Not sure that the R8 headers would fit because the R8 exhaust goes up to clear the transmission. Probably would need to cut the cats off and weld on flanges then have custom downpipes made if the shorty headers will clear the frame rails.
The high pressure fuel pump camshaft followers are different between the S6/S8 and R8 V10. I am pretty sure that the heads are extremely similar otherwise except for a few weird things probably. For example, the exhaust valves are the same but I don’t see the intake valve part numbers easily to tell there. The valves spring and retainer upgrades from APR says that they fit both engines for whatever that is worth.
Then it would be vital to see the crankshaft main and rod journal sizes for bearings. Audi limits the bearing sizes drastically on a lot of their engines like the B6/7 S4s.
Going over that right now. If it’s not Identical its Damn close. Haha
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S6 on the left with the balance shaft R8 on right
Well on the front side Crank bearing part notes say they are interchangeable. But it’s with the S6 4.0 tt 
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Thrust washer is interchangeable with the R8 4.2 so it will fit in the the main seal/Crank seal.
Edit my post here not seeing any over lap about the intake valve after all would have to see what the difference is.
Ok after searching all over I discovered that the Intake valves are indeed interchangeable as well.
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Doing some serious r&d research here I like it
Both Cranks have a rod Journal diameter of 54mm.
Rod bearings match but upon further review the Main bearing is listing size compatibility for the 4.0 Twin turbo S6. And the S6 Bearing is showing compatibility for 4.2 R8. The site wasn’t directly showing Dimensions so I found a site with exact dimensions. And Main bearing is 67mm for R8 crank and 65mm for the S6 crank. Which means you would have to lose 2 mm off the R8 Crankshaft diameter for it to fit the Main bearing Journals. And off the end where it meets the thrust bearing. Lol you might actually score big if you find a used Lambo crank out of spec or just order the billet Crank -2mm of material off the diameter which is really removing only 1 mm of material.
So I would say it’s not a direct bolt on as I had hoped but not out the realm Of possibility either. I think it would be a wonderful project. And I learned a lot about these engines. And similarities and difference’s.
Thanks Jimmybones you put a bug in my ear and I really wanted to get to the bottom of this to be exactly sure this would be feasible. Just need a good chunk of cash to get started!
As my interest continues to grow for the 5.2 V10 I think either just removal of the cats or trying to convince JHM to build the headers would be a great. From what I understand JHM has a catless tune if anyone falls into the need for that. That is a good to know
yeah, I am just happy to find this information out and have a formula for if someone wants to really make some serious power!
Well thanks to both you and jimmy I think we are learning a lot. But from all I have found and from what we are seeing here Im now more convinced we dont want to do the R8 heads here is why.
From all the data so far we have seen
that the intake and exhaust valves are the same size. so no gain there.
From what I can tell the iintake manifold gaskets are the same port size so again no gain there.
The same I can tell from the exhaust manifold gaskets. There is no port size gain there.
There is a chance that possibly some port work has been done but from the size of the pistons the chamber size would have to be the same so again no gain there.
Over all R8 heads dont appear to have any advantage that would make them worth putting on. Now you could argue that maybe there is some port work but you could just buy some old S6 or S8 heads and get them ported. Even if the R8 heads had bigger intake or exhaust ports. Porting the stock heads would give IMHO better results.
Now moving on to the camshafts. If we were to install just the camshafts our cars would loose hp and Tq. Again we cant spin our motors to 8600rpm and that loss of 2000rpm would harm the performance big time.
Also on the camshafts remember one we cant spin our motors that high due to the kind of transmission we have. With the JHM TCU tune they could in theory make our transmissions shift at whatever rpm we asked them to but our transmissions dont do well at those kinds of speeds. Maybe 7500 would be ok but still there is one big factor left.
Our cars weight is almost 700lbs more than a standard R8 we need that low end TQ to get our big heavy cars moving so putting in R8 camshafts would rob us of that much needed low end TQ.
The same argument would be made for the single stage intake on the R8 we would loose all of our much needed low end Tq.
Everything on the R8 is geared to making and maintaining a good VE at over 6000rpm. We would need to look at the shorter runner headers as well.
Given the weight of the much heavier S6 I would say a killer formula would be.
Remove the cats or get JHM headers.
Take your OEM HEADS and get them ported.
Obviously add the JHM lw crank pulley to help with the rotational resistance concerns add the intake spacers to keep everything cool and from there building the other parts of the motor as needed.
Knowing about the piston and rods is a huge gain for possibiltys there and the crank shaft while it looks like it might not be a direct fit its good to know there are options.
I agree. If someone want to take this platform to the max meaning 1000+ hp it is possible but will require a serious investment probably $25-40k depending on how good a deal you get on parts. Its nice to know there is an end game that you can achieve If you were to put in the work. Your formula is a lot more realistic and budgetable. Tho popping the hood and seeing a Lambo or R8 intake and heads would be really fun it would all be just for asthetics.
I do have another Wacky Idea ;D :o but you will just have to wait till I get a little further along with its Development.
Good point on the trans Justin, I was about to chime in on that. I would say 7500 is probably pushing it. Probably bump to 7200 decently safely maybe s little more.
Same point on the TQ, the power curve and higher low end tq at lower rpm was done by design for the heavy s6 and more daily driving. This is one big reason I like the s6/s8 v10 over the e60 M5, there is actually usable power below 4K. Now once you got moving that high Reving v10 with the 7 speed SMG was really moving especially on a roll, but man day to day and under 4500 it was a dog compared to the tqy s6.
I would be curious to see what gains would be with a decatted s6 vs. custom headers. I remember awhile back saying the stock header design itself wasn’t horrendous, but the cats and the cat placement was terrible. Basically the engineers had there way with a working design, then the emissions people came in and rained on their parade.
I like where your head is at OP, but like Justin mentioned I would go with the proven recipe, and then start thinking about a S/C before diving into a rebuild or tear down unless your motor is already unhealthy, or your up for an adventure. Then when the opportunity presents build a 900-1000 s6 :-p, I would be interested to here if any trans work might be needed at that level though.
To that end I mentioned before the RS6 trans was built a bit beefier but the shift points would be all wrong. I looked into it Rs6 has an even lower rpm power curve than we do. and the new 4.0tt trans is even lower. Long tube headders would help bring that down a bit. Long tube headers help with power down lower shorty style help move power bands towards higher rpm. We wold need shorter gearing in our trans to get to high rpm power faster. I know we are in a transmission pool with Bently Jaguar and a few other companies I wonder if any of them are geared more like that. Well back to the Books. lol
Yeah, Funny thing our cars actually have the highest rpm power bands in the transmission pool. Which among other cars Include Bently rolls royce BMW jaguar Mazrati and Kia. So yeah them. Ok but i did find a high out put version The ZF 6HP32 is a variation of the 6HP26 for high-output applications. The gearbox’s maximum input torque is 750 N·m (550 lb·ft).[11] so when you ar ready for a beefier version of our trans you got one. I saw several on german ebay for 1300-1500 Euro
Nice find on the possible trans upgrade, what makes and models specially uses that tougher trans, and is it the same TQ converter as ours? . Yeah the c6 Rs6 transmission is only slightly beefier from what i recall, possible slightly stronger gears, don’t remember the specifics, but I think that trans holds a decent amount of power since guys have been running around with tuned and full tbe on those cars for awhile.
and knockon wood I think the stock c6 s6 trans can handle a decent amount of power and abuse itself as it’s fundamentally similar if you actually pay attention to the atf fluid and atf filler and add the JHM tcu will probably help too.
That said I’ve heard people who have replaced the trans with Lower miles and they baby it and then those that have beat it up and it shifts like new.