Quote:
Originally Posted by JCL
Interesting comments on linearity. The link that used to be in the first few posts in this thread, and which is now attached above, shows some independent third party measurements from the throttle position sensor relative to the SB output. It appears from that testing, and I am assuming here that the MB model is pretty similar to the BMW model of the SB, that the SB applies a 30% gain to the throttle out put voltage. That gain appears to be constant from all the graphs in that attachment. That implies that there is no change in linearity of the signal with or without the SB. That conclusion also matches the SB web site graphs, which approximate two straight lines, but with different slopes.
A case could be made that a linear output voltage is not the same as a linear butt dyno evaluation. Perhaps much more throttle signal is required to get what feels linear to a trained driver, analagous to a stereo volume control that increases sound pressures exponentially. That is a rough analogy, but hopefully it makes the point. I agree that whether linearity is important is a subjective thing. However, the fact remains that the SB doesn't change the throttle linearity according to the tests.
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Being a newcomer, I appreciate Noodle's reposting of the white paper. I wasn't aware of it and the author's research helps me understand why and how the SB alters the car's characteristics. Deducing that the SB simply amplifies the signal certainly explains his observations.
On the matter of linearity, I have a couple of observations and questions. If I'm reading Figures 1 and 3 correctly, the x axis is a time scale and the y axis the voltage.
Figure 1 compares the accelerator pedal voltage to the throttle position sensor voltage and normalizes the two so the voltage ranges match. That seems to make sense. He makes no mention of normalizing the time scale so we are left to assume either his measuring equipment is synchronized or that he matched times at peak voltage. In this instance it probably doesn't make much of a difference.
Figure 3 compares accelerator pedal voltage response between stock and SB. Again we are left to assume the times are somehow matched so that the start of each voltage curve begins at the same time in pedal travel and the SB doesn't advance the signal as shown on their website. If SB's claim is correct and the signal is advanced and not simply amplified, then I'd argue that could translate into a more linear feel when you factor in the zero voltage at the beginning of the pedal travel. Figure 4 seems to suggest it doesn't advance it but because he normalized the voltage curves, it isn't that clear. I'd be curious to see a graph of the physical pedal position vs. voltage because that's what the driver would feel. All this though is really picking at nits and brings me to my next point.
It relates to the other major part of Mr. Bipes' paper, that of the overall effect on the vehicle characteristic, the "feel" as some would say or butt dyno to use your lingo. His explanation of the adaptive throttle and kick down position certainly makes sense and I'm sure similar systems exist in the BMWs. BTW, except for the things I noted above, I think Bipes' paper was quite well thought out. It could very well be that amplifying the accelerator signal simply tricks the car into staying in aggressive mode and that's what we feel, no shortened response time, no power gain. Then so be it, that's what I want. I'd much rather be able to control my own response than continually second guess what the vehicle will choose for me. Perhaps if BMW had a nanny off switch I'd be happy with that too. I know many M drivers deliberately switch off traction control and such other devices for pretty much the same reason.
Lastly, is it a ripoff as some here would say? Wouldn't that really depend on what's important to you? Is a 15 year old Scotch really double the worth of a 12 year old? Is adding that after market spoiler really going to improve your performance or even turn heads? Or for that matter, is a BMW really worth the premium over a Honda? I'm sure the BMW engineers had very good reasons for programing their systems the way they do but I find certain things annoying and decided to correct them to suit my taste.
Sorry JCL for the extended rant and veering off into areas outside of your response. I certainly don't intend to lump you together with the self rightuous group but that's what you get for being a reasoned debater. I hope you don't mind.