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IMSA GTU vintage racer build


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Sorry have not posted in some time.  Been busy making my own brake rotor hats.  More on that in a future post assuming I am successful.

 

These posts are now basically caught up with where I am at on the build.  Most of the stuff I will be posting from here on out will be relatively "fresh".

 

So here is the rear strut build up.  The struts are from a 280 and shortened.  The cartridges are a cheap no-name brand I bought off of Rock Auto a few years ago just for fit checks.  I just welded a spacer on the bottom so there is no chance of it not seating correctly.  I 3D printed the spring spacers and milled a button top for the spring hat to fit a thrust washer in there. The camber plate is also made by me with a 5/8 spherical bearing.

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Wow! That’s a lot of work making individual suspension components! Tell us the angle! Saving weight? Money? Adapting to unique shock dimension? I can already see it is lighter than my Ground Control sectioned OEM struts. Just curious what you are going for. Looks great though! Tons of detail in there. 

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Ah! Greg’s got similar sliding mount on the latest (Orange) CP tribute he is building. What thickness did you choose for the mounting surface? 
 

I totally get trying to save a buck! My GC plates (bolt-in for EP) were close to a grand for all four corners IIRC. I was (and still an) a suspension geometry noob so I wanted something that I knew for sure would keep the spring and strut concentric. I don’t have a lathe so I’m limited on fabricating precision components. 
 

how do you confirm tower mount consistency? I’m anxious all my rust repair may have warped the structural alignment a bit. 

Edited by AydinZ71
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On 11/29/2021 at 11:43 PM, AydinZ71 said:

Ah! Greg’s got similar sliding mount on the latest (Orange) CP tribute he is building. What thickness did you choose for the mounting surface? 
 

I totally get trying to save a buck! My GC plates (bolt-in for EP) were close to a grand for all four corners IIRC. I was (and still an) a suspension geometry noob so I wanted something that I knew for sure would keep the spring and strut concentric. I don’t have a lathe so I’m limited on fabricating precision components. 
 

how do you confirm tower mount consistency? I’m anxious all my rust repair may have warped the structural alignment a bit. 

I have GC bolt in plates for the front.  I found a universal set on ebay couple years ago.  I like their plates best, but they are kind of overkill for rear.  The rear actually use the original mounting plate.  I just cut it out to match my homemade slider.  I wonder if this is considered "bolt in"? No more hacking than cutting out for a set of bolt in plates.

Best is to somehow go by all the original holes and reference points.  The FSM has a chassis layout drawing with all dimensions.  Try to get the chassis as level as possible F/R and L/R.  Layout tape or paper on the floor and use plumb bobs to mark points like the strut tops.  That will allow you to check all the X and Y dimensions and cross chassis square.  And I use a digital level to measure stuff in the Z direction where I can.  Across strut tower tops, front cradle, etc. 

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  • 1 month later...

I am a little behind on my posts. Pushing to finish most of the serious welding so I can take it off roterssere. Here is a shot of the front sway bar attach. I was not comfortable placing it under the frame for interference and did want to go through the frame. So this is where it ended up. I didn't like putting the weight up so high so I tried to steal as much rigidity to the front as I could with it. The cross member comes very close the the head and unbolts for engine swaps. Sure looks like a GT car now. Sorry the top pic is upside down.

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Edited by clarkspeed
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Very cool! So if I am looking at it right, you have a tube welded to the frame with the sway bar rotating inside of it? I see long links I assume are intended to reach-down to the LCA’s. Also looks like it is mounted 4-6” below the elevation of the shock towers? Interesting! Excited to see it all come together! 

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You got it. They sway bar sits in needle bearings inside the 3" tube. A circle track style. The arms need to be cut about 6" and drilled for adjustment. I ordered the heim joints and links to finish out. It sits about 1" in front of the head if my measurements are correct. The pics are so damn busy I can't even tell what's going on. Anyway the tube bolts to the strut towers and the frame rails.

Edited by clarkspeed
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FWIW, I have a similar style bar and Cary and Richard suggested making boxed sheet arms for it. Those freakin arms are HEAVY. It's on my list of things to do. Idea is to cut an inch or two after the spline and weld the tube arms to that. I think it will be pretty easy to drop 10 lbs. Maybe more. Was surprised that my tubular bar with the solid ends was a couple lbs heavier than the 1" MSA solid bar I was using before.

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Boxed sheet is probably the way to go.. I went with aluminum arms. I'm not sure that is the best answer, but similar to you, I may come back to that another day. I have with steel stubs with a cr- Molly bent pipe in the rear and that worked pretty well.  Another place I may stick a camera when testing just to see what is going on. But not a lot of real estate available if I want to change it up.

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Yes I have a rear bar. It is in my thread somewhere.  Reasoning is my Z is pretty far from a stock unibody and should be a stiff enough platform. I plan to control roll a little more aggressively with bars than my other builds. 

Relatively medium to stiff springs with no rear bar and a light front bar is a proven combination on S30 Zs. Science will tell you lifting a front wheel on corner exit is lost traction, but getting power down earlier can compensate for that. When all is balanced, it just works and makes for benign handling at the limit.

 

If you are unsure of spring rates and sway bar rates on your build I may be able to help. Or if Greg gives you something, you can run with that. His recipe based on vast testing experience.

Edited by clarkspeed
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It looks like it will work so far. Everything is a compromise. The longer the arms are, the more leverage is applied. Which means heavier bar to resist. Spring rates are tricky.

 

That is where I digress from Greg. I think I can engineer this "new" car or any new race car to about 90% of where it needs to be. I am confident on what all the measurements should be. And I know exactly how to test to improve. Greg comes from 20 years of testing every damn combination you can think of on a Z car and has a fixed formula that is 98% there for a S30 chassis. But being perhaps an old but still naive engineer, I am using a somewhat blank sheet of paper., I am taking everything I know, plus improved version of everything I know he runs, plus everything I can improve for control, ergonomics, grip, low Cg, efficient aero, driver comfort, weight savings, and applying to a much looser rule book. Best part of it all, Greg will get to evaluate at some point. And hopefully co-drive somewhere if I get comfortable with reliability. But my car is not a no compromise or all out build. It still has a very strict budget limitation and has hopefully "smarter" solutions rather than money is no object.

 

 

 

 

 

 

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Makes total sense! He does have a remarkable bullshit radar, after this many years of experience. I’m surprised he still has patience for me. 
 

I too have budget limitations, which explains why you and I are doing most, if not all of our own work. You certainly have more experience than I do, so I’m certainly learning from you too. It looks like you are going to have one heck of a car! 

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  • 1 month later...

Finally got the chassis outside for some vitamin D and a good pressure wash. I quickly found out the grey Por15 is NOT the same as black. I used it over a number of parts to protect from rust and pressure wash blew it all off. The black held firm except a few spots where it covered some red rattle can primer. Over grey primer, bare metal, and light to heavy rust the black held fine. I tried plenty of different things during assembly, but I think ospho first to etch bare metal and convert any rust is still best way to start. 

 

So now back inside for painting and panel installation. Rolling and off roterssere soon!

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