Update: False. S55 engine has oversquare bore/stroke and shares "nothing" with N55!

[NISFAN]

Originally Posted by Needsdecaf

I love this discussion and can't wait until more concrete details come out.

Nontheless it should be fascinating to see how this engine performs in the real world. I predict tuners will have total nightmares with it too.

Well for tuners I think big HP gains are going to be difficult, unless they can crack the ECU. However, as the engine compensates for high temp/high altitude, I'm sure a piggy back signal bender would work quite well

[LDSM]

Originally Posted by index1489

Yep I'm thinking the lack of liners allowed them to increase the bore without lengthening the block.

I wonder if this is the same liner-less tech Ford came up with and is used on the GTR, according to this article on jalopnik, the benefits of this showed during Fords testing at 250k miles the hone pattern was still there, virtually no wear, the coating acts like a sponge pours creating a very good bearing surface.


http://jalopnik.com/5467038/the-ford...he-nissan-gt+r

Thanks for the link. Very interesting, I haven't seen that article before.

[Holset]

The S55 block definitely look sturdier than the N54/N55 blocks.

[swamp2]

The characteristics of an engine can certainly be altered by over and under square designs but the differences between them are dwarfed by the effect of turbo charging.

Using a caliper and paper print out of the new block (ugh, I am really that bad... although I could have also gone the Photoshop route) I calculate an 8.0 mm cylinder wall thickness for the S55 meaning the bore spacing is 97.6 mm. If they wanted an even mm bore spacing I'd then guess 98 mm. This makes the new block a full 33 mm (1.3 inches) longer from 1st to last bore.

Either way, I was already firmly convinced that a 1.4 mm cylinder wall spacing was completely unfeasible from a structural and thermal fatigue point of view. I posted that there was a new bore spacing at least a day or two ago here buried in one of the long discussions...

It is a new block and thus new head as well. It is based highly on the design of the N55 block but indeed has a different bore spacing.

[mkoesel]

Swamp, I agree that the S55 block pictures essentially rule out a bore increase from the 84mm of the N55 if the block were using 91mm center like that motor.

Call me stubborn, but I am still skeptical that the claimed bore and stroke (and resulting new I6 architecture) are correct. I am not saying anyone is lying, just waiting for more confirmation.

Also, as I said earlier, 98mm would be the only thing that makes sense given the N74 and existing tooling. If this is all true, prepare for an explosion in big bore and stroker kits from the aftermarket. And for those building classic BMWs with custom power trains, reliable 500hp should be possible N/A from this block.

[Boss330]

If this is correct, and if it has a 89,6mm bore then there has to be a larger bore spacing than 91mm.

Do you realize how much that affects change in tooling at the engine plant? Longer between crank main bearings, longer between cylinder bores and less space at each end if engine length is the same. Not to mention cyl head tooling.

Again if the info is correct, BMW M must have seen a MAJOR benefit of going this route. Possibly the S55 is the base for a long line of future M engines with larger volume (longer stroke) and therefore makes it economically feasible to develop such a major change from the N55?

But, doing a rough measurement of the N55 block picture, I get a bore spacing of 94mm, leaving a wall thickness of 4,4mm between cylinders with a 89,6mm bore... Where do we have the 91mm bore spacing from?
(Keep in mind that my N55 measurements were very rough and I am open to being mistaken here...)

(Doing a measurement on a picture of the N53 comes up with around 93mm bore spacing, but a very small measurement error at that scale makes a huge difference)

[Jonjt]

Originally Posted by Boss330

Possibly the S55 is the base for a long line of future M engines with larger volume (longer stroke) and therefore makes it economically feasible to develop such a major change from the N55?

I think you're on to something. I've been hoping for an M2 with an engine that is based on the S55. Since the M2 is supposed to have a straight 6, your post suggests that BMW will stick an S55 variant in it.

[NISFAN]

Originally Posted by Jonjt

I think you're on to something. I've been hoping for an M2 with an engine that is based on the S55. Since the M2 is supposed to have a straight 6, your post suggests that BMW will stick an S55 variant in it.

Or more likely a 4 pot based on a cut down S55

[Jonjt]

Originally Posted by NISFAN

Or more likely a 4 pot based on a cut down S55

I thought the M2 was supposed to be a straight 6. The M135i is a straight 6 and AFAIK, BMW has no plans to change it.

[RiverRunner]

Amazing how thin the cylinder walls are, between cylinders. I'm sure some magical engineering was done to prevent issues with heat and blown head gaskets. Looks like a groove was added to help keep the gasket in place.

[Jonjt]

Originally Posted by PackerFan

I'm sure some magical engineering was done.

Yes yes, it certainly was.

Those walls are on the thicker side, actually. Have a look at some of the large NA V8s that GM is producing. The LS7 has some rather thin cylinder walls.

[Boss330]

Originally Posted by PackerFan

Amazing how thin the cylinder walls are, between cylinders. I'm sure some magical engineering was done to prevent issues with heat and blown head gaskets. Looks like a grove was added to help keep the gasket in place.

The "groove" is only visible on the N55 engine and not the S55.

And in that direction (between cylinders) it's mostly combustion pressures that affect the cylinder walls. Towards the outside the cylinder walls are thicker as that part has to deal with the forces applied on the piston via the crank rod during the rotation of the crankshaft. Those forces act against the cylinder wall since the crank rod during large parts of the rotation is at an angle against the cylinder wall.

[Carl L]

Originally Posted by Jonjt

Yes yes, it certainly was.

Those walls are on the thicker side, actually. Have a look at some of the large NA V8s that GM is producing. The LS7 has some rather thin cylinder walls.

Yup, if I remember correctly the same is true of the walls on Merc's recent 5.5 bi-turbo when compared to BMWs 4.4 V8. Big capacity doesn't always mean bigger aftermarket gains on FI engines if initial capacity was gained through it being bored out, with exceptions and other factors involved of course.

[Boss330]

The great thing with a large bore/short stroke engine is that it's possible for BMW M and the tuners to develop "stroker kits".

With a 85mm stroke this engine gets 3219cc
With a 88mm stroke this engine gets 3329cc
With a 89,6mm stroke this engine gets 3390cc

[Boss330]

Originally Posted by swamp2

The characteristics of an engine can certainly be altered by over and under square designs but the differences between them are dwarfed by the effect of turbo charging.

Using a caliper and paper print out of the new block (ugh, I am really that bad... although I could have also gone the Photoshop route) I calculate an 8.0 mm cylinder wall thickness for the S55 meaning the bore spacing is 97.6 mm. If they wanted an even mm bore spacing I'd then guess 98 mm. This makes the new block a full 33 mm (1.3 inches) longer from 1st to last bore.

Either way, I was already firmly convinced that a 1.4 mm cylinder wall spacing was completely unfeasible from a structural and thermal fatigue point of view. I posted that there was a new bore spacing at least a day or two ago here buried in one of the long discussions...

It is a new block and thus new head as well. It is based highly on the design of the N55 block but indeed has a different bore spacing.

See my previous post re bore spacing. http://f80.bimmerpost.com/forums/sho...3&postcount=52

Where do we have the 91mm bore spacing info from?
Is it a verified measurement or just what everyone believes?

[NISFAN]

Originally Posted by Jonjt

I thought the M2 was supposed to be a straight 6. The M135i is a straight 6 and AFAIK, BMW has no plans to change it.

We'll see. I speculate on a 4 pot as it's direct rival, the AMG CLA is a 4 pot. Also I can't see BMW stealing M3/4 customers with a lower cost 'mini me'.

[Jonjt]

Originally Posted by NISFAN

I can't see BMW stealing M3/4 customers with a lower cost 'mini me'.

This is a major point of contention for me.

On the one hand, the M135i is a straight 6 and I have heard nothing saying it will ever be anything but a straight 6.

On the other, if BMW does include a straight 6 in the M2, they are going to be doing EXACTLY what they did with the 1M, the 335i and the M3.

I can't imagine BMW wanting to take market share from the M3/M4 with the M2 but, they did it with the 1M and the 335i by including potent powerplants in both of their lesser offerings. They did it twice, after all.

The fact that the M3/M4 has 450 hp leaves a lot of room for a 3000 pound, 350hp 2 series coupe but, will they use a straight 6?! An N20 derived 4 cylinder S series motor but, I hope to god that doesnt happen.

[Jonjt]

Originally Posted by Carl L

Yup, if I remember correctly the same is true of the walls on Merc's recent 5.5 bi-turbo when compared to BMWs 4.4 V8. Big capacity doesn't always mean bigger aftermarket gains on FI engines if initial capacity was gained through it being bored out, with exceptions and other factors involved of course.

Indeed.

[swamp2]

Originally Posted by Boss330

Where do we have the 91mm bore spacing info from?Is it a verified measurement or just what everyone believes?

I got that number from one of the moderators here and it was publicly posted. I have not independently verified that number myself.

[RiverRunner]

Siamese cylinders, is what they were called when GM built the 400cid small block V8. That was 40 years ago, you couldn't go too far in increasing cylinder pressures or you'd blow a head gasket.

[mkoesel]

Originally Posted by Boss330

See my previous post re bore spacing. http://f80.bimmerpost.com/forums/sho...3&postcount=52

Where do we have the 91mm bore spacing info from?
Is it a verified measurement or just what everyone believes?

I know this number has shown up in my research on BMW engines in the past. I have also seen it referred to in discussions that included engine builders as participants. Finally, it has been well accepted in any threads discussing maximum displacement for the BMW "junior six".

Did you try an internet search? I will spend a few minutes and see what comes up. I am thinking of two particular S54 discussions that went into gross details including deck height, rod length, compression height, etc.

[mkoesel]

Originally Posted by Boss330

The great thing with a large bore/short stroke engine is that it's possible for BMW M and the tuners to develop "stroker kits".

With a 85mm bore this engine gets 3219cc
With a 88mm bore this engine gets 3329cc
With a 89,6mm bore this engine gets 3390cc

Using S62 bore (94mm) and S54 stroke (91mm), you get 3.8L. Both of these dimensions should be cake for this block if it is 98mm which matches BMW V8s and V12s from N73 onward (prior V12s shared the 91mm center bore of the I6 - they increased it to accommodate the Rolls displacement).