Quote:
Originally Posted by Driver72
Yes, as I said, the aerodynamic difference is small, but it's still there.
There is a pretty decent amount of drivetrain loss between RWD and AWD.
Usually about 3-4% more in AWD.
Think about it, it's a no brainer, power being sent down a driveshaft to 2 wheels compared to power being sent down a driveshaft through a device that divides the power and that is required to turn 4 wheels instead of two.
BMW should of made the transition to sending 100% of the power to the rear at 75 mph not 100 for U.S. bound cars, that would help.
The weight difference between the two cars is officially 243 lbs not 220.
That would require an additional 20-22 hp in the 335xi to match the power to weight of the 335i, and probably an additional 6-8 hp to compensate for the additional drive train loss.
So the 335xi would need an additional 26-30 hp to match the 335i in power to weight and drivetrain (and an additional 1.5 as you stated for the aerodynamics difference).
Sounds about right, considering in that video while they were in the rain, the 335i was pulling away at a rate you'd expect to see of a car with 30 more hp given equal power to weight and drivetrain losses.
Tires at 20 psi in RWD cars would not slow you down 30 hp worth (maybe 10-12 at most). This is based on experience at drag strips and lowering my tire pressure too much and seeing my times dip a bit, but not drastically.
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Easy Killer. XIs are still BMWs...we're on the same team here.
off-topic but:
1) I guess it depends where you get your information from re the weight difference: 3825/3605 (6AT), 3814/3594 (6MT) = 220lbs
http://www.bmwusa.com/Standard/Conte...fications.aspx
2) FWIW 3-4% of 300HP is 9-12HP and 6-8HP is a 1-2% loss. One point worth remembering is that it takes about 20HP to push a nearly 4000lb car along at 55mph of which a small fraction (5hp in the link provided) is rolling resistance and the rest is the wind.
http://www.holtrv.com/pdf/understanding.pdf With that backdrop, how much HP is a front axle assembly really likely to draw?
I think we're in relative agreement that the XIs are probably slowed down 20-30HP (from weight mostly, IMO) vs a 335i which the conventional wisdom suggests is around 2+mph difference in trap speed on stock cars. ET is tough to call because of what should be a decent disparity in 60ft times in favor of the XI.
There is literally one unmodified 335xi listing on dragtimes at 101mph trap and BobVader's time/speed comes very close to matching the fastest 335Is around 13.3@103-104mph. Thus this thread attempts to bring more stock car comparisons to light as there are so many less variables vs tuned cars. The goal for me is to highlight some of the basic strengths and weaknesses of the 4 models (ok 6 for you E93 folks lurking out there).
I'll add my own experience to the list soon but please pile on with your timeslips to help set the standards for what we believe each car is capable of.
thanks
BB