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      12-31-2007, 04:48 AM   #74
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Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

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Originally Posted by bruce.augenstein@comcast. View Post
I thought we had already discussed some of this? Oh well.

Assuming regenerative braking is shorthand/marketing talk for disabling the alternator during hard acceleration so no power is lost to charging at that point, what are we really talking about here?

Assuming 125 amps at 14 volts max charge rate, and also assuming around 80% efficiency (alternator will be well over that, but some power is lost to resistance in the wiring), we're talking, what, three HP?

Now assume well under a third of that number unless you're running A/C along with the rear window defroster, seat heat on extra crispy and that aftermarket boom box in the trunk during your drag race or top speed run.

Now multipy that by 85% to get the rear wheel number...

...and you discover that two healthy hamsters can generate that amount of power.

OK. Three hamsters.

OK, now figure (and here's the real point we discussed before) that the SAE is already on board with this for the ratings run.

Either way, we're talking a dimple on a pimple on a flea's left nut. It just doesn't matter.

Charcoal filter? I must've missed that. How will that be worth 10 HP and why won't the SAE be informed?

Bruce, just FYI - a really old, almost dead thread, but your points are valid/worth responding to.

The engine specs should include with alternator so actually what it really means is that in an apples to apples comparison the M3 engine is actually making less power than any other engine without R.B. since it must have those losses included and still rate at the net output.

What R.B. offers though is IMO a good performance and green enhancement. As much as I am not fan of much BMW marketing I do think "efficient dynamics" is real and present in the car. I suspect the E9X M3 to have an alternator similar to the E60 M3, which is a full 2.4 kW this means 3.2 hp. My initial estimates were indeed quite liberal. I don't know enough about how the cars electrical system works to say how much of that peak 3.2 hp would typically be consumed and if it varies strongly with the current use of accessories such as stereo and AC.

The charcoal filter is an secondary filter in the intake tract of the E60 M5 present for (I think) insuring no loss of fuel vapors from the intake system to the atmosphere. From reading up on this over at and some tentative dynos, I think the estimate was that removing this filter was good for about 10 crank hp. I have not heard definitively if the M3 has this filter. Can some owners chime in?