Hardtop for Cobra

After trying to buy a hood from GD for some 18 months, they have now announced a hardtop. The Le Mans hardtop, is close to the original Cobra style.

At the time of posting this blog the soft top was still not available. I had a number of other options, to get a hood and I was getting very close to doing this. But I really liked the shape of the Le Mans hardtop, even if you do have to open the rear window in order to open the boot.

427hardtops produce one that looked particularly good. This is a stunning creation, has a window behind the door and stainless steel around the side screens. It may not look like a traditional Cobra hardtop, but still looks very attractive. The design was originally for a Dax Cobra, so it is not an exact fit on the GD. However, 427hardtops have done one for a GD and have another scheduled for February this year. The hardtop comes virtually finished, although it has to be sprayed after that. April looks to be the earliest they could do one for me.

The GD hardtop by comparison is slightly less expensive and looks more like the original. It does however come in kit form, although it can be factory fitted at an extra cost. It is also self coloured, so it should match the gelcoat of the car thereby avoiding the need to have it sprayed.

The GD option is slightly shorter than the 427hardtops version. The benefit here is that my fuel filler is at the corner of the boot, rather than an Aston style filler on the rear wing, so it should be easier to access inside the hardtop to fill up. If necessary the fuel filler will be mounted on the C pillar, but this will make the hardtop virtually permanent. I have been quoted 2 months (although 4 months is what it works out at in reality!).

Wind deflector part 2

After creating the template (see last post), I applied masking tape to the polycarbonate where it would be cut. Then I marked the shape of the template on to the masking tape, including the eye bolt hole centres. A soft cloth was put on the bench to avoid any scratches when cutting. The deflector was cut to the shape of the template using an electric jig saw (use the correct blade and a very slow speed to avoid melting the material - I used speed 2 out of 5). The part cut from the bottom was supported by tape to avoid it snapping when the cut was near to the end.

Polycarbonate cut to shape

Next the four holes for the seat belt anchorages (eye bolts) were drilled. A 4mm hole was drilled first as a pilot hole with a sharp HSS bit. After checking that the pilot holes were in the right place, these were then drilled to size, using a 22mm hole saw.

The edges of the polycarbonate were shaped with a file. Then they were finished off with P80, P400 and P1000 wet n dry paper. Finally the edges were buffed with a foam pad and G10 polishing compound, using the polishing machine. The edges now look like glass.

The fixings, but note that the screws used were 30 mm long

Next the deflector was temporarily fitted on to the roll hoops using just the seat belt eye bolts. The six fixing holes (to locate the P-clips) were marked on to masking tape.

A soft cloth was placed on the bench again to protect the polycarbonate and then the holes were drilled out gradually to 6 mm. It is advisable to drill in to a block of wood to stop the polycarbonate cracking. The deflector was then temporally attached to the roll hoops again, with the P-clips and using M6 x 30 mm button head screws with nylon nuts to make sure they were in the correct position.

Once I was happy with the fit and finish, I removed the protective film from either side of the polycarbonate. Then I wiped the dust from the polycarbonate with a soft cloth.

The deflector was then fixed in its final place. The metal washers go under each screw head and against the outside of the P-clip, with nyloc nuts to stop the deflector working lose (make sure that the plastic washers are against the polycarbonate to reduce the likelihood of cracking). Finally the eye bolts were refitted, along with the seat belts.

Finished wind deflector in place

Does it work? Well it doesn't stand out or detract from the Cobra's lines. It does cut down on the wind behind you head significantly, but it does not totally eliminate it. To do that a hood, a hardtop or a tin top would really solve the problem.

Wind deflector part 1

Yes, I am a wuss! Its official. The back draught of cold air and buffeting in the Cobra at this time of year especially (when it is cold) needs taming. I do have a beany hat and a scarf to help keep out the worst of the cold. But most importantly, my wife prefers her hair the right way round!

I researched the subject on the Internet, the Cobra Club Forum and read an article by Paul Hutton (which is really good) in the April 2017 publication of the Snake Torque magazine. From this research I reckoned that there was a way of cutting down the draught on my neck and my passenger's without detracting from the Cobra's lines. So here is what I have done.

Template

First the four seat belt eye bolt anchorages were unscrewed from the roll hoops. The wind deflector will fit behind the seats and onto the face of the hoops. Masking tape was applied to the body on the cabin side of the roll hoops to prevent any marks.

Eye bolts removed and masking tape applied

The template was made of hardboard. Duct tape was used to hold the hardboard in place each time it was removed and refitted.

Duct tape on back to hold template

First, the hardboard was marked up to follow the body of the car, then cut with a jig saw. After the first cut, it took a bit of messing about to get the right gap all the way across at the bottom.

Hardboard with first line drawn

Once I had this sorted I marked up the top and sides. The deflector extends 50mm beyond each roll hoop towards the outside of the car.  If the deflector extends any further it will scoop up the air passing down the side of the car and channel it behind your head, defeating the whole thing!

Then I marked up a slope - from the top middle of each roll hoop to the outside (about 75mm down from the top), before marking rounded corners. The top corners were a 75mm radius and the bottom corners a 25mm radius (hope this will be ok for the hood or hardtop I get). The template was then cut with a jig saw and planed to get smooth edges. Next I marked the eye bolt holes using a hammer against the hardboard and the mounting hole. The centre was then marked and drilled using a 6mm bit. After checking the holes were in the right place, I drilled them out to 22mm using a step drill. The hole needs to be big enough to clear the shoulder of the eye bolt.

Template cut and eye bolt holes drilled

Finally I put the eye bolts in place finger tight to check they were clear of the hole sides.

Final template with eye bolts in place

I have allowed a 5mm gap between the deflector and the body. This will allow the pressure inside the cabin to be equalised.

Material

Laminated glass - this option was beyond my capabilities to work with. It would need to be laminated to avoid it shattering if hit by a stone. Glass is expensive, not easy to cut or drill and is also quite heavy. So this was ruled out.

Perspex - easy to cut and drill. Cheap to buy and widely available. Loses transparency over time, can warp when exposed to UV light and can break in to large shards if hit by a stone. So this too was not an option for an open sports car with no top.

Acrylic sheet - easy to cut and drill. Stable dimensionally, to UV light and stays clear. It has greater break resistance than glass. On impact it breaks in to relatively large pieces, rather than small pieces or shards. Withstands large changes in temperature. Lightweight. Better transparency than glass. Expensive and harder to source.

Solid polycarbonate - similar properties and strength to acrylic sheet. Easier to source and less expensive than Acrylic.

So polycarbonate it was. I have ordered 8mm thick which by all accounts is about right. Any thinner and I risked it vibrating or flexing at speed. Any thicker and it is over doing things. The size of the polycarbonate sheet ordered is 1220mm x 360mm. Prices seem to vary quite alot over time (oil prices?), but Century Plastics in Sheffield seemed to have the best price at around £30 including VAT and carriage and their service is great.

My next post will be cutting, drilling and fitting the deflector.