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      10-05-2012, 02:07 AM   #117
swamp2
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Drives: E92 M3
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Quote:
Originally Posted by fuddman View Post
Quote:
Originally Posted by swamp2 View Post
The new engine will very likely redline in the 7500 rpm range (just a bit higher than the F10 M5). Similarly it should make constant torque to about 6500 rpm (the F10 M5 does so until almost 6000 rpm). However, 395 ft lb will make 420 hp at around only 5500 rpm. To not exceed a peak of 420 hp would require the torque to drop off steadily after 5000 rpm to only 315 ft lb at 7000 rpm along with a redline of 7000 rpm. Those simply do not seem like reasonable figures. If the engine makes torque and power curves anything like the M5 395 ft lb should make closer to 460 hp.
Where are you coming up with all this stuff? Are you pulling it out of your hat?

You need to put some substantive proof behind your "very likely" numbers because, if for no other reason, your conclusions conflict directly with what the moderator said and he has a direct line to the people who are making the car.
These are educated guesses, trends and calculations. I can provide some more "evidence" but you will have to decide for yourself. The numbers just don't make sense.

Redline: The M3's redline is typically a bit higher than the M5. The M3's engine often follows or is in some way a relative of the M5s engine but slightly improved in some small ways. The current M5 redlines at 7200 rpm. 7500 for the new M3/4 is a very reasonable estimate.

Look at the power and torque curves for the F10 M5, attached for your convenience (they are in SI units!). The curves for the new S55(?) should be fairly similar. No not identical but similar.

395 ft lb making 420 hp at ~5500 rpm is simple math, it MUST be the case, no if's and's or but's, since in US customary units:

hp = tq x rpm/5252

This is an exact equation, almost a definition and is true for all engines, exactly.

Plug this into MS Excel and start drawing some power and torque curves yourself! You just can't hit the stated numbers without either a very low redline and a strong tapering off of torque at about 5000 rpm or some very bizarrely shaped power or torque curves (perhaps impossible shapes...). Neither of these is a characteristic that will be typical nor desirable from a turbo charged M engine.

I really don't care if a moderator posted the figures or not. It is unlikely that they have a source any better than the rest of us. Ask him to name his source. Interwebs gossipers never to, thus the veracity or even likelihood of the claim can not really be established. It is up to us to use some basic math, logic and trends to see if the numbers make sense. Again in this case they don't. I would be willing to place a large wager that the actual (not stated by BMW, since they are known to underrate) specs of the car are not at all close to 395 ft lb and 420 hp. Either the power will be higher or torque lower.
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