Need help with B7 3.2 to B6 4.2 swap [Archive]

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MoneyAllTheTime

02-05-2021, 03:22 PM

Hey long time lurker here, I usually find my answers on here from another post so I rarely ever post myself but I have a project in mind and would like your help. I currently own a C5 Allroad, B7 A4 3.2 Avant and most recently a B6 S4. I have had my 3.2 fail before with tensioner issues so it was replaced and I'm honestly kind of bored with it. I know the 2.7T is the go-to swap but I have one in my Allroad and its very fun indeed but enjoy the exhaust note of the S4. I picked up the B6 S4 for a very good price but I'm an Avant kinda guy so here's my idea, swap the 4.2 BHF from my S4 into my A4... both cars are tip 09L transmission from the info I gathered. Besides ECU and harness what else would have to come off the S4 to make this happen? I've been reading SSP trying to figure out what parts are interchangeable and have been searching far and wide to see if its been done before. Any insight is much appreciated.

Gosser

02-05-2021, 03:54 PM

All I know is you will definitely want the S4 specific motor mount to subframe bracket, the piece the looks like this(this is a 1.8, not the same as a B6s4):
https://live.staticflickr.com/65535/50741361667_8c708545e9_c.jpg

I would grab the ECU, cluster and immo id48 chip/key. I would also use the S4 gear box as well, since the 3.2 TCU is not separate, where the B6/B7 S4s were still separate TCUs. Begs the question on what the FD ratio is for the B6S4. I know the B7 3.2 auto is 3.10, but not sure what the S4 is.

The 4.2 doesnt get much love, but I love it! Good luck!

MoneyAllTheTime

02-05-2021, 04:01 PM

I have both cars so everything is there for the taking. I read that the final drive ratio was 3.539 for both.

Gosser

02-05-2021, 05:39 PM

When I disassembled my 2006 A4 3.2 AT rear diff, I counted a a 31 ring to 10 pinion gear:
https://live.staticflickr.com/65535/50113651111_305a2dcd00_c.jpg
Yellow striped pinion was from my 3.2, the one in the diff is from a B6S4 MT 3.889:
https://live.staticflickr.com/65535/50113082513_9ae427bca0_c.jpg

I searched high and low for the 3.2 AT final drive, but couldnt find anything, so I took it apart after swapping it for a 4.11. I'll check my AT rear diff PR code, maybe there are different FDs for the 3.2, but I highly doubt it.

MoneyAllTheTime

02-05-2021, 08:27 PM

Here's where i got those numbers
A4

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.audiworld.com/model/a4/06/A4%2520sedan%2520v6%2520tech.pdf&ved=2ahUKEwjMteTWtNTuAhUOVN8KHWz7DLMQFjABegQIARAB&usg=AOvVaw1sNXsEx3nX_dsd9FBJ-nH1

S4

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.audiworld.com/model/s4/04/s4sedan.pdf&ved=2ahUKEwiis8-ctdTuAhXDMVkFHcnuC-kQFjAAegQIARAB&usg=AOvVaw3mYd9KpGGpcCJNsiHOtYV1

Dondbg

02-05-2021, 10:53 PM

the shaft and rear diff.
Check the axels are they same parts

Don’t throw the S4 until you are done [emoji846]

MoneyAllTheTime

02-06-2021, 03:39 AM

So either i can swap motor only keep 3.2 tranny drivetrain intact or i have to swap motor/trans/driveshaft/rear diff/axles? Does the S4 trans have better interals to deal with more power?

Gosser

02-07-2021, 08:25 AM

Those spec sheets are somewhat misleading.
For the final drive ratio, just check both cars PR codes. My 2006 A4 3.2 was a HCC rear diff, from a work shop manual:
https://live.staticflickr.com/65535/50918915576_e57e076ab0_c.jpg

I dont know the differences between the two transmissions, but you can try to keep the 3.2 and the rest of the drive train. It would just be a bit annoying if the B6 TCU couldnt control the B7 TIP and had to rip out the drive train again. If decide to bolt the 3.2 TIP to the 4.2, but make sure you slip the torque converter onto the transmission first to properly engage the transmission pump, then bolt it the trans/torque converter to the flywheel. Its a little tricker this way, but you'll destroy the internal pump if you bolt the torque converter to the flywheel, then try to install the trans.

Rear axles will be all the same.

MoneyAllTheTime

02-07-2021, 08:26 AM

the shaft and rear diff.
Check the axels are they same parts

Don’t throw the S4 until you are done [emoji846]

Axles and driveshaft are the same, rear diff is most likely different though

MoneyAllTheTime

05-13-2021, 06:57 PM

So i have both engines/transmissions out finally. I will use the b6 s4 tiptronic, one issue that popped up is the engine harness plugs don't match my b7 plugs in the ecu box. What's the best way to go about it?

Gosser

05-15-2021, 04:43 AM

canadianA4B7

05-15-2021, 05:26 AM

Didnt know b6 and b7 plugs were physically different. Either cut them off the 4.2 harness and solder in the b7 connectors, or make a jumper harness between the two. I like the jumper harness, that way you arent cutting into the B6 harness, but some people dont care about that.

Pin install removal tools are far easier the patch harnesses. If your going to be hacking things like Frankenstein be sure to label every wire with 2 wire labels. Then cut between them. That way in a few months when your trying to troubleshoot you can look back at the old connector and have a full reference of every wire. Unless your really good at making your own electrical diagrams and data sheets for making a harness patch. Audi uses similar pin ends on most ECU’s making it insanely easy to just swap pins from A to B and your build looks like it came that way from the dealership.

MoneyAllTheTime

05-18-2021, 05:19 PM

Thanks for the replies guys, trying to locate a complete harness instead of chopping a good harness. Ebay 250$ should allow me to continue this swap 😊

MoneyAllTheTime

05-24-2021, 05:48 PM

I want to try and make the patch harness, are all B7 body plugs in the ebox the same? At my scrapyard i will most likely find B7 2.0t and B6 1.8t. if they are the same connectors ill just chop both ends off each car and figure out what matches with what.

MoneyAllTheTime

06-05-2021, 04:33 AM