IMSA GTU vintage racer build

[tube80z]

And don't forget the custom mufflers or battery holds on each side of the cell that make a wall just like a diffuser.  I'd personally 3D print or buy a faux batter top or send some fake wiring to it so that it looks legit.  Maybe one could be a fuel cooler?  Just spitballing ideas to make the cell closer to a diffuser.  

[AydinZ71]

@JMortensen @tube80z

 

Man the tilted fuel cell is brilliant! Maybe on the next build… I gotta get mine on the road.

 

I can’t run a fuel cooler in EP but maybe Clark can in GTU? 

[clarkspeed]

Here are some photos of the body panels as I did a wheel check.  These are 15x8 wheels with a 235-50-15 tire.  I am planning on running 15x10 so it will be close.  I really like this body kit, it is basically stock fenders extended out 2".  It came with a cowl induction hood, G-nose, and a whale tail.  I will run the G-nose with a custom air dam.  I will probably sell the cowl hood.  And I may consider the whale tail later.

[clarkspeed]

Here are some pics of the fuel cell area.  The boxed in rear section was already in the car so I just made the panels to finish it out.  I also fabricated a cage that will bolt from the bottom and has a removable top section.

[clarkspeed]

Another post.  Getting much closer to my current state on the car.  These photos show the electrical panel I 3d printed, tabs everywhere to secure wiring, window supports, panel to mount all the electrical components, and a pic of my messy shop.

[clarkspeed]

I loaded the switch panel with switches that light whan energized and circuit breakers.

[AydinZ71]

On 9/12/2021 at 4:47 PM, clarkspeed said:

I loaded the switch panel with switches that light whan energized and circuit breakers.

Woohoo! Wish I was ready to put switches in. Did you get these from summit? Did they come with the breakers or did you wire separately? 

[clarkspeed]

I laid out the entire electrical system in PowerPoint and put together a bill of material. I will purchase most from Waytek. I highly recommend.  But I had a few surplus spare parts I loaded it with for the photo.

[clarkspeed]

These are some pics on progress with the air dam.  I kept looking at this wide body G-Nose trying to figure out a way to create a mold.  Then I realized it is a fairly simple shape and if I took a sheet of thin aluminum I could hand roll it to get the correct contour.  And even better, it would be a nice smooth finish to pull the final part without much correction.  I ended up using 2 sheets riveted together so there is a small crease in the middle.  I am smoothing the crease with body filler and rounding the corners so there is a nice smooth transition when I lay the cloth.  As you can see I laid a ton of glass for this mold and added big cardboard ribs to make it rigid.  I figure I will pull 2 or 3 air dams to start but it will always be available to pull more.  I have been working on it on the side while I am trying to finish up other stuff. Dirty work. 

[AydinZ71]

Looking good!! Did you fabricate the G-nose yourself? Any reason you wrapped the AL sheet in fiberglass, vs. leaving the air dam as AL instead? 

[clarkspeed]

The G-nose came with this crazy body kit I bought. It is exactly 4" wider than stock to match the 2" extended fenders. I decided to do the dam in glass to match what everyone was running back in the day. Like the BSR cars and Frisselle.  It needed a few curves here and there that I could not get with pure aluminum fab. And if you have ever seen aluminum air dams, they look  little getto.  Funny that a lot of people did that back in the day too.

 

My overall idea was to incorporate a lexan lower strip on the bottom that I could adjust up or down to achieve the lowest possible clearance. Lexan is the perfect material for the bottom of an air dam. 

[AydinZ71]

Sweet! Sounds like you have it figured out. The front-end scraper is a great idea. How do you plan to mold the front-end radiator shroud? Keep the slip-stream from going over the rad. Plastic or AL? 
 

ideally I want to run a air splitter from the 280z FRP bumper, and use the bottom intake for the oil cooler. Setrab makes a really neat, long oil cooler that would span the width, but they are super expensive (~$500). Their regular oil coolers are about half that. 
 

I am tearing my front-end apart. Il post some pics. 

[clarkspeed]

The radiator will have a serious slant forward. So it looks like the shroud will not be very large.  I thought aluminum but it is still open for now.  It has to slot into the opening in the Gnose. I gotta get it off the rotisserie and fit the nose to figure it out. I am more worried about getting engine air and oil cooler air. Each side of the shroud I hope?

[AydinZ71]

I have a suggestion if you are planning on rebuilding the fuel cell mount. Look into thin-wall stainless steel seamless tubing. I use it for high pressure applications in oil and gas. It’s a bit hard to weld to, as it burns through easily. However, it is phenomenally strong in tension, and has a pretty good crush resistance. It’s the lightest, strongest tube I have worked with. Not as light as AL, but stronger in tension per unit weight and weldable with a MIG. I am using it for some light structural stiffening near my radiator mount. 
 

 

[clarkspeed]

On 10/19/2021 at 10:30 PM, AydinZ71 said:

I have a suggestion if you are planning on rebuilding the fuel cell mount. Look into thin-wall stainless steel seamless tubing. I use it for high pressure applications in oil and gas. It’s a bit hard to weld to, as it burns through easily. However, it is phenomenally strong in tension, and has a pretty good crush resistance. It’s the lightest, strongest tube I have worked with. Not as light as AL, but stronger in tension per unit weight and weldable with a MIG. I am using it for some light structural stiffening near my radiator mount. 
 

 

That is interesting.  In my old car I had a cage build out of aluminum angle iron.  I had a dude where I used to work tig it all up.  It was beautiful, strong,  and light and dropped right off with 4 bolts.  I don't have the luxury of a full weld/fab/machine shop anymore.  So steel for now, fast and easy.  I may regret it later.

[clarkspeed]

So I decided to re-do the rear suspension again.  I am confident the Delrin bearings would be fine, but started thinking they do deteriorate over time.  So when I got my little homemade mill running I thought about a simple solution I could replace them with using oillite bearings.  I have used these in the past with great results.  Slightly more weight, but probably less than 1 lb overall.  So I milled out some ears that could be welded to DOM tubing with both a top and bottom weld.  Slipped in the 1" ID flanged bearings and done.  

Edited October 22, 2021 by clarkspeed

[AydinZ71]

On 10/21/2021 at 8:17 PM, clarkspeed said:

That is interesting.  In my old car I had a cage build out of aluminum angle iron.  I had a dude where I used to work tig it all up.  It was beautiful, strong,  and light and dropped right off with 4 bolts.  I don't have the luxury of a full weld/fab/machine shop anymore.  So steel for now, fast and easy.  I may regret it later.

Same. I don’t have a TIG. Lack the skill now, but more importantly a decent one is expensive! The Lincoln electric MIG already set me back $400. 
 

Honestly, steel is the way to go for structural. You don’t get as much weight/strength savings as you would imagine going AL. AL is great as skin material though, where you are not leveraging the qualities of steel on a tube frame, the way it’s essential on a unibody. 
 

your build is looking great! 

[clarkspeed]

Rule of thumb is use aluminum thickness little less than 2x steel. So equivalent aluminum structure is not so light. But when you are not super critical of structure, like secondary structure, then it becomes super attractive. I can tig steel with my welder but not aluminum. Hopefully upgrade someday.

[AydinZ71]

Agreed! Yeah the rule of thumb you provided sounds pretty close to what we apply in engineering. We use AL over Steel when considering other huge differences in performance like Ductility, machinability, resistance to chemicals and corrosion etc.

 

My lightweight-structures  professor thought a whole lecture on when you use AL and over steel. He actually got into how AL was “made” for aircraft as it meets the weight/lift performance and the forces on an aircraft are all distributed very evenly. AL isn’t great at dealing with long-term vibration, shock, heat cycling, and spot welding the way mild steel is. Unless it’s forged or cast with a lot of excess material (like an engine block), it exhibits fatigue cracks earlier than steel for similar cycling loads. However, for things like brackets, braces and forged subframe components (A-arms, crossmembers etc), it works great. 
 

he suggested going thinner steel cross-section on a race chassis vs AL. Especially if you switch to stiffer alloys (still ductile) like 304SS. Increasing stiffness does mean you need to worry more about shock and vibration, as the metal becomes less forgiving. You will obviously need to add more braces/crossmembers to increase the “truss” effect of the structure (like a bridge) vs big heavy conventional subframe rails. 

 

 

[clarkspeed]

That is why you don't see aluminum tube frame cars or nothing even close. Aluminum space frame with rivets was popular and aluminum honeycomb, and even aluminum adhesive was popular in the 70's into the 80's. Before carbon fiber took it all over. It is very malable and doesn't like point loads. That is when aircraft switch over to titanium. Still a little cost prohibitive for racing except for F1. Plus steel can still get you under most weight limitations up through Trans Am.