Quote:
Originally Posted by ZDan
Dip is a function of cam and tuning for max power at 7000. Tune for 7000 rpm peak and apparently you get anti-tuning at ~half that. I have (had) the same dip on my tweaked 240z 3.1. Doesn't matter what you do with the fuel maps and ignition timing if the engine simiply isn't breathing well at that rpm.
Forced induction should minimize the dip. You're no longer relying as much on low pressure in the cylinder to draw charge in better as the intake opens.
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It wouldn't be cams, a high strung cam has limited VE at low engine speed because it ends up pushing charge out of the cylinder. Intake tuning + intake cam advance can attempt to fix this but you're going to be limited by the exhaust gases "poisoning" the charge.
Because the cam appears to be a high rpm cam, there are no variable intakes, the torque down low approximately matches the torque peak, and the peak torque is quite low by performance engine standards, I think the most logical conclusion is that they intentionally tuned the intake for low rpm. This gives the car "better driveability" (as if you're actually going to floor it while getting groceries :P), and the kick of torque that people like to feel at low speed.
I haven't really thought or read in detail on how intake harmonics work though, so I may be missing something important.