Audi S3 1.8T AUG Build – 400bhp Target, Forged Internals Advice?

[Bigsamwiththe1.8bam]

Hello everyone,

TL;DR – I have a 2002 Audi S3 1.8T 20v. The original BAM engine failed and has now been replaced with a 1.8T 20v AUG. I am aiming for around 400bhp and would like to know if this is achievable without boring the engine. I understand this is a big target and involves significant work, but I would really appreciate advice from those who have done something similar.

Current vehicle and mods:

Car: 2002 Audi S3 1.8T 20v (originally BAM, now running AUG)

Cooling: Stage 2 AIRTEC intercooler
Intake: Forge induction kit
Exhaust: 3” sports cat and full exhaust system
Hoses: Full silicone hose replacement

I fully appreciate that these modifications alone will not get anywhere near the power target, but I wanted to give the full picture of where the car currently sits.

Recently purchased parts:

Garrett G25-660 turbo
14 psi external wastegate
Silicone turbo hose

Planned purchase:

Badger 5 / Catcams (yet to be ordered)

Now I am at the stage of looking at forged internals. This is where I would really value some guidance. I know forged rods are essential at this level, but when it comes to pistons, bearings, bolts etc., there are so many manufacturers all claiming to be the best, using different materials and coatings.

My main questions:

• Is 400bhp realistically achievable on the AUG without boring the block?
• Are forged rods alone sufficient, or would you strongly recommend pistons too?
• Which forged internals do you rate from real-world experience (rods, pistons, bearings, bolts)?
• Any known limitations of the AUG compared to the BAM at this power level?

I am aiming for a strong, reliable build rather than a short-lived dyno number, so longevity is important to me.

Thanks in advance for any advice — all input is very much appreciated.

 

[<tuffty/>]

AGU large port engine from an early A3 I assume you mean and not an AUM from a 2001 and up A3?

400hp is a very low figure for a G25-660... it will probably do close to that on the 14psi gate pressure tbh...

The Airtec FMIC won't be much good for 400+ tbh... they are typically maxed out of cooling efficiency beyond K04 hybrid power levels

You won't need B5 cams if your goal is 400hp.... std cams aren't much of a restriction until mid to late 400's

If you have an AUM engine then it will have crack rods and 19mm pins so you will need rods and pistons to get 20mm pins.. if you have an AGU then these are 20mm pinned rods... OE pistons are good for around 400/450hp but you might be best checking the bores for wear and ovality and you may need to replace the rings (gapped if needed) and give the bores a light hone

if changing pistons you will want a rebore... do not fit aftermarket pistons using a std bore size.. apart from wear and tear on the bores the materials used for most aftermarket pistons require different bore tolerances so its a false economy to not have the block bored.

No mention of the head... if AGU then that will have a large port head... AUM/BAM is small port... large port not really required for 500hp and small port better for 400hp levels... if you used the AGU large port head I assume you used the VVT from the BAM head?... please note that the non vvt inlet cam profile differs slightly too the VVT profile... there are also differences for the cam timing sensor wheel... VVT has a different wheel to the VVT so you will need to run the BAM one...

Also the AMK/BAM (K04 turbo'd engines) have additional shims on the exhaust valves....

20v heads typically suffer from worn exhaust guides after about 50k miles so you would need to get those looked at... obvs new stem seals while you are in there... for a high power build on a budget then you want to change the exhaust valves at least to inconel (supertech etc) and fit a set of cat cam gold springs as the RPM will need to be lifted to make use of the bigger turbo

ARP head studs are recommended... if you are doing a full build including the mains bearings then you should use either ARP studs or I believe some people use genuine TFSI mains bolts as they are supposed to be stronger than OE 20v but tbh ARP is probably the better bet

Use ACL bearing shells

Use I beam not H beam rods (rifle drilled for small end lubrication)

Basically have a look at Badger 5's engine parts page on their shop as everything listed there is tried and tested on the best 1.8t builds in the country

Engine Parts

badger5.co.uk

...also you may want to consider going over to a stand alone ECU like Ignitron for a big turbo build as the OE ECU while it can be tuned does not run anywhere near as nicely as Ignitron will

<tuffty/>