German Car Zone

^Yeah they are different one is anaemic() 4.0l that only gets exciting after 5000rpm(based on personal experience) and the other is 6.2 that revs to 7200 which is very impressive for it's big displacement and lack of DI,but it's indeed very exciting the cars in that segment definitely my fav type of cars

Not to be nitpicky (sorry Marcus - I agree with you in principle!) but actually I see it the other way round. Whilst all three cars employ a V8 to get the necessary motive force, they are quite different from each other even in terms of the engineering philosophies and mechanical methods employed.

The Audi RS4 V8:
The RS4's V8 is notable in that it is the only undersquare (where the piston stroke is longer than the bore width) engine here. The stroke of 92.8 mm is the longest here relative to the bore. Typically, undersquare engines are not normally associated nor necessarily suited to high revolutions, making the RS4's redline of 8250 rpm even more impressive. It hence has the highest internal piston velocity of around 25 ms-1 at max rpm. Obviously the RS4 has the smallest cylinder bore here of 84.5 mm. The RS4 employs a conventional single throttle valve and two-stage variable induction manifold. The Audi V8 has the highest specific torque per litre output at 103.3 Nm per litre courtesy of the long stroke, high compression ratio and FSI injection which is above the benchmark. The use of direct injection together with the Lexus separates this engine further from its German counterparts. Another interesting feature of this engine is that Audi has located the valvetrain drive components (cam chain and gears) at the back of the engine and not at the front like its competitors here in an effort to move weight further from the front of the already nose-heavy configuration.

The BMW M3 V8 (S65):
This V8 is heavily oversquare as per BMW's current high-revving series engines in the S85 V10 and now this V8. It has the smallest displacement and, at 75.2 mm, the shortest stroke by far - highly characteristic of a high-revving high performance engine. This V8 is the only engine to employ 8 throttle valves (one per cylinder) fed by a large inlet plenum as opposed to the conventional inlet manifolds of the other three cars here. It makes the highest specific power output per litre here though torque is the lowest. It revs to 8400 rpm and is the engine with most "zing" (lust for revs) out of this foursome. The S65 attains the normally aspirated benchmark of 100 Nm per litre.

The Lexus V8:
This 5 litre V8 was developed in conjunction with Yamaha but other than that remains unremarkable from a power output perspective. It ticks all the right boxes though, with a two-stage variable inlet manifold fed by a single throttle body. It's a slightly oversquare engine with a stroke of 89.4 mm and it revs to "only" 6800 rpm. It has the second biggest cylinder bore here after the C63. An interesting feature is that the Lexus supposedly features both direct and indirect (port) injection. Apparently. I can only see direct injection being employed. The Lexus has the second lowest specific power output to litre ratio here and makes the benchmark 100 Nm per litre.

AMG 6.3 V8:
This is the big daddy of all the engines here. It is a large displacement (6,208 cc) V8 with a slightly oversquare engine of positively impressive dimensions. The bore of 101 mm is enormous and the stroke isn't to shabby either at 94.6 mm. This AMG engine has two separate throttle bodies. As I understand, this V8 is, remarkably, also the lightest here at 199 kg. Significantly de-tuned from its application in bigger Mercedes models this engine produces the lowest output per litre yet still manages to cane the others with its highest outright power and torque figures. Specific torque output per litre of 96.6 Nm is also the lowest. In contrast to the Audi and BMW the Merc engine is the epitome of the "muscle without the fuss" approach. It's redline of 6800 rpm is more likely curtailed by the torque convertor transmission than the engine's real rev capability.

Otherwise, yes, they're all naturally aspirated V8's with chain driven DOHC and 32 valves with variable valve timing and lift.

^Very nice details

Martin my friend,C63's V8 revs to 7200rpm which is impressive for it's displacement

True enough it seems Tarek, though I do know that 6800 rpm is where the max power is produced. So at 7200 rpm the engine managment system is probably softening the power output in order to preserve the torque convertor.

Both mine and my fathers car reev to 7000 rpm, not bad. Too bad I miss another 300hp in my car

^Lol,same here my car revs happily all the way to 7000rpm but with only 150bhp

martinbo, the standards of weighting the engines has not yet been resolved, Hence, we do not know if they are compareable.

Yes, I understand this to be the case. (Please let's not go down that road again! )

Still, besides the standards employed, even if AMG are five kilo's on the optimistic side, the 6.2 litre AMG engine remains an amazing feat regarding its weight vs. displacement ratio.