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

[mkoesel]

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...

If not the exact same process, I am sure it is similar to PTWA, yes.

But that does nothing to explain away the fact that we'd still be either looking at only 1.4mm between bores (which is roughly 1/4 of what the GT500 engine has, for example), or we have a brand new BMW engine architecture for the first time in decades. Either would be a huge, shocking surprise as far as I am concerned.

One more thing: in the latter case is true, this engine is not an N55 derivative so why was BMW compelled to call it S55?

I can't make any of this add up in my head. I remain very curious to know the detailed dimensions of this engine block. I'd sure like to turn off my skepticism and get down to celebrating this newly designed engine.

[NISFAN]

Originally Posted by mkoesel

If not the exact same process, I am sure it is similar to PWTA, yes.

But that does nothing to explain away the fact that we'd still be either looking at only 1.4mm between bores (which is roughly 1/4 of what the GT500 engine has, for example), or we have a brand new BMW engine architecture for the first time in decades. Either would be a huge, shocking surprise as far as I am concerned.

One more thing: in the latter case is true, this engine is not an N55 derivative so why was BMW compelled to call it S55?

I can't make any of this add up in my head. I remain very curious to know the detailed dimensions of this engine block. I'd sure like to turn off my skepticism and get down to celebrating this newly designed engine.

It is impossible to reduce the bore spacings to 1.4mm, so they must have a new bigger pitch.

Regarding the S55 code, and whether it relates to the N55. It is feasible that the intention WAS to use a mildly modified N55, but the M works engineers steered it away during the project??? This is great as it means they did a lot of R&D to effectively produce a 'NEW' engine.

[mkoesel]

Originally Posted by Boss330

A oversquare design is better for a high revving engine as that keeps piston speeds down. Lower piston speeds is good for durability. One of the disadvantages of a oversquare (short stroke) is lack of/less torque than a similarly sized undersquare engine.

Right. So, if an over square engine is good for high revving operation then why did BMW force an under square design onto the ~8000 RPM S54, only to turn around and reverse that for the ~7500 RPM S55. You see? Your rationale does not cover it. I am not saying you are wrong, but there is very clearly more to the story.

More torque? Ok, let's prove it.

Remember that a long stroke means a longer arm from crankpin to crank center, and as we all know Torque = Force x Arm. So the longer the stroke, the longer the arm from crankpin to crank centre is and more torque is made.

How much more torque, then, from the engine with the longer stroke? Can you calculate it? Before you run those numbers, let's keep in mind that any increase you make in stroke while keeping displacement and cylinder count the same means a commensurate decrease in bore.

[mkoesel]

Originally Posted by NISFAN

It is impossible to reduce the bore spacings to 1.4mm, so they must have a new bigger pitch.

I, too, said in another thread that this is impossible, but I am tempering that for now until we have all of the facts. I certainly agree it defies logic.

There is another possibility here, as well, besides the new engine architecture. That is, it could be errant data. I.e. it could just be a plain old mistake.

[mkoesel]

By the way, if this is an all new engine my guess would be a 98mm bore, meaning half an N74 V12. It could then be built using the same tooling as that engine.

That would also mean 3.8L is possible, or even more.

[NISFAN]

Originally Posted by mkoesel

I, too, said in another thread that this is impossible, but I am tempering that for now until we have all of the facts. I certainly agree it defies logic.

There is another possibility here, as well, besides the new engine architecture. That is, it could be errant data. I.e. it could just be a plain old mistake.

True, the fact that the old stroke size is the new bore size adds some weight to that assumption

BTW, the torque output from changing bore/stroke combo's can be simulated. There are specialist engine simulation software available, which computes loads/vibrations/torque, etc. But rule of thumb is a longer stroke always gives more torque than same displacement short stroke engine.

[NISFAN]

Comparing the two pics in the previous page, and crudely measuring the various components, it is certain that the bore size is bigger than N55. The strange thing is that block height is also bigger on S55. Block height is typically linked to stroke length (yes block height can be stretched to obtain a long rod to stroke ratio, but unless the ratio was way out on the comparable engine, a smaller stroke would alter this any way).

My money is on this being a bigger displacement than 3litres.

[mkoesel]

Originally Posted by NISFAN

True, the fact that the old stroke size is the new bore size adds some weight to that assumption

We are thinking alike here...

BTW, the torque output from changing bore/stroke combo's can be simulated. There are specialist engine simulation software available, which computes loads/vibrations/torque, etc. But rule of thumb is a longer stroke always gives more torque than same displacement short stroke engine.

I've seen the claim many times but never the proof. One thing I have done is looked for evidence among production engines and there is no consistency. Now granted, I have never examined the entire torque curves.

The elephant in the room here is that we are suggesting that BMW chose a very long 90mm stroke design for the S54 - far from optimal for a high revving design - all in the name of engine torque which we all know can be adjusted at the wheels with gearing. I call shenanigans. The long stroke is there only to get to 3.2L with a 91mm bore center, I say, which they needed to hit power goals. If they had been given a starting platform with a 98mn bore center (for example), then I would bet my life we'd have seen a short stroke engine more like an S65. And furthermore, I doubt peak torque would be appreciably less for such an engine.

[Boss330]

Originally Posted by mkoesel

Right. So, if an over square engine is good for high revving operation then why did BMW force an under square design onto the ~8000 RPM S54, only to turn around and reverse that for the ~7500 RPM S55. You see? Your rationale does not cover it. I am not saying you are wrong, but there is very clearly more to the story.

More torque? Ok, let's prove it.



How much more torque, then, from the engine with the longer stroke? Can you calculate it? Before you run those numbers, let's keep in mind that any increase you make in stroke while keeping displacement and cylinder count the same means a commensurate decrease in bore.

First point:

S54 was NA so it needed all the help it could to create some decent torque. To increase torque you can go FI or longer stroke... Since the S54 is not FI they had to go longer stroke. Makes perfect sense on a NA engine that also has to combine HP with a minimum of torque in a "heavy" car.

The S55 uses FI to overcome the torque deficit a short stroke has and can reap the rewards a short stroke and large bore gives you without suffering less torque.

A oversquare design has so many benefits for high performance (see my previous post) that it is commonly accepted as the best design for high rpm and high HP.

The N55 has allmost the same CC but has a 89,6 stroke and 84mm bore.

So, the S55 has 9,6mm less stroke and "only" 5,4mm more bore than the N55. The N55 has a 12% larger/longer stroke than the S55, but "only" 6% less bore. I'm pretty sure that difference would be noticeable and measurable in a comparison of the two engines (in a similar state of tune, like in NA conditions).

[mkoesel]

Originally Posted by NISFAN

Comparing the two pics in the previous page, and crudely measuring the various components, it is certain that the bore size is bigger than N55.

I looked at that also but came away unconvinced either way. It is hard to gauge scale.

The strange thing is that block height is also bigger on S55.

Could it simply be a closer view?

Block height is typically linked to stroke length (yes block height can be stretched to obtain a long rod to stroke ratio, but unless the ratio was way out on the comparable engine, a smaller stroke would alter this any way).

Deck height of an N74? Perhaps?

My money is on this being a bigger displacement than 3litres.

I have to assume that if the reported bore number is indeed correct then so is the stroke and thus the displacement as well. But certainly the possibility for increasing displacement by the aftermarket would be there.

[Boss330]

Originally Posted by mkoesel

...or we have a brand new BMW engine architecture for the first time in decades. Either would be a huge, shocking surprise as far as I am concerned.

Isn't the 1,5l 3cyl a completely new design, part of the new line of modular engines?

[mkoesel]

Originally Posted by Boss330

Isn't the 1,5l 3cyl a completely new design, part of the new line of modular engines?

As far as I know it is 91mm more center. I believe it has the exact same 84x89.6 bore as the N55 (plus all modern BMW I6 engines) and the N20. It, and the rest of the coming B* lineup, evolve the BMW inline family but do not completely reengineer it.

[Boss330]

Originally Posted by mkoesel

I, too, said in another thread that this is impossible, but I am tempering that for now until we have all of the facts. I certainly agree it defies logic.

There is another possibility here, as well, besides the new engine architecture. That is, it could be errant data. I.e. it could just be a plain old mistake.

Agreed on errant data and which is why I had "if correct" in my first post. But if it's errant data they have also come up with the CC of 3027.

Wonder if this cc has just been calculated from bore/stroke or was provided to the media at the workshop?

[NISFAN]

Originally Posted by Boss330

First point:

S54 was NA so it needed all the help it could to create some decent torque. To increase torque you can go FI or longer stroke... Since the S54 is not FI they had to go longer stroke. Makes perfect sense on a NA engine that also has to combine HP with a minimum of torque in a "heavy" car.

The S55 uses FI to overcome the torque deficit a short stroke has and can reap the rewards a short stroke and large bore gives you without suffering less torque.

A oversquare design has so many benefits for high performance (see my previous post) that it is commonly accepted as the best design for high rpm and high HP.

The N55 has allmost the same CC but has a 89,6 stroke and 84mm bore.

So, the S55 has 9,6mm less stroke and "only" 5,4mm more bore than the N55. The N55 has a 12% larger/longer stroke than the S55, but "only" 6% less bore. I'm pretty sure that difference would be noticeable and measurable in a comparison of the two engines (in a similar state of tune, like in NA conditions).

I don't agree with your last paragraph. Bore is used as a common easy measuring yardstick, but it is actually piston area that counts. As bore is squared in the formula Pi D^2/4

This gives us piston area of 63.053 for the S55 and 55.417 for the N55. Which makes the N55 12.1% smaller in 'effective bore' vs 10.7% larger in stroke.

The weird thing is.....long strokes are FI friendly, as there is more density of Fuel/Air in the cylinder, it takes longer to burn. Also, smaller bores make detonation easier to control.

[Boss330]

Originally Posted by mkoesel

As far as I know it is 91mm more center. I believe it has the exact same 84x89.6 bore as the N55 (plus all modern BMW I6 engines) and the N20. It, and the rest of the coming B* lineup, evolve the BMW inline family but do not completely reengineer it.

The B38 has a 82.0mm bore and a 94.6mm stroke. It's a completely new engine family, not related to any other BMW engines.

http://www.e90post.com/forums/showthread.php?t=744332

[Boss330]

Originally Posted by NISFAN

I don't agree with your last paragraph. Bore is used as a common easy measuring yardstick, but it is actually piston area that counts. As bore is squared in the formula Pi D^2/4

This gives us piston area of 63.053 for the S55 and 55.417 for the N55. Which makes the N55 12.1% smaller in 'effective bore' vs 10.7% larger in stroke.

The weird thing is.....long strokes are FI friendly, as there is more density of Fuel/Air in the cylinder, it takes longer to burn. Also, smaller bores make detonation easier to control.

Thanks for the correction

[mkoesel]

We are going in circles.

I still don't believe the S54's design was chosen for performance reasons (engine torque), but instead for cost reasons (using the existing architecture to get to 333hp). Hence, I am skeptical that they've gone the route of developing a new architecture for what is by all appearances a less compelling case for it with the S55. Alpina shows us the feasibility of a production 410hp twin turbo BMW I6 with an 84mm stroke and 89.6mm bore. Surely 430hp or more is also possible. S55 revs higher, yes, sure. But not 8000 RPM like the 91mm stroke S54 does.

Originally Posted by Boss330

First point:

S54 was NA so it needed all the help it could to create some decent torque. To increase torque you can go FI or longer stroke... Since the S54 is not FI they had to go longer stroke. Makes perfect sense on a NA engine that also has to combine HP with a minimum of torque in a "heavy" car.

The S55 uses FI to overcome the torque deficit a short stroke has and can reap the rewards a short stroke and large bore gives you without suffering less torque.

A oversquare design has so many benefits for high performance (see my previous post) that it is commonly accepted as the best design for high rpm and high HP.

The N55 has allmost the same CC but has a 89,6 stroke and 84mm bore.

So, the S55 has 9,6mm less stroke and "only" 5,4mm more bore than the N55. The N55 has a 12% larger/longer stroke than the S55, but "only" 6% less bore. I'm pretty sure that difference would be noticeable and measurable in a comparison of the two engines (in a similar state of tune, like in NA conditions).

[mkoesel]

Originally Posted by Boss330

The B38 has a 82.0mm bore and a 94.6mm stroke.

My mistake, then, I apologize.

It's a completely new engine family, not related to any other BMW engines.

http://www.e90post.com/forums/showthread.php?t=744332

Completely new? I don't see the bore center and deck height listed. Sadly I cannot read thoroughly to see if they are there. The modern N55 isn't really related to an old M50 in any way either, but there is evolution there.

[Boss330]

Originally Posted by mkoesel

My mistake, then, I apologize.



Completely new? I don't see the bore center and deck height listed. Sadly I cannot read thoroughly to see if they are there. The modern N55 isn't really related to an old M50 in any way either, but there is evolution there.

Well, what is "completely new" anyway I'm sure there are design elements from previous BMW engines in it

[mkoesel]

Originally Posted by Boss330

Be that as it may, here is what UK magazine CAR writes after the workshop:

And, finally a picture of the block:

Great info.

I still want to know bore center before I believe. And I can't tell that from pictures of the block.

[mkoesel]

Originally Posted by Boss330

Well, what is "completely new" anyway I'm sure there are design elements from previous BMW engines in it

Just like an N54 shares nothing but a few specs with an M50 as well. No one calls it completely new though.

[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.