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m6pwr 11-29-2012 01:50 PM

The virtues of our 6 cyl. N55 engine
After reading a thread about the supposed disadvantages of the N55 vis-a-vis the N54 twin turbo, I came across a N55 BMW Training Manual online that sheds further light on the subject. Admittedly, the N55 is not as easily tunable as the N54. That was recognized from the very beginning due to the number and arrangement of the turbos. But there are other considerations.

Some of the advances incorporated into the N55 have been well publicized: Average 8% better fuel economy; lower CO2 and NOX emissions; peak torque earlier (1200 rpm vs 1400 rpm); and no turbo lag. But a review of the BMW Training Manual on the N55 shows many detailed refinements that taken together make a great engine (the N54) even better. The following is a summary (the numbers in parenthesis refer to the page numbers; the training manual pdf can be viewed by Googling “pdf n55 engine”):

New coolant passages between cylinders to improve cylinder cooling (p.14 & 81).

New lightweight cast iron crankshaft (6.5 lbs lighter) (p.14).

New design con rod that spreads power-stroke forces more evenly on the wrist pin (p.19).

Oil supply in oil pan vacuum pump now lubricated by filtered oil vs. unfiltered oil (p.22).

New ecu-controlled electric oil pump reduces parasitic power losses and optimizes both volume of oil pumped and oil pressure (p.24).

New cylinder head with third generation Valvetronic reduces emissions and improves fuel economy, and now has cooling passages for the fuel injectors (p.32 & 80). New Vanos is lightweight aluminum and provides faster adjustment of valve timing (p. 44).

New cylinder head cover incorporates completely redesigned crankcase ventilation system to better separate oil from blow-by gases (p. 34 & 38). Improved crankcase ventilation extends oil service life (p.16).

The camshafts are now a lightweight hollow design (p.41).

New, simpler, less complicated Bosch solenoid fuel injectors specially adapted to the combination of Valvetronic III and turbocharging (p.49).

New vibration damper on the belt pulley reduces belt load for better belt life (p.53 & 54).

New twin scroll turbo provides enhanced throttle response and incorporates a new electric diverter valve that eliminates surges in boost pressure and reduces stress on the turbo bearings (p.65 & 91).

Less complicated exhaust system that provides one catalytic converter vs. two as on the N54 (p. 67). Improved oxygen sensors that provide faster response (p.95 & 96).

A new engine-mounted DME module that considerably simplifies and shortens wiring (p.82).

Ignition coils redesigned and “sturdier” (per the manual) (p.94 & 100).

As to the sturdiness of the N55: Two N55-powered f30 335’s were raced by a South African team in 2012 (including being raced in Germany at the 24 Hrs of the Nurburgring). Other than a modified turbo, racing ecu, and aftermarket exhaust, the N55 engines were stock and produced 408 hp and 443 lb ft of torque. According to a representative of the team, in an email, the engines ran the entire 2012 season without any engine failure or need to be “refreshed”. See

The X Men 11-29-2012 03:42 PM

m6pwr, nice write up. I knew there was some difference between the N55 and the N54, but did not realized that the N55 was so much more advance. So is it true that the N55's block is made out of a alum mag alloy and the N54 is alum?

jason60050 11-29-2012 03:49 PM

Great write up! I love BMW

Quacker 11-29-2012 05:29 PM

Just read the entire PDF. Very entertaining!

RambleJ 11-29-2012 05:51 PM

The car needed a modified turbo to get to 400hp???? :eek: Give me back my N54 please!!

m6pwr 11-29-2012 07:32 PM

Both N54 and N55 have aluminum blocks with cast iron cylinder liners.

FWIW the ADF team ran an e90 335 in the Bridgestone Production Car series in 2011 and it had a stock N54 putting out 300 hp (maybe they thought the N54 wasn't strong enough to run a full season of racing in modded form :)). Just joking!

I don't know the particulars of the N55 turbo mods the team ran in 2012, and how the series they ran in differed, if at all, re mod restrictions. It may have been technically possible to do mods that produced greater power/torque but not possible under the 2012 rules of the series.

As I mentioned, I think it was realized at the outset that the N54 is more tunable (based on my memory of an article in the CCA mag Roundel when the N55 first came out) . But in stock form I think the N55 is easily the equal of the N54. I had a Z4 N54 with the Dinan Stage II mod (385 hp and 424 lb ft torque). With the 7 speed dual clutch tranny it was a rocket ship. But all that added boost had its price. I did used oil analysis and the percent fuel dilution went thru the roof. Didn't keep the car long enough to know if that might ever have had any deleterious effect in the long run.

Me - - I'm perfectly satisfied with the N55 in stock form in the 535 Msport. Great engine, great car. And I'm reasonably confident that if I keep it, it will last a long time. Will I have to worry about intake deposits? Hopefully not with the redesigned crankcase ventilation. Will the injectors last longer than 75-100k mi? Will the turbo last any longer? Don't know. Time will tell.

schnell525 11-30-2012 10:57 PM

From my E60 and F10 535xi's, (outside of hes. from the N54) I think the N55 was a bit nicer of an engine. The transmission of course comes into as a differentiating factor. The N55 definitely helped with the turbo lag and it would drive more smoothly. Out of the two engines, I think I liked th N55 better--but the F10 is a bigger boat than the E60.

PeterC4 12-01-2012 04:24 AM


Originally Posted by RambleJ (Post 7222145)
The car needed a modified turbo to get to 400hp???? :eek: Give me back my N54 please!!

??? So you would race a car for a full year with what....a Dinan tune and a bottle of water for the cockpit? I don't think the modification of the turbo was solely to create horsepower. It's one thing to tune a car to drive around the street, its another to race it for 24 hours. No doubt the car was modified for the race track. Not with standing all that, it seems to be fairly resilient. The early N54's had their issues.

Alan L. 12-01-2012 05:44 AM

Stock for stock i think the N55 feels better than my N54 E90. Sounds and feels a bit smoother. Having a tune on it thats a different story because the N54 makes a ton more hp/tq. I hit 350whp and 400wtq with just a tune and exhaust with my N54 where as now i am probably barely getting 300whp and 350wtq with the same mods.

Seems like a lot of the enhancements listed above makes the motor less robust compared to the old motor though. lightweight sounds like less strong to me. I believe the N54 had a forged crank,rods and possibly pistons which is why guys have already pushed that motor over 500whp without any issues.


PeterC4 12-01-2012 07:31 AM

Alan, have you enabled the "Sport Meters" through coding? I would like to see if someone with a tune has looked at the reported torque and hp after their tune. I haven them enabled and I get some strange (very high) torque readings, like 400 ft lbs. Doubt the accuracy of that, but I'm curious as to how others read.

SuperTerp 12-01-2012 09:56 AM


Originally Posted by RambleJ (Post 7222145)
The car needed a modified turbo to get to 400hp???? :eek: Give me back my N54 please!!

I have one now it I'll always take it over an N55 :D

Elias 12-01-2012 12:50 PM

I had an 09, E90 535i i loved that car the N54 is a beast takes tunes very well the N55 is a more tamed version unfortunately!:tsk:

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