Swapping a D2 S8 motor in a A6 4.2?

[FROZEN337]

I have to opportunity to put a D2 S8 motor (have the complete car, 2003 S8) in my 2001 4.2. Wondering if someone may know of any major issues, what would have to be changed (exhaust manifolds or accessories) to get it in the car? What all of the harness has to be used and would it be a plug and play?

The S8 is going to scrap, but the motor is fine and I can get it for near free! It has less miles then my car and was maintained by an OCD owner, just want to know, labor PITA aside, would it be worth it in the long run?

[Nollywood]

You'll need to swap the oil cooler and filter assembly from the A6 4.2 block. The C5 housing incorporates the passenger's side engine mount, and has a traditional screw-on oil filter. The D2 S8 has a paper element in an enclosed bowl.

The D2 S8 engine harness is not compatible with the C5 chassis - at least, not plug and play. It's also routed differently. I would use the original C5 harness. The S8 motor is a higher-revving unit - different camshafts and cylinder heads, different injectors. The intake manifold is also a dual-stage, your 4.2 is a 3-stage.

You won't achieve the output of the S8 with your C5 4.2 ECU. Different timing map and cam profiles. If you want to end up with at least close to the S8's output, you'll need to run the S8's ECU to match. You'll also need to code the S8 ECU to your IMMO, else it won't run.

If it's done properly, it's worth the effort.

[FROZEN337]

I figured I would need the ECU from the S8, do you know if it is comparable with the A6 or will I have to run it in some sort of piggy backed way? I would like to end up with a OEM quality swap, kinda like some Audi/Skunk Works freak, with S8 power/performance!

[Nollywood]

The OEM S8 ECU is compatible with the C5 A6 4,2. No need to run a piggy-back system.

[FROZEN337]

If I use the existing C5 harness, do I need to change much around for the connections, re-pin connectors or splice new ends? Would I be best off mugging to S8 harness for various plugs and/or ECU connector?

Trying to get as much info ahead of time, so I hit as few bumps as possible!

[ddillenger]

Nollywood got it backwards. The s8 uses a 2 stage intake, your car uses a 3 stage runner design. Not a big deal if you use the s8 gearing, but you may get a dip in the powerband with the a6 gearing. As for the harness, the ecu pinouts are the same. It's all plug and play (slight modifications, nothing worth talking about). If you need the immobilizer defeated, or have any ecu related questions, PM me.

[mithril]

The D2 S8 engine harness is not compatible with the C5 chassis - at least, not plug and play. It's also routed differently. I would use the original C5 harness. The S8 motor is a higher-revving unit - different camshafts and cylinder heads, different injectors. The intake manifold is also a 3-stage, your 4,2 is a twin.

Vice Versa actually. 4.2 A6/A8 use a 3 stage variable intake runner, the S6/S8/Phaeton use a 2 stage and the RS6 and B6 S4 a single stage. Not sure about the 4.2 Allroad or Touareg.

You won't achieve the output of the S8 with your C5 4,2 ECU. Different timing map and cam profiles. If you want to end up with at least close to the S8's output, you'll need to run the S8's ECU to match. You'll also need to code the S8 ECU to your IMMO, else it won't run.

True, you'll need the S8 ECau to get the right timing maps as well as to match the intake. You should also get the S6 or S8 airbox for the vac actuated WOT flap.

[Nollywood]

Vice Versa actually. 4.2 A6/A8 use a 3 stage variable intake runner, the S6/S8/Phaeton use a 2 stage and the RS6 and B6 S4 a single stage. Not sure about the 4.2 Allroad or Touareg.

Thanks for the correction, I realised what I'd done, once I'd posted it, haha.