VVT-I vs ACIS

[darkwolf]

Basically what's the difference.

I know that VVT-i works with oil pressure and varies the timing of the intake(?) valves where as ACIS controls the amount of air going into the manifold. But other than this can anyone explain to me the difference? I know the genII 3s-ge with ACIS makes 160HP and the GenIV with VVT-i makes 200Hp.

Just done some browsing on the net and can't really find an explaination of exactly what each does.

Help appreciated - oh I did use the search function first.

[Adamal]

VVT-i advances the cam shaft(s) depending on the revs.

ACIS is for adjusting the intake runner lengths. Refer to Helmholtz.

[darkwolf]

I'm not sure I understand entirely. Their is a lot to learn about Helmholtz the man himself but I don't really get how this answers the ACIS question aside from maybe compressing the air through acoustics?

Anyone have anymore info or should I spend more time with my friend google?

[Adamal]

Well, with ACIS, it changes the length of the intake, because this has an effect on the power made throughout the rev range.

This is why intake trumpets aren't recommended for street cars, because they're a tuned length for high revs and give very bad power figures down low.

What ACIS does is make the intake longer for low revs, then shorter for higher revs, to help give a better spread of power throughout the rev range.