Since the moment we learned of the N55 replacing the N54 we ‘ve asked ourselves one simple question, are we getting a more efficient yet less powerful engine? Automobile magazine has wondered the same thing and (thanks to dyno testing the N54 over the years) has some solid data to help figure it out all. So lets start the fight. Here ‘s an excerpt from the Automobile piece:
>The 2007 BMW 335i ‘s N54 twin-turbo six is rated by its manufacturer at 300 hp and 300 lb-ft of torque. And when we put the first 335i coupe on the rollers, it laid down a very impressive 275 hp and 300 lb-ft of torque. In awful conditions, too: 92 degrees of humid, Fahrenheit heat.
>Remember — the power measured at the 335i ‘s rear wheels should be lower than the engine ‘s rated power. Some of the engine ‘s output is lost to friction in the transmission, driveshaft, differential, axles, wheel bearings, and tires. The dynamometer we used to measure the 335i ‘s output is a DynoJet model, and DynoJets tend to read higher than other dynos, but the output was a good bit higher than we expected.
The gist? The N54 is an incredibly consistent and underrated engine in all of its various forms. The 335is version is equally consistent and underrated but about 20hp more powerful. (The full numbers after the break)[poll id= “7 “]
Now enter the N55…
>And now to the N55: well, it doesn ‘t, in fact, make as much power as the others N54s we ‘ve tested, but it does make slightly more torque. Peak numbers were 266 hp and 302 lb-ft. Before you start typing your “N55 sucks! ” forum posts, let ‘s remember that while the N55 put down 10 less horses than two of the N54s, a third N54 produced 10 more horsepower than the others. Meaning: 10 hp is within the noise when you ‘re at this power level — it ‘s a variation of less than 4%. And you can easily see 4% variance between runs on the same engine.
So wait a second, they ‘re kinda the same?
>In fact, the only real difference between the regular N54s and their successor, the N55, is that the N55 ‘s output drops off more as it approaches its maximum speed. This isn ‘t a surprise-the N55 has only one turbo with which to force-feed the engine with air. To keep turbo lag at a minimum, BMW likely used the smallest turbocharger possible that could achieve the (modest) boost levels that the N55 runs on. A slightly larger turbo might have increased high-rpm boost (and thus, power) slightly, but it ‘d come at the expense of greater lag. And besides, we ‘re talking about an engine that over-delivered to begin with.
>The end result? We can finally and directly compare an early N54, late N54, high-output N54, and an N55. The N55 exhibits less turbo lag in normal street driving, and even though its peak output was near the bottom of the group of engines we ‘ve tested, it ‘s still well within its rated peak horsepower output — and well above its rated peak torque output.
So the moral is yes, the N54 is more powerful. But the difference isn ‘t huge and it ‘s mostly within the test ‘s error margin.
Source: Automobile Magazine