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Audi S4 Tuning Guide

S4 Tuning / S4 Buying Guide


This tuning guide is based on the B5 S4 with the 2.7litre twin turbo motor. These cars can be now picked up for between 3 to approx 8000GBP, which, given the fact that its engine is based on the humongously more expensive RS4, makes the S4 a bit of a bargain. The S4’s 2.7litre turbo can be tuned to over 500bhp on standard engine internals making it possibly one of the cheapest 500bhp cars you can buy. Here’s how to get an S4 to the magic 500bhp mark

S4 Tuning / S4 Buying Guide

S4 Tuning – Brakes

The standard S4 brakes could be better. They fade after just one big stop. This can be largely sorted with the use of some high quality performance brake pads. If this still isn’t enough for you the next step is to increase the diameter of the brake discs. There are a number of ways of doing this and all methods require upgrading the wheels from 17s to 18s. HiSpec make a kit for 1500quid and this should be up to the most extreme track use. There is also an option of fitting the B7 RS4 brakes which use 8pot Brembo calipers. Speak to MRC for more details.

For the rear brakes a easy option is to get S8 caliper brackets which gives the ability to fit S8 discs. Calipers are extremely long lasting with the only really problem coming from the ABS electronics. The ABS circuit board can be reconditioned for a few hundred quid but if you want to replace the complete module this will set you back about a grand.


Related Pages:
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Audi Performance Exhaust Manufacturers
Turbo replacement parts

Turbo Manifolds

Turbo diverter valves

Suspension upgrades

Upgraded suspension bushes

Engine mounts

Exhaust systems

Ignition parts
S4 Tuning / S4 Buying Guide

S4 Tuning – Suspension

S4s with over 60-70 thousand miles ask if the front suspension arms have been replaced. There are 8 in total, 4 each side and when the ball joints wear out you have to buy a complete arm. The full set will cost around 600GBP. Any rattling over bumps is most likely the anti roll bar links which are much cheaper. Springs and dampers can last for a 150000miles.

One of the most cost effective improvements that can be made is H&R anti roll bars. The ride comfort stays the same but the car corners flatter and they give the S4 a more neutral balance.

For track days a coil over kit is the way to go, Bilstein and H&R both make a kit for the S4.

MRC Tuning S4, my word, this flies

Just to put it into perspective, this S4, according to the video does 100-120 in just over 3 seconds, the new Mazda RX-8 R3 with 228bhp does it in 10seconds, the Lambo LP560-4 and Porsche 997 GT2 do 100-120 in 3 seconds. For the Lambo you’ll need 147,000GBP, for the GT2 131,000GBP, for the S4 you don’t. Rapid doesn’t really cover it. If you cant wait for the link at the bottom which takes you to S4s for sale in the UK. Its here  S4s for sale on Autotrader

S4s for sale on PistonHeads

S4 Tuning – Bodywork

The shell is galvanised so there shouldn’t be any rust. If there is rust it most likely be under the handle trim on the boot. If there is rust then suspect an accident repair, likewise if the doors don’t shut cleanly.

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S4 Tuning – Engine

The 2.7l V6 Twin Turbo motor comes with 265bhp as standard. To get over 300bhp a simple remap to up the boost from 0.5-0.7 to 0.9-1.2bar, MRC can do this for you for 400GBP. Combine the remap with a performance exhaust system and larger, second-hand RS4 intercoolers and the motor will be making around 330bhp. The pre cats can be removed and the car will still pass the MOT. Milltek, Supersprint and Scorpion make exhausts for the S4.

340bhp is about the limit of the standard K03 blowers. The next step up the turbo ladder is the K04 turbo. They are nearly the same price as the K03 turbos so its a no brainer upgrade. The K04 can supply enough air for 370bhp with a remap and the standard injectors and fuel pump. Uprated the fuel pump to a Bosch motorsport item and the injectors to 440cc capacity squirters and your looking at 450bhp with a suitable remap.

ebay has listings for K04 turbo upgrades although data on inducer and exducer sizes is a bit think on the ground. The “upgrades” appear to have the same dimensions as the stock RS4 turbos. You can find them here

For the magic 500bhp 600cc injectors are required, hybrid K04s, tubular or ported original manifolds, thicker head gasket and a 3inch bore exhaust. The RS4 has uprated internals over the S4 but it is believed the S4 internals are hugely over engineered anyway, the RS4 internals are overkill.

This website has an exhaustive description of the turbo upgrade options available for the S4

Although the engine is girder strong, the bits that are hanging off it are not. The biggest thing to look at  on the FULL service history is the service intervals. Fleet cars had a variable service period which could be as long as 20.000 miles which is no good for the S4.  Have a butchers through the filler cap and you can just about see the cam lobes, check them for wear and listen for rattles. Sorting them out is 3 and half large.

What your looking for is an Audi NON variable service history and best of all, a service history from a VAG specialist garage. While your checking the cam lobes, have a look at the underside of the filler cap, if it’s black and burnt then the engine has been abused.

MRC Audi S4 – Click photo to visit the MRC website

Apart from the service intervals, oil changes and the cam lobes there are 3 major areas which can cause and/or lead to stress inducing bills.

1. Boost leaks, not a problem in itself but they can lead to the turbos over speeding as they try and maintain the programmed pressure. Woo ooo like noises from the turbos can point to them needing changing in the not to distant future. Screaming sounds from the turbos will mean they are shot. It’s 1200GBP plus VAT to change the turbos.

2. MAF sensor, if this fails the hotter exhaust gases can destroy the lambda and EGT sensors, 106 per side for the lambda and 139 for the EGT sensors. 80GBP for the MAF.

3. Recirculating boost valves, the diaphragm can fail leading to loss of boost and therefore power. S3 ones can be used as replacements as they are only 24GBP. Uprated valves are also available from Forge Motorsport.

These 3 faults can get by a Audi main dealer service as they don’t trigger fault codes.

Cambelts, used to be changed every 80k but its down to 60k now, better safe than sorry on this. 695GBP for changing the cam belts when its done by MRC but they change nearly every component that comes into contact with the belt as well including the water pump.

The exhaust manifolds have push fit pipes inside them which can come loose and rattle. Manifolds are not expensive due to many owners upgrading to tubular items, its the labour that costs here, 950GBP of it. Its a good opportunity to upgrade the turbo and change the cambelts while your doing the manifolds.

S4 Tuning – Transmission

Civil engineering more than automotive engineering went on in this area. The standard box is good for 650bhp just change the oil every 100k or 3 years to keep it fresh. If there is any area that can be found wanting its the clutch. 370bhp is the standard clutch’s limit. Fortunately the RS4 clutch is a straight swap and this can hold 500bhp with no problems. The clutch can be changed when your changing the turbos.

S4 Tuning – Interior

Audi are famous for being the best at comfortable and ergonomic interiors and the S4 is no exception. The S4 came with coloured inserts on the seats which breaks up the dark interior. The build quality of the interior means that the mileage of the car shouldn’t be obvious as it wears so well. But as always check the drivers seat bolster and steering wheel for a clue if the mileage on the clock matches with what your seeing on the interior.

The standard radio can play up with volume knob going on sporadic holidays. If its on the fritz a new radio is required as it cannot be repaired.

The centre LCD display on the dash in between he rev counter and the speedo can loose a few lines of pixels. MRC have now found someone who can repair it.

Audi S4 Tech Spec:

Engine: 2.7 V6 Twin Turbo 30Valve

Transmission: 6 Speed, 4wd, Torsen Centre Diff and Electronically Locking Front and Rear Diffs.

Brakes: 321mm Front Discs – 255mm Rear Discs with ABS

Suspension: Macpherson Strut

S4s for sale on Autotrader

Related Links
Practical Performance Car Magazine for the full S4 tuning and buying article (June 2008)

Audi S4s for sale on EBay

Audi S4s for sale on EBay USA


Find performance parts on ebay

This page was last modified Jun 20, 2021 @ 1:36 pm

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2 thoughts on “Audi S4 Tuning Guide

  1. Hi Richard could you please tell me where I can get the egt sensors for my b5 s4 at the price mentioned on your site …
    What a great read you’ve made with brilliant to the point info on this great car ..


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