Audi never sold the B8 S4 Avant in the United States, so enthusiasts build their own. This Moonlight Blue A4 Avant received the supercharged 3.0-liter V6, the seven-speed dual-clutch transmission, the sport rear differential, the subframes, and the axles from a 2012 S4, along with KW coilovers and upgraded brakes. Bidding stands at $12,000 with six days remaining at no reserve.2012 Audi A4 AvantBring a TrailerWhat it's worth right nowSwapped cars like this rarely have direct comparables, so value comes from the donor parts and the build. A B8 S4 Avant swap documented on Audizine tallied $39,300 in labor, the base Avant, and the donor S4, while shops have quoted $8,000 to $10,000 in labor alone for a similar conversion.Build quality and the California certification place this one above an ordinary A4 Avant. The S4 drivetrain, the referee approval, and the suspension and brake upgrades add real value, while 124,000 chassis miles and a narrow buyer pool hold it back, and builds like this rarely recover their cost. Fair value lands between $16,000 and $24,000, with $20,000 most likely. No reserve means it sells.2012 Audi A4 AvantBring a TrailerCondition and detailsThe conversion is thorough. The seller reports the S4 donor supplied the supercharged V6, the dual-clutch transmission, the sport rear differential, the exhaust, the cooling system, the driveshaft, the subframes, and the axles, along with the S4 grille, diffuser, mirror caps, badges, seats, steering wheel, and instrument cluster. During the swap the water pump, crank pulley, belts, valve cover gaskets, spark plugs, low-pressure fuel pump, and timing cover seals were replaced.2012 Audi A4 AvantBring a TrailerThe chassis upgrades are substantial. KW V2 coilovers, 034Motorsport strut mounts, a Meyle front control arm kit, adjustable anti-roll bars, and a strut brace sit alongside Porsche Macan front calipers, S4 rear calipers, slotted discs, ceramic pads, and stainless lines. The engine runs 034Motorsport software and the transmission an aftermarket tune, and the seller cites 034Motorsport's rating of up to 430 horsepower on 91 octane, with no dyno sheet provided.2012 Audi A4 AvantBring a TrailerPaperwork and condition need weighing. The seller states the timing chains and tensioners are original and appeared in good shape when inspected, and the car passed a California referee inspection, with the BAR label on the door jamb. The hood carries rock chips, which the seller has photographed. The 19-inch wheels were refinished. A pre-purchase inspection should include a scan of the engine and transmission software.The offerSpecificationDetailMakeAudiModelA4 Avant Premium Plus with S4 drivetrainYear2012Mileage124,000 miles shown on the chassis, drivetrain reported at 105,000 to 106,000 milesEngineSupercharged 3.0-liter V6 from a 2012 S4PowerNot specified by the seller, 034Motorsport rates its tune at up to 430 horsepowerTransmissionSeven-speed S tronic dual-clutch automaticDrive typeAll wheel drive with S4 sport rear differentialExterior colorMoonlight Blue MetallicInterior colorBlack leather and AlcantaraCurrent bid$12,000 with six days remaining, offered at no reserveInterested in this car? View the listing here.What makes the S4-swapped A4 Avant uniqueIt fills a gap Audi left. The B8 generation offered an S4 Avant in other markets but never in the United States, so American enthusiasts began converting A4 Avants with drivetrains from wrecked S4 sedans. The B8 chassis was designed to accept multiple powertrains, which makes the physical swap straightforward, though the wiring and electronics take far more work.2012 Audi A4 AvantBring a TrailerCertification is what separates good builds from risky ones. A swap that passes a California referee inspection can be smog-tested as the donor model, which makes registration far simpler in other states as well. That paperwork, combined with quality parts, is why a well-documented conversion like this one draws serious interest.My takeAt $12,000 with nine bids and six days to run at no reserve, my call is $20,000, with $24,000 possible if a wagon enthusiast values the California certification and the parts list. What makes it compelling is the thoroughness, since a full S4 drivetrain, KW coilovers, Macan front brakes, and a referee-approved conversion create the S4 Avant Audi never sold here. What tempers it is mileage and audience, because 124,000 chassis miles, original timing chains, and a buyer pool limited to swap enthusiasts weigh on the number. Confirm the referee paperwork, then bid.Disclaimer: This post is for informational purposes only. We are not a dealership or broker. All vehicle specifications, pricing, and availability are subject to change without notice. We are not responsible for typographical errors, omissions, or the accuracy of the provided information. Please verify all details directly with the seller.