Originally Posted by Robin Hood
The 3 litre turbo 6 puts out less HP/litre than its 2litre turbo 4 brother, that's what we already know and thats what we are talking about. The more hp/litre of the N20 is excellent, but its downside is that it's more stressed out than the relaxed N55. I gave some examples(458/z06Vette, both NA).
So anybody who says the N20 is easily tuneable to 295/300BHP; Fair enough, but keep in mind a N55 is ALSO tuneable to 100BHP MORE easily.....
And still running fine, which means YES, with 69HP/litre whatever it IS MORE RELIABLE than 'my N55' and 'your N20'. Which means the N55 is logically more reliable than the N20....
Of course the N20 is more "stressed" than the N55, that is bourne by the BMEP figures. We can see that IC engines gets more & more "stressed" as time goes by, but it's debatable as to whether we should use the term "stress" or "efficiency".
I remember abt 15yrs ago, our physics class did some calculations & found that most petrol IC engines in the day had an efficiency of abt 30-40% (most of the energy is converted to sound & heat rather than kinetic energy). Recently, Mazda proclaimed that there are still a lot to gain from developing petrol IC engines by increasing efficiency. Therefore the gain in BMEP may be due to increase in efficiency rather than "stress". As the N20 is newer than N5x series, it's likely that BMW have applied even more advanced design into the N20 & so the marginal "stress" maybe less than we thought.
If u talk abt tuning, there's no need to argue cos inherently one has displacement of approx. 1,000cc more than the other. Naturally the N20 can be tuned to levels of a stock N55, but one cannot defy laws of physics.
Whether old engines are more reliable than news ones, again not enough statistics yet. Remember, new engines are much more complicated than old ones, so potentially more to go wrong. Plus, it seems that things nowadays are built to cost, so sometimes the design is quite marginal. As for the M52, before the technical update the cylinder liners had problems with high sulphur fuel.