Building an "A" type hip-spoiler for the Manta

When I finished my six year Manta conversion into a look-alike Mclaren, I no longer had the wherewithal to start on the M8A spoiler. I didn't want a wing to match the "B" body being this was mostly a street car, and the "A" spoiler is unique enough to compliment what had been accomplished already. So three years later, and having thought about how I would build it, yet not make it weigh a ton, and not being satisfied with a similarly shaped aluminum one that just wouldn't be "right", I dove into this mini-project. As it turned out, this seemingly simple idea and piece was probably one of the more complicated parts I've built for this car. Based on some very good scale drawings and photos, I came up with the dimensions, which appear to be reasonable once I was able to visualize it with foam-board template taped to the car:
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One of the many challenges was to build this to fit the car like a glove, yet fabricate it without destroying the existing paint. This was done by carefully laying up masking tape to cover the existing paint, very evenly, anywhere fiberglass would be laid. Then I laid up a mounting flange onto the tape, which would be used to fasten the completed spoiler in place using 1/4" screws around the periphery of the mounting flange. The subsequent pieces of the spoiler would be bonded onto this mounting flange:
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Next up was to build the "down-planes" as I call them; the side pieces with a slight angle to them. They had to be bonded onto, and thus become another layer of the mounting flange sides. In order to save as much weight as possible, I had to make the spoiler hollow,which means I had to build two plates, or panel faces for every aspect of the spoiler, two surfaces for each side's down-planes, plus a front and rear-facing plate for the main spoiler panel. The passenger-side down-plane, top and bottom plates:
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Once I completed the down-planes, I laid up the front and rear-facing plates for the main spoiler panel. I used a sheet of .125" aluminum as a buck to obtain a smooth even finish on each plate's exterior side. These plates had to be at least 83" wide, and are roughly 1/8" thick (4 layers of 2 oz mat + a couple of layers of thin cloth):
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To ensure the front and rear-facing plates would be at the proper angle, I hot-glued some wood guides in place, and then bonded the rear-facing panel onto the mounting flange. The goal here was to have the front-facing panel be parallel and aligned with the angle of the body's rear lip and integrated spoiler already existing. My goal was to simply continue that angle upward another 6.5" taller:
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After the rear-facing panel was bonded in place, I installed threaded inserts into the mounting flange for additional insurance that the spoiler would stay in place at high speed. First I located the inserts, then wrapped them in fiberglass so that they were bonded to the mounting flange. Once this was done, I could go forward with bonding the front-facing plate:
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I then bonded the front-facing plate in place, using spacers, between the front and rear-facing plates, all along the edges to ensure the spoiler would have uniform thickness along the entire edge and into the down-planes:
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This is where the project is at this time. Next addition will be a cap along the entire periphery of the spoiler to tie the front and rear-facing plates, as well as the upper and lower down-plane plates. The original spoiler on the team cars use wood as a core. I will fill mine with expandable foam. The spoiler will be about 5/8" thick at the edges throughout the entire assembly, but will be thicker at the base of the main panel to ensure rigidity against rearward force from oncoming air at speed. A total of 6 internal 1/4" bolts, and 29 external screws (similar to the team method on the external screws) will affix this spoiler in place. The main deviation from the team spoiler design is that I will use the internal bolts (using the inserts with bolts coming up through the bodywork from under the bodywork), and the fact that this is a one-piece spoiler instead of two halves being joined in the middle. Anticipated weight will be 25 lbs.

With cap installed, and with most external fasteners in place, but not finished:
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To ensure the body under the spoiler was sufficiently strong to handle the forces imparted into it from the spoiler, I've added two perpendicular flanges (3" deep) on the inside of the rear vent panel, that extend from the upper rear body lip, down to the lower valance, and which are used with two 3/8" bolts to hold the rear of the body panel in place (as well as act as hinges).

nice work. great car.

Awesome!

Fiberglass work is pretty much finished at this point. Ready for Duratec, finish-sanding, and paint. Final weight came in at 24 lbs without paint. Will be moving forward with perhaps some quickly fabricated fences for the front bodywork to improve that end's downforce as well:
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I really like this build. I think making scoops functional, adding spoilers that work and other functional body mods really take the "kit" out of the car body mold and take it to a new level.

What do you do for filters on your stacks?

The current set-up is triple screens at the top of the tubes (progressively finer mesh). I have no idea of how much efficiency is lost being screen isn't that efficient for passing air. I occasionally run K&N stack filters, which I'm sure is more effective and efficient, but it really detracts from the CanAm look, and as little as this car is driven, not sure in the long run how much different engine wear would be.

First coat of Duratec, and having to address some pinholes. Starting to shape up nicely now.

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And wet sanded. Ready for the paint!!!!
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Underside of the mounting flange to show this is basically a hollow piece (foamed in) of roughly .140" thick fiberglass. Once screwed in place, very rigid and sturdy considering the underside of the rear hatch has also been reinforced along the back panel, with large ribs spanning from the top lip, down to the hinge-bolts, so that nothing collapses at high speed.
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Spot-faced all the screw holes for neatness, and especially for those holes that were in the middle of a concave curve, or where the surface of the flange was not parallel with the fastener head. Lastly, and almost forgotten completely, a hole was required for the back-up/rear view camera. the old camera was in poor shape, so I replaced it with another that had to be mounted differently. Good old Ebay…nothing sold a couple of years ago is sold today. Fortunately, whenever I buy anything for the car, I buy spares. So I've got several new cameras, thus if this one fails in the future, I've got another identical to it. Now it's officially ready for paint...if it ever warms up again...while I'm in town....grrrrrrrr.

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Very nice work.

Contingency plan: If the rear spoiler upsets the balance, or provides too much rear downforce, I'm fabricating some fences and a dam for the front of the car to provide some front downforce. The fences should keep the air from spilling over the side/front of fenders, and thus force the air over the top of the front of the car. The dam should improve the high pressure over the top of the radiator cover.

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Squirted some paint on the spoiler. Still needs a clear coat, but have some blemishes to resolve before that happens.

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Looks awesome!!!

Hi Terry do you mind sharing what was the actual color/paint code you used to paint your replica? I've been looking for the right color, I've sampled ford school bus yellow and from the modern BMW Mini Cooper cars, volcanic orange B70 and Mellow Yellow A56, now looking at Hyundai Veloster yellow (Sun Flower SYYH). All touch up samples but they just don't look right, maybe touch up paints I got were just not mixed that accurately.

This is a case of the blind leading the blind. I went with what my eye saw, and that may be different than what someone else's eye sees. I tried to consider photos of original McLarens, taking into consideration different film coloring and age of photos, etc. So basically a crap shoot. What I came up with was using a Fiat color (keep in mind, my computer bit the dust, am awaiting the backup for all the data I had on it, and a new computer is on the way, so this is off the top of my head) called Arancio Narciso. AR68412 is a ProSpray number (2005 Fiat color) based on a can of touchup I still have in the garage. If I remember correctly, it's a pretty simple formula of red, yellow, white, and black. I reduced the red, increased the yellow (by maybe 20% ???) to obviously reduce the red, and increase the yellow for a slightly less red than the fleet color to make it more orange in my own opinion (duh, yeah, but I had to say that). Also, I may have reduced the black a little, and increased the white (by maybe 5%) to increase the tint, or make it less intense. who knows if its right?

Google the color, and you'll sort of see what it looks like. IMHO, the color in can is more intense, which is why I tinted it down, and made it more yellow for my car.

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