To convert 2001 A6's 4.2L engine to S8's specs, I need...

[GTA_Driver]

Cams. Intake? Exhaust manifolds? ECU? Is this interchangeable/compatible? Will the ECU from S8 work on A6 if the engine is brought up to spec? Any difference in transmission between A6 4.2L and S8? (This is more for reliability than anything). Looking to get my 4.2L to about 350+ HP naturally aspirated.

[v8a6]

...or around that time. From what I have read Cams, Intake manifold, (S6 exhaust manifold, since according to April in another post S8 would not fit in the engine bay,) should give you the power you are looking for with custom tuning, using maybe Lemmiwinks.

The S6, and maybe the S8, also has a 'trap door' in the bottom of the airbox which opens under WOT. Another member (PaulW I think?) wrote that he had to tape his shut during track use because it would let in hotter air from the engine compartment than the colder air at the regular inlet. So in the end, I dont know how important this would be in the conversion.

Dont think the ECUs are swappable.

Many people have asked this question before, btw, and in the end most agree that it is not economically feasable. The main cost coming from the cams.

I just picked up an S6 dual-stage intake manifold (the same one is used in the S8 I think) myself from ebay. I dont know however if this alone, with the proper tuning, will bring any power gains without the accompaning cams and exhaust manifold.

Anyone else care to speculate?

If you do get a line on some cams, Im sure many people would be interested in purchasing them, including myself.

Might be even better off looking for the cams used in the SPYKER version of the engine since its about 400 hp.

Anyone want to organize a group buy

[GTA_Driver]

I wouldn't mind investigating this further, i understand to take the cams out is an involved job.

Does anyone do ECU tuning for these cars? There will be little benefit spending thousands without it.

[v8a6]

But a much better option would probably be to just wait for the PES supercharger mentioned in threads below. Estimated 450 Stage One output for about $6000 plus install with a custom programmed ECU included.

Or just buy an S8.

Regardless, Ive already replaced my transmission once at 60K miles with stock hp on my 4.2, so any kind of increase obviously puts it at higher risk to fail.

Good Luck.

[MP4.2+6.0]

Kind of an old post I am replying to, but FWIW:

Check into the spec's first. I always read these posts about hotter cams on the S'es, but I'm not so sure. Also remember the cam advance is controlled in large measure electronically (though presumably not the lift).

Find a HP and torque curve for the two motors. As I recall, the extra HP is ONLY up above the regular 4.2's redline. The S6 is geared materially lower than the A6 4.2 too, so don't get thrown off by looking at 0-60 without considering the gearing. Same general issue on 4.2 vs. 2.7 too w/ the 2.7's way lower (numerically higher) final drive ratio. If you want to speed up 0-60 on a 4.2, I bet the single biggest change you could make is to swap in the S6 tranny and related rear end with its different final drive. 2.7T gears would be better yet, but its tranny wasn't rated to handle the V8's HP/torque, and many of us know the tranny isn't bulletproof in 4.2's to begin with. Remember you need to do both pieces to make it work, and it is likely to throw a CEL with the different gear ratio unless you can recode the ECU somehow.

I know the S 4.2 has the modified airbox. A cheater trick there would be to run another hose into the side of the airbox (before the filter of course) with a PVC plumbing fitting at the box ducted up with flexible hose to the front of the car. I think there is room for a 1 1/2" plus hose, certainly if run down toward the fog light area as a cold air intake point. There was an old post on this in the C5 pages years back. I also know from taking off the throttle body at the back of my 4.2 recently, it is sized slightly smaller than the intake manifold to which it is bolted--akin to tamping down HP with a restrictor plate? Maybe the A8 or S6 or S8 one is sized up to the full manifold size. A friendly parts counter man might be able to dig into this or examine the actual parts. Finally I know from toying with a Bosch MAF on its last legs, power went up materially when I simply took out the various screens in the airflow passage--engine rev'ed easily into the redline and bounced off the limiter before tranny could even make the shift. Consider too the 4.2 has essentially the same airfilter as the 100HP 2.1L inline 5 in the C3 Audi 5000 from 15 years back; by my calcs it's undersized (and no, don't use a K&N; the oil kills MAF's) and obviously in the RS6 they went to a whole second airbox. All of those are clues to me a bunch of the power delta may just be the flow on the intake side, plus presumably opening up the exhaust side with RS6 exhaust or something similar aftermarket.

And again, I'll reemphasize the redline delta too, which would require some kind of electronic tweaking to the ECU and likely TCU/TCM too. Just focusing on cleaning up intake and exhaust breathing (including the throttle body) may be the most practical thing here if you don't have electronic/tuner access for the black box stuff.

[v8a6]

It has variable dual stage runners, like the S8 from those years. Ours are three-stage stock.

I have to do a little more research and find out at what rpm the S6 shift to the shorter runners for more HP. Also, and electronic device to control the gate will have to be setup. I still havent decided if its worth the install or not. Once I get it Ill post in the A6/S6 forum for more help/advice.

Any thoughts?

Anybody know how many hours labour to install the intake manifold?