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03-06-2013, 10:51 AM | #221 |
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OK fine... in that case my M needs more torque too. That is why I kept the 520. Whenever I feel the M3 needs more power I just hop into the 520 for a couple days.
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03-06-2013, 05:56 PM | #222 |
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I think the tuning of the D modes for the DCT could have been a lot better, as it downshifts too slowly, and upshifts into 7th far too quickly. I've tried some of the higher D modes, and it seems they mostly just want to hold the gear longer before shifting, but don't solve my other issues. I find it ludicrous that the gas savings for EPA rating could have been that signficant to make it worth programming the DCT to shift into 7th at 40, and I can't imagine it's good for the engine. Personally, I only notice the "lack of torque" issue that so many complain about when running in the D modes. Shifting manually, shifting more like what a typical 6MT driver would do, it always feels like it has plenty of power.
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03-06-2013, 06:16 PM | #223 |
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There are a few weak points of the car: weight, low end torque (below 3,500 rpms) and brakes.
I don't go to the track anymore so none of these really affect me. But as my past experience hast taught me weight is the biggest enemy. If the weight of the car was leas the power to weight ratio would increase and even though the torque figure would be the same the car would automatically accelerate faster, therefore our problem would be solved. The brake issue is being resolved with the next M3/4 but I wish they would have fixed it with this generation. Oh well...
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03-07-2013, 11:56 PM | #229 | ||||
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The headers have proven that they flow extremely well at outputs that are much higher than OEM, for example stroker motors and SC'ed cars are running these and aftermarket headers have showed no substantial change in the output of the engine. That would lead me to believe that they are not tuned for strictly low RPM torque since that would be compromising the high RPM performance of the engine........ Besides, they are not even a long tube design, they are a short-medium length header that is equal length. Look at the primaries from cylinder 1 and 5, they are not overly long, all of the other bends in 2,3,4 and 6,7,8 are just there to make all of them equal length. Compare them to many other long tube headers on the market and you will see what I mean. Quote:
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03-08-2013, 03:19 PM | #230 | |||
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They are in fact a ton longer than the intake runners, which are designed to provide high rpm cylinder filling. Look, I'm not talking about flow capacity. I'm talking about the natural resonance of these individual pipes. You know. The time necessary for the exhaust pulse (pressure wave) to reach the collector, and the inevitable vacuum wave that travels back up the pipe to the cylinder head. If that vacuum wave hits the exhaust valve as it is just opening, the pressure wave out of the exhaust port/valve begins to empty into a partial vacuum, thus making for a more efficient flow. The pipe length combined with the speed of sound constant dictates the engine speed at which this resonance is most effective. Same thing on the intake, except in reverse. My position is that the relatively long exhaust runners build torque at and around 3900 rpm, while the much shorter intake runners build torque at high rpm. These two factors are one of the keys to a long, flat torque curve. Quote:
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Oh. Was that a run-on sentence? Sorry. Bruce |
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03-08-2013, 03:40 PM | #231 | |
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Great "in between" discussion going on in this thread. Very informative. |
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03-08-2013, 04:22 PM | #232 | |
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http://ktmmad.com/2013/01/18/bore-an...epower-part-2/
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03-08-2013, 07:24 PM | #233 | |||||||
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spoken like a true Fanboy, and I absolutley agree
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03-08-2013, 07:28 PM | #234 |
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Now for my 2 cents
Weight... But I understand the compromise of modern design and luxury requirements. If this car was built 10 years ago it could be a lot lighter, but alas it would not have the S65 which is a marvel of modern design. So I will take the current compromise.
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03-08-2013, 10:49 PM | #235 | |
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One thing I need to clear up with you is that intake and exhaust tuning in the traditional sense on and engine with variable cam timing is not nearly as important as in an engine with fixed cam timing. I am very aware of the use of resonance tuning in intakes and of the use of scavenging to tune exhaust headers. With the S65 both duration and overlap are adjustable so essentially the intake and exhaust length is not nearly as important as in other engines with fixed cam timing. I am thinking that they tried many combinations of intake and exhaust lengths in testing and came up with the best compromise in the torque curve. Also worth mentioning is that not only primary length is important in header design but diameter is critical too....... Too large a diameter and low RPM torque will suffer, regardless of primary length. The intake runners or header primaries were most likely picked based on the VANOS systems ability to vary cam timing, more importantly the rate. As RPM's rise in the engine and piston speeds increase obviously the rate of VANOS adjustability is going to remain static. I am thinking that the intake and exhaust manifolds are both designed for higher RPM since the VANOS system has less time to vary timing at the higher RPM. In the low to mid RPM range the VANOS system has adequate time to vary the timing to exactly where it needs to be to meet the optimum characteristics of the intake and exhaust runners to obtain near max VE at all times. I may not be correct but I think that if the engineers designed the exhaust headers to work best at lower RPM the higher RPM of the engine would most likely suffer. If you look at the S54 for example, the header primaries are much longer than the S65 yet the torque peak is higher. What do you think?
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03-08-2013, 11:48 PM | #236 | ||||
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My perusing of S54 exhaust manifolds shows shorter runners. I've given you my thoughts on the discrepancy between intake and exhaust runner length on the S65, and why this is so. So give me your thoughts on why this is so. You think this is an accident? Bruce |
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03-09-2013, 12:01 AM | #237 | |
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Now, if the duration would vary, the resonance could be leveraged over a broader RPM band. But I don't believe that Vanos has the ability to change the duration. Last edited by CanAutM3; 03-09-2013 at 10:14 AM.. |
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03-09-2013, 01:24 AM | #239 | |||||
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Everything you say is correct and with a proper thought process. My only argument is that I don't think that the header design is the single thing that moves the torque peak lower on this engine. I feel that the intake and header design was a compromise to get a torque curve that stayed flat almost till redline with the help of a sophisticated variable cam timing system. |
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03-09-2013, 08:38 AM | #240 | ||
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Last edited by CanAutM3; 03-09-2013 at 10:12 AM.. |
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03-09-2013, 12:01 PM | #241 | ||||
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OK, we're so far down in the weeds now that I am quite sure other readers think we're so anal that we had to've been potty trained at gunpoint.
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This hardly counts as a change of duration. Quote:
(Speaking of phasers, wouldn't it have been great if just once, Captain Kirk had said (when visiting a hostile planet) "Set phasers on extra crispy!" But I digress. Quote:
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Bruce Last edited by bruce.augenstein@comcast.; 03-09-2013 at 12:39 PM.. |
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03-09-2013, 12:29 PM | #242 | |
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For sure! It is nice to have a conversation/debate with someone who is on the same page! I have thoroughly enjoyed this discussion so far!
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