Fabricating hood scoop and bad at math... any help?

I wonder if any of you can help me with some design/math problems. My high school math ran out right at A2 + B2 = C2 (which has totally come in handy) but there might possibly know some formulas that could help!

Here’s the situation: I’m trying to fabricate a hood scoop for the beater race car (73 Dart Sport)

• 24” wide – this part is easy
• 25.5” long from front of scoop to cowl – this is where it gets complicated
• And… have the top in two parts:
  • First part is “flat” on top and 15.96871” long (hooray for A2 + B2 = C2 !!)
  • Second part (angling down tow cowl) is I don’t know how many inches long.
• Furthermore… as the air filter is level with the engine but the hood slopes downward, the scoop needs to be higher in front than in the back.
• So… the front of the ‘flat’ part of the hood scoop needs to be 4” high off the hood and the back 3” high. I have mocked this up with cardboard and can easily cut out vertical side strips that are 4” tall at one end and 3” at the other
• Thus the sloping back part will be supported by vertical triangles…
  • BUT it is clear to me that I cannot use a right angle triangle as it changes the angle. I tried this and it looked wrong.
  • I don’t know how to do the math for non-right triangles!
• Finally, I need to add an inch to both sides and the back to bend at a 90* angle to bolt/rivet to the hood.

Attached are various pictures/schematics. Is there something obvious I’m missing? Is there a formula I can use to figure out how long to make the "slanty" part" (back 3rd)?

The eventual goal is to have hard numbers for all dimensions and try to cut this out of a piece of flat sheet metal (so 2-dimensional), then bend the metal with a sheet metal brake in the right places, and then weld the seams.

Any magic formulas you might know?

I failed math so many times, I can't even count...

First, sorry for being long winded here... it’s really a lot simpler than I’m making it sound! I’ll try to get a diagram up later to show what i mean.

That triangle can go a lot of ways depending on how you want the finished product.

If you want the sides vertical like in the diagram, it can be a right triangle; it just has to be perpendicular to the hood, not to the top of the scoop like you have it now.

if you want the sides slanted like you have it mocked up, things get a little more complicated. You can either a) keep the top of the hood and the slanted back one rectangular sheet, in which case you will need to bend the sides where the triangle meets the oddly shaped quadrilateral. In this case the shape of the triangle will depend on how much you slant the sides. For instance, if you have the sides slanted 45* you will need an isosceles triangle. The shape of the triangle will change directly in proportion to however much you change the slant of the sides.

Option b) comes in if you want to keep the sides straight in line with each other. In this case the top and back won’t be able to be a rectangular shape. The easiest way IMO to cut that out would be to cut the sides like you want, then mark the top to fit.

I think about this sort of thing in terms of geometry so I don’t have any formulas for you, sorry.

Your "?" dimension is 9.96242942259"
Sorry I couldn't be more exact!

I ran into that problem too so I just cut a hole in the hood and bolted on a aftermarket air filter housing, then sealed the carb to the underside of the hood. No scoop. I fitted an oiled cotton filter and done. My car ain't that fast tho...

ocdart said:

Your "?" dimension is 9.96242942259"
Sorry I couldn't be more exact!

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I think that only works if the angle is 90 degrees. It's not. I mocked it up in cardboard and it doesn't work. The angle is smaller than that, by a smidge.

I should have mentioned that my cardboard mock-up was originally made with 90* angles on the triangles and it caused a gap in the middle, from the sides to the hood. So I cut it from the bottom front corners to the back, making it a little shorter. Was just trying to see how it would look and didn't have exact dimensions. But definitely want to have measurements right before I start cutting sheet metal.

Check it out: a triangle calculator tool!
https://ostermiller.org/calc/triangle.html

ScamperTom said:

If you want the sides vertical like in the diagram, it can be a right triangle; it just has to be perpendicular to the hood, not to the top of the scoop like you have it now.

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Thanks ScamperTom - It took a minute to wrap my brain around what you were saying but now I get it.
If I make the triangle 90* perpendicular to the hood, it changes the distance from 3" to 3.1", which I can do easily and accurately.
If 8.5" hood side (base) of the triangle, then the '?' side becomes 9", which is also great.

You could just cut the hole, mock up the air cleaner, put spacers on top of it, then put your scoop "top" on.

Once that's attached, you can just "fit the sides and back to your liking/requirements, take some measurements, and be done. might work easier than trying to use straight edges, since the hood has a curve/slope to it that changes from front to be. it's not flat, so you can't really use a flat edge anyway.

Cuda416 said:

You could just cut the hole, mock up the air cleaner, put spacers on top of it, then put your scoop "top" on.

Once that's attached, you can just "fit the sides and back to your liking/requirements, take some measurements, and be done. might work easier than trying to use straight edges, since the hood has a curve/slope to it that changes from front to be. it's not flat, so you can't really use a flat edge anyway.

Click to expand...

That is a really good idea. Some part of me loved the idea of designing something using math but this is much more pragmatic! Thank you!

Trevor B said:

That is a really good idea. Some part of me loved the idea of designing something using math but this is much more pragmatic! Thank you!

Click to expand...

Well, you can still use math to size the opening and determine the actual air flow requirements etc. Keep in mind though how many aircraft are built by hand. Home builders use simple tricks like this all time especially using fiberglass or other composites, especially before CAD was the norm and people had to "loft" wings and compound shapes with fricking pencils. lol.

I am thinking of making a scoop for our 65 Valiant that looks like the 66-67 hemi scoops. Low and wide. I happen to like that look and I believe if the opening is close to the front, it won't just be cool looking (or not) but should actually catch some air.

Looking forward to what you come up with.

-=C