New Audi S4 B7 Engine Transplant into an S4 B6

The S4 Project

The S4 High ShineNow the trouble begins!

After about two years in storage we drag the brand new engine out of a fabulously clean family owned and run house removal/storage company in Bangor

P1070785This was the smallest unit available at the time and it was as clean and dry inside as it was on the outside

The Smallest UnitIt took a forklift to set it safely on my bike trailer

P1070765Ratchet straps to hold it in place for the journey

P1070769To keep road dust and stones off the engine I wrapped it in a film

P1070807I met this strange man while I was there

P1070773To buy one of these brand new engines as complete as this one (I just needed to add a power steering pump, starter motor, aircon pump and flywheel) would cost about £15,000, I was lucky enough to buy this for £3,500 and it was one of six from a bankrupt kit car company, very lucky indeed

P1070818There’s that man again

IMG_20140906_114406Ready to travel so we headed to the workshop

P1070829The steel bench at the workshop for a good working height

P1070831Stow away lifting gear was so handy



P1070840I kept the engine on the factory wooden pallet as long as possible as it things so much easier to work at



Here we’re getting a feel of the tight engine and compression


The new unused exhaust port, lovely!

Exhaust Port

The compact standard exhaust manifolds were removed and a set of free flowing RS4 headers fitted, these arn’t a direct fit and had to be modified as the RS4 uses a different cylinder head with different port spacings, they really brought the engine to life and added a little more of a harsh sound and that was welcome

P1070755I had these flanges laser cut to fit the S4 heads and a well known race car manufacturer adapted the headers to suit

Laser cut exhaust flangesWelded inside


and out, they have been fitted to my car since November 2015 with no issues at all

The gearbox support brackets being attached

IMG_20140906_170620New stainless steel exhaust gaskets


The flange surface being checked


This is the first look at the headers on the engine


Sitting nice, plenty of clearance so far


But when the water cooled alternator was fitted I could see a water cooling pipe had an issue

(Since doing this mod I realised there is an easier way round this issue and that is to fit the RS4 alternator bracket, spring loaded tensioner and belt)

The original manifold had more than enough clearance


but the pipe couldn’t be fitted once the headers were installed

Alternator Bend

To get round this problem I had to modify the pipe, cut at 45º then used the small part that fits into the alternator, I used a 4″ long steel tube with a outside diameter of 12mm and an old steel I spacer tube and drilled two 12mm holes

IMG_20140916_164238When fitted together the spacer tube was plugged with a bolt at each end then cut flush

IMG_20140916_164339The holes were drilled slightly off centre


This is what I was looking for, just need a kink in the pipe to make it almost level as the air should not get trapped


Brazed to seal it up, a little kink to point it where it needs to go and the end heated and hammered to swell it to help keep the hose on when under working pressure

P1030596Now it skims across the top of the alternator


Pressure tested under water

P1030650And painted with Smoothrite to finish off


Close but not touching so needed a little more clearance


Some heat applied and a little reshaping and it was ready to fit

P1030579Heat reflective wrap for obvious reasons



IMG_20140906_181203There’s a lot more surface area with headers to give off heat, so to protect wiring, water pipes etc insulation is a must and it also helps with scavenging



P1030674A pair of RS4 engine mount heat shields were fitted

RS4:S4 Engine Mount Heat ShieldIt came with this Flywheel/ring gear item for an auto box so it had to go


and the JHMotorsport lightweight aluminium flywheel fitted


At first I went by the JHM fitting instructions which were to force it on (as it is an interference fit) but I didn’t like this idea so stopped and removed it, I found the harder crank shaft was scrapping little pieces off the flywheel that would be trapped between the crank and flywheel, this could cause the flywheel not to sit flat against the crank and cause an off balance vibration


Half an hour in a low heated oven to expand it so it would just slide on, the old fashioned way!


Lightweight Flywheel

a new B7 RS4 clutch was fitted

RS4 ClutchThat’s as far as I can go until I get the gearbox out


Just in time mum


Time to get dirty

Drain all the liquids, washer bottle water, engine coolant, engine oil, gearbox oil, power steering oil and air con gas

P1030466The step by step guide was supplied by “that man,” it helps add confidence


Headlights and bumper next


Labeling the fan control module and ambient temperature sensor plugs


Air con gas still oozing and swelling the glove


This R134a gas should not be released to the atmosphere as it may burn a hole in the chemtrails, then the man-made clouds wouldn’t form and we’d get sunshine…

Sky 1

The front panel next, all pipework and electrical connections will be marked when disconnected


disconnect cats




Inch by inch, disconnecting things as they come into view or reach


So easy to break something at this point as you feel it’s got to come out now



Funny enough the last thing to disconnect is the starter as it’s cable is very long


Whats he grinning about, it’s to go back in again!



Split the box from the block


Side by side, now we can start swapping parts



Will it ever run again?


There really is a lot going on in there


Gunk, scrub with brush then power wash the worst items

Power washed parts No Reg

The engine has been bought by an engineering company in Germany so has to be stripped


Power washed


Wrapped and ready to travel, they were in the UK buying engines here and there then came to Ireland specially for this engine


More of mums scones tea and coffee


The Gearbox

A popular upgrade for the S4 is the fitting of the RS4 B7 40/60 centre diff which replaces the S4 50/50, this puts more drive to the rear wheels makeing it easier to steer under power

I bought a low milage B7 RS4 box but the final drive ratio is different although the gear ratio’s are slightly closer so with a mix of the two I would have a one off box and the best of both worlds

Gardiner Transmissions were recomended by a friend and that was a mistake

Gardiner Transmissions 1

the manager said “I’ll get them on a bench next week, strip them and give you a call to discuss what’s required”

That was great to get this done so quick as I was imposing on my brother inlaws garage space

Loads of Gearboxes

I called “each week” to see how things were coming along

“I have a bench cleared and them on it and will get a look at them shortly” he said

After THREE weeks I’d had enough and drove up to see what was going on

Looks more like a floor than a bench to me as I found them still on the floor!!!

My 2 Boxes on floor

I put them in the boot and put it down to a bad choice

Gear Boxes Rescued

A search of the internet and I found SNJ Motors, a quick chat with Neil and I knew he was the man so I left the boxes with him


later that day I was back to collect, no messing around here

These are the unused S4 gears and the RS4 diff

S4 GearsHere is the unused S4 50/50 centre diff which is fitted to the rear end of the gearbox

RS4 40:60 Diff

That same day the box was on

Box OnA JHM Delrin gear linkage bush was next to help tighten things up

Delrin Bush

The alloy JHM’s alloy short through shifter was fitted to remove the excessive movement that is apparent with the nylon Audi item

Short Shift

The man says it’s ready!

Col Thumbs Up

It’s that time again


Now to install it


It’s nicely balanced with the chains on the two rear lifting points



At this point it can still go wrong, things can get smashed, bent or forgotten





At last


Along with two new belt pulley bearings and a new belt I added another aluminium part, the JHM Lightweight crank pulley, it may not look like much but the weight difference is amazing

New Front Pully Etc


The headers are sitting quite accessible


The RS4 B7 has two cats on each pipe, a pre-cat, and a main cat that’s high flow


Here the Pre-cats have been chopped out

RS4 Cats Removed




Their sitting as they should, nice and high



The original exhaust would restrict the flow as the bore is now too small and the silencers arn’t free flow


and it looks tired too


I picked up this nice X-pipe that will help scavenge

X pipe

Inside the cross over

X pipe Inside

Scott and I treated ourselves to a weekend of fantastic motorsport at The Goodwood Festival of Speed on June 2015 and stopped off at MIJ Exhausts in Birmingham on the way to have them make up a new stainless steel system, I had spoke to Jay (the proprietor) about the install on the phone and emailed him too


The first thing the guys done that I liked was to weld easy exhaust removal flanges


Lovely welds and a hand made system that lay flat on the floor with my X-pipe in there too


The lads took their time and done a fantastic job


One step at a time


They even made the silencers from scratch



Well fitted with plenty of ground clearance



Even though the straight through silencers are this small the sound was kept to a lovely soft tone but part of that is down to the X-pipe


The dreaded 2K drone was now a problem and I called MIJ from Goodwood and booked it in to have that issue resolved on my journey back to Ireland


The guys made up larger 6″ silencers


That helped a little but also silenced a little more, the drone was still a problem, since Jay was away having his Skyline ECU setup by professionals in Saudi I decided to leave it like that for the moment and talk to him later

I called MIJ and asked if Jay could contact me about the problem and left my number, I emailed and called again but the life time guarantee looks like internet data only, for the moment!!!

I have discovered a possible fix for the drone issue and spoke to another manufacture for costing for this, £200

I’ll get to that later.

Intake Manifold Spacers

The JHM Intake manifold spacers separate the aluminium cylinder heads from the aluminium intake manifold managing to accomplish at least two worth while improvements, (1) extending the length of the inlet tract, (2) reduce the intake air temperature, combined these make a noticeable improvement to the torque, a slightly sharper response and I’m lead to believe more power too.


I’ve had these a while now and eventually got round to fitting them, I kept my iPad nearby to refer to and it just a couple of hours.



It was interesting to see how much carbon deposite there wasn’t!



I thought it odd that the under side was sprayed black


Everything, no matter how insignificant you think it might be, all add up to make an impressive difference




The longer bolts supplied didn’t have washers like the original and I found that they wern’t going to be easy separated so I went ahead and fitted them without the washers, but as I tightened them I had a bit of a shock


even though I was being very careful it felt like I had just stripped the threads in the head!
I took the bolt back out and found the narrow head of the bolt broke off a sliver of the shoulder around the bolt hole in the manifold allowing the bolt to go a little farther into the hole, I fitted washers on all the fourteen bolts to be sure.


This is what it should look like


as expected there’s a slightly wider gap between the slam panel and the V8 – 4.2 trim



sitting a fraction higher now



To improve the handling Bilstein’s were fitted to the already lowered suspension, this gave a lovely controlled feel


Just before the next modification a set of RS4 B7 brakes were fitted.

To be continued


18 thoughts on “New Audi S4 B7 Engine Transplant into an S4 B6”

  1. This is interesting. Thanks a lot for sharing. What was the motivation for the engine swap? Did something happen to the original engine?


    1. Where’s your location?
      As soon as I heard the startup rattle I kept an eye out for an engine.
      It used quite a bit of oil through the valve guides although the compressions were all good, I came across bankruptcy stock which including 6 complete S4 engines one of which I got about the same cost as having the timing gear replaced so I just had to do more than just a straight swap, and it all was well worth while, better than I/we expected, much more powerful than we thought so the next stage should be the same again!


  2. Wow, what a lucky break coming across 6 engines! I’m in the US. Otherwise, I would offer to take one off of your hands for you. 😉 I’ll continue to follow this page. You have some of the most detailed information I’ve found about these cars.


  3. Great work here daviem – nice to see another local Audi maniac getting his hands dirty in the murky world of not bolting on go faster parts from big name vendors and defending himself from the flack of many a ‘murrican fanboy. Also admiring the accusump fix for the depressing V8 startup rattle that my 2003 B6 S4 Avant also exhibits…. then there’s the noisy wheel bearings… the rubbish clutch / caramel flywheel… the flimflam glovebox, ghosts in the sunroof switchgear and don’t get me started on the front wiper mechanism or the devils very own invention – secondary air injection.


    1. Nuge

      I appreciate your comments and your understanding of the effort that has gone into this.

      If you want to make a good car brilliant you need to put some effort in, then when you have sorted your issues you’ll not want to part with it, you know what I mean…

      I removed my front wiper mechanism recently, dismantled it and rebuilt it with grease, now it’s smooth, quite and fast.

      I have another set of converted RS4 Headers if you know someone that wants to bring their S4 to life just let me know.


  4. Hello,
    Did all of the electrical components match up? And did any of the electrical components or any other components give you any problems in regards to putting a B7 engine into a B6?
    And what were the codes of both of the engines, and which engines are compatible with the 2004 S4 sedan with a BHF 4.2?
    The engine in my B6 dropped a valve and I found a B7 4.2 for sale in Canada. I am in the USA.
    Please get back to me, thank you.


    1. Hi Safi
      The engine I removed was BBK (don’t have the code) and the engine fitted BHF 023145.
      Everything is in the same place so no modifications required, but I was prepared to swap any item that may have had an updated plug etc from my old engine to the new one but no need.
      One thing to keep in mind is (if your car is a manual) that the B6 flywheels give bother so it’s recommended to update to the B7 flywheel, I went for the solid lightweight aluminium type but there is also a lighter than the original solid steel type.
      One thing that was different was the fuel rail, the old was two pipe (return) and the new was single.
      There is a timing chain mod that you can do, I think you replace a plastic guide with a stronger RS4 item, check with JHMOTORSPORT.
      I would recommend the Accusump mod too, easier to connect before the installation.
      I have a PDF of how to remove the engine if you’d like it?
      I disconnected individual electrical connections and didn’t remove the loom.
      Best luck.


  5. Hi i had just finished swapping my b6 s4 motor for a low mileage b7 s4 motor into my 2004 b6 s4. I was wondering if you had to do anything with vag-com or ecu with the newer motor in. I tried to start the car for the first time bit it just idles very low at about 300rpms and shuts off after 10 seconds. I tried this about 6 or 7 times.


    1. Hi Marc
      Where abouts in the world are you?
      No VAG-COM or ECU changes, your engine only has sensors sending information, same sensors on the B6 engine, take a look at your fuel system, it could be pressure, you didn’t flatten a pipe?
      Check induction, coolant level, oil level and pressure. Let me know how you get on.


  6. Checked everything so far i smell fuel from the tail pipe while cranking so i assume the fuel pressure is fine. Just no spark. I will dig into this deeper but thank you for the info on vag com and ecu i was worried i would have to change the ecu.
    Pennsylvania, USA


  7. Well my Chains have jumped, I’ve managed to source a low mileage engine as mine has done 140k
    Just out of interest did the other engines get sold?
    Would love to stick a now block in!


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