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Audi A4 B6 1.8TStage 1 to Stage 4 tuning guide

The B6 A4 uses the same 1.8T 20V as the Golf GTI Mk4, mounted lengthways, with front drive or quattro. Most remaps and many engine parts are shared with the Golf, but the turbo, downpipe and intercooler are specific to the A4. Its stock outputs were 150, 163 and 190 PS, depending on the engine (BAR-TEK's engine-code list). Audi's own spec pages for this car are no longer online.

Years: 2001–2005
Engine: 1.8T 20V turbo four, lengthways (AVJ, BFB, BEX; AMB in the US)
Drive: Front-wheel drive or quattro; manual or automatic
Stock power: 150, 163 or 190 PS (tuners' figures)

Power by stage

Audi's figures for this car are no longer online, so stock is from tuners' pages. Stage 1 to 4 are the tuners' own claims, and none says whether its figure is at the engine or the wheels. The lower end of each range is usually the 150–163 PS car. Stage 4 is BAR-TEK's forged-engine package; bigger claims exist but we found no complete big-turbo kit for this car.

Stock150–190 PS

Stage 1195–225 hp Stage 2208–240 hp Stage 3247–265 hp Stage 4320+ hp

Names with an arrow go straight to that part's product page for this car. Names in a dashed outline are other brands that make the part; exact links for them are being added.

1

Software only

195–225 hp

A remap claims about 195–225 hp. APR and Unitronic both have files that run on 95 octane, which suits Israeli pumps. REVO's page for this car is gone, and RaceChip sells only a throttle-response box for it, with no power claim (its page).

Typical cost: remaps $366.95 on sale (APR); turbo-parts Kit 1 with diverter valve and filter €399; BAR-TEK Stage 1 parts €480.62 (software extra).List prices, Sept 2026, before shipping, import tax and fitting.

Stage 1 tunes compared

Tune	Fuel	Claimed power	Claimed torque	Notes
APR Stage 1	95 / 98 / 100 RON	215 hp	245 lb-ft	A4 2002–2006 and quattro 2002–2005; $366.95 on sale
Unitronic Stage 1	95 RON	205 hp	230 lb-ft	16.5 psi
Unitronic Stage 1+	98 RON	215 hp	245 lb-ft	Higher boost than Stage 1
turbo-parts Kit 1 (190)	—	225 PS	310 Nm	€399 with a modified diverter valve and filter; the 163 PS kit claims 195 PS
BAR-TEK Stage 1 (190, BEX)	102 octane recommended	215 hp	340 Nm	Parts package €480.62; software not included
Superchips Stage 1	—	196 bhp	319 Nm	Listed for the 163 bhp Cabriolet only

Before you buyFix boost leaks, coils and a worn timing belt first; Integrated Engineering calls the timing-belt tensioner "a concerning weak point at just about any power level" (its build guide). If your car is an automatic, ask about the gearbox before you tune: we found no maker page giving the torque limit of the multitronic or Tiptronic, or a gearbox tune for them.

2

Injectors, downpipe and intercooler

208–240 hp

On the A4, Stage 2 usually starts with the bigger 386 cc injectors from the Audi TT 225. With them, APR's Stage 1+ claims 235 hp and 275 lb-ft. Unitronic's Stage 2 claims 225 hp with the injectors and a downpipe, and BAR-TEK's Stage 2 package claims 240 hp.

Typical cost: turbo-parts Kit 2 with sports cat €795; Techtonics downpipe $286–$291 (no cat); front-mount intercooler €350 (turbo-parts) or CA$1,034.73 (CTS); BAR-TEK Stage 2 parts €1,478.35.List prices, Sept 2026, before shipping, import tax and fitting.

Stage 2 packages compared

Package	Fuel	Claimed power	Claimed torque	Required hardware
APR Stage 1+	95 / 98 / 100 RON	235 hp	275 lb-ft	TT225 injectors (06A906031J)
Unitronic Stage 2	—	225 hp	255 lb-ft	TT225 386 cc injectors and a downpipe
turbo-parts Kit 2 (190)	—	235 PS	330 Nm	€795 with a 200-cell sports cat; the 163 PS kit claims 208 PS
BAR-TEK Stage 2 (190, BEX)	—	240 hp	360 Nm	Parts package €1,478.35; a sports clutch "urgently" advised

Parts list

Bigger injectors required OEM TT225 06A906031J034 Motorsport injectors
APR's and Unitronic's Stage 2 files both use the TT225's 386 cc injectors.
Downpipe required Techtonics (quattro, 5-speed)Techtonics (quattro, 6-speed)Techtonics (quattro, automatic)Techtonics (front drive, 5-speed)CTS Turbo test pipe (race)
The downpipe differs by drive and gearbox. Techtonics' quattro 5-speed pipe comes without a catalyst, and CTS's test pipe is for competition use only.
Intercooler recommended CTS Turbo front-mount intercooler turbo-parts front-mount intercooler
With turbo-parts' kit the secondary-air pump has to be moved and the fog lights no longer fit.
Diverter valve recommended 034 Motorsport diverter valve
turbo-parts includes a modified valve in its Stage 1 kit, because the stock one can leak boost.
Cat-back exhaust optional Milltek cat-back systems
Milltek lists separate systems for the 163 PS 5-speed and 190 PS 6-speed quattro, $1,474–$1,671 on sale.

Before you buyA downpipe without an approved catalyst won't pass inspection. BAR-TEK "urgently" advises a sports clutch from its Stage 2 up.

3

K04-015 turbo

247–265 hp

The lengthways 1.8T takes the K04-015 turbo, not the Golf's K04-001. APR's K04-015 kit claims 247 hp and 286 lb-ft on 93 octane with exhaust work only, and Unitronic's Stage 2+ file claims 265 hp and 300 lb-ft with a K04-015 and the 386 cc injectors.

Typical cost: K04-015 turbo $2,045 (034) or APR's kit $2,608.95 on sale; turbo-parts hybrid Kit 3 €2,350.List prices, Sept 2026, before shipping, import tax and fitting.

Turbo upgrades compared

Kit	Fuel	Claimed power	Claimed torque	Notes
APR K04-015 turbo system	93 AKI	247 hp	286 lb-ft	$2,608.95 on sale; shipping "coming soon"; injectors sold separately
Unitronic Stage 2+	—	265 hp	300 lb-ft	K04-015 and 386 cc injectors; 22 psi
turbo-parts Kit 3 (hybrid)	—	260 PS	355 Nm	€2,350; needs a large intercooler, 63.5 mm exhaust and downpipe

Parts list

K04-015 or hybrid turbo required APR K04-015 kit 034 Motorsport K04-015 turbo turbo-parts hybrid FrankenTurbo F21L
034 sells the turbo alone for $2,045. FrankenTurbo's F21L is on pre-order and has no power claim.
Front-mount intercooler required CTS Turbo front-mount intercooler turbo-parts front-mount intercooler
turbo-parts' hybrid kit needs a large intercooler; CTS says its core is made for the K03 or the K04-015.

Before you buyA changed turbo and exhaust usually aren't legal without approval. On an automatic, get the shop to confirm the gearbox can take the torque before you start.

4

Built engine

320+ hp

Past about 300 hp the 1.8T needs a stronger bottom end: Integrated Engineering calls the stock rods "the primary concern and weakest point around the 300-400hp power level". BAR-TEK's forged package claims 320 hp and 405 Nm, and it recommends a 70 mm downpipe because there's little room in the tunnel. We found no complete big-turbo kit for the A4 B6.

Built-engine options compared

Package or file	Fuel	Claimed power	Claimed torque	Notes
BAR-TEK Stage 3 (forged, BEX)	—	320 hp	405 Nm	Parts package €4,776.81
BAR-TEK Stage 4 (BEX)	—	666 hp	—	Parts package €7,129.55
Unitronic big-turbo 630 cc file	—	"Up to 500HP"	—	For a GT28–GT30-class turbo with 630 cc injectors

Parts list

Forged rods required IE drop-in rods 144x19 IE rods 144x20
The block is the same 06A as the Golf's, so the same rods fit; IE's drop-in set costs $542.99.
Big turbo required Garrett GT28Garrett GT30
You'd need a custom manifold and downpipe; no maker we checked sells a complete kit for this car.

Before you buyThis is a custom build: plan for the engine, fuel system, clutch or gearbox and a custom map, not just the parts above. Ask the shop to show you a longitudinal 1.8T it has built before.

Watch: real builds

From tuners', shops' and motoring journalists' own YouTube channels. Nothing loads from YouTube until you press play.

StockCommon problems of the Audi A4 1.8T to check before you tuneStuie's Garage on YouTube

Stage 1A B6 A4 1.8T on a Stage 1+ tune, reviewedSir Merv on YouTube

Stage 3An A4 B6 1.8T with a K04 turbo on the dynotimeattack rs on YouTube

BuildHow to make 300, 400 and 500+ whp from a 1.8T 20VChris VS Cars on YouTube

Stage 4A big-turbo A4 B6 1.8T with an EFR 7163: 625 whp on the dynogurvir44 on YouTube

All build videos, by car

Questions to ask the shop

Which engine is in my car (AVJ, BFB, BEX or AMB), and do you have a file for its engine computer?
Is the file made for 95 or 98 octane, and what does it make on Israeli 95?
Is my car a manual, multitronic or Tiptronic, and how much torque will the gearbox take?
For Stage 2 and up, which downpipe and catalyst will still pass inspection?
Will you check the timing belt and tensioner, the coils and boost leaks before you tune?
For a K04-015, which injectors and intercooler do you use, and who supports the file afterwards?

Compare side by side: Audi A4 B6 1.8T vs VW Golf GTI Mk4 1.8T