The Phoenix - The GP Roadster Project

So last year I fabbed a prototype "bikini" top for the GP Roadster. It was quite effective, and kept me and passengers mostly dry during a drenching trip to the Dragon, and other times also. But I thought it would be even better to have a removable hardtop that didn't flap in the wind, that could be faster to fit in the rain, and that folded to stow in the back. So I've been thinking about that for about a year.

Given the curvature of the roof, the best way to accomplish this would be to start with an OEM roof skin. Sadly, I thought of this shortly after I had sent the GP donor chassis to the shredder last year. Because I would have loved to have had the roof of that car as a starting point. Well, water under the bridge.

New roof skins are about $600... so I searched for a good deal on a salvage roof. Found one about an hour away, for a couple hundred bucks. So I started with this...


There's a lot of steel in the roof assembly. The perimeter of the roof has up to four layers of steel reinforcement, spot welded into various sandwiches with air gap in between, to make the roof strong and stiff. I knew some of this would need to go, to fit over the cage... but also knew it would be trial and error to figure it out.

First, chopped off the C-pillars and hatch mount... I knew I didn't need this part.


Then I made a template of the curve of the windshield header seal on the cabrio, traced this onto the roof, and rough-cut it using the nibbler. I intentionally cut it a bit large, knowing I'd probably need to trim it down later. But I just wanted to be able to lay it in place, so I could start strategizing on the fitment.


Took several hours of iteratively trimming and test fitting, to finally determine that ALL the structural stuff needed to come out to make it fit, just leaving the single layer skin. I had also thought I might be able to retain the flange that held the upper window seal, to use the OEM seal from the GP... but eventually determined that wouldn't work... just not enough clearance for the cage. So after hacking on the roof some more, I finally had something that would lay in place. Then was able to determine where the cut needed to be to best mate to the header seal, mark, and cut it again. Success!


Then time to figure out the length and shape for the rear. I played around with some different concepts, but eventually decided to leave it "flat" but cut it to the same curvature as the top of the new duckbill spoiler. So I copied that curve onto a piece of cardboard, made a template, marked the roof with about 6" of overhang in the center, and cut it with the nibbler.


The view of the overhang, from the driver's seat:


So it's fitted!
Next steps: pull some dings out of the skin, cut it down the middle so I can either fold it or stow it in two pieces (to fit in the rear), prep and paint, and install edging and mounting hardware. I found the hardware I want to use, and ordered it today, along with the edge trim. I'll start on prep and paint tomorrow. Hopefully I'll have the hardware in a week or so, and will finish it up then.

 

Thanks! It probably won't stay red for long, though I kinda like it too. But GPs have silver roofs...

 

Yeah, I'm fond of the CR also. It was a poor quality respray of a factory white (I think) roof, and clearcoat has failed... so it's gonna need paint regardless. So I haven't been careful to try to preserve it. While I'd like for it to look nice, the reality is it's gonna get banged up no matter what I do, hauling it around when it's off. So I'll probably end up doing something that's easy to touch up... single stage, no clearcoat. I'll see what I have left in my paint bin... I think I may have gotten some silver plasti-dip type stuff that I experimented with (but didn't use) for the cage...

Once I split it and paint it, the whole thing will get edging all the way around. I have a 4" wide neoprene rubber strip coming; my thought is I'll bond that to the inner surface as a foldable seal. I'll see how that works and adapt as needed. I may add additional structure to the inner surface to stabilize it... I'll see how it behaves once I have it hinged and mounted with the latch hardware, and go from there.

 

Yup. I did a rear fit today. Plenty of room, since I don't have the meth cell in there anymore.

 

Pretty busy week, working on the roof.

Sand and prime the roof panel. Not going for perfection; it's gonna get banged up anyway. Just want it "decent" for now.


Measure, mark, and split the panel with the nibbler.


Applied a few coats of silver wheel paint, which is a pretty close match to the Pure Silver. Painted the underside with satin black chassis & roll bar paint. Just going for "good enough" for right now... if it all works out, I'll take it apart and refinish later. Added edge trim all around both panels.

Now, to attach it... I spent the better part of a year searching for the best attachment approach for the roof. I looked at hundreds of different types of hardware. Things that were designed to hold on roof panels... and just about everything else you could imagine. Dick suggested last year that I use hood pins. I was headed that direction, but really didn't want pins sticking up through the roof. I looked at several kinds of flush-mount latches. The Quik-Latch latches looked perfect for the application... but they are $300 a pair! And I was probably going to need 8 of them...

Then I found a source for Chinese knock-offs of the Quik-Latch. Yeah, I know. I'm not usually into such things... I buy the real deal whenever I can. But there's no way I was going to buy $1200 worth of latches for my roof. $100 total, shipped from China, was more in the budget.



These are pretty slick. Billet aluminum latches have a ball bearing ring that snaps closed around a ball-top adjustable hood pin. Push the button on the top to release, it stays released until you press it back down on the ball.



Spring tension in the latch should help dampen vibrations. At least that's the theory. I measured and identified locations where I'd have enough clearance for the "stack height" of the assembly, and where the roof skin was flat enough for the latch.

The adjustable pins are designed to mount through sheet metal with nuts and washers. But that's not appropriate for mounting on the roll cage. So I drilled the cage and installed 8 M12 outserts. Yeah, I know... holes and roll cages aren't a great combination. If it was a wheel-to-wheel race car, I'd be concerned about it. But it's not... and I'm not. I avoided bends and junctions that will see highest stress in a catastrophic incident.

Measured and cut down pins to an appropriate length to provide the necessary adjustment range in each location.



Fit the roof panels in place, adjusting the pins to hold it at the desired ending height. Lined everything up, including the center seal for the panels, and taped into position. Checked, double checked, triple checked, and then marked the center points for the latches on the bottom of the roof where the pins touched.



2" hole saw to cut holes for the latches... install latches... and the moment of truth!






OMG! It actually works!

I'm most excited about the tight fit against the factory convertible roof seal at the front. Should be leak-free!







I'm actually a little surprised how well it came together. But the first real test... how secure it is when driving?

I did a total of two hours of spirited driving, over smooth and rough roads, at speeds up to 90mph. Zero wind noise, zero whistling, zero rattling. It's just on there, solid. Relatively quiet, calm, and civilized in the cockpit. With the windows up, the heat actually works and makes the car quite livable for four-season use.

I can install and remove the roof in about a minute, maybe less. Stows in the boot; I need to work up a secure storage method so it's protected and doesn't shift around back there. That's next.

I'll be able to test it in the rain this coming week, to see if I'll need to make any adjustments, or add any window seals, or add any "wings" in the rear to prevent blow-back. But judging by the airflow in the car today, I don't think it's going to be a problem. Very calm inside with the windows up.

 

Thanks Dave!

That's a very useful technique I've used many times, on "normal" cars. But it doesn't really help much on a car that leaks by design. :devil:

The question in this case isn't "does it leak?" because of course it leaks A LOT... the question is "how much water blows in when driving in a downpour at 70mph... and from where?" I'm perfectly OK being damp on a wet day. That's the price of weirdness. It's just a question of whether I've yet achieved an acceptable level of semi-dryness. I'm pretty confident it's not going to leak much, if at all, from above. The seals are good. The latches themselves are mostly sealed, but will probably seep a tiny bit. The big question is how much blows in the sides and rear. Which are open.

Sadly, the hose doesn't understand fluid dynamics and airflow. So real world testing is the only way.

 

Yep - They're really a cool design, and work well.

Quik-Latch makes a smaller version of them (about half as big) that would be ideal for many applications (and perhaps some of yours!), and are in the $20-25 price range per latch. Why they feel they can charge $150 per latch for the same thing, scaled up slightly... well, that's what made me buy from China.