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Old 01-07-2013, 01:46 PM
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Bönz Bönz is online now
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Location: Michigan
 
Join Date: Jun 2012
Posts: 436
Mein Auto: 650i
I've stated this in another thread. Valvetronic is only a throttling system. It is more effective on a normally aspirated engine as it reduces intake vacuum and theoretically improves the fuel mixture by inducing additional swirl. By itself, valvetronic does not and cannot increase power (assuming equal maximum valve lift). All the power increase on both the S63 and N63 Tu's comes from increased boost, CR and other related software changes. Valvetronic may play a role in maintaining efficiency/emissions with the increased power of the Tu engines, but it doesn't add power.

CR is mechanical. It is the volumetric ratio of the combustion chamber with the piston at TDC (top dead center) to the bottom of its stroke. The larger the ratio (more compression) the more power, efficiency and potential for pre-ignition (bad). Forced induction engines raise cylinder pressure by compressing the intake charge, effectively increasing the compression ratio. That's why boosted engines typically have a lower mechanical CR. That's also why we need to use premium fuel. It has higher resistance to pre-ignition. Intercooling also reduces potential for detonation.

Then there's ignition timing, valve overlap, valve timing and fuel injection timing. All these parameters are computer controlled and have a direct impact on power, efficiency and emissions. Bottom line: The N63 is capable of just as much power as the N63 Tu. Maintaining emissions and reliability while doing so with aftermarket SW and mods is the sticky point.

BTW. I have read (not experienced) that valvetronic actually has worse throttle response than a regular butterfly system.

Good catch on the final drive Dunderhi. I hadn't noticed. In theory this would hurt acceleration off the line even with the slight additional engine torque. But given the 8 speed tranny and all that power (either engine), it really comes down to a good launch - especially with RWD. The higher drive ratio should result in better mpg, assuming you're not Southy running around in Sport mode all the time. It is odd that BMW giveth with one hand and taketh away with the other.

So Southy, you can relax. WIth the simpler more responsive standard throttle, lower rear end ratio and some after market boost - our 2012's should kick 2013's butt.
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