Thread: Carbon Flox
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Old 05-14-2022, 08:40 PM
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wirejock wirejock is offline
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 5,502
Default Plenum

Originally Posted by JDA_BTR View Post
I'm curious what you used to form the plenum to keep the material flat across the engine and not sticking to the baffles.
Technically, I didn't make the plenum. It's an RV Bits plenum but I sure cursed it. It didn't fit so I basically made one after it was carved up. I had to cut the flanges off and fab new ones as below. Also had to sand off the gel coat because it was cracking and flaking off. The inlets were layups on molds made from foam plugs. once the pieces all fit, I just added glass to lock them together then removed and finished. It drops right in.

If I were to make one from scratch, this is how I would do it.
Fit the cowls and baffles. Fit so the gap is correct and uniform.
Install the baffles and cowls.
Draw a line on the inside of the top cowl by reaching inside. Basically just the forward baffle and the side baffles.
Remove the top cowl.
Measure and finish drawing the baffle lines on the inside of the top cowl.
Lay down some plastic. Probably in strips due to the curve.
Wax it.
Layup the plenum right inside the cowl. Two or three layers is plenty for a srart. When it cures, transfer the lines before popping it loose.
Trim outside the lines so there's extra. That will yield a pretty close form.
Tape off the inside and outside of the baffles and cover everything.
Wax the tape.
Layup strips of glass all around folding the excess over. Two layers is plenty here as well.
Lay the plenum lid on top
Pop it loose. It will be an ugly mess but should be attached enough to hold it's shape.
Trim and sand till it fits then add layers inside to reinforce the side flanges and a layer of carbon outside to make it purdy.

Same process works to make the inlet boxes. Layup right inside the baffles then pop it loose and finish on the bench.
Mine is a little different because the inlets are molded to match the cowl inlets and sealed with a sleeve.

A mold is always preferred but the top cowl is basically a mold. The finished plenum will mirror the shape of the inside of the cowl.
Larry Larson
Estes Park, CO
E-mail: wirejock at yahoo dot com
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I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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