Detailing differences between n54 and s55

[JoeFromPA]

Hi all,

As we learn more about the S55, some of it's top-line specifications seem very similar to the n54. Same size, bore, and stroke I believe. Twin turbo of course, Etc.

Ultimately, the n54 is and was an absolutely wonderful and revolutionary engine and platform - albeit with cooling and fueling issues that seem to have been resolved since it's debut. The n55 that followed was somewhat of a minor step backwards, albeit with increased reliability.

I'm of the stance that if M took the n54 and simply took the steps necessary to make it an M engine, that's ok. If BMW took it and designed new cylinder lining, pistons, crank, cams, and other internals and simply designed it to better handle ~380whp stock - then I'm all for it.

What I'd like to do is take a moment and detail the differences we know about thus far in the s55 compared to the n54. I've tried to list all the things I know off the top of my head, but please add to it and I'll edit this post:

1. Closed desk (stronger casting, heavier but with less flex/better vibration suppression and better cooling/heat capacity)
2. Forged crankshaft/better crank for high RPM operation/harsher operation
3. Different piston design
4. Spray on cylinder lining - better design, lower friction, better sealing, better wear, longer lasting
5. Valvetronic added AND unique valvetronic changes allowing the continued firing of 2-4 cylinders when off-throttle to continue turbo spool up/reduce or eliminate turbo lag
6. Significantly enhanced cooling in terms of the block itself and ancillaries
7. New turbos. I've read both Mitsubishi or Honeywell - not sure which it actually is. I suspect they will be very similar in size to the n54 though, by which I mean SMALL turbos capable of the fastest response at the expense of flow volume. Edit: It appears likely the Mitsubishi TF035 is the chosen turbo family with design elements unique to the S55. Not confirmed.
8. New exhaust manifold-to-turbo design for less restriction/faster response
9. Magnesium oil pan
10. Revised oil pump and pick-ups better suited for track use
11. A lot of "efficient dynamics" ancillary changes from the n54 such as EPS, alternator disconnecting, etc.


We all know it's spec'd for 106 more tq and ~100-125 more hp, which is essentially a tuned n54 from an output perspective.

However, I'm more interested in the totality of their changes and assessing the s55 as a whole.

Things I don't yet know about:

1. Flywheel (is it the same as the 1M in addition to the 1M's clutch/trans)
2. Cams and cam profiles
3. Head/intake design

This is not a thread for bashing the S55 or otherwise. It's a thread for early technical information sharing and analysis.

[aus]

Nice. I was wondering the same thing.
Lets hope BMW did something about the gunk build-up on the intake valves too.

.

[JoeFromPA]

Originally Posted by aus

Nice. I was wondering the same thing.
Lets hope BMW did something about the gunk build-up on the intake valves too.

.

Thanks. To be clear, like any changes, they SOUND better but they may ultimately be problematic. For example, spray-on cylinder lining has been used in a number of applications with great results (compared to sleeves) - but that doesn't mean it'll yield the same result for the S55. I think it will, but ya never know.

...

I have an n54 and at 94k miles it still hasn't needed it's valves cleaned. I'm sure it'll come, but honestly let's say the s55 needs it every 50k miles and it's the same process as the n54 - that's a $350 cleaning (as it is now via good indy service providers). On an m3, that's pocket change maintenance.

[Boss330]

Some info on the turbos:

From this photo it seems the S55 has a TF035 Mitsubishi turbo.



This is the flow chart of one version of the TF035:



Overview of Mitsubishi turbochargers:
http://www.mtee.eu/products/turbocha...harger-line-up


The numbers I can read from the designation is:

TF035HI 4W-11HE17-6.0


The number should decode as follows:

TF035: Turbo Family
HI (or HL): Shaft and Wheel combination
4W: No idea
11HE17: Turbine and compressor sizes (a "normal" TF035 usually has a 10-14 size compressor, this has a 17 compressor - a "normal" TF035 supports around 240hp)
6: Turbine housing A/R

Since it seems the compressor unit is quite a bit larger than a std TF035, they should be able to support boost and air flow of well over 250hp each.

[Alessandro]

Originally Posted by Boss330

Some info on the turbos:

...

Since it seems the compressor unit is quite a bit larger than a std TF035, they should be able to support boost and air flow of well over 250hp each.

+1

cant wait for the M4 should be good

[JoeFromPA]

Huh, very surprised by that turbo if that is chosen. Mitsubishi is a huge turbo manufacturer and makes both great and poor turbos.

The TF035 family turbo is used on the BMW 320d and other small displacement engines and is generally not a really well regarded turbo (was also on the Subaru Forester I believe).

Now that being said, you can take almost any well cast turbo housing and upgrade the turbines, shafts, and bearings and have a masterpiece. So if Mitsubishi is upgrading the internals for BMW as a specific application for the S55, then I'll reserve judgement.

[mkoesel]

Originally Posted by JoeFromPA

Hi all,

As we learn more about the S55, some of it's top-line specifications seem very similar to the n54. Same size, bore, and stroke I believe. Twin turbo of course, Etc.

...

The n55 that followed was somewhat of a minor step backwards, albeit with increased reliability.

I'm of the stance that if M took the n54 and simply took the steps necessary to make it an M engine, that's ok.

I prefer to think of the S55 as a combination of the best traits of both the N54 and N55. While it is true that it is a twin turbo design like the N54 and unlike the N55, it also has Valvetronic like the N55 and unlike the N54. Naturally there will likely be other differences from the N54 too, which resulted from lessons learned over the past 7+ years of experience with turbocharged engines.

2. Forged crankshaft/better crank for high RPM operation/harsher operation

The N54 actually has (or at the very least had) a forged crankshaft as well.

5. Valvetronic changes allowing the continued firing of 2-4 cylinders when off-throttle to continue turbo spool up

Just the presence of Valvetronic at all is a change from the N54. Don't forget about the new anti-lag system too, which was almost surely made possible by the addition of Valvetronic.

[JoeFromPA]

Mkoesel - I updated my posting to clarify that valvetronic is being ADDED.

Also, I read one BMW engineer's account that they actually spent a lot of time around crankshaft development. I'll try to update that when I know more, but yes, both the n54 and s55 have forged crankshafts. The n54 for at least SOME iterations had cast pistons, not forged, whereas the S55 is being reported as having forged pistons.