I've always liked the idea of a variable length intake manifold on my Gen 1 Insight to improve torque off boost. (It's turbo'd and doesn't use IMA.)
The Australian Ford Falcon six cylinder has featured over the last few decades a really nice variable length intake, with the changeover effected by butterflies inside the manifold.
Generic pic of Falcon engine bay (inlet is the snail-like casting):
Lots of Falcons were sold, so the cost of the inlet is basically nothing - eg US$15 from a wrecker. Here's what it looks like inside. Note the butterflies that cause the air to pass through the longer runners (the snail). When open, the air takes a shortcut.
I sliced it up and bent some heavy wall aluminum tube that will connect to a manifold plate. Shown here with standard intake manifold in background. The bent tube is much longer than it will finally be. I have a TIG welder but I don't know if my skills will be up this one - might need someone else to do the welding.
My measurements indicate these runner lengths (approx):
- Std Honda - 330mm
- New intake manifold short - 350mm
- New intake manifold long - 610mm
It's not a quick project, so don't expect results next week. Will be interesting to see if it makes an improvement - lots of unknowns like the impact of larger runner diameter, different plenum volume, etc, etc.