IMSA GTU vintage racer build

[AydinZ71]

That makes a lot of sense! Yeah watching several of the GoPro vids Greg was gracious enough to send me, I’m learning his driving style and how it relates to how his car is set up. You are spot on about him being the inspiration for removing my rear bar.
 

I have stiffened the heck out of the front subframe and rockers (mostly in service of rust replacement). Have not stiffened the rear all that much besides the welded tower braces, cage terminal on towers, and connecting the floor pan stiffener through to the rear forward LCA cross member. We’ll see!

 

Greg is building an new car for Vintage btw. 

Edited July 30, 2021 by AydinZ71

[clarkspeed]

And some really bad weld porn in this post.  These were the rocker panels I had to build from scratch. I think I mentioned earlier, for body work I shoot to get close and make it up with very thin bondo to fill in any voids.  No hammering of welds, just hours of grinding.

 

I also threw in a rare rocker panel selfie with uncontrolled Covid hair growth.

Edited August 12, 2021 by clarkspeed

[AydinZ71]

Looking good Clark! Here is my usual PPE look. 
 

I truly appreciate the hours of work this kind of detailed metalwork takes. It’s a jigsaw puzzle, and with heat… nothing stays put the way you expect it to. 
 

what gauge steel did you use for the rocker skin? 18? 20? I find 20 to be reasonable as far  as weight and stiffness for skin material, but 18 is so much easier to weld-to. 
 

I completely rebuilt my rockers too, with internal bracing. You probably saw those photos in my thread. I used the thin “slip-on” rocker cover for my rocker skin since they were cheap ($35 a pop?) and are no longer a key structural component. 

[clarkspeed]

I think I used 18, it it pretty stout with the bend in it. It would take quite a hand punch to bend it.

[AydinZ71]

Yeah 18-gauge with that curvature will be pretty strong  good luck and looking good Clark! 

[clarkspeed]

For this build I decided to jump in with both feet and learn how to build fiberglass.  I found out early on that I would need to build up a custom air dam so I decided to build out a door as a trial to learn the process.  I have done plenty of small FG projects but never something large that involves building a mold tool. 

 

You can see the process in the pictures.  First sanding and waxing the door (plug) and applying mold release.  Then a layer of gelcoat and then laying down multiple layers of heavy matt until the mold has enough strength and rigidity not to break when pulling the final part. 

 

The only mistake I made was not smoothing out the original door.  I thought it looked fairly straight but it turned out to have some waves in it.  It also had some small flaws I thought would be easy to correct in the mold.  I was dead wrong. It would have been much easier to correct the flaws on the original door than to work on the mold.  You can see the final surface on the mold. 

 

Then I prepped the mold, laid in some layers and a new door popped out.  It's hard to tell in the pictures but the surface finish turned out great.  I added some cardboard rolls in the back to make it stiff.  It is attached to the car with push button locks and pins on the bottom. For the final touch I 3d printed a door handle. 

[JMortensen]

It looks like you just molded it, no vacuum. Is that right? I bought a vacuum pump and haven't used it yet. Can infuse resin or lay it up wet and then apply vacuum, and can get fairly complicated. I got majorly sidetracked, but would like to get back to it at some point.

[clarkspeed]

9 hours ago, JMortensen said:

It looks like you just molded it, no vacuum. Is that right? I bought a vacuum pump and haven't used it yet. Can infuse resin or lay it up wet and then apply vacuum, and can get fairly complicated. I got majorly sidetracked, but would like to get back to it at some point.

You are correct Jon. I assume vacuum bagging is the difference to make really light weight parts. As you can see, the door has a lot of resin in it and that equals thickness and weight. It's got to be 2 or 3 lbs heavier than it should be. And of course I laid in 1 or 2 more layers than I needed to.. I was just happy to get a ready to paint door out of the process. I am going to experiment with more cloth than matt with the air dam since I don't have any sharp edges to deal with. I think I can get to more like a normal FG part say from the 80's. As I mentioned in another post, I have a Z Trix hood and that thing mind boggling. I can't imagine it being more than 1lb heavier than carbon fiber.

But the other thing I learned in this process is I don't like it! It is quite tedious mixing resin, applying layer, repeat, repeat, repeat. The bigger the part, the more you repeat. You can only get so much down in 20 minutes. I mix a quart of resin each round. So my conclusion is small parts and repairs are fine, body panels are a total pain in the ass. Much cheaper and easier to purchase, if you can. 

[AydinZ71]

@clarkspeed when I spoke to John at Ztrix (I have his frp hatch), he mentioned how complicated the resin process is and how he has perfected a super lightweight means of preparing an s30 hood. Something special about the resin if I recall. I’m going to be ordering a hood soon and il ask him more about it in detail. I believe he sells a super-light version as well for more $$. He mentioned the hood doesn’t really benefit from carbon fiber since it’s not a true structural part. I tend to agree. It’s all about rigidity (stiffness) vs resisting stress (yield strength) like a structural piece would require. A crossmember for example would benifit more from carbon fiber. 
 

You certainly get my respect Sir! I thought rust repair was tedious… not compared to moulding FG body panels through to filler & paint 

[Ironhead]

My freakin car is half Ztrix, and I agree their parts are great, particularly considering the offerings I have seen from some other suppliers of Z body parts.

 

For a show car, even the Ztrix parts are going to require a lot of work.  But for a track/racing car, you can pretty much just paint em and go.

[JMortensen]

16 hours ago, clarkspeed said:

...As you can see, the door has a lot of resin in it and that equals thickness and weight. It's got to be 2 or 3 lbs heavier than it should be. And of course I laid in 1 or 2 more layers than I needed to.. I was just happy to get a ready to paint door out of the process...

But the other thing I learned in this process is I don't like it! It is quite tedious mixing resin, applying layer, repeat, repeat, repeat. The bigger the part, the more you repeat. You can only get so much down in 20 minutes. I mix a quart of resin each round. So my conclusion is small parts and repairs are fine, body panels are a total pain in the ass. Much cheaper and easier to purchase, if you can. 

Yep, my front end is way heavier than it needed to be also. Didn't want to make a mold. Also went twice thickness on Knytex, which was totally unnecessary in retrospect.

Totally agree about it being a PITA and not fun, but I want to do a diffuser and floor pan, some diffusers for the front splitter, dive planes, some other stuff. Stuff you can't purchase, or that wouldn't fit my car if it was made to fit a stock one.

[AydinZ71]

3 hours ago, JMortensen said:

Yep, my front end is way heavier than it needed to be also. Didn't want to make a mold. Also went twice thickness on Knytex, which was totally unnecessary in retrospect.

Totally agree about it being a PITA and not fun, but I want to do a diffuser and floor pan, some diffusers for the front splitter, dive planes, some other stuff. Stuff you can't purchase, or that wouldn't fit my car if it was made to fit a stock one.

speaking of diffuser, I reinforced the rear skirt and added welded tabs with nuts ready to go, for a diffuser to be attached. Curious what you  and Clark may do differently. Here are a few pics 

[clarkspeed]

I REALLY like your reinforcement of those panels. That rear skirt is so easy to damage. Mine is so wrinkled I may just cut it off and replace like the rockers with little heavier metal.

As far as diffusers, they are pretty much illegal for many of us. I'm pretty sure EP does not allow either. But I would say that looks like a good way to attach one!

[AydinZ71]

@clarkspeed Hey thanks A bunch Clark! Means a lot. Yep… diffusers are illegal in EP  

 

I had the whole rear end torn apart so I figured why not add attachment tabs in case I ever try a diffuser in a non SCCA sanctioned event. At a minimum, it is much more ridged and “catches” less air at speed as a result. 
 

For the reinforcement, I cut a 5/8” steel tube (1/16” wall) down the centerline to create two semi-circle cross sections. I figured the full tube itself was overkill. Along the length of the skirt (Kinda hard to make-out in the photo) I bent a 1” wide strip on 18-gauge sheet into 90-deg angle stock and welded it lengthwise to the skirt. The angle stick makes the skirt more ridged, and the vertical semi-circle beam keeps the leading edge of the skirt “put”. 
 

I need to read the GCR more carefully. All the restrictions on body panels seem to be limited to extending “beyond OEM” panels. Il see if there are restrictions on underbody plates. Even if I can’t run a true diffuser, I’d love to seal the cavity between my fuel cell and the rear skirt. It’s just a tornado of Eddie currents back there. I know we can run a front-end splitter from the leading edge of the air dam up to the axle/steering crossmember. 

[clarkspeed]

I was thinking the same direction. I am building mine loosely to GT rules which allows for a flat bottom. So I was thinking about putting a close out panel there.  But I'm not sure how I could work that around the fuel cell. I can't really work on that area now until I get it off the rotisserie.

[joyce_mor]

Progress looks good despite the problems you encounter. I am excited to see the outcome of this build. By the way, I recommend that you check out 4WheelOnline in case you need some aftermarket accessories for this vintage car. 

Edited August 23, 2021 by joyce_mor

[clarkspeed]

Here are some photos of panel cutting and fitting.  Once I was satisfied with the layout of all the interior bits I started planning out the panels.  I used 18ga aluminum for interior panels and 18ga steel for the fire wall.  I started at the front and went panel by panel working my way toward the back like a puzzle.  I took my time and tried to bend or bead panels that seemed too floppy.  It came out ok. I am actually thinking I need to clean up the original chassis some so it looks as good as the sheet metal section.  I put everything in with clecos and drill all the holes for rivets.  All the removable panels have 1/4 turn fasteners.  I was a little concerned about getting a good seal from the engine bay, but it seems ok.  I was not sure about either welding or riveting the fire wall but ended up drilling for rivets in case I need to rip it out later.  I will probably seal all the riveted panels with RTV or similar.  Once everything was fitted I pulled it all out and put on a shelf.  I think I will install the firewall before I paint the chassis, but paint all the interior panels separate.  I have been thinking a lot lately about colors since I am getting ready for paint.  I think I will go with a light metallic grey for the interior and gloss black for all the suspension parts.   

[tube80z]

On 8/18/2021 at 8:06 AM, clarkspeed said:

I was thinking the same direction. I am building mine loosely to GT rules which allows for a flat bottom. So I was thinking about putting a close out panel there.  But I'm not sure how I could work that around the fuel cell. I can't really work on that area now until I get it off the rotisserie.

 

Make the fuel cell a diffuser.  You can install it so that it's tipped toward the front.  Or keep the cell you have and build a box that holds the pumps and lines.  I've seen a few local GT-1 cars that had a setup very close to this.  Definitely a grey area that may be called out.  

[JMortensen]

Got that one from Coffey back in the day...

[clarkspeed]

Thanks guys! That is the kind of cool ideas I need for this thing. Only problem is I inherited a heavy 1/8 thk x 2.5 angle iron fuel cell frame in the deck. I hate looking at it.  I will need to rethink this, but that is what I had in mind was a flat "protection" panel starting at the aft suspension mounts and terminating at the rear valence and somehow still capturing the envelope of the cell. I think if I keep things flat with no vanes I might be able to get away with it. That tilted cell would definitely make fuel pickup much easier!