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09-25-2013, 02:51 PM | #1 | ||||||
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Update: False. S55 engine has oversquare bore/stroke and shares "nothing" with N55!
The M3/M4 tech specs has been revised to include the following:
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The short stroke is good for high rpm and lowering piston speeds at high rpm. It will also give it a more rev willing character and sharper response. I suspect that the tech used instead of cylinder liners is what allows for the big bore in the N55 engine. The bore/stroke really sets this engine apart from the 335i (N55) engine and is nothing that a tuned 335i can compensate for. The engine's will act, feel and sound different. According to Auto Motor und Sport the block is a brand new development with focus on strength and light weight: Quote:
-Maximum HP between 5500-7200rpm (should be 5700-7200rpm) -Maximum torque between 1800-5700rpm http://www.auto-motor-und-sport.de/n...n-7741783.html EDIT 26.09.2013: Here is what UK magazine CAR writes after the workshop: Quote:
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CanAutM3 has pointed out that there seems to be a slight "problem" with the quoted HP and Torque figures: Quote:
![]() ![]() And, finally a picture of the block: ![]() To me, this makes the S55 a genuine M engine ![]() ![]() A few pictures of the N55 for comparison: Last edited by Boss330; 09-27-2013 at 02:12 AM.. |
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09-25-2013, 03:17 PM | #2 | |
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Sorry for the confusion. Fixed to be clearer now.
Quote:
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09-25-2013, 03:25 PM | #4 |
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09-25-2013, 03:45 PM | #5 |
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09-25-2013, 03:46 PM | #6 | |
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It is significant because it should be much freerer revving than the lazy n55. |
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09-25-2013, 03:55 PM | #7 | |
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But a comparable engine, but with longer stroke, would make more torque under same boost conditions. Or the same torque with less boost. But I'd rather have a bit higher boost to compenaste the torque lost due to shorter stroke and the higher rpm/lower piston speeds possible on a short stroke engine. It should feel much more alert than a "lazy" N55 335i. |
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09-25-2013, 04:09 PM | #8 | ||
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A side effect of the short stroke, is the cylinder pressure will still be very high at end of stroke, which means more pressure to power the turbo. ![]() |
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09-25-2013, 04:26 PM | #9 | |
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09-25-2013, 05:36 PM | #11 |
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I really hoped they could find a way to stretch the position of peak hp, but I think what they've done here is struck a good balance between fuel economy and the ability to still track the car to an extent. It will not be able to compete on a track with an NA engine of similar peak power, but hey. It will be great for DD'ing. Welcome to 2013 I guess!!
Not using liners is a surprise to me. M must have done their homework.
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09-25-2013, 06:34 PM | #12 |
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89.6mm bore really does mean this block is completely redesigned.
Cylinder spacing of the small block 6 has always been 91mm. It's not possible to run with a 1.4mm wall thickness, so it looks like tuning options with the wider bore spacing could reap better rewards than first thought. |
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09-26-2013, 01:54 AM | #16 | |
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Bore/stroke is apparently from BMW so I hope this turns out to be correct ![]() Engine characteristics is just, from my standpoint, based on engineering principles related to long vs short stroke. A short stroke engine is by definition able to rev higher at lower piston speeds and has sharper response. There's less inertia to overcome when accelerating the crank on a short stroke engine. How THIS engine feels we don't know yet, but by definition it should be more responsive than the N55 (unless BMW M has engineered it to feel lazy...) |
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09-26-2013, 03:47 AM | #17 |
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What is the bore center dimension of the S55?
I am having a very hard time believing that they've increased the bore center only to achieve essentially no displacement increase. Sure, the stroke decrease is great, but they've avoided it for years with the S50->S52->S54 even as RPMs were pushed higher and piston speeds went up and up. Why the change now? If we really do get a new longer block, then this is arguably the single biggest piece of engine news from BMW since they reintroduced turbocharging seven years ago. It would mean a square bore 89.6 x 89.6 3.4L engine is possible - the first time we can (safely, reliably) go over 3.2L with a BMW I6 since they retired the "Big Six" decades ago. And without resorting to an iron block as every OEM I6 engine above 3L from BMW has used. And if we don't get a new bore spacing, I am at a complete loss for words as far as the incredible 1.4mm between cylinders. |
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09-26-2013, 04:13 AM | #18 | |
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I hope that what we see is the basis of what happened with the E36 engine. First a 3l then a later version with 3,2l. This engine leaves (possibly) room for displacement upgrades down the road and/or CSL type versions with larger volume than the std. engine... On a NA engine they wanted the longest stroke possible to gain some torque for driveability, hence why the old engines had a fairly long stroke. On the S55 the FI takes care of the torque deficit present in a short stroke engine. You can have your cake and eat it ![]() ![]() Last edited by Boss330; 09-26-2013 at 04:39 AM.. |
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09-26-2013, 04:46 AM | #19 | ||
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Thank you.
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Color me a very deep shade of skeptical. ![]() Getting back to the S55, I accept that the new spray on lining allows for a larger bore. But I still think the bore center must be greater than 91 mm now and I am very eager to know if this is the case. |
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09-26-2013, 05:05 AM | #20 |
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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 |
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09-26-2013, 05:27 AM | #21 |
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Comparo with Alpina
It will be very interesting to compare the new M3/M4 with the already available Alpina B3 Biturbo F30 (also with xDrive):
-410 HP -600 NM -0 - 100 in 4 seconds (with xDrive). I will have a testdrive with the Alpina on October 4th ![]() |
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09-26-2013, 07:03 AM | #22 | ||||
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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. However on a FI engine, boost can be increased to make up for the torque deficit. In a high performance FI engine then, a oversquare design makes a lot of sense because it has so many advantages over a undersquare design. So, no this didn't happen by coincidence. A large bore/short stroke gives many advantages in breathing (larger valves), less friction, less heat, lower piston speeds. In a high perf engine a large bore/short stroke will allmost allways be the best solution for high end power, high rpm and agility. With FI you can also compensate for less torque, which the old M3 engines couldn't. Quote:
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