Quote:
Originally Posted by uspspro
It's amazing that people are still talking about power band like it's the same thing as responsiveness.
Sure a small or VGT turbo might make full boost by 2000 rpm or whatever, on a dyno pull starting at 1500. That's where the power band starts, cool.
However, transient response is "what do I get right when I step on the throttle?" How long does it take to get the engine's full output (at a given rpm)? On an NA it's almost instantaneous, same with a SC. With a turbo, no matter how low of an RPM it can make boost, it's still needs to spool after you crack the throttle and adds to the transient response.
For example a Rotrex setup will make less low-to-mid range torque than a properly sized turbo setup, but the Rotrex will still have a sharper response to throttle inputs in the real world.
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Bingo. I work with small jet engines that can output over 2500HP. Getting that power quickly is difficult though. Hence my VG turbo comments. You can design a turbo to patch up a point on the power curve steady state but the transient response of the turbo is going to lag behind during fast transients from low power.
I currently drive (and love) a 2007 WRX. Fast throttle changes lead to very obvious turbo lag. It can be obnoxious when you suddenly want power unexpectedly. If you know ahead of time you can usually compensate but you don't always know when a hole is going to open up in traffic or whatever.