Tuning the Audi 1.8T engine.

"Audi you make it go so fast?"

VAG 1.8T 20v Petrol engine as fitted to Volkswagen/SEAT/Audi cars: 150-240 bhp from the factory.

The 1781 cubic centimeters in this 20 Valve turbo charged engine represents what must still be one of the most tunable engines around today and is found in family cars like the A3 and A4 and on sports oriented models like the TT, and the S3.

The fact these engines can be tuned to such extremes indicates the versatility of them.

The 20 valves are arranged with 3 intake valves and 2 exhaust valves per cylinder.

1.8T Tech guide

(The exhaust valves are somewhat larger than the intake and this intake configuration makes the engine an efficient one).

The compression ratio is set to 9.5:1, but,  a slightly lower 9:1:1 in the 240 bhp versions of this engine, 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 is solidly constructed and can handle power levels up to 240bhp in factory tune and many owners have reported much higher power gains than that.

The most common turbos fitted are the KO3 & KO3s (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 300-350bhp 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 TT aftermarket clutches are likely to be the best option.

The stronger engines had pistons from forged aluminum 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 and retaining reliability.

When planning upgrades it is worth finding out if your engine has the forged components already. (Generally speaking the AGU APH ARX AUM AVC AVJ AWC AWD AWU AWV AWW BFB AJQ APP ARY AUQ BEX AMK APY APX and BAM came with forged cranks but there are some exceptions to this list.)

The 1.8T engine as fitted by Audi is arguably 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 so you might have to clean it off as the stamp often gets covered in grime.

The engine codes are (This list is not exhaustive and covers the most popular engines, some engines were only available in selected markets.)

Large Port size Head Engine Codes: Typically 97-99: AEB, AGU, AFY, AJH

1.8 T Turbos

The following engines were typically fitted with the KO4 turbo as standard and were small port engines: APY, AMK, APX, BAM, BFV

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

It is usually easier to remap the standard KO3 engine and set the boost to 1 bar as per a number of aftermarket Audi tuners standard remaps. but the KO4 changes the characteristics of the engine and gives a more rewarding drive pulling hard and when the KO3 starts to run out of steam around 5000 rpm the KO4 still delivers good power so is the logical track day or drag strip turbo.

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. A number of aftermarket turbos are available which fit the standard down pipe and they can be tailor made to suit your requirements with many drivers looking for a mix of economy below 2500 rpm and massive power gains from 3000 to 5500.

1.8T weak spots and problem areas.

Weak spots - the engine oil used in your Audi must be fully synthetic and changed at the correct service intervals (check your owners manual for details but it is typically a long life Audi service of around 24,000 miles or standard service around 9000 miles.

This depends on how the car is driven so if you are are a heavy footed driver or make lots of short journeys on a cold engine the service interval is reduced from these figures).

Use of the wrong type of oil will cause the oil pump to seize causing a catastrophic loss of oil pressure and engine failure and unless you can prove that the correct oil grade was used the warranty is invalidated.

Audi long life oil lasts for up to 24,000 miles but all other synthetics are only recommended for 9000 miles. It seems sensible to change the oil & filter frequently as metal particles can cause damage to the engine as they become suspended in the oil. The engine takes 4.35 litres of fully synthetic 5w-30 oil (Audi long life oil must conform to VW 504 00 or 507 00 (Castrol SLX long life III is the special Audi approved 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.

Fitting a blow off valve or dump valve can cause problems with the engine management as there is a loss of system pressure. There are now VAG friendly dump valves that also recirculate the lost pressure keeping the ECU happy.

The air flow sensor can become soiled particularly if you use a filter which is impregnated with oil. Take off the air flow sensor and clean with a IPA based solvent if you notice any hesitation or problems that can be assigned to a faulty MAF.

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Your Constructive comments on this article

27 Responses to “1.8T engine Tuning”

  1. Nathan says:

    I build a auditt which we stroked to a 2.1L and fitted a t3 t4 hybrid turbo. I am sitting with a huge problem in that the throttle closes itself under hard boost. Is there any way of solving this problem. On the dyno the car acts normal but on the road it starts having a mind of its own.

    • TorqueCars says:

      It’s hard to tell without running a full diagnostic but here are some things to bear in mind. It sounds like the car is going into limp home mode or the anti knock protection is kicking in. I suspect you need better fuelling. Did you uprate the fuel pump and injectors? On the dyno the air intake is usually warmer therefore less oxygen is available on the open road the air intake is much cooler and it could just be the difference between the car running lean or not. Check the boost levels when this happens and see what happens to the fuelling.

      This topic is better discussed in our forum where you’ll get the benefit of all our Audi tuners opinions and advice.

  2. Ken Cain says:

    I used Red Line Synthetic oil in my 2000 Audi TT (1.8 turbo). I run my car hard often and have had not problems with its performance. And as soon as I get a second car to become my daily driver I will strip the TT down and build it up for time attacks while staying with the 1.8 turbo engine. A friend once told me that Audi’s will surprise you. He was right about that. Life fast and live free.

  3. bheki says:

    hi there i have an 1.8t agu its been remapped boosting 1.3 bar and exhaust system of 63mm from turbo , now my problem its got a big flat sport and jerks on low rev all my turbo hoses are ok what can be the problem its

    • Barry says:

      The jerk is from too much boost at low RPMs. I had the same problem with a stock 1.8t Passat. I had it worked on and they pinched the line to the waste gate and it was running full boost all the time. It was like some was on and off the gas pedal until about 3000 rpm then it would take of and I mean nearly twice as fast as when the hose wasn’t pinched. Hopes this helps.

  4. Ken MacLeod says:

    Have ’98 A4 with 1.8 liter engine. Almost destroyed engine. O-ring between oil filter flange and turbo oil cooler assembly dried out and leaked badly. Easy fix, and nothing but a cheap o-ring.
    Owners of older models Audis should replace this o-ring.
    Unit located where oil filter screws on, between the filter and the engine oil flange.

  5. ali says:

    can i fit the audi S3 engine in to my audi A.3 1.8L

  6. Chris Bendure says:

    4.35 liters would blow the deals on your engine. My car takes 3 3/4 quarts at the most. Thats right to the top line on the dipstick. It’s a 2003 1.8 turbo a4. If I put 4.35 liters oil in it would be over flowing out of it! U guys should check that!

    • TorqueCars says:

      There would appear to be some differences between these engines across the range. Perhaps the Transverse A4 1.8’s have a slightly different sump capacity, we will reflect this point in the article. A larger capacity oil filter was recommended in 2001 on the A4’s dated 96-06 see the Audi Technical service bulletin for details of this 17/04/01.

  7. jerome. Roberts says:

    where is the boost valve locate on the APU engine

  8. michael says:

    hi great forum was just wondering if i would gain even more power from putting tt injectors along with the ko4 t into my passat b5 1.8 t thanks for the info supperb

  9. Rick says:

    I am building a 1.8t endurance roadracer for the Chump series. It’s in a 2000 a4 and have the following questions:
    1. I’m not certain that the motor in the car is the original. It’s an ATW. Question I have is “did the ATW come in the 2000 a4”?
    2. Next, I’m looking for a spare motor. What codes are compatible with ATW?
    Can i use any engine code just as long as I get the ECU that comes with it?

  10. Ricky says:

    I noticed that your list does not include the “BFB” head engine code. Is there a reason for this? Also, are you certain that the connecting rods are forged? I’ve read articles stating the opposite.

    • TorqueCars says:

      We couldn’t cover every engine code, but we’ve tried to cover the most popular blocks where reliable data could be sourced. NB: Not all engines had forged components which explains the discrepancies you’ve pointed out. Forged components cannot be identified on the engine code alone, the year of manufacture also comes into play.

  11. Phill says:

    Hi, I have a NB 150bhp it’s been remapped, I’m fitting a K04 turbo & FMIC I was just wondering if fitting the 225bhp injectors & the 4 bar fuel req it wound make a difference or just over fuel it’s self ?

    Cheers phill

  12. Tommy says:

    Fantastic article in plain english:)
    I have a 1.8t with a k03, id like to changed to a k04 but haven’t got lots of money, there are cheap (200ish) k04 turbos on ebay etc… are these cheap for a reason? ie build quality or to VAG just want to much for OEM?
    many thanks

    • TorqueCars says:

      We have heard of cheap import turbos suffering from premature failure, sadly the quality control and casting of these cheap imported turbos can often be far from ideal. Not that all are bad, but we would tend to source a local reconditioned one or used one with some kind of warranty. You do get what you pay for.

  13. Jure says:

    Fantastic article, thanks for putting it together. I have a 1.8 tfsi (160 ps) engine and thinking of mapping it to say 210 bhp and 300 NM torque, which is what most tunners offer as stage1. Do you think this would require a turbo and clutch upgrade to retain reliability? The stock turbo is K03 on my unit. Appreciate your input.

    • James says:

      I have a 1.8T ’11 A3 and also looked at remaps. The Bluefin looks like a good option but I’m also keen to find out if I’ll be able to maintain reliability. It’s still under manufacturer warranty so wanted to check before doing anything. According to the Superchips website it’ll give a 47 bhp increase which I assume would be within the thresholds of what the engine/clutch could handle without any upgrade. The article says that engine puts out up to 240 so hopefully my assumptions are correct! The only other question is whether, if I buy and install a Bluefin remap, Audi would know that I have done so use it for a bit and return to normal map before putting in for a service?

    • Tam says:

      Have you remapped using bluefin? I’m thinking of this for my audi

  14. tony says:

    hi could you tell me if the 1.8t sport 2001 avj engine has these forged rods please

  15. Matt says:

    Just had my A4 1.8T remapped, stage1, it wasn’t dyno’d but the nice chap at the tuning centre said its up to about 195ish from 150 bhp. So I’ve been driving around a couple of days now and the car has just been transformed into a bullet on wheels, it was nippy in the first place but like the nice chap at the tuning centre says the stage one is the best map to do for the money and the gains you achieve are excellent!! Stage2 & 3 require some hardware.
    Now I’ve got no complaints but just a couple of questions.
    What boost psi would it be running on this stage1
    And should I preorder a clutch and if so would the TT 225 clutch fit?
    It has the AVJ lump in it with a aluminium forge type DV which I can change the spring, hence the question about boost pressure.
    And I can tell you this car is fast I’m just so shocked at that a bit of computer wizardry can turn it into a beast!! I love it, power band from 2500 up and just keeps pulling!!
    Great info by the way and glad to know that my AVJ engine is a strong one.

  16. Dante says:


    Just purchased a Leon mk1 AUQ and I love it, but I want a remap, should I also change the exhaust + intake, or the stage 1 works fine with the stock parts?

    Also thanks for the post, very helpful.


  17. Shayden says:

    Hi guys…
    I would like to know if and Audi ADR cylinder head will fit on an APT bottom end.

  18. Patrick says:

    I have a 1999 A4 Quattro 1.8L turbo. Can anyone help me with how to set the timing on both crankshaft and camshaft pulleys. Setting timing from scratch as if the belt broke. Where are the marks? thanks \!!!

    • TorqueCars says:

      I’ll be surprised if the valves are not damaged, have you done a compression test? I wouldn’t try this at home, take it to an experienced mechanic, you can’t play around with timing belts and pulleys without causing a lot of damage if you get it wrong. The main timing mark is on the crank, then you need to find TDC and set the cams accordingly.

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