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Lexan - Polycarbonate Rear Targa Glass?

I'm wondering if any of you track guys have seen or heard of anyone replacing the 36 lb rear 911 Targa glass with a lighter weight version made of 3/16" mar resistant polycarbonate (Lexan).

I have found a Porsche 944 example and several Corvette examples, but no Porsche 911 Targa examples.

http://emracingcorp.com/scripts/prodView.asp?idproduct=905



2008 Z06 Corvette Frame Mounted Wing and Lexan Rear Window - Excelsior Motorsports


Post by sc racing
lexan windshields - DragStuff
Quote:
I used 3/16". On the windshield Im just going to screw it every 3 inches and it will form because of the shape of the body. We made one at work for an 05 Corvette rear window it has close to 90* bends on the sides and is curved front to back when we finished screwing it on it looked like it was vacuum formed. I made my side mounts with 3/8" tubing that came in the kit and formed them to the old glass so the sides will fit the weatherstrip along the roof just like the glass did.
Looks real to me, not sure why all the louver vents.
https://www.pinterest.com/pin/414049759462676541/

Quote:
deutsch-nine-porsche-944-turbo-rear-vented-lexan-hatch.jpg (1000×633)
I'm sure that it can be done, I just haven't found an example of someone doing it - yet.

This is the tread which got me thinking about it:
Budget Targa Top - Super lite

Curious as to what the weight savings would be.
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Old 01-28-2016, 07:00 PM
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I am no expert but I did do some internet research. The best way is to have a huge oven that would heat the plexi in and a form ready to slump it onto. I am assuming that is out of the question?

They really aren't hard or complex bends, but they are large bends. You can do it, but not easy and or not cheap, if I was doing this I would make a wooden buck using my original glass as a template. Then I would clamp down the center and use heat guns and work my way out to the edges. The problem is heating the large surface area and clamping, bending etc. when you only have two hands. You'll need helpers.

Another option would to use your original window placing it upside down and bend it cold to clamp the center and then using heat and gravity to slump the plexi glass into the original window, but I think it would be risky to your original glass. Perhaps you could build a support for the original glass.
Old 01-28-2016, 08:46 PM
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Do you remember this thread?

DIY Forming Lexan Canopies
Old 01-28-2016, 09:27 PM
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Quote:
Originally Posted by snbush67 View Post
Do you remember this thread?

DIY Forming Lexan Canopies
Yea, I have that thread bookmarked already.

On one website they provide the math on thickness and cold bends. The thinner, the more you can bend it. Not sure if it was for polycarbonate or acrylic though, will have to Google it again, too many bookmarks at this point.

I bet 1/8" would cold bend, but you would need support spars to keep it from blowing out at speed.

I think snbush67 is correct about needing to apply heat, but the vette guy said he did his cold, so I'm fairly confused at this point.

I've used either 1/4" or 3/16" smoked acrylic on my hovercraft, the windscreen bend I played with was 18"-20" radius and that seemed to max it out without stressing it too much. The Targa glass is nearly 90 degrees at the hoop, similar to the vette though.

I just don't understand why I can find dozens of pictures of rear plastic windows on 911 coupes, and not a single Targa.

The Cabriolets and Targas can be found with fiberglass hard shell caps, that seems to have filled the track market.
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Last edited by kach22i; 01-29-2016 at 06:49 AM..
Old 01-29-2016, 06:45 AM
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To be clear I was asking about air-cooled era targa tops.

However, I did find this one for the 996, Makrolon is a trademark name of Polycarbonate.


Classic Hardtop CT 996-001
Quote:
Classic-Hardtop for Porsche 911 (996) Specifications: • Carbon composites high-tech structure • Stainless steel locking devices • High-tech nano-coated Makrolon rear window (Scratch-resistant and anti-static coating) Exterior: • surface of the roof parts: body color or visual Carbon with clear lacquer • Surface Targabügel: body color or clear-coated carbon with clear lacquer • Colour of the rear window: medium gray Optional: transparent, and dark gray Interior: • roof parts: Carbon • Targabügel: Porsche Alcantara dark gray • Rear carrier: Porsche • Leather: selection ! Weights: rear part 18 Kg Roof Parts 9 kg aerodynamics: Closed cw 0.28, roof cw open: 0.30 Please select the postion Shipping Methods Extra. ATTENTION! IMPORTANT ! Price change from 1.1.2013 New price:.. € 14,950 including VAT Secure yourself the old price if ordered until the end of 2012





Other products:
http://www.gtn-automotive.com/gtn/sites/gts_e.html
Quote:
The GTS-Top is made of innovative and advanced materials, for example: extremely lightweight and highly robust carbon fiber (CFRP) for the frame, with Makrolon glass, hard anti-scratch coating, stainless steel fasteners with Teflon bushings and modern EPDM seals.

It is 2 kg lighter than the already light original one.

.........................after a long development time of more than 2 years and great expense, we had to wait for the approval by the German authorities. Without getting a very special document, we are not allowed to use the roof for legal road use.
EDIT:

Polycarbonate = Makrolon
Préparation: Allègement Porsche 924...

Quote:
Hayon arrière en Makrolon.
I had Google translate parts of that page, for some reason it's not automatic.

Quote:
Same for the rear window, which can be replaced by a plexiglass model (forbidden!), Lexan or Makrolon. Several companies sell on the Internet (see links), and a member of club9.24 has already manufactured a rear window Makrolon. Price: € 550 without the reinforcement or fin ... Cher, and fragile (unbreakable, but beware of scratches), but very light! It's quite comical as a material, it bends

I mounted the tailgate + 4 side windows with sliding window for the driver. The result is not bad at all for craftsmanship! But it takes more than 850 € ...
- Weight of original tailgate (+ fin 944): approximately 25kg
- Weight of poly tailgate (without spoiler): about 7kg.
And another 18 kg won here!
I intend to be a spoiler 968 Turbo RS in the future, poly course, but it's a matter of the budget, rather short right now ...
I redid the seal all around silicone seal.

Otherwise, I began to climb the small side windows Makrolon also ... Not easy! I have already made 6 claws
Question weight:
- Macrolon: 725 grams a pair!
- Glass: 1590 grams a pair!
Less than half
But beware: too pronounced weight gain in the rear of the vehicle will cause an imbalance of the car, that too much weight on the front. So I think that a rear window Makrolon (for example) must be accompanied necessarily a hood and front fenders poly ...
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Last edited by kach22i; 01-29-2016 at 08:49 AM..
Old 01-29-2016, 08:28 AM
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I would think cold bending 1/8" lexan would be tricky. As you probably know, the stuff is pretty strong and doesn't like to do sharp bends. It might be hard to keep it in place when mounted on the car. Not many people race targas, and those who do often just remove the rear glass and run it as an open car with a low front windscreen. This may explain why you can't find any vendors selling targa lexan "glass." Maybe call Shields and some of the other Lexan windshield vendors and see if they'd be willing to do one for you? Maybe they've actually done them and just don't advertise it due to the limited market?

Scott
Old 01-31-2016, 06:01 AM
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Thank you for the input stownsen914.
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Old 02-01-2016, 06:38 AM
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There are plenty for the 944. Not sure if you could reshape one of these?
The red 944 with the louvres is photo shopped.
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Old 02-03-2016, 02:57 PM
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This place does nice work but not cheap.
Around $400+ for a rear window.
SHIELDS Premier Windshields - Racing Windshield Pricing and Models

I used flat material and did it for closer to $150.
On both my Camaros we cold bent and attached the plexi to a frame.
My source for plastic in San Diego.
Custom Plastic Solutions for Over 100 Years | ePlastics®
This place I used said that when they make a buck and try to heat form the material it can take 3 or 4 tries to get a good piece.

Old 02-06-2016, 07:48 AM
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Quote:
Originally Posted by ted View Post
I used flat material and did it for closer to $150................

On both my Camaros we cold bent and attached the plexi to a frame
Looks like it came out nice.

From the extra spars and the fact you were able to cold bend it, I'm assuming you used the thinner thickness 1/8" polycarbonate, right?

Would you even dare try your radius of cold bend in the 3/16" thickness?

A friend of mine owns a plastics shop and does lots of fabrication. I owe him lunch anyway, need to talk to him this summer about this.

One of the motivations I'm having is surface rust near the rear glass rubber seal (small spot on drivers side), and the rubber seal looking tired.

They say if you can see any surface rust it's actually much worse under the seals than you think. Fixing rust seems like a good idea, even if you cannot currently see it. If I'm going to take the glass and seals out prior to painting (old paint too), then I might as well save some weight in the process.

It is a slow process, but I'm in no hurry.
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Last edited by kach22i; 02-06-2016 at 12:20 PM..
Old 02-06-2016, 12:13 PM
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Quote:
Originally Posted by kach22i View Post
Looks like it came out nice.

From the extra spars and the fact you were able to cold bend it, I'm assuming you used the thinner thickness 1/8" polycarbonate, right?

Would you even dare try your radius of cold bend in the 3/16" thickness?
We did use 1/8 polycarbonate on both Camaros.

The older Camaro has a flimsy hinged rear window like a 944.
Since the flat poly piece wants to flaten out we added a dzus fastener on each side to keep it tucked in.
I would not want to use 3/16 on this set up.


The newer Camaro has 1/8 polycarobonate as well.
But that window in fixed where the entire rear body section is removed with the rear window.
The 1/8 thick worked perfect with no side stiffeners needed.
I suppose on this fixed rear window you could try 3/16 but the 1/8 does a fine job in the back.

We used 1/4 polycarbonate for the windshield.
Old 02-11-2016, 07:50 AM
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Midwest Eurosport had one made for a customers SPEC 911.
They used the factory targa glass to have one made.
I believe it was Five Star who made it.

Eurosport - The Midwest's Largest Porsche Specialty Repair Shop

Brian Weathered is the owner and can point you in the right direction.

He said they( Five Star?) made a mold, so it should be straight forward to get one made.

I was just racing against this car at Sebring, so I know it exists...
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Old 02-11-2016, 02:45 PM
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Thanks, I will look into this when I get more serious.

Many things on my to-do list first.
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Old 02-12-2016, 06:35 AM
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1981 Porsche SC Targa parts & more

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OEM Porsche 993 heat exchanger part # 993 211 337 in used good condition.
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9-1981 York Automotive air compressor date 9 - 1981 used York Automotive airco compressor # EM 219680 Borg Warner Company. $ 125.00 = S&H from 85377

Rare lightweight racing 7 pieces of Lexan / Plexi windows/headlights/vents/targa rear window $ 500 +S&H

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1981 SC Targa bar for sale in good condition and complete with the 4 mounting suds $ 900.00 + S&H

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Old 03-02-2016, 06:04 PM
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heat bending acrylic or polycarbonate isn't as hard as it seems. You can generate enough heat with a bank of heat lamps or infra red elements like the ones used at auto body shops to cure paint. There are a number of ways to make a quick buck to drape the plastic over.
Even a couple of these would do the trick, then when you're done bending you can heat your patio with it:
Heaters | Patio | Solaira Infrared Heaters - GlobalIndustrial.com
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Old 03-03-2016, 11:09 AM
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I realize this is an old thread, but did some of you guys actually fabricate a rear lexan window? And if so: how did you do it?
Old 02-06-2017, 12:54 PM
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Quote:
Originally Posted by Nux View Post
I realize this is an old thread, but did some of you guys actually fabricate a rear lexan window? And if so: how did you do it?
I am not an expert, but have worked with Lexan (polycarbinate) and Plexigass (acrylic)

Heat forming acrylic will need about 275 degs to get it pliable. Polycarbinate, on the other hand needs about 375 degrees.

Polycarbinate will cold bend to a certain degree, it will not crack easily or shatter.

Acrylic is much more brittle and can crack or shatter if bent cold.

Problem with trying to cold form the rear targa window form polycarbinate is you will have to screw it down securly to hold it in place. The other issue is the rear targa window has a slight compound curve which will not be replicated with a cold bend.

For a race car or hot rod I would just get some polycarbinate sheet 3/16" thick and screw it in place.

If you want to pass it off as OE, it could get expensive.
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Old 02-07-2017, 06:48 PM
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Originally Posted by Trackrash View Post

For a race car or hot rod I would just get some polycarbinate sheet 3/16" thick and screw it in place.

If you want to pass it off as OE, it could get expensive.
Thanks. I'm trying to build a 2000lb targa hot rod. I think I'll try a combination of screw and heat bend along. We'll see how it goes.
Old 02-07-2017, 10:24 PM
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Reviving this to see if anyone has an update.
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Old 10-17-2017, 12:24 PM
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hardly an update, but I have a 5mm polycarbonate plate ready for my rear targa window. Hope to pull the window this week. The plan is to cold bend and screw in place. We will se if I'll need to heat bend as well - if that is even possible.
Old 10-18-2017, 03:38 AM
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