than the original rear diffuser and adds a large exposed carbon element to the bottom of the bumper.

A CAP Gloss Black Front Lip was installed along the bottom of the front bumper to add more definition to the lower front end.

The lip follows the contours of the bumper and uses predetermined mounting points for a secure installation. We chose the gloss-black version to add contrast without making every exterior component exposed carbon fiber.

The factory mirror caps were replaced with CAP V2 Pre-Preg Dry Carbon Fiber Mirror Covers.

Unlike overlay-style covers, the V2 design directly replaces the original mirror caps, giving the carbon fiber a cleaner and more integrated appearance.

The direct-replacement design retains the factory mirror shape and mounting while adding exposed pre-preg carbon fiber to the side profile of the S4.

We installed the CAP V3 Pre-Preg Dry Carbon Fiber Spoiler on the S4.

The V3 features a more aggressive profile than the factory spoiler while following the shape of the trunk for a clean, OEM-level fitment. Its pre-preg dry carbon fiber construction adds a sharper, more performance-focused look to the rear of the car.

Installation required removing the factory spoiler, cleaning and preparing the mounting surface, and securing the CAP V3 in place with 3M tape.

Less than a month after purchasing the S4, we moved into the first performance upgrades with the exhaust system.

We replaced the factory resonated mid-section with CAP 3.0T Non-Resonated Midpipes.

The CAP system replaces the factory 2.25-inch resonated piping with a larger 2.5-inch mandrel-bent 304 stainless steel setup. The kit also incorporates heat-shielded flex sections and precision-machined flanges for a direct bolt-on installation.

Removing the factory resonators opened up the exhaust note and allowed more of the 3.0T EA839 V6 sound to come through, while the larger straight-through piping provides a less restrictive exhaust path than the stock midpipes.

It attaches after the downpipe and retains the factory catalytic converters, meaning the midpipe upgrade itself does not trigger a check-engine light. It can also be paired with the OEM downpipe, CAP downpipe, or other compatible aftermarket downpipes if the exhaust setup changes later on.

As one of the first modifications installed after purchasing the S4, the non-resonated midpipes gave the car a noticeably more aggressive exhaust note while beginning the performance side of the build.

Shortly after purchasing the S4, we completed its first oil change under CAP ownership at approximately 110,000 km.

Even though the car had only covered a few thousand kilometres since purchase, performing the service early gave us a known maintenance starting point rather than relying entirely on the previous service history.

We used an oil extractor to remove the old engine oil through the engine bay, allowing the service to be completed cleanly without removing the underbody panels. The oil filter was replaced with a Hengst filter, and the 3.0T EA839 V6 was refilled with approximately 7.3 litres (7.7 quarts) of Liqui Moly Top Tec 6200 SAE 0W-20. Audi lists the 2021 S4 3.0T oil capacity at approximately 7.3 L with a filter change.

This established the first oil service interval we could track ourselves as the S4 moved into long-term CAP maintenance, product testing, and development.

SERVICE SUMMARY

Mileage: Approximately 110,000 km
Service: Engine oil and filter change
Oil Used: Liqui Moly Top Tec 6200 SAE 0W-20
Oil Capacity: Approximately 7.3 L / 7.7 qt with filter change
Drain Method: Oil extractor
Oil Filter: Hengst filter
Engine: 3.0T EA839 V6
Oil Change During CAP Ownership: #1

On March 25, 2025, we purchased this 2021 B9.5 Audi S4 3.0T with 107,631 km on the odometer and added it to the Can Auto Performance in-house R&D fleet.

The S4 was purchased in clean, stock condition with no major modifications installed, giving us a solid starting point for documenting real-world B9.5 Audi S4 maintenance, product fitment, carbon fiber development, and future performance upgrades on the 3.0T EA839 platform.

S4 PURCHASE SUMMARY

Vehicle: 2021 B9.5 Audi S4 3.0T
Purchase Date: March 25, 2025
Mileage: 107,631 km
Engine: 3.0T EA839 Turbocharged V6
Condition at Purchase: Clean, stock condition

BASELINE INSPECTION

Before beginning any modifications, we completed a baseline inspection to document the S4's condition and identify any maintenance or mechanical concerns.

The inspection included:

• Engine oil and coolant leaks
• Brake and tire condition
• Suspension components
• Underbody condition
• Engine bay condition
• Battery condition
• Belts and hoses
• Exhaust condition
• Warning lights and fault codes

The S4 showed no visible oil or coolant leaks, no warning lights, no active fault codes, and no drivability concerns. The brakes, tires, suspension, underbody, engine bay, battery, belts, hoses, and exhaust were all found to be in good condition.

POST-INSPECTION RESULT

Overall, the S4 was clean and mechanically sound at the time of purchase. With no major faults or immediate repair concerns found during the initial inspection, the car gave us a solid stock baseline for future maintenance, fitment testing, and performance and exterior development.