Quote:
Originally Posted by Boss330
I completely agree that the S65 sounds much closer to the Ferrari flat plane crank engine, which is down to rpm in particular.
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Thus in large part contradicting your earlier belief/statement that the crankshaft type was the largest determining factor in an engines acoustics.
Quote:
Originally Posted by Boss330
I think we just emphasize different traits to the engine design. For me, there is two separate V8 designs: Cross plane and flat plane. The rest is, for me, just variations on a theme depending on what use the engine is intended for (i.e DOHC, cam in block, 4 valve/2 valve etc.). You can change that hardware on both designs and it will obviously change the engines characteristics, but no matter what you change of other hardware, a cross plane crank and flat plane crank engine will still be very different.
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And I've already demonstrated the the sum of other design choices can easily overwhelm any effects or advantages of a flat plane design. Yes all things equal a flat plane is a better foundation for a very high performance engine. Sure it is a useful geometric/kinematic archetype classification system but beyond that I have shown its just not as important as you think.
Now all this being said I did perhaps publicly but certainly privately had hoped the S65 would be a flat plane design. The reason BMW did not was because the S65 is simply the S85 V10 from the M5 with two cylinders lopped off. However, another significant factor is engine balance. A cross plane V8 has near perfect first and second order balance whereas the flat plane V8 achieves first order but not second order balance. This makes the cross plane superior from an NVH standpoint (and as you stated somewhat inferior for an all out race/sports engine). Typically extremely high rpms are hampered in a cross plane V8 design but that obviously wasn't much of a real world limitation in the S65 (unless you call 8400 rpms somehow not high). BMW M had their cake and ate it too in this regard.
It's probably well overdue to get back to talking about forced induction...