slate blue

The problem you have when you weld the 928 is the zinc on the body. Grind it away and you make the panel thinner and easier to blow a hole. Don't remove the zinc, well, just don't go there. Weak welds, plus the metal sometimes will vaporize. I used acid to remove the Gal, that worked O.K but that is not an enthusistic O.K when I changed the battery boxes on my 928s.

I have been told that MIGs used with brass wire and these are inverter MIGs that can weld zinc coated panels. I haven't seen it done but give me your questions and I can ask for you. When you remove the Gal you need to treat it otherwise you WILL get rust. Normally a very thin paint will be able to seep into joints with a capillary action. That is what you want. I was told that laser welding is what some car companies are doing these days, very little heat into the panel.

Greg

jon928se

I agree with your first statement

Don't agree with this one

In short -Do not weld electro plated zinc or hot dip plated zinc (galvanised) steel components. The zinc oxide fumes generated when welding will kill you a few days later.

Cheburator

Had a body shop take out the sunroof roof skin and weld in a brand new Porsche non-sunroof skin in on the racer. Cost me $1000 equivalent and the peeps at the body shop bitched and moaned to high heaven. Drilling the spot welds was bad enough, but the zinc made them ill when they were welding the new skin back on. Must say though, they did a great job... And Porsche only wanted $200 for the new panel which weighs nothing...

mark kibort

thats why im leaning toward a full cut out of the sunroof structure, and cutting a panel out of the roof piece to fit. zirque fittings or a weld job, I dont know yet. again, it would be nice to have it removeable, have the main structure in tact, but have all the weight out of it by cutting it all out. Ive done the cutting before, but with a nibbler, you can only get so much out. after studying the structure for a while, i think we can get most all of it out,leaving just the sunroof hole.

Here are a few shots of what ive done so far. just playing around cutting the inside stuff out, which wont hurt anything either way, but it does look like you can get most all of it out, especially, if you take a grinding wheel and cut the vertical structure that attaches to the sunroof opening , all the way around the roof.

pics of the first cuts, and a pic of the donor roof for comparison

mk

mark kibort

see where that drain line is? With all the bottom sheet metal removed, as shown in the second picture with it bent down, if you follow the drain line position with a sawsal, you could cut the entire sunroof box out, and only have a thin steelwall hanging down from the roof, all the way around the front of the sunroof area. other than that, there would be no weight difference between what is left and the non-sunroof roof. in fact, you could cut it totally out atthe sides, and up front, as you can see from the front of the roof picture, the vertical wall is butting up against the normal roof structure. so, in that area alone, because it is not welded to the roof structure, you could use a grinding wheel in the front area only, to remove most of it. you could even leave 4 tabs so that you could make "L" brackets to hold a sunroof copy panel , in place and even make that removeable with wing nuts or something.

just some thoughts.

mk

slate blue

I bought the last sunroofless roof panel for the early bodies 78-89, there is 3, 90-95 panels left then they are being discontinued like the early ones. I am going to use this panel to make my carbon mold.

Interestingly, the mold needs to be made from carbon also due to the temperature that the pre-preg sets off at. I am going to put a couple of layers of aramid into the mix also to hold it together in case of an accident. I am hoping the seller can advise on basic lay up angles and techniques. They say you need special shears to cut the aramid as it is very tough.

My research indicates pre-pregs being much easier to use effectively and I plan to use a powder coating oven to cook it. It will be in a vacuum bag and I already have a good air cond pump for the vacuum. My estimate for the weight of the finished panel is 2.5 to 3 kgs max.

BC

Did you ever make this panel?

slate blue

BC I made some progress with research but no panel, what I know is the weight of the finished 928 panel should be around 3 kgs certainly no more than 3.5 kgs, I bought a brand new factory panel and I bought a sunroofless GTS roof complete with all its bracing and it will make the perfect mould for this job. I also found an oven that I can use for the "cooking" it has the temperature control that is required for high temp composites. I also have the vac pump too.

I also found out a way to make your own pre-preg carbons, via youtube and made contact with a composite supplier in the UK that supplies the F1 teams. That will be useful for 1. getting the right epoxies and 2. being told how to lay up the different weaves for strength. We also have the correct glue that BMW uses for their roofs which is from Valvoline.

I don't want to bore people but my health hasn't allowed anymore progress, I wish I could bring in a partner that was keen and had some contributing funds, the other aspect I would like to tackle when this project is started is a flush fitting windscreen. I believe it can be done in a design appropriate way. This should cut drag and feed more air to the spoiler. I may also look at the rear spoiler, deleting the wiper area and extending the spoiler in proportion and or adding a gurney flap.

These changes together may help the underbody flow and downforce. It is basically what Ferrari did with the 599XX. As we know that car develops more than a 1000 pounds of downforce without wings.

BC

Great, thanks for the info. I always felt that smoothing the body is a good idea

Rob Edwards

Wasn't sure where to put this, but for S's&G's I happened to have a more or less complete set of sunroof guts in one place. Total weight of all removed pieces is 23 lbs 14oz:

emeegee

can you please share the information with me?