03-13-2014, 03:45 PM | #67 |
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03-13-2014, 03:55 PM | #69 | |
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P.S I'm an automotive engineer working with modified vehicles and have taken several courses on engine management basics. I'm NOT an expert on engine management though. |
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03-13-2014, 04:03 PM | #70 |
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Owned Supra, rx7, 3000gt, 300zx, and 335i, all were the turbo versions and none of their ecus reduced boost as a result of knock(they all had knock sensors); the f10 m5 is no different as it manipulates timing to deal with knock:
"Knock has a lot to do with the octane rating of the gas that you put in the car. The recommended gasoline octane rating for the F10 M5 is AKI (Anti-Knock Index) 93 with AKI 91 as a minimum to not impair performance. Actually "octane rating" is a misnomer. While higher octane can prevent knock, it is not the only way of doing so. So AKI is the correct term. However, as the engine is knock controlled, the lower ratings will not damage the engine. Higher AKI ratings mean the fuel can be compressed more before detonation, which means that more energy can be extracted during detonation. An overly low AKI will require the DME to retard timing to prevent knock which is inefficient and long-term damaging. Higher AKIs are of no use, since the car cannot increase compression ratios past its design point" I have been following the bms boost controller since the beginning and it was made clear that the default setting of 2.25 was to be used with a min of 91 octane and the 3.00 setting was reserved for race gas. Given that, using 94 octane with the 3.00 setting can certainly cause a dyno chart like the one in question if timing is being pulled as a result of detonation. I doubt the computer is trying to protect the tranny.... Cheers Last edited by IANNUZZI; 03-13-2014 at 04:18 PM.. |
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03-13-2014, 04:17 PM | #71 | |
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03-13-2014, 04:26 PM | #73 |
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Nope. Just a car enthusiast with a warped (and not necessarily good) sense of humor. But I make up for that in my choice of cars.
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03-13-2014, 04:39 PM | #74 | |
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Octane rating is not a misnomer but is the official description of a fuels performance. Here in Europe we use the RON rating (which is the most widely used rating), while in the US the average between RON and MON is used and is called the Anti Knock Index. But AKI is just a product of two octane ratings. Higher octane ratings has nothing to do with "compressing the fuel". Fuel is a liquid and can't easily be compressed, unlike air. But higher octane numbers allows for a higher CR in the engine as the fuel is more resistant to knock. Agree that in a situation where the BMS is providing more boost and knock occurs that the DME is pulling timing and dropping power and torque as a result. |
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03-13-2014, 05:02 PM | #75 | |
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First the DME is perfectly capable of reducing load as a function of knock. It's simply not part of BMW's logic path. It's not programmed to work that way. When knock is detected the DME reduces timing by 3 degrees in the cylinder it was detected in. Boost remains the same. When repeated knock is detected in the same cylinder the DME again reduces timing 3 degrees. If knock continues the DME decides the cylinder is experiencing preignition rather than detonation and a zero boost limp code is triggered. As knock is not detected timing is slowly increased back up to its learned maximum. The learned maximum is based on a long term octane adaption trim. If you want to test this for yourself monitor boost/timing while on 93 octane, then pump in a few gallons of 87 octane, note how timing shows knock indications, and how boost is unchanged. When I say torque is largely independent of timing what I mean is that as it goes through this process of reducing timing 3 or 6 degrees those variances have a subtle impact on peak torque figures. But a dramatic impact on peak HP figures. The "torque loss" in the dyno is not consistent with knock in my professional opinion. If you'd like some additional evidence here please take it up with BMS directly on their forum. Here is a screen shot of the load to knock table from an MSD81 DME. The more negative the index the higher the "knock". As knock increases at lower RPM the DME actually raises boost slightly. Even at it's most extreme boost reduction would be around 6% (this factor is multiplied by a load target that runs from vacuum to full boost). I happen to know the DME limps out with "super knock" codes at around -70 and never actually gets to the point that the logic dictates lowering load significantly. This is how it's been programmed from the factory. The s63tu uses the same basic table values. Again, if you chose to doubt this, please take it up with BMS directly. Finally, neither of you answered my question as to why the 100% stock M5 running 94 octane, DCT, in 5th gear, "lost" 50 wtq in the midrange in the dyno chart I posted above. There was zero knock during this run. It "lost" torque because the DME decided to lower its load target in the midrange to protect the DCT trans. I believe the same thing happened during the dyno we are discussing. Mike |
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03-13-2014, 05:30 PM | #76 | ||
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Thanks for the info anyway From what you said then, we can conclude that there is nothing suspicious about the dyno results he got and that his numbers are representative of a BMS set at +3. Further since his dyno numbers and graph is quite normal that it's perfectly safe for him, based on your interpretation of his dyno run, to run +3 on the BMS with 94 octane fuel? BTW I have seen plenty of dyno charts without that drop of torque in the midrange. Also on DCT cars in 5th gear... But I see your point that some 5th gear dyno runs do provide a drop in torque in the mid range. But I have never seen a torque curve quite like his before... Possibly down to operator and dyno settings as well? |
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03-13-2014, 06:20 PM | #77 | ||
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Please stop tiring yourself out . |
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03-13-2014, 07:04 PM | #78 |
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Lots of interesting info. Never seen a screen of the DME folder tree.
Thanks for the good reads.
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03-13-2014, 08:29 PM | #79 |
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And showing a screenshot of the MSD81 ECU 's programming tables from a N54 car proves nothing about the content of the S63 TU's tables or it's control capabilities .
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03-13-2014, 09:05 PM | #80 | |
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Unrelated to anything M5. Just a general statement.
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03-14-2014, 01:19 AM | #81 |
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