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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
| Posts: | 575 |
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As I recall, the airbox you are pulling molds from has a square spigot where most would be round to accept a flex duct. That was a Lotus Excel airbox, and a thermo-valve attached to the square, and the far end of the valve was round to accept a flex duct. With out that valve as a square to round adapter, it would be best if your airbox simply had a round spigot.
I don't have any Excell dimensions for you, but on the late 1970s Lotus Elite-Eclat air boxes, the spigot for the flex duct is two inches long. It starts out a little smaller for ease of starting the flex duct onto the end, then at the one inch mid-point, it steps up a bit larger in diameter for a more snug fit. I've measured two...
One starts at 85.5mm (3.37") and steps up 1mm to 86.5mm (3.41").
The other is 1mm larger in diameter, starting at 86.5mm (3.41") and stepping up 1mm to 87.5mm (3.45").
They're visually very similar, but a closer inspection shows they came from different molds. So I wonder if the 1mm increase in diameter was intentional, or just a casual difference on a non-critical part?
The flex duct is somewhat compliant, and it's a slight stretch fit onto the spigot. So with that fit, the flex duct would stay in place without a hose clamp... although I used one.
The Elite-Eclat duct wasn't just off-the-shelf flex duct. It was a custom part that tapered to a smaller diameter at the forward inlet end. Unfortunately, it was a Lotus-only part and is no longer available new, so not a help to you.
I suggest that you choose a readily available flex duct in the 3 3/8" - 3 1/2" ID range, and make your airbox's spigot to fit whichever duct you choose. If it helps fitting everything into a snug engine bay, then I don't think there would be a problem with using a smaller ID flex duct. The small inlet end of the tapered Lotus duct was only about (guessing from memory) 2.5" ID.
Laundry dryer flex duct won't work, it needs to be rated for automotive or aviation engine bay use. Check the websites for Pegasus Racing, Racers Warehouse, and Aircraft Spruce & Specialty.
FYI... in order to quiet the induction roar, Lotus laminated the outside of the airboxes with a rubber material that's about 1/8" thick. It's strong & fiber re-inforced... it reminds me of conveyor belt material. Plain rubber sheet would be easier to work with, but it would have to be an automotive grade that could put up with heat and petroleum products. Use a high temperature adhesive.
Regards,
Tim Engel