Definitive Guide to Building Your VW/Audi 1.8T 20V Engine For High Horsepower

IE's complete guide to building your 1.8T 20V for power and avoiding engine block failure

    This in-depth article will educate you on the 1.8T bottom end in stock form, how to upgrade it correctly to meet your performance goals, and what IE offers for your build.

      SECTION 1

      First launched in 1996, VW's 20-Valve 1.8L Turbocharged Engine has become an icon and popular engine for tuning and building horsepower. Lovingly referred to as the 1.8T 20V, this engine has spanned many variations across generations of VW and Audi platforms. Popular vehicles include:

      • VW MK4 GTI
      • VW MK5 Jetta
      • VW MK4 GLI
      • VW B5 Passat
      • Audi 8N/MK1 TT
      • Audi 8L A3
      • Audi 8L S3
      • Audi B5 A4
      • Audi B6 A4
      • And more

      1.8T 20V 058 & 06A BLOCK TYPES

      The 1.8T 20V has been mounted transverse and longitudinal in many VW/Audi models, receiving dozens of updates and different engine codes. However, they can all be dialed down to two main generations of engine blocks, 058 and 06A.


      The first generation longitudinal 058 blocks are found in early Audi B5 A4, and VW Passat produced from 1996 until midway through 2000. 058 blocks have an internal intermediate shaft that drives the oil pump, and these use an external water pump driven by an accessory belt.


      The second generation 06A block was introduced in mid-2000 and mounted longitudinaly (A4, Passat) and transverse among many VW and Audi models. Model years 2000.5 and newer use 06A block. This new generation received many updates, most notably the timing belt-driven water pump and eliminated intermediate shaft. The oil pump was also updated to chain driven by the oil pump drive gear located on the crankshaft snout. Watch the video below on how to identify your 1.8T 20V block type:


      1.8T 20V STOCK MAIN CAPS

      Both the 06A and 058 1.8T 20V use 5 two-bolt main caps. There are 4 outer main caps and one center main cap that contains crankshaft thrust bearings (also commonly called thrust washers). Factory main caps MUST be reinstalled in the exact location and orientation as removed.

      NOTE: All 1.8T 20V main caps use M10 threads, however, the main stud lengths vary between 06A and 058 engine blocks, as noted below:

      • 06A main bolts - M10x80mm 
        Manufacturers Part Number: N90130001
      • 058 main bolts - M10x65mm
        Manufacturers Part Number: N10263801


      All 06A and 058 crankshafts are manufactured with an 86.4mm stroke. Crankshafts found in 06A platforms are forged or cast iron. 058 crankshafts are cast iron only. The timing belt drive gear and crankshaft damper are attached via a 4-bolt interface. The crankshaft trigger wheel is partially used with the crank sensor to determine engine RPM.

      NOTE: 06A and 058 Crankshafts have different trigger wheels and can not be interchanged. 

      • 06A blocks use a thin slotted-style trigger wheel.
      • 058 blocks use a thick dented-style trigger wheel.


          All 06A and 058 connecting rods measure 144mm in length on the center-to-center dimension and have a big-end journal width of 24.90mm. The connecting rod wrist pin size and taper vary depending on engine codes.

          • A tapered 19mm wrist pin (144X19) is the most common connecting rod size in 06A engine blocks.
          • 225HP 06A models (Audi TT & S3) have a non-tapered 20mm wrist pin (144X20).
          • 058 1.8T engines are most commonly found with a non-tapered 20mm wrist pin (144X20).

          1.8T 20V STOCK PISTONS

          All 1.8T 20V engines feature a stock bore size of 81mm. During its long run, 058 and 06A 1.8T engines featured factory-cast and forged pistons ranging from 9.25:1 to 9.3:1 compression ratios.

          NOTE: None of these factory pistons were designed for high horsepower, cast, or forged, and they are much less robust than forged aftermarket pistons.


          SECTION 2


          Rod bearings, main bearings, and thrust bearings must be replaced anytime you remove them or replace their components (rods, crank shaft, main caps). We highly recommend using a performance main bearing and rod bearing as power levels increase. The main advantage of performance bearings is their tri-metal composition to withstand added bearing loads ability to withstand crankshaft flex. Performance bearings are also treated with specialty coatings to reduce friction and wear further. 

          NOTE: All IE 1.8T 20V Connecting Rods are only designed for tanged style rod bearings. Tanged bearings locate and lock into the journal, reducing the chances of bearing spin and less chance of bearing failures.


          Much of the factory main bolts, head bolts, crank bolts, etc., are one-time use stretch bolts and must be replaced with either new factory replacements or aftermarket upgrades once removed. New stock bolts are adequate up to the 300+ range. At 400HP and higher, we recommend upgrading with IE/ARP hardware options. Common one-time use enge block hardware:

          • Head bolts (10x) 
          • Main studs (10x)
          • Flywheel bolts (6x)
          • Crank damper bolt (1x) 
          • Crank damper pulley to timing gear bolts (4x)


            Upgrading your engine bolts is a good practice with any performance build. However, it is highly recommended if you plan on pushing your car further than 400HP. As an added bonus, ARP hardware is reusable and does not need to be replaced if removed.

                        1.8T 20V TIMING SYSTEM UPGRADES 

                        The 1.8T timing belt system is a concerning weak point at just about any power level. The most common timing failures occur at the timing belt tensioner and drive gear. A failure at either location can result in immediate timing loss and a complete engine failure. IE timing solutions are engineered to strengthen these interfaces and help protect your newly built engine investment from an unfortunate loss.

                        SECTION 3
                        BUILDING YOUR BLOCK FOR POWER

                        A large aftermarket for the 1.8T 20V engine ranges anywhere from subtle stock engine 30HP ECU remapping all the way up to big turbo builds generating 500+HP -or more! To help you determine the best combination of parts for your power goals, we have separated each section and part upgrade recommendations by horsepower levels.  

                        300-400HP CONNECTING ROD UPGRADE W/STOCK PISTONS

                        The factory connecting rods is the primary concern and weakest point around the 300-400hp power level. The most common practice at this point is to perform a mild build with IE forged connecting rods and retain the stock pistons. This is an affordable, proven, and reliable combination for this power level. The weak points of the factory connecting rods come down to two main design limitations:

                        1. Very narrow beam design that leads to bent rods under increased torque.
                        2. Inferior metals (stock rods are usually made from sintered iron) compared to aftermarket forged rods. These weak alloys lead to broken connecting rod beams.

                        NOTE: In high mileage or worn blocks, upgrading with overbore aftermarket pistons may be necessary if the piston-to-wall clearances can not be set correctly.


                        • 144X19 Drop-In H Beam
                          This connecting rod is engineered with a tapered 19mm small end for use with the stock pistons found in most 06A blocks. Not compatible with Audi TT and S3 225HP models with 20mm non-tapered wrist pins. 
                          IE part number: IERHVA2
                        • 144X20 H Beam 
                          The early 058 blocks, along with 06A TT and S3 225HP engines, will typically require a non-tapered 20mm small-end rod to be used with stock pistons. Common 20mm wrist pins engine codes are AEB, AGU, AMK, AMU, APX, ATC, ATW, AWD, AYP, and BEA.
                          IE part number: IERHVA1

                        400-500HP CONNECTING ROD UPGRADES

                        To ensure reliable operation at power levels exceeding 400HP, replacing the connecting rods and pistons with high-performance forged upgrades is necessary. All 1.8T aftermarket piston & rod combinations offered by IE use a non-tapered 144x20mm connecting rod for robust strength.

                        • H-beam 144x20
                          Proven reliable, lightest weight
                          IE Part Number: IERHVA1

                        • Tuscan I-beam 144x20
                          Our highest quality connecting rod. Strong and reliable, superior strength-to-weight ratio, included rifle drilling for extended wrist pin life. 
                          IE Part Number: IERTVA1

                        400-500HP PISTON UPGRADES

                        Choosing the correct piston forging for your build depends on what you will use the vehicle for most of the time. Stronger material forgings excel under constant cylinder pressures, such as during extended track use. Still, they can have more expansion resulting in rattles during cold starts and increased blow-by on daily driven or weekend road warriors. 

                        NOTE: IE always recommends a slight overbore 0.5mm piston to ensure proper piston-to-wall clearances.  

                        • Mahle pistons
                          The perfect option for street builds and daily drivers. Features a strong, yet quiet piston operation with tight piston-to-wall clearances due to the low expansion alloy.

                        • JE pistons
                          IE's choice for heavy track and some road use. These tough 2618 alloy forgings are available in many compression ratios and bore size options.

                        • Wiseco pistons
                          An affordable yet good quality option for track and street use that also features a tough 2618 alloy.

                        500HP+ Connecting Rod Upgrades

                        When building past 500HP, that power is only spread across 4 cylinders, subjecting each rod to extreme pressures. The difference between reliable power and a window through your block is a rotating assembly that can withstand these loads. IE's Tuscan connecting rods have been engineered with a unique I-beam "egg" shape, which lowers stresses by as much as 20% compared to less evolved designs. This also evenly distributes the high compressive loading from high boost pressures onto the connecting rod beam, reducing piston stress and providing a stable foundation for the rod bearing.

                        • Tuscan I-beam 144x20
                          IE's highest quality connecting rod offering a superior strength-to-weight ratio, tested over 1000BHP! 
                          IE Part Number: IERTVA1

                        500HP+ STROKER PISTONS (06A ONLY)

                        Building past 500HP on a 1.8L engine requires spooling a huge turbo, which can result in severe turbo lag, even on modern "fast spooling" turbochargers. Combining 83mm overbore "stroker pistons" with a 92.8mm stroker crankshaft results in an increased displacement of 2008cc (2.0L). A stroker build yields more horsepower and torque on the same boost pressure, less chance of detonation due to lower peak cylinder pressures, faster spool, and produces more power on lower octane fuel.

                        • IE Spec Mahle Pistons
                          IE has teamed up with Mahle to design the ultimate 1.8T stroker piston set. These pistons deliver OEM fitment, OEM-like wear characteristics, ideal compression ratio, and very stout wrist pins.

                        • JE Stroker Pistons
                          Recommended for serious track/drag use, these pistons feature a lower 9.5:1 compression ratio and strong forgings ideal for extreme boost.

                        • IE Race Spec JE Stroker Pistons
                          The ultimate stroker piston used in all IE race engine builds. Features upgraded oil ring support, tool-steel wrist pins, FSR "short" skirts for reduced weight, and more!

                          500HP+ TOOL STEEL WRIST PINS

                          Why did we create a section just about wrist pins? We have seen endless builds fail due to under spec’d wrist pins. Many piston manufacturers use a lighter spec pin that works for lower horsepower builds, however with higher HP levels and raised cylinder pressures you need a stronger wrist pin. For any build using JE pistons, we recommend upgrading to the tool steel wrist pins. 

                          NOTE: Be sure to always check the material specifications and wrist pin wall thickness to avoid any pin failures!


                          500HP+ STROKER CRANK (06A ONLY)

                          Our forged stroker cranks begin as factory-new VW/Audi 2.0 FSI crankshafts. The crank is modified with a specialty press-fit oil pump drive gear in-house to fit your 06A 1.8T block. This modification produces a drop-in 2.0L crankshaft solution that requires no engine block modifications to install.

                            500HP+ BILLET MAIN CAPS (06A ONLY)

                            The stock main caps are cast and lack the rigidity required for a reliable, high-powered build. As an upgrade, we offer billet steel main caps that are far more rigid and will help to reduce main bearing wear.

                            NOTE: Requires specialty machine work. Check with your machine shop before ordering to ensure they can align bore and hone main caps.

                            500HP+ GIRDLE PLATE UPGRADE (06A ONLY)

                            Breaking into the 700+HP range? To prevent excessive main bearing wear and crank walk, consider reinforcing your 06A block with an IE girdle kit.
                            • IE Ultimate Girdle Kit
                              Our Ultimate Girdle Kit includes a set of our "Tallboy" main caps as a level and highly stable foundation for the girdle plate. Complex machining is required to be installed. The main caps stand proud of the deck and then must be machined flat. 
                              IE Part Number: IEBEVA13

                            • IE Standard Girdle Kit
                              Our Standard girdle installs with your stock or IE billet main caps to offer a more straightforward install solution with less specialized machine work. Spacers are used on the top of the main caps and then machined level to form a flat surface for the girdle plate.
                              IE Part Number: IEBEVA9

                            This concludes our complete parts guide on building a 1.8T 20V bottom end. Thanks for reading! If you have any questions or need help putting together your build, IE's Horsepower Specialists know these motors inside and out; please contact