2.5 V6 Quattro B5 - Engine Swap and Stage 2

quattrosun

Member
Joined
Oct 20, 2024
Location
Scotland
TDI
1.9 AFN; 2.5V6 AKN
I have an early (2001; AKN) audi A4 B5. The Fuel pump blew on the M6 at 200k miles. I am looking at options for replecement and figured it would be worthwhile putting in a lower mileage engine. I have sourced a 170k AKN engne from a car of the same year and model (150hp). But I also have an option to buy a lower mileage (117k) engine from a 2001 B6 quattro (180 sport).

Does anyone have info on whether this will plug in? I know it will bolt up but I am concered about coding of fuel pump/immo/clocks etc.

Advice greatly appreciated. I have already pulled the engine. I plan to upgrade injectors and turbo on whichever engine goes in :cool:.

edit* the B6 engine is complete but in a water damaged car. ECU and relays have been pulled so this is obviouly a gamble. Also interested to hear opinions on that.
 

d24tdi

Veteran Member
Joined
Jan 6, 2019
Location
MT
TDI
BHW x3, BEW x2, ALH x2, AHU, 1Z, AFB, AKN, BCZ, BDH
We never had any of these engines here in North America (officially at least) so expertise here on this forum is pretty thin, given that most members are in the US and Canada. There may be UK and European groups that would have more to add.

That said, some of us have seen them and dealt with them. My impression is that the base engine components are the same or at least interchangeable all the way from the earliest engines to the late series with rollerized valvetrain and upgraded heads. There *may* be some differences in internal components between the "low horsepower" (150hp) and "high horsepower" (163-180hp) versions for each series such as pistons and compression ratio. I believe most components are the same and the main differences throughout the entire range of the 2.5L V6 have to do with fuel pumps, injectors, turbos (hi/low HP), and then the change to roller heads for the "Bxx" code engines. Emission system components also changed along the way -- some have EGR coolers and electronic throttle flaps whereas others done, for example. Finally, there were various different engine control system iterations (early MSA, later EDC) and different ECUs and wiring harnesses to go along with them. But probably all of these things can mix and match if you know what you are doing. I do know for sure that folks have done the conversion from sliding finger to roller heads on the early engines and that is doable with no struggle.

Bottom line, if I had to guess, I would think if you wanted to change engines you could accomplish that by taking the low mile engine (which, if out of a B6 platform car, would probably be a late roller cam Bxx motor) and then transferring over all of the external components from your existing engine: wiring harness, turbo, exhaust, inlet system, etc. Not certain about fuel pump and injectors compatibility -- you would need more research there.

HOWEVER: I would also think about another point. If all that went wrong with your engine is the injection pump and the engine ran well otherwise, why not replace the failed VP pump with much less work and just continue on with your current engine? Did you have any concerns with compression, oil use, operation, etc? If not, keep in mind that the engine you have now is a known quantity that you can speak to the maintenance and functionality of. Any used engine is a gamble. It might have lower miles but you have no knowledge of its past upkeep or any issues it could have. If it's been exposed to flood damage then you have that huge variable in addition.

TDI engines, including the V6, can last many hundreds of thousands of miles with good care. The only inherent question mark on the early AKN-era V6 engines is condition of the cams and followers, depending on how well they got regular oil changes. You can look at that easily enough, and replace if needed, or even change to roller heads from the later donor motor if you really want to dig into it. By keeping your existing engine you also avoid any questions about compatibility with a different year motor and its components. The AKN is already a high-output 180hp version so a nice place to start. If it's in good condition at 200k, which it easily could be, then you could upgrade the IP and injectors on it and tune for them, and have a very nice running setup.

Just some thoughts. Mainly, envious of your B5 with a factory TDI V6! Keep it going one way or another.
 

d24tdi

Veteran Member
Joined
Jan 6, 2019
Location
MT
TDI
BHW x3, BEW x2, ALH x2, AHU, 1Z, AFB, AKN, BCZ, BDH
One more thought -- of the few members on here who do have some 2.5L V6 knowledge, @adamss24 is one of them. I am paging him here for you as he may be able to add more comments or correct any mistakes/gaps in my novice post above. :cool:
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
AKN is 150bhp, AKE is 180 Bhp. I have a b5 with an AKN Engine to which i fitted a AKE Block with cam Roller bearing cylinder heads. Everything is plug and play but you have to use suitable engine head bolts as they’re different !
Everything can be mix and matched however there is difference between vacuum pumps so you have to use the one suitable and the vacuum hose needs A bit of a fettle.
As above, if the rocker finger engine is in good shape why change ? Engines go long time with decent maintenance !
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
If you go to the trouble of changing engines then replace the exhaust manifolds, they are breaking internally and will destroy your turbocharger turbine wheel. The v6 tdi respond well to tuning, bosio race 683 nozzles and gtb2260vk/ gtb2056vl is as plug and play as possible.
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
When I rebuilt my “new” engine I was a little stubborn, plan was to buy a nice 1.9 tdi quattro sport and swap a highly tuned engine which I have on a mk2 golf. Unfortunately I didn’t find the right car at the right price and setled for a b5 v6 tdi quattro as it had better kit and was tastefully tuned as well: rnse media system with Bluetooth streaming, recaro fully electric seats, rs4 b6 steering wheel (fully working), Bose, genuine towbar, front s4 bumper and was a straight car with original paint !
I had the AKE engine in a car in my yard and many, many parts leftover from yesteryear ! Mainly I had a pair of cam roller heads (brand new) which I bought in 2004 from Jeremy Lear in uk. Trouble was they were both Left hand side cyl heads but they were complete with genuine billet camshafts (not the problematic hollow cyl heads). I also had brand new injectors with Bosio race nozzles balanced at United diesel in uk. Tuning wise I fitted a hybrid gtb2260vk and a chipped ecu which I mapped with the help of Razvan Albulescu- also member on this forum- which helped me on several projects long the years !
Soon I found out the side Intercoolers on the b5 don’t flow great and I used seat exeo cores with alloy end caps and made larger Intercoolers which they barely fit behind the s4 bumpers. I didn’t want to use a FMIC as I didn’t want to chop the genuine bumper too much and wanted to keep the stealth look as authorities are notorious with modified, old cars !
Car is a hoot to drive, plenty power and a few weeks ago i sheared bolts on a rear driveshaft...
I have upgraded brakes to rs4 genuine brakes on the rear and a mix and match 350mm front brake system with Mercedes ml v8 discs and some brembo 4 pot calipers of unknown origin (Mitsubishi evo 8 o believe) which still gives me a bit of a headache as car has upgraded alloy uprights (c5/b6) and nothing fitted properly !
While I had it I sourced a rear s4 bumper and a replica rs4 tailgate spoiler. I also fitted a 3D dash dysplay - this made the biggest impact to modernising the interior !
Wheels are Audi A8 d3 18”x 9” wide commonly known as fat 5 ! They are very heavy but look right with a 30mm drop on eibach springs and kyb SR shock absorbers. So far the car needs thicker rear antirol bar and strengthening brackets and better suspension- a kw variant is on the cards next year. I also have a gte2260vz to fit when i can find time for it, the kit is mainly built but time is scarce ! As the weather turns bad I will put it in storage for the winter as I hate cleaning salt from it’s underside- I have a Tiguan r line 4 motion to drive in bad weather !
So there you have it: my 1 year project which is becoming one too many !
 

quattrosun

Member
Joined
Oct 20, 2024
Location
Scotland
TDI
1.9 AFN; 2.5V6 AKN
Thank you both @d24tdi and @adamss24 (who has already given me some excellent advice outside the forum.

I am impressed by the knowledge on this platform and will admit I had no idea it was mainly made up of members on the other side of the pond!

I have decided to keep this as simple as i can. I plan to replace the engine like for like (the AKN at 170k is off a friend and known to be good, the original engine was leaking oil and long overdue timing belt etc).

I have discovered that tuning of these early TDIs is not straightforward and I need to find someone capable of socketing the ecu (with programmable PLCC32 chips) before I move forward with bolt on upgrades.

Since starting this thread I have found some people in the UK still tuning these cars so parts are not as scarce as I feared.

I will endeavour to update this thread as things progress but it's mid winter here in the Scottish Highlands...far too cold to be spinning spanners 🔧


Thanks again for the advice here. It's much appreciated.
 

quattrosun

Member
Joined
Oct 20, 2024
Location
Scotland
TDI
1.9 AFN; 2.5V6 AKN
Its back to below zero and snowing here so things have slowed down. I have the replacement engine on a stand ready to go back in as soon as waterpump and thermostat arrive. TB kit and all pulleys siting on the shelf.

I have pulled the clutch and it's v. worn so think I will replace this while I'm at it. I have part numbers for sachs SRE clutch and pressure plate which i will go for if I can find someone to chip my ECU. These are:

Sachs Performance Clutch Pressure Plate 883082 999754 £255 + VAT
Sachs Performance Clutch Disc 881864 999526 £210 + VAT

I have been unable to find anyone who can carry out soldering work on my ECU so it's looking like tuning is going to be more challenging than I expected. I do have someone local I can ask but I expect too complex. After this i will still need someone who has the programmer to read and write files, plus someone to actually write the custom tune...

Once the engine is timed up and back in the car i think I will throw some Allroad injectors in, do the cam cover gaskets and see how she runs.

At this stage I will be in a better position to look for a turbo and injectors and find someone to write a tune.

Unfortunately ribble valley diesels no longer stock the P970 nozzles (firad) as they were unhappy with performance. It would be good if there was something available which delivered less fuel than bosio race for these cars.

I will see if I can work out how to post pics to update some of the progress made. I have pulled and inspected exhaust manifolds (look very clean) and begun swapping over of my known good ancillaries.

Now just waiting for the sun to come back out!
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
I could probably get you a chipped ecu with stage 1 chips written on a pair of chips, however if you want a custom tune then you need a custom setup meaning loads of logs with vcds. Unless you go for exactly the same setup as I have and maybe make a “one size fits all” tune...
Good you found Sachs SRE parts numbers, it’s a good idea to replace while you’re at it however the stock clutch can take some abuse- later 2.5 tdi LUK clutch takes easy 550Nm.
I still have original Sachspressure plate on my car but with a stronger 2.0 tfsi disc on v6 hub I had. It holds well so far with no signs of slippage as yet !
 

quattrosun

Member
Joined
Oct 20, 2024
Location
Scotland
TDI
1.9 AFN; 2.5V6 AKN
That could be a good option. Nobody in the UK wanted to touch the ecu so I had been thinking about keeping it simple and just running BAU (auto) injectors with the Van Aken tuning box. But unsure if this will actually result in any extra power.

If I took you up on the offer of a chipped ECU would this take better advantage of the upgraded nozzles compared to say Steinbauer/Van Aken box?

Could I reasonably expect to get 225ish bhp from stock turbo? I now have 2 VNT20 turbos in good nick. Good news about stock clutch, I may be able to save a few quid sticking with OE.

I also have a spare AKN ecu i could trade/exchange if you did have a socketed one for sale.

No rush my end, snow and holidays have put a total hold on any deliveries and I have some work to do on the Octavia & 4runner when the weather clears up!

Cheers
 

quattrosun

Member
Joined
Oct 20, 2024
Location
Scotland
TDI
1.9 AFN; 2.5V6 AKN
Luk clutch fitted engine now ready to go back in. I have split and cleaned the original turbo and have found someone with a set of BAU injectors from an auto allroad in Scotland.

Just a Sunday update :cool:

 

d24tdi

Veteran Member
Joined
Jan 6, 2019
Location
MT
TDI
BHW x3, BEW x2, ALH x2, AHU, 1Z, AFB, AKN, BCZ, BDH
All looking very nice and good to keep up with what you are planning and assembling. Cool to see someone doing good work with the 2.5 V6! These engines are unfamiliar beasts here in North America where they were never originally sold... But I happen to now have three of them sitting on the floor here :p and am getting ready to proceed with a swap of one of them, a BCZ, into my 2001 6-speed Allroad in place of a gas engine hopefully this year. The other two, AKN and AFB, can hopefully serve as parts sources if needed but I do not have a clear feel of what combinations from which engines can work successfully together. So trying to learn as much as I can about them, and reading of projects by those across the pond like you who know them firsthand is helpful and fun to watch.

So, what is the final recipe of parts you are settling on here? BAU injectors, stock ECU and VP44 pump, your original AKN ECU and harness, stock VNT20 turbo and new stock style clutch?

Will be very interested to see how the setup comes together and how you like it. :cool:
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
I would not use old exhaust manifolds if possible, They are known to fail internally and damage the turbine wheel and geometry in the process ! Gat a fab shop to fabricate a pair of exhaust manifolds from thick 3mm stainless steel bends and pipe.
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
D24tdi: the best would be to use a bau/BDG/Bdh engine or ake with cam roller heads. They are plug and play, only need to use later cylinder head bolts as heads are shallower.
 

d24tdi

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Joined
Jan 6, 2019
Location
MT
TDI
BHW x3, BEW x2, ALH x2, AHU, 1Z, AFB, AKN, BCZ, BDH
Good to know. The BCZ is similar with roller heads but a few less HP, correct? Do you know what all the differences are between the BCZ spec and the BAU/BDG/BDH? Would a set of BAU injectors bring a BCZ up to the 180hp level of the others?

Thanks for your info! Like the OP in this thread I expect to have plenty of questions for you as I dig into the V6 engines over time.
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
Good to know. The BCZ is similar with roller heads but a few less HP, correct? Do you know what all the differences are between the BCZ spec and the BAU/BDG/BDH? Would a set of BAU injectors bring a BCZ up to the 180hp level of the others?

Thanks for your info! Like the OP in this thread I expect to have plenty of questions for you as I dig into the V6 engines over time.
Yes. As far as I know bcz is also a cam roller head design. I believe it’s a de-tuned engine from factory...I had one at some point in a c5 allroad 2004 and it didn’t make as much power as the 2001 allroad or the 2004 BAU engine ! So probably pumps and injectors might be smaller as well !
 

d24tdi

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Joined
Jan 6, 2019
Location
MT
TDI
BHW x3, BEW x2, ALH x2, AHU, 1Z, AFB, AKN, BCZ, BDH
@adamss24 thanks for the above. That sounds right based on what I have seen. I'll have to take a rocker cover off at some point and see what kind of valvetrain is in there.

It is interesting -- I have four of the 2.5L V6 engines in total; a BDH in a 2004 Passat and then three loose complete engines that were supposedly runners when pulled, an AKN, AFB, and the BCZ...... Visually, not a single one of the four is exactly the same as the others. Differences in computers (MSA vs EDC), harnesses, EGR plumbing and valves, inlet throttle (some have a vacuum ASV like an ALH and others an electronic throttle body like on a PD), and valvetrain are just the parts I can see from the outside, or already am generally aware of. Beyond that, other hardware/software differences I don't even know about probably exist. Lots to learn on these, seems they really made a lot of different versions of the 2.5L for all their different applications, so the learning curve will be long.

I wish there were a reference published somewhere that explained the differences between each engine code and what is compatible/interchangeable between which versions/generations (this would have helped the OP above too), but have never been able to find such a thing, certainly at least not in any English-speaking group where I could search for it. So all we've got is asking those in other parts of the world who are experienced with them..... like yourself. Maybe you want to write a Wiki style article that lays the whole thing out someday, or make a spreadsheet? I will help with whatever I can and will find a place to post it online! :cool:

As far as I know the total number of 2.5L V6 engine codes is pushing nearly a dozen, between the early finger follower Axx/late roller Bxx variants, and the various different output levels and engine management platforms and fuel/emissions systems, so it would be quite a project.

Don't want to distract any further from the OP's thread here but I may start one of my own later this year with further questions as I wade into the V6 projects. Thanks for sharing what you can from your side of the pond.
 
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adamss24

Veteran Member
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Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
I would use the BDH engine you have complete if possible however you need to delete the egr cooler and the motor used throttle valve/intake valve. Basically every mix of cylinder heads will work on each other block assuming you have the right vacuum pump and intake throttle valve (so. Are electric and some are mechanical/vacuum anti shudder valve. There is difference in rods and pistons, early AFB/AKN used a higher compression ratio and later AKE/BAU/BDH/BDG used a slightly lower CR hence why later engines are quieter.
B** engines Achilles heel is the hollow cams, when the timing method is “mark and pray” valves kiss the pistons and it’s a matter of time when the head will drop a valve. Another issue I found is when the egr cooler punctures internally, the engine starts to ingest coolant and it hydro locks this in effect is breaking the presses rings on the hollow cams.
Audi introduced a billet camshaft conversion but they are hard to come by and rather expensive ! I remember my first set I bought from dealer I could have bought 3-4 used good engines with the money !
Headbolts are different between rocker finger heads and cam roller heads (later havr shallower head as the cams sit lower in the cylinder head). I would also use an older AKE/AKN ecu especially the AKE had less emission restrictions: it’s not duration limited to 50/55mg/stroke as later ecu’s and AKE is a edc15 which supports flashing trough OBD.
Later ECU have more maps (higher memory as well) so they are smoother and more eco friendly !
Also early injectors had 5 holes and later were 6 holes. Diffas mentioned they all inject the same although I found BAU (euro3) makes more power compared to BDG/BDH (euro 4) albeit equal (same injectors, same pumps and same tuning).
I used Bosio race 683 in AFB/AKN injector bodies as they were designed one for the other. They idle well, make great fuel economy (6.5 L/100km) and they last long time.
There are other nozzles offerings from Recambo but they are not as consistent as Bosio and certainly don’t last as long ! I had Bosio on cars which made over 80k miles and they were perfect and smooth running !
All in all it’s a very, very good engine once you iron all bugs out and a damn good lighter and less complicated than a 3.0 tdi engine !
Early AFB year 98 on sport models had a 3.0 block which made more power than later blocks...look under the Injector pump for factory casting marks... you see a 2.9L or a 3.0 you got a rare block... every other one have 2.4/2.5 cast into the block...
 

d24tdi

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Location
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TDI
BHW x3, BEW x2, ALH x2, AHU, 1Z, AFB, AKN, BCZ, BDH
Lots of great info here, thanks!

So it sounds like the later roller valvetrain Bxx engines with hollow cams have their own issues? They resolved the lobe/lifter wear by going to roller followers but created a new problem with the cams? But it only occurs if there has been a piston-valve contact event?

If you were able to choose between an early sliding finger type Axx engine valvetrain or Bxx roller heads, which would you prefer with all things considered? Sounds like there pluses and minuses to both setups.

Do you see the early style sliding followers as able to have a good lifespan if motor oil quality and maintenance are kept up well? I have spent a fair amount of time around Volvo's old PRV V6 gas engines that had a similar reputation for cam/follower wear, with a sliding finger design not unlike the early 2.5 TDI V6. But I found with those that use of good synthetics changed on time really makes it a non-issue. The people that had problems appear to have been "value" focused Volvo owners who got used to Volvo's 4-banger tractor motors that could survive enormous abuse, running way too long on the cheapest oil around and breaking timing belts with no consequence, then when they subjected the V6 to that kind of brutal neglect it didn't respond well. Makes me wonder if someone could have good results with the early 2.5 heads if they were religious about keeping them up.

The BDH engine in my 2004 Passat runs but it has an intake thump noise, similar to a failed lobe/lifter on a PD or a bent pushrod on other engines, and you can hear just a very faint valvetrain tap too. I haven't investigated yet but am assuming maybe there's a failed hydraulic lash adjuster or a bad roller bearing in one follower. Hopefully nothing more sinister. Seems to certainly prove that the roller heads are not immune to problems though. And I know for a fact that this is not the first set of heads this motor has had on it, though can't speak to how many miles these heads have.
 

adamss24

Veteran Member
Joined
Nov 2, 2005
Location
Great Britain
TDI
audi a4 2.5 tdi 98 quatrro 6speed
On my b5 curently on 400k on the dash, the old engine lasted really well with only 3 dropped rocker fingers and very little cam wear. Cams are t hen original ones as they have Audi casting marks on them and their own part numbers. I took it off the car and built a “new engine@ because the old one was leaking oil from somewhere. The engine was so caked in oil and grease that I didn’t want to wash and see where it’s leaking from so I had parts and I’ve built another engine with bits from both: AKE block and new BAU/ BDG/BDH cylinder heads...so far so happy !
 

quattrosun

Member
Joined
Oct 20, 2024
Location
Scotland
TDI
1.9 AFN; 2.5V6 AKN
Glad I started this thread, some great knowledge exchange happening and i am sure to refer back to it.

Not much to contribute to the above but my original AKN engine made over 200k on original cams with minimal wear, certainly they were not the issue at the end of its life. It was also leaking so much oil the timing belt was almost a wet belt! Part of my decision to swap the engines over.

To stay on topic. I have the engine back in the bay but fighting to align bellhousing bolts. Luckily my other half has offered to help when the weather warms :cool:

I don't know if Adammss24 has any sage advice here? I have the trans jacked up and have managed to get the balance shaft in part way, but really struggling to get the bellhousing properly aligned. Cheers

 
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