'91 Audi 90 2.5L 5 cylinder AEL swap

DangerBoy

Well-known member
Joined
Jan 16, 2010
Location
Calgary
TDI
2010 BMW X5 35d, 1997 A6 Wagon AEL 2.5L TDI quattro 01E Six Speed Manual (Salvaged 2018)
Hello everyone!

A while back I did a swap with my AEL into a C4A6 Avant. It was a fantastic car in many ways but it was physically quite long and I wasn't a big fan of the handling.

Late last year I was hit and the rear of the car was damaged to the point that the car isn't really repairable although the diesel specific parts and driveline are fine, in fact the car still can be driven just the whole rearmost portion of the car is crumpled.

I have a chance to pick up yet another C4 Wagon to swap again and this would probably be the easiest route but I also found a 1991 90 20V quattro 5 speed that has a body in good shape. Granted this car isn't all that common as it is in it's own right but I figured it could be really fun to throw the AEL in.

The 90 sedan according to my research is one of the best handling 5 cylinder cars Audi made in that era (1980-1997), and is a bit lighter, narrower and shorter than the A6 I have now.

I've seen a B4 90 AEL swap on another Audi site but that car had the V6 so a bunch of custom fab to the sheetmetal was needed and I would prefer to not go that route. I have extensive CNC machining equipment so machining brackets and such is preferable to burning paint and worrying about messing up the Galvanized coating these cars have.

5 cylinder to 5 cylinder seems at least initially more favorable, though the battery looks like it would need to be relocated elsewhere. I understand the RS2 has it in the rear trunk anyway so I may be able to even find the parts from a euro salvage yard. I met a guy locally that has a 90 20V that is being worked on, I'm thinking of dragging my 3D scanning equipment to his place and scanning the engine bay to compare it against the C4 to confirm there is enough room with the AEL having the VE pump drive coming off the back of the cam.

I guess the RS2 had a 01E so the mounts to make the 01E from the C4 may be possible to find as well as suitable shift linkage assuming I can't make the C4 work. The C4 linkage is adjustable in length.

Anybody have any feedback on this project? I notice the hubs are 4 bolt on the 90 and I assume drivelines will need to be modified to work with one another. The C4 TDI has tripod inner joints on the axles so I'm not sure if I can swap hubs from the C4? I can only assume it runs larger splines and bearings? My C4 cluster comes apart inside so the extra gauges don't need to be attached to the main board but I don't have a 90 cluster to compare if the C4 could fit in the same housing? I would prefer to keep the all digital setup with autocheck from the C4. It would seem likely the B4 and C4 share the same main boards and the B3 and B4 share the same housing at least on the exterior so with enough messing around I could make a clean solution.

I picked up a 2010 BMW X535d and although that car is really fast for such a large vehicle it doesn't get anywhere near the economy the Audi did and it's an automatic, a pretty good automatic... but automatic all the same. Mine has had the alphabet delete and it is the most putrid smell I've ever seen come from a car. The Audi would smoke a little when cold but it didn't smell anything like what the BMW does.

I hope everyone is enjoying 2019 so far!
 

vtpsd

Veteran Member
Joined
Aug 15, 2013
Location
Vermont
TDI
03 jsw TDI, audi 90 AHU swap
I have a TDI 01e in my 91 90 quattro with an AHU in front of it. I used axles from a b4 body 90 fwd auto, they have the tripod joints that bolt to the TDI 01e and the outers match the 90 hubs.
 

DangerBoy

Well-known member
Joined
Jan 16, 2010
Location
Calgary
TDI
2010 BMW X5 35d, 1997 A6 Wagon AEL 2.5L TDI quattro 01E Six Speed Manual (Salvaged 2018)
Thank you for that helpful information, what did you do for the shaft that runs to the rear diff, does the 90q shaft just bolt up to the 01E? If so I'm surprised and certainly would not have bet that it would have.

Edit 1 - I just looked and found your thread on another Audi forum, you mention you were going to try the Audi 4000 shaft to go to the back but I didn't see confirmation if that is what you went with or not. Can you confirm what you went with? I'm curious if there are any physical differences in material thickness between a 4k driveline and the A6 driveline that was originally attached to this 01E.

What did you do for 01E transmission mounts? Did you find RS2 mounts?

Edit 2 - I see you found something that resembled the RS2 patterns but built by someone as opposed to cast. Did these line up well for you? I can grab a couple chunks of aluminum and machine these from solid I just need some to use for reference. Does anyone know anyone that have some of these that they would want to lend out for a few days? Because the engine mounts are already in place on the car I can always use them as a position reference and make new trans mounts to suit.

What do you think about an AEL in that car? With a larger VNT turbo (I have one pulled from a Sprinter Van) I figured this AEL with an AXG Tdi ECU and injectors would go well, or maybe aftermarket injectors if required. My understanding is the AEL shares many components with the 4 cylinder diesels of the same time period so there is no reason to think I can't do roughly 125% output of whatever is being done with the 4 cylinder engines... whether or not my flywheel and clutch can handle that is a totally different story.

When I ran this engine in the A6 in stock condition I really missed VNT from the ALH I had before.
 
Last edited:

vtpsd

Veteran Member
Joined
Aug 15, 2013
Location
Vermont
TDI
03 jsw TDI, audi 90 AHU swap
Thank you for that helpful information, what did you do for the shaft that runs to the rear diff, does the 90q shaft just bolt up to the 01E? If so I'm surprised and certainly would not have bet that it would have.

Edit 1 - I just looked and found your thread on another Audi forum, you mention you were going to try the Audi 4000 shaft to go to the back but I didn't see confirmation if that is what you went with or not. Can you confirm what you went with? I'm curious if there are any physical differences in material thickness between a 4k driveline and the A6 driveline that was originally attached to this 01E.

What did you do for 01E transmission mounts? Did you find RS2 mounts?

Edit 2 - I see you found something that resembled the RS2 patterns but built by someone as opposed to cast. Did these line up well for you? I can grab a couple chunks of aluminum and machine these from solid I just need some to use for reference. Does anyone know anyone that have some of these that they would want to lend out for a few days? Because the engine mounts are already in place on the car I can always use them as a position reference and make new trans mounts to suit.

What do you think about an AEL in that car? With a larger VNT turbo (I have one pulled from a Sprinter Van) I figured this AEL with an AXG Tdi ECU and injectors would go well, or maybe aftermarket injectors if required. My understanding is the AEL shares many components with the 4 cylinder diesels of the same time period so there is no reason to think I can't do roughly 125% output of whatever is being done with the 4 cylinder engines... whether or not my flywheel and clutch can handle that is a totally different story.

When I ran this engine in the A6 in stock condition I really missed VNT from the ALH I had before.
I did use a 4000 shaft, and it fits perfectly. I'm not sure what you mean by material thickness of the driveline, but all audi stuff of that era is so overbuilt, that there is zero strength concerns. I had a 90 quattro 20v that I put a huge turbo on and a beefy clutch and it ran 11.7@125mph on a stock driveline.

The trans mounts I used worked fine, no issues there. The shifter linkage is from a b5 s4 and is modified to work with the stock shifter on the 90.

As far as the AEL goes, I have no experience with them. I will say that, though the 90 is smaller and lighter than the a6 (and other large chassis cars), the weight balance is worse. A 5-cylinder out in front of the front axle is a lot of weight, quite a ways out. I think the larger ass of the bigger audis actually helps balance them a bit.

the 90 can be a bit frustrating because it tends to understeer pretty bad. The AHU in my car actually helped this quite a lot.

That being said, I still love 5-cylinder audis, they force you to learn how to use the scandanavian flick to get the car rotating in the corner and then power out. I'm sure one would be lots of fun with a tuned AEL, just dont expect better handing than the a6.
 
Top