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The 1MZ doesn't see much of a gain with the short runners because of the relatively conservative cams. Now let's say we had a system like VVTL-i, and the low range lobes were tuned for the long runners, and the high range lobes were tuned for the shorter runners and ACIS and the cam switchover point occured at the same RPM. Guess what? BIG power boost.
The high lift, high duration cams in combination with the short runners creates excellent top end power, but we don't have a variable lift system.
The shorter runners combined with the stock cams at low revs effectively bogs the motor. Motors need the intake tumble effect to create any real usable power at the low end, and that's just what the longer runners do.
In effect, you're handicapping the ACIS system (and the motor) by statically inducing a fixed intake runner. The longer runners work best from 1000-4000rpm (or whatever range the ECU is tuned for), and the shorter runners from there on.
The 3 stage system offers mid-range torque improvement from 3000-4500rpm, but can only be found on the pre-DBW VVT-i 1MZ. I think it's funny that every Toyota V engine gets an ACIS system, but all of the 4 cylinders, with the exception of the 3SGE, do not.
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