2007 BMW 335i Coupé

In the Name of Science, Seven Thousand RPM

Testing the Dynolicious software with a BMW 335i.

Andras Horvath drives his BMW 335i with the author riding shotgun

It is when you approach six thousand RPM that the quicksilver rasp enveloping the tight cabin takes on the urgent menace of something not quite meant for public roads. As the tach shoots for seven thousand, your muscles tighten for the robotized upshift, chief amongst them the tensors tympani in your middle ears.

Lithograph of the middle ear, showing the insertion of the tensor tympani muscle on the malleus. Source: Gray’s Anatomy

Their function is to pull on the malleus, the largest of the ossicles in the middle ear. The malleus in turn tenses the tympanic membrane, protecting the auditory system from extreme amplitudes of noise. Which is exactly what BMW’s N54 engine produces in copious amounts at high revs.

The example at hand powers a 335i coupé and we are on a mostly deserted stretch of blacktop, making speed runs for science.

Clenched in my white-gray fingers is an iPhone 3G and I am about to have a 180-pound hairless monkey land on my sternum.

I have never before sat in the 335i, a car considered by many to be on par with the E46 M3, which makes the greatest noise this side of Emilia-Romagna. The performance figures are within a few percent: the M3 has 333 horsepower to propel 3,460 pounds to 60 mph in 5.2 seconds, while the 335i needs only 200 milliseconds less to do the same to its 3,527 pounds with 306 hp from its twin-turbo six.

Heavy, yes, but this thing will outrun a Lamborghini Miura.

Screenshot from Dynolicious showing the profile screen for Handras’s BMW 335i

Of said numbers, we need the weight. The rest we measure with our roadside dyno outfit: a pair of hands—mine—and a telephone. It is an iPhone 3G running Dynolicious, a piece of software that uses the phone’s accelerometer to record performance data. I hold it steady, press reset, then try to hold on as Handras, the car’s slightly edgy owner, drops the clutch. Or whatever passes for a clutch in a modern Bimmer with computers wedged in between your senses and the mechanicals.

One g of deceleration sounds barely more than bouncing up against a wall, especially when compared to the g-load of Formula One drivers and fighter pilots, yet the human body is quite unable to treat it a normal. The inner ear has evolved to treat one g coming from the direction of your feet as dandy. When said acceleration comes not at your soles but at your clavicles, your vestibular organ is visibly distressed.

The seat belt bites into my chest at 1.03 g. Data gathering complete.

A cushion of electronic music keeps us giddy in the cool August night as we clamber out of the car to look at the results. When you consider that the measurements were taken with a telephone instead of specialized equipment, the results are all the more remarkable. Both acceleration and deceleration figures are spot on with their official counterparts:

Dynolicious stats after a run with a BMW 335i, showing a 0–60 time of 5.39 seconds and max braking power of 1.03 g

Those who have driven it say the N54 feels naturally aspirated. This is due to the fact that it uses two small turbos with the pressure dialed all the way down to 5.8 psi. This does get rid of the turbo lag but does not get rid of a BMW straight six’s unique selling proposition: that noise.

That noise between six and seven thousand rpm.

That noise you want to wallow in.

Amateur science has never been such fun.

Published on Tuesday, August 12th, 2008


By omm:

Maybe you have right.
But I think, the atmosferic straight 3-3.5 litre straight six is The Engine.
It s linearity and metallic roarring in revs are in the top of 6 cylindre voice toplist among with the bubbling porsche boxer.

Oh, and if you want G’s, try the Nose. It’s very very horrible.

Posted on Tuesday, August 12th, 2008

By g:

The application is really cool, do you need a jailbroken iPhone / Touch(?) to run it?

I’m wondering how precise the measurements are, coming from the iPhone accelerometers. I don’t think they are meant to measure any high g’s, taking into account their original role. (eg. turning around the screen orientation)

Posted on Thursday, August 14th, 2008

The application is really cool, do you need a jailbroken iPhone / Touch(?) to run it?

You can buy in the App Store for $10 and use it on any phone running 2.0 I guess.

I’m wondering how precise the measurements are, coming from the iPhone accelerometers. I don’t think they are meant to measure any high g’s, taking into account their original role. (eg. turning around the screen orientation)

I’d have to get in touch with some serious hardware geeks for that—all I know is the stats we measured were very believable. As far as I remember, the manufacturer claims to measure acceleration times down to 0.01 of a second. I’m not so sure how that factors in with g-loads.

Posted on Thursday, August 14th, 2008

Nice ride, but I’d prefer SL MB to Bimmers… Otherwise, i gotta checkout this iphone-thingy…

Posted on Saturday, August 16th, 2008

“I’m not so sure how that factors in with g-loads.” – g, itself is the value of the acceleration of a free-falling body, 9.81 m/s^2. g-force or g-load is the measured acceleration expressed in g-s. So 9.81 m/s^2 is 1g, 19.62 m/s^2 is 2g, so on. Don’t know how good the iPhone’s measurement system is, but it should be capable of detecting high accelerations – a sudden move of the apparatus can cause tens of gs. I don’t think this is the weakness of the system. But try to measure the acceleration of something vibrating – an old washing mashine, for example, I suspect that iPhone won’t be to good at that…

Posted on Saturday, August 16th, 2008

And to think that I used to be fairly competent in understanding basic science. Mein Gott!

On the other hand, Dynolicious has suddenly become the iPhone’s unique selling proposition.

Posted on Monday, August 18th, 2008

By xtal:

if you want exact values, get a PDA and an OBD2 interface:
(or with a tool like DigiMoto PDA, you can also read and erase OBD error codes.)

the OBD2 port in the E92 is in the legroom on the driver’s side, next to the engine hood release lever.

Posted on Thursday, August 21st, 2008

0% drivetrain loss?
Peter, Peter…

Approximately 15 percent for stick-shift cars and 25 percent for automatics.


Posted on Saturday, November 8th, 2008