I'd like to point out some principles of throttle design, pedal mapping, and torque control calibration:
Throttles are inherently non-linear due to the laws of physics. Cable-driven throttles from "the good old days" were never linear either. Here's an interesting picture I pulled off Google image search of a cam-type mechanical throttlebody linkage.
Just like a camshaft to operate cylinder head valves is an eccentric circle, a cam to operate an old throttle has different ramp rates depending on where you are in the rotation of the cam. So let's dispel that myth of "my old blahblah had a linear/almost linear throttle."
Here's the physics behind why a throttle valve is non-linear. The throttle works on a pressure difference upstream and downstream of the valve.
When the valve is nearly closed, you have what's called "choke flow." The air reaches the speed of sound as it passes through the opening. This is called the "sonic area" in throttle body design and throttle calibration. That zone behaves differently than when the throttle is open further.
So depending on the opening angle of the throttlebody, the air could be flowing at a constant velocity and then suddenly as the valve opens further, the air velocity drops.
Quote:
Originally Posted by SkullWorks
you will find if you actually make the pedal to TB a direct correlation that 50% is essentially the same as 100%
As with most modern engines the TB is simply WAY TOO BIG for the actual airflow demands...
For example, I have a S13 track slut, it makes 450hp 390 ft lbs, I have a ~70mm TB on that car...after ~60% you achieve the same exact power curve as WOT. I use this range to setup boost VS TPS...works great
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Consider the basic relationship between opening area and volume flow and it will all make sense.
So in conclusion, even before drive-by-wire throttle valves never behaved linearly. The relationship between the gas pedal position and the opening of the throttle valve was never linear either.
Now, can we prefer a different response curve to the way the car came from the factory? Sure. That's what software tuning is for. Think about it this way...
with cable throttle you were stuck with whatever non-linear response curve the engineer chose, but with modern tuning you can make your electronic throttle behave according to your preferences.
I'd also like to point out that engine torque control on a modern engine includes not just throttle valve but cam phasing/valve lift, spark timing, air-fuel-ratio, and wastegate position (in a car with a stock turbo). So this discussion of response vs gas pedal position really includes the whole torque model rather than just the opening of the throttle valve itself.