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Old 05-12-2020, 03:25 AM   #1 (permalink)
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Insight Gen 1: variable length intake manifold

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.

Modifying the Aerodynamics of Your Road Car

"Your book is unique! It was high time that someone covered vehicle aerodynamics through the practical eyes of someone like you."

- Dr Wolf-Heinrich Hucho, the founder of modern vehicle aerodynamics

Last edited by JulianEdgar; 05-12-2020 at 04:14 AM.. Reason: typo
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