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      08-07-2009, 11:01 AM   #61
The Cthulhu

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Join Date: Jun 2009
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Originally Posted by jeremyc74 View Post
Sure it does, but it's all pointless when we have REAL WORLD numbers to use to compare two cars, and we KNOW that a Lotus isn't much, if any, faster than a tuned 135i in a straight line. Bringing all that stuff into the discussion is just an attempt to cloud the issue.
I'm not attempting to cloud anything, I like both cars... I wouldn't have purchased a 135i if it didn't kick ass. Modeling just happens to be what I do for a living, and I do it in my free time as a hobby.

In fact, I threw together a Matlab gui a while back to model straight line performance based on start speed and selected gear. You can even account for shift time (but not powershifting). I found that start speed can make a tremendous difference, so I'd say a lot of real world numbers can't accurately depict a specific situation. I included torque curves, gearing, drag, area, humidity, temperature (although I have yet to make temp and humidity affect a torque curve... gibbs free energy, ideal gas law, and a whole lot of physics didn't work so well).

Even though I had to benchmark everything and apply a few fudge factors for mechanical losses, it's better than going by numbers that don't tell the whole story. If you aren't breaking your wheels loose or limited by any other weird boundary conditions, modeling and calculation work very well. So much better than searching for an appropriate comparison to numbers that someone else logged. The things I went nuts over (temp, pressure, humidity) mattered so little compared to unknowns in other people's recorded times (like how they shift, how long they take, and how many people are in the car).

Peak horsepower means about as much as the peak wattage advertised on an amplifier. Things like 60-120 mph times are useful as table values (in my case for benchmarking), but only if you're going from 60-120...

This is a long way from a kill story, but I just wanted to explain that I'm not attempting to lose anybody in the numbers, rather, quick back of the envelope calculations can determine if someone is full of shit or not.