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240z SCCA vintage race car, restoration


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Thanks John! Clark! The more research I did, the more I became convinced it was a matter of will (on the part of the shop), and less a matter of technical feasibility. 6061-t6 just won’t bend… it will snap like a branch. Looking at tables, YouTube videos, and my material science book, heating to it’s annealed temperature WHILE still on the press is the key. If you tried to anneal the whole piece before bending, it needs to spend more than a day in the oven (at a whopping 950 degrees), slowly dropping the temperature to avoid hardening. This alloy is a tricky beast! It transmits heat so well and has so little heat capacity, that letting it cool in open air after heating is enough to kick-start the hardening process. 
 

The BMW end links are 10mm, with the exception of a dinky 8mm stud used to attach to the LCA. I’m sure it was a size restriction as a bolt-in replacement for the beemer, otherwise it makes no sense. I cut out the old carriage bolt and modified the clevis for a 10mm. Now I can get on with the mounts. 

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Okie dokie… progress is slow on account of having offspring and needing to work for a living, but the 14-gauge plates are done and mocked-up ready to weld. Once welded to the bottom of my stainless frame rail, I will reinforce the rear (engine side) with reinforcing to stiffen the mount. I’m happy with everything so far. As long as everything articulates as expected with the car on wheels, this should work out quite well! I feel no slop in the system, as the brass bearings are a zero clearance fit, and the end links are heim joints. 
 

PS: I downsized from a 36” bar to a 33”. Greg runs the 36, but this worked better for me. 

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On 1/31/2022 at 2:07 PM, AydinZ71 said:

@JMortensen ah cool! I figured from the emphasis on spline count that the industry has more or less standardized. Since they only sold one OD for the “standard” bar, I also assume this was for swapping convenience. What I’m really missing is tangible experience on how critical the sway bar is in the overall handling of the car for a road coarse. I have a bit of experience on just how important it is an autoX, since you are constantly changing directions. I need to get on a track! 
 

@tube80z absolutely! I have not experienced swapping out bars with different spring rates myself, but it makes total sense. I assume this has to be based on “feel” after a test drive, since it’s hard to factor in so many variables ahead of time. Precise length of arms from mounting hole to bar, bar material and dimensions (AL in my case), how orthogonal the forces from the links are relevant to the radius of the arm/bar, so on… 

 

 

Personally I think ARBs are just as useful to road racing as they are to autox.  I know a lot of people like to argue that point but they are a tool help with setup.  I can tell from my hillclimbing days that my car was easier/nicer to drive when using ARBs to balance the fast corners.  You can spring the car stiff enough to not need them but if you don't have a really smooth course it will not put power down as well and the car will have a lot more of a snappy feel when loaded up and ride over bumps.  In the end it's all down to how you like the car to feel and what makes you confident in how the car behaves.  If you have no confidence and feel is crap it doesn't matter how fast XYZ driver is with a similar setup.

 

What I learned about the splined bars is that you need to rate test them about 3 times before they will read the same.  If a bar is used then it will probably do this.  I bought some from Roush years ago that were supposed to be used and came in new packaging.  You can rate test them on the car locking the other opposite side at level ride height and then handing weights from the spindle or weld a hook to an old steel wheel and bolt that on to simulate the best experience and then hang weights from a chain and use a laser level on the wall or piece of plywood or similar.  Your just looking for what happens hole to hole.  And you can run both sides in different holes to split the rate (most people forget this).  The advantage to this method is you will know what the installed rate at the wheel is.  That's what you need for all the spreadsheets that calculate wheel loads.

 

You might as well make some droop limiters too while you are there.  If you add a forward facing arm you can build a stop using a pivoting foot bolt (https://www.mcmaster.com/leveling-pads/).  Or use the arm side and capture how far it can extend.  Just make sure there's enough clearance for the wheel/tire combo.  

 

Hope that helps,

Cary

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@tube80z thank you for all of the golden insight, as always Cary! i especially like the idea of having different end-link positions on both sides. I didn’t think about how that would work until you mentioned it! I plan to run the current setup and shake out the cobwebs before I worry too much about the transience of the bar resistance. What you describe makes perfect sense! I likely have several months of tweaking the suspension and engine before I hit the track, but I plan on buying several bars used as well (thinner and thicker wall thickness). Hopefully the bar o have now will be “broken-in” before I get to the track this summer.
 

Since I had the whole suspension installed temporarily, I was able to weld the uprights to the frame with the bar attached. This ensured I had perfect alignment and zero pre-load in its resting position. After the uprights got welded to the frame, I added two 14/gauge gussets to each side. 90% of the resultant force should be up/down so this setup should do just fine. I may add one more horizontal to tie the bottom of the gussets, but have not made up my mind yet. 
 

time to disassemble the front suspension, get everything painted/coated, set it aside, and prepare the engine bay for primer. 

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That is a beautiful install.

 

My experience with bars is I usually use about a 3/4 hole spacing on adjustment. I start with front light setting and try to induce oversteer. Then gradually stiffen front until it disappears. If you can't get oversteer, then reduce bar size. If you run f/r bars you obviously have 2 choices on adjustment. Once I adjust past that oversteer threshold I stop. 3/4" hole spacing on the arms is actually a fairly large change in spring rate. It's a simple math equation to check this. A blade style adjuster gives an infinite adjustment but I have never driven with one and not sure if the cost is justifiable. 

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@clarkspeed thank you Clark! Really appreciate it my friend :) Turns out I spaced the arm holes (5 total per arm) 3/4” apart without even realizing it. The end link I’m using has 10mm fasteners (3/8” more or less), and I ensured a minimum wall-thickness between each hole of 1 diameter, hence 3/4” center-on-center. 
 

sooooo latest updates:

 

1) Disassembled front suspension and finally had a chance to paint the struts and knuckles. Had to remove the brake hose brackets to section them, so added them back. I biased them towards the rear (wheel-well side) because I was worried the OEM length hoses I bought  last year (duh) would struggle with the extra track. Although EP only allows +1”, I actually have enough adjustability for +2”. In fact, the shortest it can go now is +3/4”.  
 

2) added another small gusset at 90-degrees to the sway-bay mount because… well, because if I stare at something long enough I keep noodling improvements. 
 

3) Found an oil catch-can that was in stock, had a top fitting, was large enough to meet regulation, reasonably priced ($90) and actually lightweight (NOT billet). Mounted it at an angle on the drivers side. It’s not ideal to mount at an angle but in this precise location, it’s a straight-shot from the block breather tube to the can. I could have added bracketry to make it level, but that just adds weight.  I plan to run the top of the can to the carb-side of the engine air filter so I have less fumes to breath. I don’t have windows, after-all. 
 

4) coolant overflow mounted on drivers-side, near where the alternator hangs-out. Keeps the overflow line short, and again no brackets. 
 

5) helper springs and spacer sleeves came in 

 

mall the little things… soooo close to primer 

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Another way to incorporate adjustability into the system is via the end link mounting brackets (that are bolted to the LCAs).  You can fabricate brackets with multiple holes, to allow for multiple mounting points for the end links.  Or you can make a bracket with a single mounting point that is “off-center” (I.e. slightly inboard or outboard of the carriage bolt  used to mount the bracket on the LCA) — for adjustability, flip the mounting bracket 180 degrees to position the end link mounting holes to the “more inboard” or “more outboard” position for stiffer or softer effective sway bar springing.  Hope I’ve explained that in an understandable fashion.

 

The more options you have for adjustability and fine-tuning will be especially helpful when you’re at the track, with limited time and facilities.

 

I’ve looked at the cockpit-adjustable and blade-style sway bar systems with envy, but have yet to engineer a sufficiently durable and cost-effective solution.  One of the many items on an infinitely-long “to do” list.  😆

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@jhm thanks John! Totally makes sense! Unless you are connecting the end-link directly to the strut assembly, anywhere along the LCA will have less travel (max at LCA-strut mount, 0 at crossmember pivot heim) and therefore, less leverage on the arm. I thought about doing this, but got nervous with the EP requirement to maintain “OEM attachment points” with “introduced adjustability”. Hence the bolt-in camber plates. If I had more experience with the judges, I could consider adding a few mounts along the length of the LCA.

 

I did weld a thick fender washer to the mounting hole, reducing the ID down to a clearance fit and stiffening the mount. i did this because I suspected the heavier spring and cornering loads are introducing some “slop” (movement/strain) at the OEM hole who either had worked it’s way loose over time or the PO had widened. Also got rid of the OEM end-link bushing perch so the carriage bolt sits flush. The bottom-side nut will also have a fender washer, but didn’t see a need to weld that one now that the through-hole ID has been corrected. 
 

Y’all have given me a lot to think about! Gosh, I really need some track time before I have any idea what I’m doing adjusting this sucker 😂

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Good call, Aydin...strengthening the end link attachment points.  Also, with your adjustable LCAs, keep in mind that whenever you lengthen them (for increased track width, additional negative camber, etc), you are also reducing the effective spring rate of the suspension...both the coil over springs and the sway bar springing.  Changing one element of the system can affect so many other components.  Can’t wait to see your car up and running!

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I have never found a need for the blade style bars. And that is a direct statement to my level of driving and sensitivity. I normally adjust with 1/2 holes until I feel oversteer, then back off one adjustment. And never touch again unless something else changes. There are a lot of suspension details burried in above statement, but it's a pretty good start point. Maybe I am naive, but it doesn't seem you need to be so close on on roll spring rate to justify the added expense of a cockpit adjustable bar.

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Ok… never done this before. Bought a devilbiss gun for $40 on eBay last year and finally got the chance to take it for a spin. I’m using Speedokote 2K DTM primer in the gallon size. Threw my rear wheels on and carted the sucker out to my driveway. 3 hours of spraying, and she is coated! Everything from the door/fender jam forward is complete. Really excited, because now I can actually see an end in sight! Glad I didn’t try to do it all at once, as the primer does not flow as well as I’d hoped (Need to buy a reducer for it). Now I need to fabricate an AL gauge/switch cluster (so I can weld the roll-bar mounts) clean/scrub the interior and I can primer through to the rear door-jam. 
 

OH! ARC switch cluster came in. This sucker in neat! Fuses and relays all-in-one, with a ribbon cable to the switches themselves. 

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Posted (edited)

Questions for my experienced friends:

 

1) speedometer - I was eyeing the auto meter GPS units. Anyone have any experience with these? Full digital dash or data logger is not in the budget at the moment so looking for a top-gap. I could run no speedo and assume based on gearing. 
 

2) I’m ready to fabricate my gauge and switch cluster. Any strategy, or tips to keep in mind? I bought a 1’X5’ sheet of 5032 AL 0.08”thk for the mounting surface. Gauges on hand: 5” tach w/light, fuel level, volts, fuel pressure, water temp, oil temp, oil pressure. My nascar surplus gauges came with a water pressure gauge too, but I don’t think this is necessary.

 

3) where did you guys source your polycarbonate from? I believe I need 6mm for the windshield and  3mm for the hatch. I have a spare glass windshield I plan to use as a template. 
 

4) anyone attempted a custom air box for SU’s (class rules). I can certainly fabricate the box but curious which filter folks are using. I can use the OEM dimensions but assumed I could source a larger unit which may flow better? I am sourcing air from in front of my rad support. My understanding of fluid dynamics is a filter closer to the carbs will create less pressure drop along the intake ducting. 
 

here are some before shots just for shits and giggles, comparing to my most recent primer pics. 

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Edited by AydinZ71
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Yeah that’s what folks have been telling me… I was just thinking the speedo would help as another data point during driving like checking cornering speed, tuning the suspension, etc. il see if I can get away with driving it on the street locally and maybe to the track, but I have not decided yet. Definitely not a grocery getter but taking it to a gathering once every month or so. 

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Planning out the gauge and switch cluster. This panel will be made from 0.080” 5052 AL. Tach can be conveniently mounted to the roll bar here, but I have some feedback from folks suggesting it be between the steering wheel spokes. It would be mounted off the steering rack in that case. 

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That is becoming a seriously nice looking race car!  And I have seen quite a few.

 

My suggestions to your questions:

1. No one really runs a speedo (more weight, doesn't make you faster.) Could be a data point to check if you have improved on corner exits, but tach does the same.

2. Dash and gauge design can be whatever.  Just sit in the seat and see if you can read it. Tach doesn't have to be in center.

3. I just googled around for local plastic/composite  suppliers. No shipping needed.  My local guy has 4x8x1/8 in stock and can order anything else.  Just get straight polycarbonate, no special coatings needed as long as you take care of it and use proper materials to clean it.  Not a bid deal to cut and mount.

4. I could not find anything either.  I  designed a 3d printed "kit" design if interested.  And a SU velocity stack also.  Pretty simple, uses 3/4 aluminum angle from HD and aluminum sheet which you probably already have. Attached is a pic.  Let me know if interested and I will see if I could put another together and what it would cost.  I have a ton of shit like this I intend to sell some day when I get more time.

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