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09-26-2013, 06:51 PM | #67 |
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Quickie search so far yields:
http://www.clublexus.com/forums/1731672-post60.html Anyone have access to electronic back issues of that publication? And that's N52, not N55, yes. But surely if the N55 had increased the bore spacing it would have made big news long ago. I'll keep searching. Feel free to join me or at least stop me when you are convinced. |
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09-26-2013, 06:57 PM | #68 |
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Here's a VAC crank with a ridiculously long stroke (a length which incidentally could get us into 4L plus territory for this supposed new block). Not proof of anything, but does show the measures people have gone to in order to get more displacement from the S54.
http://www.vacmotorsports.com/catalo...troker-kit.htm Granted they also sleeve, probably to keep the thing from grenading. Don't get me wrong - these guys are competent. |
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09-26-2013, 07:20 PM | #69 |
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http://www.m3forum.net/m3forum/archi.../t-427444.html
Good enough for me. I read it on the internet so it must be true. Please feel free to research liberally if you are looking for more answers and need affirmation. But yeah, I really just want to know the story of the S55 beyond all uncertainty. Amazing how much mystery this car has provided us, eh? Every time we learn more, we realize still how little we know. |
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09-27-2013, 02:50 AM | #70 | |
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If so, BMW really has gone to town with retooling for the S55. They MUST have seen major benefits and possibly a long lifespan for the S55 engine Last edited by Boss330; 09-27-2013 at 02:56 AM.. |
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09-27-2013, 03:07 AM | #71 | |
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CanAutM3 has pointed out that there seems to be a slight "problem" with the quoted HP and Torque figures:
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First post edited to contain this info |
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09-27-2013, 06:12 AM | #72 | |
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Maybe the S55 is larger than 3L. Maybe. But now we are throwing good logic after (possibly) bad. |
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09-27-2013, 06:23 AM | #73 | |
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And speaking of people commenting through other channels, a knowledgeable forum member sent me this regarding the earlier discussion about the relationship between stroke length and torque:
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09-27-2013, 06:40 AM | #74 | ||
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Quote:
Quote:
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09-27-2013, 06:46 AM | #75 |
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09-27-2013, 07:16 AM | #76 | |
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However undersquare (with a large bore and short stroke) means the possibility to fit larger valves increasing flow. Some info I found doing some searching: ------------------- A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM, and have less peak potential than a shorter stroke motor. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions. Bigger bores with shorter strokes have the potential to turn higher RPM's, and larger/more valves will fit into bigger combustion chambers. Since the HP race involves turning ever higher RPM's to make more power, the oversquare motors have increased in popularity particularly when it comes to motorcycles. Due to the emissions requirements, the lack of widespread consumer interest in 10,000 RPM cars, and the better reliability from lower RPM's, most car/truck engines are nowhere near as oversquare as motorcycle engines. While it would be interesting to check how one bore/stroke combo would compare to another, it's important to remember that any results you find would be different with other engine combo's. Port size/shape, camshaft profile, exhaust backpressure, intake shape/length, piston style, compression ratio, and a thousand other items would affect the results. Each change would favor one bore/stroke ratio over the other. It's the overall package that counts, not one specific item. Huge ports, aggressive camshaft profiles, short intake (high RPM type motor) would likely show a preference for an oversquare motor. ------------- Agree that on a turbo motor many of the points above aren't that critical and a undersquare engine would have sufficed. But, if bore/stroke info is correct, i give credit to BMW M for choosing a engine concept that is generally better for a high performance, high rpm engine. Especially given the work involved in this... |
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09-27-2013, 07:41 AM | #77 | |||
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... which would have come in handy on all BMW I6 engines in the recent past as well, including the S54 and other M engines. So, I stick firmly by my point that there is no compelling technical argument for avoiding an over square bore (and bore center increase) for so long. There may have been other reasons at play (costs of tooling or unavailability of more flexible tooling), sure. Quote:
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09-27-2013, 08:19 AM | #78 |
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Agree that a short stroke/large bore engine would have made even more sense back in the NA days.
Possibly a sign of larger budgets and/or larger production volumes that makes it economically viable to do this now. I also see the advantage of being able to increase stroke and/or bore in future versions of this engine. Might be an indication of a long term engine platform. |
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09-27-2013, 10:21 AM | #79 | |
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I see no reason why torque won't increase for a given displacement and more stroke. Just saying. Last edited by Jonjt; 09-27-2013 at 10:27 AM.. |
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09-27-2013, 11:51 AM | #80 |
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From experience with bikes where the difference between bore & stroke is a lot bigger than among cars a larger stroke/bore ratio is used for and results in torquier, low revving engines.
Here's a vivid example of my current V-twin bike vs. a similar sized V-twin of very different character. Ducati 748 Bore x Stroke: 90x58.8 mm ( My bike ) Harley Davidson 883 Bore x Stroke: 3.0x3.8 inch In my practical experience from bikes of all types the bore x stroke makes a huge difference in the engine character where long stroke yields an engine with low end grunt and lower peak rpms while a short stroke yields a much racier character with a weak low end but high peak rpms and hp. The S55 vs N55 difference is however relative minor but still the lower piston speed at a given rpm and larger fuel intakes (valves ) should make room for higher rpms. It makes me wonder if there is a sigfiicant room left that will be utilized to push peak power and redline significantly higher up in the rpm range with a comp. pack. Are the small Mitsu blowers up to feeding the required pressure? The reason BMW has not implementd a shorter stroke before is likely to find the best balance of both HP and TQ for a road car. They've done a good job at that. The shorter stroke is likely also part of why the M4's TQ is rated lower than that of an Alpina B3. |
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09-27-2013, 04:55 PM | #81 |
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I'm thinking this will be the replacement block for the N55. That block has been around for some time now.
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Let me get this straight... You are swapping out parts designed by some of the top engineers in the world because some guys sponsored by a company told you it's "better??" But when you ask the same guy about tracking, "oh no, I have a kid now" or "I just detailed my car." or "i just got new tires."
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09-27-2013, 06:19 PM | #82 | |
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Now that being said there are inconsistencies with 395 ft lb and 430 hp at 5500 rpm, that point is simply impossible. I think its obvious that when BMW said more than 369 ft lb they were not being inconsistent. ~410 ft lb actual is a much better and self-consistent estimate if ~430 hp is the actual power (i.e. not underrated).
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09-28-2013, 01:48 AM | #84 | |
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In the first post it was claimed from one of the sources that max hp began at 5500rpm while you had max torque until 5700rpm. According to CanAutM3 that can't happen. And the dyno graph backs this up. Max hp starts at 5700rpm, or at the point where torque starts falling off. Hp and torque also doesn't add up but that makes sense as BMW has said substantially more than 369ft lb, which makes sense. |
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09-28-2013, 03:19 AM | #85 | |
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Yes, still agree on this. Torque is probably going to be ~410 ft lb.
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09-28-2013, 05:11 AM | #86 | |
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Hopefully we get a full engine deep dive soon from the horses mouth. |
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09-28-2013, 05:35 AM | #87 | |
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A rebuttal from out mystery scientist (in his theatre?)!
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(I apologize for the rather unconventional chain of communications) |
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09-28-2013, 06:39 AM | #88 | |
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A tidbit to ponder over, is that in a petrol engine, the combustion process is over by around 14-16 degrees crank shaft angle ATDC. It is this critical stage that help the extra leverage at small crankshaft degrees make a significant difference in torque. The view is helped by the thought that no matter what force you apply to the top of a piston at TDC, the torque read at the crankshaft will be zero. Also..... The main long stroke = higher torque basis is derived in part, in the commonly accepted view that long stroke engines produce peak torque at lower revs than a short stroke engine. They are simply more efficient in this range. We also know that it is easier to produce higher torque figures at lower engine speeds. For example, if we were to take a particular engine fitted with a medium cam profile and measure the torque, it would typically be higher than the same engine with a high duration camshaft. The high duration camshaft would develop the torque higher up in the rev scale, and the engine would physically produce more power, but peak torque would be lower (typically). (Of course a short stroke engine would favour building torque at higher revs, but the increase in torque would not be as significant) Finally, on turbo charged engines, peak torque/power is limited to the onset of detonation. It is commonly understood that a wide flat disc (short stroke) is worse than a smaller higher disc (when talking about the shape of the squish area). This allows a long stroke engine to have more ignition advance, or more boost pressure for a given capacity. These two factors produce more torque in an engine. The above is a general view, of course, there are exceptions. Last edited by NISFAN; 09-28-2013 at 06:56 AM.. |
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