Quote:
Originally Posted by swamp2
Thus in large part contradicting your earlier belief/statement that the crankshaft type was the largest determining factor in an engines acoustics.
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Which was written on an iPhone and was therefor very short without all the possible "if's and but's"... My statement as regards the videos should obviously have been more precise for you. It sounds more similar to the Ferrari
than the Mustang does. It doesn't sound the same. It sounds more similar just as any engine would at revs approaching the 458's redline. My son has a Focus with a 2l engine with a redline at 7400rpm, that engine sounds more like the Ferrari than a 2l with 6000rpm redline. But no one would mistake it for a Ferrari... Even though in reality a highly tuned NA 4 cylinder at 9000rpm sounds more like it because of the same crank design and firing order.
I'll try to restate my point in the simplest way possible. A straight piped S65 and a P65 sounds different BECAUSE of the crankshaft. Take any V8, change to a flat plane crankshaft and the engine will sound very differently. I'm not talking about how different exhaust sytems, intake systems etc. can change the sound. Because those are added on parts that can be changed on any car. Yes, of course the exhaust system is vitally important to the sound level. But, just as you can put a straight pipe system on a M3, so can you on a Mustang etc... That changes the sound pressure (noise level), but won't get rid of the V8 burble that is due to the two adjacent cylinders firing in a row on the same bank.
You would never say that a 4 cyl engine sounds like a cross plane V8 would you? Notice that the flat plane crank V8 actually is a two 4 cyl engines coupled together with the same firing order as a 4 cyl engine (for each bank)? This makes a flat plane crank V8 sound very differently to a cross plane engine, and perahps even a little bit uninspiring at idle (since it sounds more similar to a 4 cyl engine at idle).
Quote:
Originally Posted by swamp2
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...
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Even though the S65 is a S85, minus two cylinders, doesn't mean it couldn't have been flat plane! The P65 is...
The NVH issues are probably the main reason BMW didn't go that route.
Quote:
Originally Posted by swamp2
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.
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Eehhh...??? So you are saying it's better for a sports/race engine, and at the same time saying it's not important? And exactly which quality of the engine are you referring to when you say it's "not as important as you think"?
What have been my points is:
A flat plane crank V8 engine makes a different sound than a cross plane engine
A flat plane V8 has better exhaust scavenging (due to more ideal firing order)
A flat plane V8 has a lighter crankshaft, meaning sharper response
A flat plane V8 is preferred for high rpms and power (and often come in cars where NVH issues are expected and accepted by the owners)
I have not claimed that it's impossible to make a high performance cross plane V8, just as it's also possible to make a low performance flat plane V8 (if someone should be stupid enough to pursue such a option)
Yes, you can make a high performance cross plane V8 (just look at the S65 and NASCAR), and I have never claimed otherwise. The hardware needed to do that is the same hardware needed to make high performance on a flat plane crank V8. So, in that respect the S65 (or any other high performance NA engine) is more similar to a Ferrari engine than it is to a plain Jane V8.
Just as a Ford Racing 5.0L Aluminator engine also is more similar with 100hp/l:
http://fordracingparts.com/parts/par...KeyField=23300
Which again leves us with one major difference, the crankshaft layout. And, that is more important than just creating a different sound. It gives the engine sharper response and better exhaust scavenging. Meaning it's easier to achieve more power as the exhaust scavenges the cylinders better. Which then can either give you more power with similar cam timing, or less aggressive cam timing and same hp.
Both layouts have their pros and cons, but for uncompromised power, the flat plane is preferred.
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