IMSA GTU vintage racer build

[Dat73z]

@AydinZ71 in my experience welding the cast s30 strut material you'll want to preheat and ideally have a big bucket of sand or something to cool it slowly. It welds really easy but it will crack out if you're not careful. 

[tube80z]

On 1/9/2023 at 2:13 PM, AydinZ71 said:

 

Ah! hey, that's helpful Cary! Silly question, why the 13" wheels? 

 

The main reason was weight.  Moving to 15 inch wheels in the combo I was using added almost a hundred pounds to the car.  This was an autox/hillclimb car and not a road racer.  I wouldn't have used 13s on those.

[jhm]

2 hours ago, tube80z said:

The main reason was weight.  Moving to 15 inch wheels in the combo I was using added almost a hundred pounds to the car.  This was an autox/hillclimb car and not a road racer.  I wouldn't have used 13s on those.

 

I can second that!  I’ve had a couple sets of 13” wheels and really liked them for auto-x.  In addition to the weight advantage, the smaller wheels can lower the CG without compromising suspension geometry.

[JMortensen]

If you've got How to Make Your Car Handle, p3 (first page of actual writing) has a Z on 13s next to a stock one. Always wanted to do it, eventually ended up with brakes too big to make 13s work.

Edited January 12 by JMortensen

[AydinZ71]

Sorry for hijacking your post Clark! Looking forward to your next update. 

 

@tube80z ah yes! This brings back memories of a previous discussion. I recall you mentioning you got a Z down to ~1800lbs, and one way you did so was through clever selection of wheels and tires. 

 

 

@Dat73z thanks for the tip! The strut tube itself was really easy to weld-to. Il have to practice on some spare material from the cast lower section of the strut. Sounds like it’s much harder material.

 

 

[tube80z]

On 1/13/2023 at 4:22 AM, AydinZ71 said:

Sorry for hijacking your post Clark! Looking forward to your next update. 

 

@tube80z ah yes! This brings back memories of a previous discussion. I recall you mentioning you got a Z down to ~1800lbs, and one way you did so was through clever selection of wheels and tires. 

 

 

My car was 1850 with 5 gallons of fuel in the cell and had an easy 100 pounds that I could have removed.  I had to run that much fuel as the cell wasn't installed properly and it would have fuel starvation.  I dropped a bunch of weight from the front hubs/brakes when I redid them to lose much lighter Wilwood calipers.  Someone had spent hours grinding the 4-piston Toyotas down to the size of a Wilwood Dynalites.  Hubs were steel and couldn't have been changed to Aluminum.  Car had a steel driveshaft, R200 diff, and all the stock crossmembers.  I had a super-heavy Optima deep cell battery (65 pounds) because I had alternator problems until I switched to a modern Kubota tractor version.  All in all I thought there was an easy 100 pounds of weight I could have removed getting the car into the 1750 range.  I've seen other Z's that low so mine isn't an outlier, just not a normal compared to most.

 

Wheels, tires, brakes, clutch/flywheels, transmissions, subframe braces, all are hidden weight that really adds up.  Even too much MIG welding.  I started to look more and more at modern panel bond techniques as a way to save weight.  Riveting brackets that didn't need to be unbolted, etc.

[clarkspeed]

Hear, hear, now. This is my thread.  Just kidding, if anyone has any race car related posts, bring them on!

 

I spent a week or 2 trying to find a way to run 13's on my car. Tires are available for some wide wheels. And SCCA GTLite runs them. But in the end I didn't think I could get enough braking performance. So I focused on 15's and ignored 16's which is what everyone in my class runs. I have been super focused on reducing unsprung weight, especially rotating weight. A little less focused on sprung weight, so I hope that doesn't come back and bite me. But I do have some changes that could be implemented at a later date.

 

Interesting enough, the John Thomas 240 which has won like 8 or 9 solo championships, has like a Arizona big brake kit. Way overkill. But he also runs like 100lb of balast instead of a passenger seat. He won another in 2022 as a guest driver. Fast dude and super nice guy.

 

Not alot to show since last post. Sometimes you go backward to go forward. But definitely putting in some hours.  Been  planning and buying stuff for electrical and brake plumbing and clutch.  Also realized I have about 20 parts I need to 3d print, so I got the machine running 24/7 in Nylon.

 

I don't think I could build this car without the 3d printer. Example #64-i have 3" 3ft long orange brake hose. My run will need to be 4 to 4.5ft.  I will just design and print out a 3" dia. brake hose union. No problemo.

 

Here is a pic of the coolant tank mounted and my revised front control arm. I found the steering knuckles hit the original sway bar clevis I had welded in. So I relocated the clevis opposite the shock clevis. In the end this should actually be a stronger connection and give me a little more room for the brake cooling hose. 

[clarkspeed]

Finally got the hood located today. My original design using aluminum pins into the firewall did not look good. Pins were too long and created quite a lever arm. So I went back to my design from years ago but upgraded with some 3d printed brackets. Hood now slides into 3 cowl panel channels and will latch in the front. I drilled those holes in the hood like a confident person after measuring 3 times.