Are stock 3 and 5 series HP Underated?

[g4ian]

I can't understand how the stock 3 and 5 series are as quick as they are with there hp ratings. To me it seems there lbs/hp ratings are worse, yet they make good times in 0-60 and the 1/4 mile. I was in the process of trying to put some numbers together last night, but my wife came home and that ended that. Anyone care to explain?

Thanks,

g4ian

[ryoken]

Sure. There are several things that come into play here. One is gearing. BMW is very careful about selecting the right ratio for each gear in the transmission. They have 3 different gear ratio sets for the 325/330 manual/auto combinations, IIRC. Plus, peak HP does not determine acceleration times.. it's the torque curve that does that. BMW engines have a flatter torque curve, and 90% of the torque available through most of the RPM range. The VQ35 has a peakier torque curve.. more up top, but less down low.

If you look at the two torque curves on a dyno chart, the one with the greater area under the curve from idle to redline is going to have more oomph. Plus, you throw in gearing and weight of the vehicle.

So, the weight is fairly close, but the 3 has a flatter torque curve and a more optimal gearing setup.

[DHCrocks]

good question, I was wondering what their numbers were too, since I read a few articles in magazines that also stated that BMWs engines are under rated. anyone got dyno numbers from stock BMWs?