Details on BMW's new N55 engine have been out since last summer, but we haven't discussed them much here beyond telling you that it's the best of the 3 engines (2 for us) that BMW will offer in the 2010 BMW 5 Series GT. But this isn't just a turbocharged inline-6 the company has made specially for misshapen crossovers. Rather, this engine will replace the current twin-turbocharged inline-6 we know as the N54.
The N55 shares its all-aluminum block, direct injection system and 10.2:1 compression ration with the N54. And the weight difference between the two is little more than 4 pounds. But the new engine differs in two key ways:
--> It has a single, twin-scroll turbocharger (which BMW calls "Twin Power") instead of two smaller turbochargers.
--> It is the first BMW inline-6 to use Valvetronic (er, make that the 2nd, as the N52 engine, seen in the 2006 330i, had it first), whereby an electric motor built into the cylinder head continuously varies the amount of valve lift.
The addition of Valvetronic reduces fuel consumption by 8 percent. It also quickens response time when you're cruising along at low load and have a sudden, urgent need to be at wide-open throttle. And peak torque (still 300 pound-feet) comes in at just 1,200 rpm now instead of 1,400 with the N54 engine. Peak horsepower is still listed at 300, but the power curve doesn't taper off as soon.
More details and potentially interesting graphics after the jump.
This graphic shows the twin-scroll turbocharger. Obviously. Here you see the divided exhaust streams for the cylinder banks; they don't meet up right before they enter the turbine.
"With this separation of the two streams, we increase the momentum of the fluid -- revving up the turbine quicker," Raoul Holder, senior product development engineer, told journalists gathered at this week's BMW University seminars at the North American HQ in New Jersey. "That gives us the possibility to have high low-end torque combined with very high power output."
"This has the same advantages as two small turbines (as on the N54); it's just combined in one housing (in the N55)," he added. BMW could have used a single, twin-scroll turbocharger on the N54 engine, Holder said, but company officials were concerned the quality would not have been up to par at the time the 335i coupe launched in 2006.
This graphic shows a claimed 2.25-second transition time from low load to full load with the N55 turbo six versus 2.75 seconds with the N54 engine.
rallyandbosox says:
07:24 PM, 11/11/09
Excellent write-up Erin. I was curious as to exactly why BMW is ditching the twin-turbo engine so quickly but it makes a lot of sense now.
Will the N55 make a 335i cost any more compared to the N54 model?
blueguydotcom says:
07:43 PM, 11/11/09
Will they fix the HPFP issue 335is have?
bimmerjay says:
09:53 PM, 11/11/09
"It is the first BMW inline-6 to use Valvetronic, whereby an electric motor built into the cylinder head continuously varies the amount of valve lift."
That's not correct, the N52 engine (first introduced in the U.S. in the all-new 2006 E90 325i and 330i sedans) uses the Valvetronic system, and was actually the first application on a BMW inline-six. The N55 will be the second application since the N53 (has DI) and N54 were not fitted with it.
"BMW could have used a single, twin-scroll turbocharger on the N54 engine, Holder said, but company officials were concerned the quality would not have been up to par at the time the 335i coupe launched in 2006."
Talk about quality, kind of ironic considering all of the problems the HPFP had not only at launch but for *several years* after the introduction of the N54 engine despite subsequent pump redesigns. 2009 models were still having failures. N54's in '07 and '08 335i's also had a waste gate rattle issue - which for almost a year was "fixed" by a programmed throttle lag to slow the actuation of the gate. There were also some scattered VANOS cam problems.
Full disclosure: I am now on my third BMW with an N54 engine - two are currently in my garage - and none of them have had a lick of trouble, with anything except for my 2007 335i coupe's squeaky right rear brake pad sensor. Go figure.
bimmerjay says:
09:57 PM, 11/11/09
Oh and how could I forget BMW's omission of a secondary oil cooler, which was only begrudgingly fitted to all sport-package-equipped 335i's as of March 2007 production, previously only MT cars with the ZSP option got it. So add overheating on sans-oil cooler cars under hard use to the list of the N54's early woes.
bimmerjay says:
10:12 PM, 11/11/09
@rallyandbosox,
"Will the N55 make a 335i cost any more compared to the N54 model?"
It shouldn't, not based on the engine alone at least. It is considered a direct replacement for the N54, not a step-up like the N54 was to the 255 hp N52B30 engine in the 330i. There is speculation the engine will be fitted to the face-lifted 3-Series coupe and convertible this spring.
hondacura4 says:
10:34 PM, 11/11/09
To make this simpler, the improved N55 just makes the same peak power/tq but makes the power/torque sooner vs the N54. In essence, BMW just fattened up the power under the curve.
Bimmerjay, my younger brother has a 2008 335i 6MT sedan and has yet to have ANY problems. I think his car has right around 23K. Love the package and the power but I find the previous N/A 255hp 3.0 I6 to be more entertaining.
zoomzoomn says:
04:50 AM, 11/12/09
This car can also be tuned to more like 400hp. I have read some blogs on some downsides even with the stock setup. Some fuel system reliability issues.
blueguydotcom says:
07:00 AM, 11/12/09
Maybe the HPFP/turbo issues are isolated. Given what I've been told at the dealership, it's a big enough issue that BMW is pretty willing to help people get out of their 335i if they've had multiple turbo issues.
charlesncharge says:
10:39 AM, 11/12/09
@bimmerjay:
"It is the first BMW inline-6 to use Valvetronic, whereby an electric motor built into the cylinder head continuously varies the amount of valve lift."
What the above should've mentioned, was that it's the first I6 application of BMW's Valvetronic, combined WITH turbocharging. As you're obviously aware, the N54 engines lacked Valvetronic; VANOS yes, Valvetronic, no. Valvetronic is similar to Fiat's new Multiair valve control system. Nissan/Infiniti's 3.7L V6, also uses something similar.
BTW: I've got an '08 135i, that's just had its HPFP replaced.
eriches says:
11:01 AM, 11/12/09
@ bimmerjay: Indeed, I was careless with the facts about about Valvetronic. The N52 engine sure does have it. I'm going to run a correction. Thank you. -- Erin Riches
charlesncharge says:
11:20 AM, 11/12/09
@eriches:
Please don't be too hard on yourself. A lot of us are just real sticklers, myself included.
Keep up the great work - I still say you're one of the best!
BMW Valvetronic:
http://www.youtube.com/watch?v=BWsRSfe7K4M
bimmerjay says:
11:57 AM, 11/12/09
@charlesncharge,
Correct, this is BMW's first application on a FI inline-six. One thing I do not like about Valvetronic - it adds considerable weight to the engine and increases reciprocating mass (needs heavier valve springs, etc) which in turn limits redline. This is but one reason it's not used on ///M engines. It didn't negatively affect the N52 engine in any perceptible way (I had an '06 330i), but I didn't miss it on the N54. However if the next-gen version being fitted to the N55 improves fuel economy without any negative performance effects, I'm all for it.
@Erin,
Thanks for correcting... and may I say, you are one of my all-time favorite writers on Inside Line! Thanks for all the great work.
charlesncharge says:
12:57 PM, 11/12/09
Here's yet another BMW self-promotional video, just in case anyone else is wondering what all the fuss is about:
Valvetronic: http://www.youtube.com/watch?v=zW8rub-yuZQ&feature=related
shaddai says:
03:44 PM, 11/13/09
"The N55 shares its all-aluminum block, direct injection system and 10.2:1 compression ratio with the N54" - this should tell you everything you need to know about whether or not this engine addresses the HPFP issues. My vote is no.
maxnix says:
07:43 AM, 05/29/11
So, any other internal differences? It is rumored the N54 has a forged crank while the N55 does not. Can you comment?
Also rumored that while the N54 employs Mahle pistons, the N55 are sourced from Turkey. If true, i there any material difference? Connecting rods or bearings?