Bimmerfest - BMW Forums - View Single Post - n55 vs n55HP - How do we get that extra power and torque?
View Single Post
Old 01-31-2013, 08:30 PM
cordoor's Avatar
cordoor cordoor is offline
cor door sedan
Location: Utah
Join Date: Jun 2012
Posts: 1,104
Mein Auto: 2013 550i xDrive
Originally Posted by dunderhi View Post
The link below calulates 4000lbs will need 313hp to attain 100mph in a 1/4 mile
Ok, my OCD just kicked in.

The 535i (RWD) is 4090 pounds according to BMW's website. That calculator says 320 HP is needed to reach 100 MPH at that weight (319 HP doesn't quite get you to 100, 320 gets you a bit over).

But I don't know how that calculator could be accurate.

HP is just a calculated value. It is calculated by multiplying the torque by the RPM and then applying some other adjusting number that pulls it into the range its in (I don't remember what that is).

So if you are looking at a graph of HP over RPM's, what matters in terms of power to the pavement is the area under the curve. And as everyone has noticed, there is more area under the curve on the right side of the curve (duh). So the goal is to get to that right side of the curve as quickly as possible and then to stay there as long as possible.

Gearing is critically important to this. With an 8 speed tranny, you can stay near the right side of the curve longer because when you shift from say, 1st to 2nd, the RPM's drop, but they don't drop as much in an 8 speed tranny as they would in a 6 speed tranny. You get to stay more towards the right side of the curve and so you put more power to the pavement (more area under the curve there).

So gearing matters. I don't see a way to input gearing on that calculator. But not only that, they are only asking for peak HP, so I can't see how they can calculate how much power you put to the pavement and consequently, how quickly you get to 1/4 mile.

Reply With Quote