RyanPerrella

There are bonding agents (glues) now that far exceed what spot welding can do in terms of strength in the chassis

That being said, I still would never consider some fly by night panel maker suitable for replacing the roof of my car. The roof is an incredibly important structural part of the car. Its not like a fender which is really just cosmetic and has nothing to do with chassis rigidity.

I dont see how you rip out the roof of a street car and make it better than what porsche did.

Also factor in the custom trim and head liner you need to fabricate, the weight of the bonding material to the overall weight of the steel skin vs CF skin. I imagine when you consider all this your weight loss is negligible if not making it heavier and perhaps MUCH MUCH weaker. True carbon doesnt stretch, it cracks and breaks, steel is much more forgivable. Also keep in mind BMW spent millions of dollars developing the roof od the E46 M3 CSL, that technology then went into the 6 series and the E92 M3. I dont know how they did it, (never cared to read about it) But i can say with some confidence that their method if far more involved than what the local glass fender guy around the corner is doing with pre impregnated carbon.

Also YOU MUST put structural carbon in the autoclave. You need the heat and the pressure to get that "strong as steel, light as a feather" effect. the carbon used on hoods and body panels that you see on your riced out civics does not use and in those applications the carbon fiber weave is there for cosmetics for those that like it.

This has come up a few times but I dont see how any of you would think this is a good idea for a street car.

Although, if you have a full tube frame car, or a 928 with a full cage which really in the end makes the roof unnecessary then by all means add a carbon roof if you must.

I dont see why people are still considering this though, its incredibly silly if you ask me.

RyanPerrella

Is that a ZR1?

Notice the aluminum frame there?


or is it magnesium ?

Are you CF guys going to have the local joe blow make up those for you as well?

again, i suggest you all research this topic much more before you go cutting your tin tops off.

RyanPerrella

Play with carbon fiber for a rear diffuser, or with front fenders or hood, or bumper covers

but the roof is an incredibly important part of a closed coupe structure and the last thing i would modify on a 928.

You know how they always say that cutting the roof off the Aston Martin whatever makes the convertible version an inferior car to the coupe? Sound familiar? Well you would be doing the same here by cutting out the tin.

Ive said enough, i hope im wrong for those that want this but if anything i think you all need to do allot more research before you do something as drastic as this.

slate blue

Well I am no expert, I do know more than most on this topic, read two books on it. I do have access to some expert carbon people when I go about this. I know the glue BMW use, which is made in the US. Different weaves have different strengths. Also different resins have different strengths and properties like resistance to heat for example. It also depends on how much resin is left behind, the way the weave is draped etc. I think a lot could be learned just be measuring the thickness of the BMW roof panel.

In respect to the autoclave, I don't know about the heat aspect being so important. Unless it is similar to the way they paint cars at the factory. You see our cars are painted in what is sometimes referred to as 2 pack. When you paint your car you will note that it is not as hard as factory job. It does harden up after about a year. I suppose that depends on the climate and how much you leave it in the sun.

Getting to my point, the factory doesn't use hardener, it uses heat. Try it if you don't believe me. Heat two pack paint without the hardener and you will send it off and it will be harder than if you had put the hardener it. You see one way causes a chemical reaction and resultant heat, the other way is direct heat. However the heat used is greater than in booth. There is no plastic in the car at the time as such they can really crank it up. So maybe the same principle.
The heat in the climate would eventually fully harden it up IMHO. The pressure just gets rid of extra resin.

Greg

JHowell37

Carbon fiber is incredibly strong went bent or stretched, but weak when compressed or exposed to a high shock. A carbon fiber bar is very difficult to bend, but will easily crack if struck with a hammer. I agree with Ryan that it's probably unwise to think that some fly-by-night hack is going to make something in his backyard tool shed that will be safer then the factory roof.

Oh btw, the glass roof on that Corvette IS NOT a stressed member, and hasn't been since the C4. That's why the C5 and C6 both use latches to secure the roof panel and not bolts. For trolling purposes it's a fine example.

ptuomov

Two questions:

Does someone sell a whole kit to remove sunroof from an '87? That is, the panel, interior lining, dummy switch, etc. The whole kit to bring the car to the same condition as if had rolled from the factory without the sunroof.

What's the benefit? How much weight savings and more importantly, how much more headroom?

Rob Edwards

Tuomo-

Definitely no kit, and I'm pretty sure the non-sunroof panel is NLA from Porsche. That said, several folks have done the sunroof delete- S4ordie is in the midst of it right now .


Purported headroom gain = 1- 1.5"

Other threads:

https://rennlist.com/forums/928-foru...oof-panel.html

https://rennlist.com/forums/928-foru...n-sunroof.html

S4ordie

Rob you are right on the "in the midst" statement. Last I visited the car at the body shop it looked like there was about 2 inches (50 mm) of gained headroom over before (with sunroof). Now this does not include the new headliner and sound deadening I plan on putting in there as well. In regards to the weight of the panel, it was not very heavy - Ronn Ruff body/paint guy, guessed to to be about 6-8 lbs (2.7kg - 3.6kg). I had all the braces and brackets replaced as well along the windshield and rear hatch with NOS.

I do think there are a few of the sunroof delete panels available but they are in Germany. One of our suppliers might be able to hunt one down for you.

I just don't see the weight savings of using CF instead of a sunroof delete steel panel.

mark kibort

Yes, there is a lot of weight that needs to be cut out with a sunroof set up. with patience and a nibbler, grinding wheel and sawsal, you can get most of it out. then, you have to find a way to plug the big sunroof hole. Im temped, after driving 1000miles with my new replacement racer, to make a zirque (?) fitting set up, to make it removeable to have a sunroof when im not racing and on the street. I will probably cut the entire roof out, or do it the right way , by drilling out the spot welds and use the spare roof Anderson gave me with the car. however, it would be nice to cut out a big square and then have that zirque fitted, so that i could almost have a convertable! Lots of options . Ill probably start a thread about it shortly.

I dont think i need to do the entire roof removal, as i can just cut out a perfect sized square of the entire roof removed and then just tig weld it in place and use some bondo to finish it out. Im leaning toward some kind of removeable top set up and maybe an extra bar in my cage to cross the roof to make up for the safety loss factor.

slate blue

Mark reference to you using a tig to weld some thing like a panel, mmm, I have done this and I think a mig is better. I didn't think it would be the case but the tig is just like an oxy and the mig has less heat into the panel. Unless you are worrying about sparks flying around because it is not all masked up. My bet is that panel beaters will stay with the mig and not just because of the cost.

Greg

jon928se

Can't believe that folks are talking about a solid carbon roof panel.

If you were making something like a replacement A Arm then it would be a solid lay up. However for a roof panel which is structural you would almost undoubtedly use a carbon/nomex foam/carbon sandwich to achieve the requisite stiffness without the need to lay up a million layers of carbon.

Even if the roof was purely to keep the rain out it would probably be lighter to do a sandwich construction than a solid layup, as the solid would use more carbon and resin just to be stiff enough to prevent it oilcanning . (Think of Rolf Harris and his wobble board.)

This isn't new technology - been used in production sailing boats for at least 20 years.

For durability and impact resistance I'ld seriously consider using kevlar rather than carbon in some of the layup. While kevlar is not as strong as carbon weight for weight it does have the advantage of remaining intact after impact.

mark kibort

I thought the tig would localize the heat better, vs the Mig, but Im no welder. (but ive seen it done on TV and at the track ) (and I have stayed at a holiday inn.)
My BMW buddy bruce said that they did a sunroof delete with a regular non sunroof top and mig welded it, but the heat and welding, stretched the panel and it rippled. im thinking the 928 roof being made with stronger steel, and my thoughts of using a much larger panel size, might not end up with the same issues.

tonight, im half way done by cutting the inside area of the sunroof structure. I think Ill have most of it removed after im done. there wont be much left besides the sidewall structure of the sunroof enclosure. that could be cut out too, at the expense of a slightly larger hole than the current sunroof. then, I could cut out a piece from the donor roof and mig it in there. OR, im really thinking of making is some kind of removable piece. driving around today with the roof open, really makes me think! Nice to have a 928 on the roads again!

RyanPerrella

seen it done on TV? Oh dude give yourself credit, your a PRO

S4ordie

Oh no he isn't. He stated he has stayed at a Holiday Inn. That doesn't make you smarter. You must stay at a Holday Inn "Express" to get the real intelligence infusion.

Regarding MK's refernce to staying at a Holiday Inn ... for the ROW folks there is a series of advertisements in the U.S. for Holiday Inn Express, a low cost hotel chain. Typically it shows a scenario of some high education circumstance, (a group of surgeons about ready to make the first incision.... one of them is talking random jibberish about surgery until someone asks "Are you a surgeon?" The reply is always the same "No, but I stayed at a Holday Inn Express! last night" indicating obvious high intelligence for making such a prudent choice. My favorite? The Rabbi..... enjoy.

http://www.metacafe.com/watch/779934...n_express_ads/

JHowell37

Just a suggestion Mark, when you remove the panel from the donor and drill out the spot welds, drill from the backside so as much of the donor panel stays intact. Then on the car you wish to attach it to, drill those spot welds from the outside to leave that car intact.

You can get a spot welder from Harbor Freight and make all of the spot welds yourself.

The problem with heat when it comes to any kind of welding can be dealt with easily. Just move around to different areas of the panel you're welding. The problem excessive heat causes is metal shrinkage. This is why heat is used to correct issues of oil canning when damaged metal is straightened.