Figured the stock ECU would not work with a pressurized system.
What does the 2003 RS6 have for an ECU? (Same basic engine, so I'd think if we can put that into the S8, it work with less time invested to completely write a new fuel/spark map for this engine.)
That is one way to get a turbo back there.. I'd rather not lose my spare tire/trunk however.
If you buddy put a large puller type fan on that intercooler, it would have worked better, pulling air and dumping it into the trunk, with that large hole cut in it for the turbo would be fine. (However, at speed, I'm not sure what would be the case, if it's low, or high pressure, and that might make cooling interesting if the air flow is cut down by the flow of air over/under/around the body of the car.)
I know the stock car is setup to have areas of LOW pressure just behind the rear wheels, and that's why Audi, and many others have vents there, to pull air out of the car's interior at that point.
Of course, with the large hole cut in the rear trunk pan/floor, that's all out the window pressure wise.
The Comp turbo's are an option, but the design of the one I linked is better I think, and with the VATN v/s Waste Gate, there is better flow, and less lag, so perfect for this setup, since you want massive flow, as you only need 5 to 6 psi on the stock CR. (And if I have to pull the heads to put a thicker gasket to lower static CR, then it's defeating my idea of not making this a seriously complex upgrade to the S8.
)
Also, the simple nature of this turbo I linked allows for the plumbing to be less complex, no Waste Gate needed etc. Bring the dual exhaust together into one T3 flange, mount the turbo, and you have one outlet, that you can then split into the stock dual tip setup. Simple and easy. Given some time, I might even be able to fit it all into what's left of the stock muffler, turning it's case into a heat shield of sorts, and a "panel" to hide the turbo from interested eyes... I like a stock looking car, and this mod might keep it somewhat stock looking, but the turbo sound will be there no doubt, but not too loud.
Another option would be two smaller turbo's, but at 2500.00 each, you are 5k in just those two before you figure out the fuel system.
My thought is one of the larger units, run it at 5psi, add a piggy back fuel computer that only adds fuel under boost, and have them just prior to the throttle body, say 4 large, 780cc units, seperate fuel pressure regulator. Adding the fuel there would further cool intake charge temps, and even as complex as the S8 intake manifold is, fuel moving under pressure at that intake speed while the engine is boosting, should stay in suspension pretty well, and as noted, cool the air very well at the same time.
I think there are piggy back fuel systems that use a wideband for fuel trim feedback, and give you a goal to set, and maintain. (Say 12.5 at 5psi, and 14.5 at 1psi with the system keeping it rich enough to avoid melting down pistons in the area between 1psi and 5psi.)
Anyone have any experience with how much air pressure the stock S8 can "read."
I know it's got to handle sea level pressure, and normal variations in barometric pressure, so those of us that live at higher altitudes, can in theory, run some boost, and not exeed what the stock fuel system is designed for anyway.
Another option is going stand alone, like the Megasquirt.... but with a throttle by wire, that's not my first choice. (Also the fuel computer and other stuff is tied into this.. like your cruise control? It's part of the ECU I'd guess.)
I wonder what the guys selling superchargers for this 4.2 are doing? (They clearly have fuel figured out to 6psi.)
2nd January 2013, 04:16 AM
Linear Mode
