Quote:
Originally Posted by IANNUZZI
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
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On a modern ECU, it's easier and faster to alter timing than to reduce boost. So pulling ignition timing and/or altering fuelling is preferred over dropping boost. But in a situation where max ignition timing and fuelling changes doesn't sort the situation, I'm pretty sure the DME can control/drop boost. I'm also pretty sure that the DME adjusts boost, fuelling and ignition together/simultaneously and not separately and without considering the other parametres. And when you didn't see a drop in boost, how do you know that boost wouldn't have been higher without knock? (how did you monitor that BTW? Datalogging that shows knock and boost is pretty much the only way you can confidently claim that knock and boost levels are not related).
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.