Fiberglass roof

jacko241 · 12-24-2005, 08:22 AM

I am considering replacing the steel roof on my 1977 tub based SCCA GT-2 911 with one of the new fiberglass units from GT-Racing that includes the cowl and window surrounds. Of course my car has a full 8 point cage that is tied to the rear to each side of engine just behind shock mount crossmember, and to the front at each shock tower, and then forward to the pan just ahead of each wheel housing. Do you think I will lose any significant chassis ridgidity? It will produce a significant weight reduction, as the 'glass part only weighs 14.5 lbs.

jwerion · 12-24-2005, 02:26 PM

Joe, I am in the process of doing this conversion as well. The glass roof from GT actually weighed 21 lbs but I am not planning to use the front cowl section and will cut it off 2/3 of the way up the A- pillars. Mine weighed a little more because I had them gel coat finish the inside of the roof as well so it has a nice clean look to it. The shop doing my work is 3R racing in Denver Colorado. They feel that with the cage I have in the car it will not effect the rigidity of the chassis. However to make sure there is no flex or that the chassis does not spring or distort, they will mount it on there chassis/frame machine and take some measurments before they cut the roof off. If your roll cage is fairly substantial you should not loose much or any rigidity.

jacko241 · 12-24-2005, 03:28 PM

Thanks, Justin. I wonder exactly how much weight it will save? It is certainly a good place to remove it.

jwerion · 12-24-2005, 03:54 PM

Joe, I will let you know the exact weight savings once I get it cut off and installed. I estimate the weight saved to be between 37-42 lbs after it has been installed. This is a fair sum and as you know the best place for it.

rich22 · 12-25-2005, 10:33 PM

Please let us know what they tell you, as far as measuring any flex.

The other nice thing is if your cage is not 360 degrees welded up, you can get that finished with the roof off.

78targa · 78targa's Garage

Just to chime in here. I have a targa to coupe conversion that was originally done by TRE Motorsports. They fabricated the roof for me which included the cowl all the way back to the tail. You will need to fab in the rear quarter windows, but I can tell you the piece is light!

I run with a stock windshield too and the fitment was very good. Unfortunately I can also attest to the car's ability to take a hit and have the roof stay on.

Although I lost a quarter window, The roof stayed intact when we hit a rock (think cliff face) in the PS rear quarter going 90 or so MPH. Ugly hit that crumpled the floor pan forward by a foot or so. The cage does its work. I like the idea of being able to complete all of the welds on the cage. It also will lower your center of gravity and you get to cut out alot of steel.

The fiberglass roof pieces GT sells are nice, but having the cowl FG is a real weight saver. Besides, it allowed me to put in a cool single wiper...

jacko241 · 01-04-2006, 04:40 AM

The new roofpiece GT offers now includes the cowl also. Thanks for the info!

jwerion · 01-13-2006, 10:00 AM

Joe,
I was mistaken on the weight savings estimate. The metal roof it self weights between 38 & 45 lbs depending on how much of it you cut off and whether or not it has the liner still attached or a sunroof.

I used the complete roof available from GT racing but I had them add gel coat to the inside as well for a nice clean finish. This brought the weight of the new roof up to 21# from about 15#. I didn't think it would add that much weight but it did. I installed the entire GT roof except the front cowl and a large portion of the A pillars.
The weight savings off of my 78 SC non sunroof coupe cut off at 4" down from the roof on the A pillars or windshield surround, cut at the top of the B pillars at the point of connection with the roof, and all the way down to the rear cowl & cut off evenly at the base of the rear wing windows. I also added the flush mount window kits front and rear so this added some weight as well. The total savings was still 16# I still have some work to do on it so this may come up to 17 or 18 lb savings.

The chassis was welded to a table square and level with measurments taken before cutting the roof off. Once the roof was off we welded the top of the cage and checked all the welds and cut it loose from the table and it did not fle or twist at all.
I am still glad I did it but I would not get the inside of the roof gel coated again in order to save the weight.

jacko241 · 01-13-2006, 11:43 AM

Thanks for all the info Justin. That is an impressive amount of work. I don't think I am willing to go thru that much work to save less than 20lbs. I changed my battery to one of the Odyssy PC680 and saved 25 lbs over my old one, so i am spoiled!

78targa · 78targa's Garage

Well, I think that it would only make sense if you were starting with a clean Targa or Cab. You can often find these tubs for less and avoid paying a premium for a tub. I don't think I would cut up a coupe.

Now having said that, I do like the idea of being able to get full access to the joints on the cage for improved rigidity.

jwerion · 01-13-2006, 07:58 PM

78TARGA I agree with you, Had I planed on replacing the roof with a composite one from the beggining I wouldn't have spent so much time finding a non sunroof SC coupe. But things change and this is where I am at today.
Still a 16-20 lbs weight reduction from the top of the car is going to have much more efect on the cars handling than 20+ lbs from else where on the car.
I am not sorry I did it, I just wish I had not had the inside gel coated and added that extra 5-6 lbs of weight.

78targa · 78targa's Garage

Hey I am completely with you on going with what you've got. I don't know how many times that has driven my decision-making. People always asked why a raced a targa...my answer...because that's the one I've got!

Thanks for sharing the info. Interesting on the weight change with the gel coat. I keep looking at the unfinished fiberglass on the underside of my roof and think I should do something with it. I think I'll keep it the way it is.

the '69 is going to be as light as I can make it. no carbon fiber stuff as I can't afford that, but we are going to great lengths to remove unnecessary weight.

If I get a chance I'll weigh the roof to compare.

Not to get too OT on this thread, but what do you think about SCCA? Is your car competetive in GT2?

jwerion · 01-13-2006, 08:55 PM

Casey, I think SCCA is going thru some big changes right now with the GT classes. They are moving to an SIR set up on all motors to help level the field which will be good for the class long term but they are implementing it to quickly in my opinion.
last year was my first season racing and I was third twice and 2nd once I blew the motor in race 4 trying to take second. I have a lot to learn and just need to get more seat time. My plan is to move up to the 3.8 ltr. motor in the next rear or two. But to be really competitive nationally the 3.8 ltr air cooled 2 valve motor needs to have a weight of 2,220lbs or 2,280 max which is inline with the other top placing cars at the runoffs. SCCA racing is alot of fun and very challenging, I really enjoy it.

I think they will move some of the smaller motored Porche's 2.2 thru 3.2 to GT3 with some added weight this would be the best thing for those cars and the GT3 class.

jacko241 · 05:58 AM

Justin, I hope you are right about the move to GT-3 for those of us running engines under 3.4 litre. Although I won the SCCA Central Florida Region Championship in GT-2, and 3 races, when the nationally competitive cars showed up I was a mid packer at best. However, we did find the used 3.0 engine I bought and have been running only had 36mm venturis in the carbs

, so we should pick up some significant HP with the change to 42mm.

jwerion · 01-14-2006, 06:54 AM

Joe,
If you have a non sunroof coupe or even a sunroof coupe and where to use the entire roof piece from GT racing including the front cowl section you would save considerably more than I did. I would be at a weight savings of 22 lbs if I had not had the inside gel coated and I did not replace the front cowl or most of the A pillars. I think you would save around 28-30 lbs altogether. Also when you replace the roof the gutters are removed as well.