[mkoesel]

Originally Posted by Remonster

By the way, if we're talking specific power output the Koenigsegg Agera is the highest production car I can think of. The regular Agera makes 192hp/liter (960hp from a 5 liter twin turbo motor) on pump gas. It also makes 1030hp on 98 octane and 1140 on E85 but obviously that's a different story.

True enough. For whatever reason, boutique cars, although technically production cars obviously, are typically not considered by volume manufacturers when claims about engine properties and features are being made. As someone else pointed out earlier, the Mitsubishi FQ-400 actually made 200hp/L when it was in production, but that was a very limited car sold only in one country (if I recall).

Originally Posted by rs_philly

There's no way they will have a M235i with an N55, and an M2 with two cylinders less. And yes, I would only consider the I6.

What makes you so sure? As others have mentioned, the original M3 had an I4 while the 325i of the time had an I6. I believe that the second generation M5, which had an I6, was around when BMW first released the V8 in the 5 series as well.

Now, if the M2 does get an I4, what does that say about the chances for the M235i to get the new B68 I6 after it appears next year in the 4 GC (if rumors hold)? The new motor should be capable of quite a bit more power than the N55. So would they just keep the N55 in the M235i or would they switch to the B68 but in a relatively low state of tune?

Originally Posted by M12Power

Maybe, but I would be more impressed if it were normally aspirated. Getting high specific output through forced induction is not that hard. At the simplest level, all you need to do is to increase the boost.

Well, sure, 175hp/L+ from a naturally aspirated engine would be ridiculously impressive for a production car. Most purpose built racing engines don't even make that kind of power per liter of displacement. It takes a lot of air moving through a cylinder in a short amount of time to get that much power. Typically that is achieved with extremely high RPM, like a super-bike motor, which usually has a very short stroke. And efficiency takes a big toll when you move that much fuel through the cylinder.

Getting high specific output through forced induction is not that hard.

If it were truly that simple of a matter to make big power from production turbocharged engines (which must meet very stringent reliability and efficiency goals), then it would be more commonplace. What AMG has done is really quite impressive for an engine that will be produced in significant volumes.