when comparing 40valve, non-fsi v8 4.2 engines...

Anyone know what differences they have ?

What makes the different powers?
Camshafts? Camshaft timings?
valves, head machining? other ?

Jamez.

Cams, compression ratio, ECU, and exhaust are definitely different. There may be other changes also, but these four would be enough to explain the various hp levels.

BTW: Audi's naturally-aspirated non-fsi 4.2L 40V motor is used in the Spyker, which is available with either 400 or 450 hp!<ul><li><a href="http://www.audiworld.com/news/00/spyker/content.shtml">Spyker</a></li></ul>

I'm thinking S8 probably has a less-restrictive intake than A6 / S6.

that does remind me of a possible 5th difference -- the intake manifold may be different.<ul><li><a href="http://forums.audiworld.com/a8/msgs/79585.phtml">Intake manifold change</a></li></ul>

there are two sets of intake runners/paths built into the manifold.

for RPM's below 4000 (for arguments sake), air travels through the full length of the intake plumbing.

when the engine turns at 4100rpm, there's an actuator mechanism that opens up butterfly valves. These holes are located way closer to the outlet ports, and not only lessen the distance air has to travel to get into cylinder but also allows more air to be gulped in.

confusing enough? heh, look for some 12v reference in case yer still confused

1.) The impact reduced gross weight has on 0-60 performance
2.) The value of a 6-spd manual over our ZF box.