Tuning the VW 1.8 Turbo engine

"The 1.8T is one of my favorite engines!"

VAG 1.8T engine Volkswagen/SEAT/Audi: 150bhp-240 bhp from the factory.

The 1781 cubic centimeters in this 20 Valve turbo charged engine represents what must be one of the most tunable mass produced engines around today.

The 20 valves are arranged as 3 intakes and 2 exhaust valves per cylinder. (The exhaust valves are larger and the intake design makes the engine an efficient one).

We have an updated version of this engine tuning article in our Audi section, so please see the updated article for 1.8T Tuning.

The compression ratio is set to 9.5:1, but,  in the 170bhp engine compression ratio is 9.3:1 and a slightly lower 9:1:1 in the 240 bhp versions, which although high for a turbo gives plenty of low down torque.

Technical information of this engine: Bore size of 81mm (3.19in) a Stroke of 86.4mm (3.40in) and a Rod Length of 144mm

The peak power band is between 2000 and 5000 rpm, and delivers good fuel economy as well around 34-38mpg.

The turbo delivers a boost pressure of 8.7 psi or .6 bar on most variants of this engine although the 180bhp engines run 11.6 psi from 2002.

The standard cast iron engine block can handle power up to 240 in factory tune and many owners have reported much higher power gains than that.

The most common turbos fitted are the KO3 (150-180 bhp) and KO4 (210-240).

A remap on a standard engine will typically yield around 40-50bhp increase, and, with the addition of a higher capacity turbo, a freer flowing intercooler and efficient induction and exhaust design, power gains to around 300bhp-350bhp are possible.

Expect to have to upgrade the clutch when increasing the power of the engine or the clutch life will be dramatically reduced.

The pistons are forged aluminium Mahle, with fracture split forged steel connecting rods mated to a forged crankshaft which is capable of handling far more that the mild 150bhp tune.

Volkswagen 1.8T engines represents one of the most easily tunable engines today.

The engine code is found at the top part of the engine near the valve cover on the side etched into the head. The engine codes are

  • Small Port size head Engine Codes:
    ADR, AMB, AMU, APT, APU, ARG, ATC, ATW, AWM, AWP, BEA
  • Large Port size Head Engine Codes: Typically 97-99:
    AEB, AGU, AFY

See our video which covers all the principles of tuning the 1.8T engine.

Best Engine Mods for your car

  1. Mapping - remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.

Typical stage 1 mods often include: Remap, Panel air filter, Sports exhaust, Lighter flywheel,

Typical stage 2 mods often include: Power/Sport clutch, Ported and polished head, fuel pump upgrades, Fast road cam, high flow fuel injector, Fast road camshaft.

Typical stage 3 mods often include:
Upgrading forced induction (hybrid turbo or KO4 upgrade), Internal engine upgrades for stronger parts (pistons/head/valves), Competition cam, Engine balancing.

Porting and flowing the head is really effective, and we recommend a 5 angle valve job to maximise flow into the engine and this makes the engine give better low end torque and increases it's efficiency.

A fast road camshaft is one of the most effective mods you can do on the 1.8T engine, apart from a remap, or turbo upgrade.

The competition cams are not great at low RPM so driving in traffic can be tricky but a fast road cam works really well.

An obvious upgrade path for KO3 turbo owners is to swap in a KO4 turbo.

The software take a lot of getting right for the maximum power gains but interestingly most people report that the KO4 turbo runs fine on the standard manufacturers ECU Map.

You will need to ensure that the engine is not starved of fuel so will need to uprate the fuelling.

If you find you suffer from flat spots and surges after your modified parts you should check the fuelling and try a higher octane fuel as well. Larger injectors will enable you to supply sufficient fuel to the engine.

A fuel pump will only deliver a finite amount of fuel, so you may need to uprate this if your injectors are demanding more fuel.

If you balance and blueprint the engine you'll be able to raise the redline, and this should give quite a bit more power, if your turbo can supply enough air.

It is usually easier to remap the standard KO3 engine and set the boost to 1 bar.

Fitting the KO4 turbo changes the characteristics of the engine and gives a more rewarding drive, pulling hard, and even when the KO3 runs out of steam around 5000rpm the KO4 still delivers good power.

You may think the KO4 is more prone to lag but this is not the case and both are very similar as far as low down low boost power goes.

We've found some hybrid turbos around, which use the KO3 case, but reworked internals and these are great turbos.

There are also twin scroll turbos around now which are a great innovation.

Weak spots - the engine oil must be fully synthetic and changed at the correct service intervals.

Use of the wrong type of oil will cause the oil pump to seize causing a catastrophic loss of oil pressure and engine failure.

The engine takes 4.35 l of fully synthetic 5w-40 oil  either Castrol 5w40 synthetic or motul 5w40 synthetic depending on engine code. (Interestingly the Audi variants of this engine require 5w30 fully synthetic oil.)

Some users have reported problems with early coil packs but most of these will have been replaced now and newer coil packs do not seem to have any problems.

The ecu will not appreciate a blow off valve venting to the atmosphere and this will cause an error code to appear on a diagnostic.

Partially venting BOV's are available but we have not had any feedback on their effectiveness on the VAG 1.8T engines.

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3 Responses to “Tuning the VAG 1.8T KO3 & KO4.”

  1. jack says:

    Hi, I wish to know about the Audi TT petrole engine 1.8 Turbo 5 (year 2000)
    are used in what other Cars models by VW & Audi,Thanks.

  2. Mhd albaali says:

    thanks for the useful information, though i would like to ask: if replacing a KO3 turbo with a KO4 only would be useful to an AGU unit and how much hp could be gained from that?….. many thanks in advance!

  3. Francisco says:

    Depends on several factors:
    Garret GT3071R with 3076 shaft
    Turbo pressure (assuming 1,2kG)
    Fuel (assuming Ethanol E85)
    Exhaust and downpipe (assuming 3″)
    You easily will get 360HP on the wheels at dyno

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