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08 Sky Redline, 5M
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Discussion Starter #41
2021.02.22:
Took out 5lbs of sound deadener:
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Discussion Starter #42
2021.02.25: Almost finished with tow strap install. I got good guidance on this post: My relatively clean recovery strap solution for track...

I wanted to make sure that they didn't pull out if for some reason they took a sudden jolt. I added some box tubing inside of the front beam, and in the rear beam too, as well as a big steel plate inside the top section of bumper. Hopefully not needed, but I felt if the torque on the bolt was excessive it could deform the beam or start to tear the bumper beam, and having extra meat there to keep the beam together couldn't hurt. I had to trim the foam bumper pieces a little for clearance. I mis-angled the first hole I drilled on the rear bar, it was too far back and I could not fit the nut, so I had to drill a 2nd one. I drilled them off center because the foam insert plug is at the center and there's already a hole there (too many holes worry me). The rear bumper bar isn't perfectly vertical at the back so I had to angle the drill bit to get an even offset at the top compared to the bottom.

I got my extra long bolts at McMaster-Carr (mcmaster.com), stuff is affordable there. I also got a 12 inch drill bit, needed to drill the bars in one continuous, straight, shaft.
I used 160mm bolts on the rear, the 140s on the front, and some washers from the local hardware store.
Still need to cut the holes in the bumper covers.

On the front end I had to make a big notch on the front bumper support beam to clear the bolt.

91280A747Medium-Strength Class 8.8 Steel Hex Head Screw, Zinc-Plated, M12 x 1.75 mm Thread, 140 mm Long, Packs of 5
91280A747Medium-Strength Class 8.8 Steel Hex Head Screw, Zinc-Plated, M12 x 1.75 mm Thread, 160 mm Long, Packs of 5
91280A747Extended-Length Drill Bit, Uncoated High-Speed Steel, 15/32" Size, 12" Overall Length
90576A119Medium-Strength Steel Nylon-Insert Locknut, Class 8, Zinc Plated, M12 x 1.75 mm Thread, 12 mm High, Packs of 50

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This little 1x1 box inside of the front bumper bar.
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example of the rear bar inner support box tube before pushing it into position
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Discussion Starter #43
2021.02.28: Got the Werks brace welded today. Needs some grinding and a coat of paint.

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I know yo probably don't care to much about this being that you are building a race car. I rounded the edges of the flat bar that are to the front of the car. I thought that the flat bar would hum.. aero wise it is probably a smart thing to do. I know it would be the most minuscule benefit but those do add up. kind of like the 5 lbs in sound deadening
 

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Discussion Starter #45
2021.03.06: The wheel spacer post. A multitude of errors/learning happened along the way on this.

In order to put Brembo brakes on the front, I needed a set of wheels spacers. @shabby gave a great source of completely custom spacers from Custom Wheel Adapters, Wheel Spacers, Hub Rings for your car! | Motorsport Tech So I ordered a set of front spacers, and a set of rear custom spacers with longer studs. So the Sky uses M12x1.5 wheel studs/nuts. I had ordered a set of ARP studs from my local autocross parts dealer, the same as I used on my Trans Am and I figured the knurl size was a standard thing since it was a GM car (WRONG). For my rear wheel adapters, I sent a set of studs to MotorSportTech to install. I took my front wheel hubs to my local shop for them to press out the stock studs and put the new ones. Well they informed me that the knurl size was wrong. The studs I had were .509 knurl, and the Kappa uses .580 knurl. So I quickly looked on the ARP site and found that a set of "older GM cars" studs had the right knurl size, but were imperial threads, 7/16x20. I looked on a chart and thought that it showed me that it was nearly the same as M12x1.5 (again WRONG). I had them 2nd day shipped to me. So I got them, the knurl looked OK, but then clearly the M12 lug nuts did NOT fit. So... do I switch the whole car to the SAE studs? I would have to ship MST a different set of studs quickly, I had no idea when they would start making my adapters. I looked again online for something that would fit, any other kind of metric stud with the right knurl.

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Well wouldn't you know someone on this forum had already found the right ARP studs - "Miata rear axle" studs. Only comes in a 4 pack, and costs ~$25 per pack, part number 100-7720. So Summit had those in stock too, again got them 2nd day'd to me. Why I did not see them on the ARP website was that the knurl size is 0.579 .... not exactly 0.580 ... so my page search didn't reveal something so close in size when I searched for text "580". These already came with one flat size on the head so I didn't have to grind them. My shop put them in without issue.

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Issue #2 was that I got the rear adapters back, and they were good ... except they did not sit flush onto the brake rotor. I noticed there is a little lip on the rear wheel hub nose, and it was touching the adapater where the inner bore had a small radius. The radius was too small. So that needed re-machined a little larger.

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Issue #3 On the front I did a test fit of the Brembo caliper and the new rotor, and the front spacer. The front spacer has a nice nose/hub bore built into it so the wheel is easy to center when you put it on. The spacer fit perfectly with the stock brake rotor. But when I put on the bigger rotor and spacer, there was a gap between the spacer and the rotor. The inner bore of the spacer had a "stop flange" at the very end of the inner bore, and it lined up exactly with the hub center. But the new brake rotor was less than 1mm thinner at the mounting area ... thus the spacer touched the end of the hub before it touched the brake rotor. So that needed machined a very miniscule amount also.

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The good news is that a 13mm spacer on the front works perfectly and gives me an easy finger width or maybe 3/8 of an inch clearance on stock rims.

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I found a local machine shop that was able to machine the clearance on both pieces in 2 days even! Only charged me $50. What a deal! The smaller spacer had a tiny amount of heat expansion from the machining, but not enough to change fitting in the wheel, just gives a little more friction.

Issue #4 The "dust sheild" or whatever that is, touched the new bigger rotor at the very bottom where it kicks out a bit to clear the lower control arm. That was easily fixed with the angle grinder.

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So the last step I need to get is new longer brake hoses. The stock ones measure about 14 inches, but even at full lock, they are awfully stretched and bent over at the hardline mount. I am going to get lines about 18 inches long b/c the brembo caliper is about 2 inches narrower on the inner side to start with.

I also needed to replace some of the wheel hub bolts, as a few of them seem a little rounded, which only happens if you have to fool with them a bunch. The GM bolts were $9 each, a little pricey IMO. But in my TA I had "hub problems" (a known issue with 4th gens for those that race/ax hard) with some harrowing stories, so I don't want to take chances.
 

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Discussion Starter #46
2021.03.06 I got a new Werks set of intake tubes, and the standard bolt size for the pressure sensor is M6x1.0 but the tube that came with my car had a M5x0.8 allen bolt used, inside of a helicoil. Why? Because the 3 bar sensor has a steel sleeve and it is offset just far enough to make it impossible to put it on with some modification. Again, found elsewhere in the Kappa-verse was the post to just push out the metal sleeve. OK, done in about 4 minutes with a 10mm socket and the right size allen socket as the pusher. Now it bolts onto the tube with the 6x1 bolt, no mods needed.
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Discussion Starter #47
2021.03.03 I got the rear brace mounted. I had also cut the main exhaust pipe and put it back together with a butt-clamp so I could take the exhause off from the engine without having to remove a load of suspension parts. You can see the shiny clamp on the photo. I have yet to put the diagonal bar on the bars yet. To put the brace front bolts on I did not even have to lower the car or lift the A arms, there was just enough space to use an open end wrench, flipping it for a partial stroke each time.

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Aren't those nuts that hold the front of the frame brace so much fun to put on?

And here comes the question of the day.... why did you need to use a stud adapter? all you needed to do to run the Brembo calipers was change the studs to ARP studs and use a wheel spacer. and I believe the wheel spacer that is needed is 12mm for the wheel to clear the caliper. If you change the wheels to after market and get something with a proper offset for the caliper the spacers are not even needed. you definitely didn't have to go with those monster adapters that's for sure. and the only reason you needed to change the studs to the ARP studs was to get the increased length for the spacer so a stud adapter does not need to be used. If using the adapter like what you have there is no need to change the studs at all.

If you put the calipers on and then put a stock wheel into place it is going to touch the caliper before it gets seated onto the hub. take a ruler that has a millimeter scale on it and measure the distance between the hub and the mating surface on the wheel. add a couple of mm's to it and you are good to go.

I am pretty sure that you only need a 12mm spacer (1/2") when using stock wheels. when using aftermarket wheels the thickness of the spacer is going to be determined by the offset the wheel has. I think the stock offset is 55mm. so if the aftermarket wheel has an offset of 67mm no spacer is going to need to be used.

The OE studs are 1.750" long and the ARP studs are 2.750" long.
 

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I would send the lug adapters back and tell them to machine them properly. provide them the images of the problem. At that point you can probably instruct them to remove the studs and just use the thing as a spacer at that point. It is going to be stronger used as a spacer. it is also going to be less weight. I say stronger because the std that is holding the actual wheel on is going to be pressed into steel instead of aluminum.

The best thing is to get the 12mm spacers. the further out the wheel is from the wheel bearing the more stress it puts on the wheel bearing. you only need 2 - 3mms of clearance between the wheel and the caliper. a fingers worth of space is not needed. If there is the expectation of the wheel flexing that much then you should be running steel wheels instead of alloys.
 

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Issue #2 was that I got the rear adapters back, and they were good ... except they did not sit flush onto the brake rotor. I noticed there is a little lip on the rear wheel hub nose, and it was touching the adapater where the inner bore had a small radius. The radius was too small. So that needed re-machined a little larger.
I told him about that issue like 10 years ago, can't believe he didn't fix it.
 

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I am pretty sure that you only need a 12mm spacer (1/2") when using stock wheels. when using aftermarket wheels the thickness of the spacer is going to be determined by the offset the wheel has. I think the stock offset is 55mm. so if the aftermarket wheel has an offset of 67mm no spacer is going to need to be used.
Caliper clearance is not directly related to offset. It has to do with the shape of the spokes. I've got two different sets of wheels with 41mm and 42mm offset and Brembos, with no spacers. Quite a few threads at Cobalt SS sites with folks looking for aftermarket wheels that work. Some work, some don't. I made a carboard template with the shape of the caliper and hub for when I was looking at wheels to get me in the ballpark.
 

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Discussion Starter #52
@kgschlosser I'm going to be putting 18x11 wheels on, that's why I need the big rear spacers.

And the 18x11s will have the right offset and spoke clearance, so the spacers are only for using the stock/street wheels.
 

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how thick is that adapter? if it is 1" or less then you can eliminate the studs. the ARP studs you put into the hub are 1" longer then the stock ones and you will not have an issue with using a 1" spacer. It is going to be stronger using a single set of lugs to hold the wheel on.

I know that the offset is not a perfect means of knowing if the spokes on the wheel are going to hit or not. It is a way to get close to them not hitting the caliper. no spacer is ideal. but if one is used having it as small as possible is going to be ideal.

if you look right on RPM's website they have the 4 piston Brembo big brakes. and they specifically mention the 12 mm offset. They also charge 90 bucks additional is using the stock wheels. this sounds about correct to get the 10 ARP studs and the 1/2" spacers. II am sure if you called RPM they would tell you the exact thickness of the spacer they use.

I am curious to know how much additional stress is put onto the wheel bearing by using spacers, I am going to try and figure that out.
 

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Discussion Starter #54
2021.03.08: Brakes done

I got the last piece I needed, brake hoses, made locally at a hydraulics hose supplier. The Brembo's are on, the hoses are on (a little longer than stock to account for the ~1.5 inch width difference from stock caliper to new caliper). Not stainless, I don't know that it matters that much to me as long as the hoses work. Had help from my trusty assistant to bleed them out, no drama there. Using EBC Blues to start this year.

Stock caliper: 11 pounds
Brembo caliper: 7 pounds
New rotor +1 pound (part number 25994100 and those are the expensive ones not the cheap ones, came with the car purchase)

It's technically ready to be driven now as the major mechanicals are fixed. Still waiting on shock/springs tho. Waiting on the race rims still.

My wife said it needs a "serious" horn tho, like an air horn. No argument from me!

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Yes the swaybar needs reinstalled. :giggle:
 

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I told him about that issue like 10 years ago, can't believe he didn't fix it.
I re-cut both the inboard radius and outboard hub rings on mine, as well as the entire OD, and a skim cut all the way across the front face to get them to fit like I wanted/needed. The only thing I didn't touch was the bolt patterns. But ordering from him was cheaper than just getting aluminum blanks and tooling in the size I needed, and saved me a few hours on the bridgeport.

2021.03.08: Brakes done
... Not stainless, I don't know that it matters that much to me as long as the hoses work. ...
Stainless lines don't do anything other than add some durability, heat resistance, and bling. They have all the stiffness of one of those paper Chinese-finger-trap kids toys and use the exact same rubber hose underneath for the bits that matter. [Edit - I stand corrected on this below.] The reason people claim they make a difference is because changing them forced them to simultaneously change out their old junk brake fluid.
 

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.........
I am curious to know how much additional stress is put onto the wheel bearing by using spacers, I am going to try and figure that out.
Stress on the wheel bearing is determined by the relationship between the center of the tire's contact patch and the center of the bearing. Regardless of how you get there, whether by changing the wheel/tire width, the wheel offset, or by using a spacer, moving the contact patch outboard is going to increase the bearing load by the same amount.
........
Stainless lines don't do anything other than add some durability, heat resistance, and bling. They have all the stiffness of one of those paper Chinese-finger-trap kids toys and use the exact same rubber hose underneath for the bits that matter. The reason people claim they make a difference is because changing them forced them to simultaneously change out their old junk brake fluid.
Wouldn't that depend on the specific brake line? I agree that the difference is minimal for modern lines, but the materials are not usually the same. OE brake lines are normally EPDM with rayon reinforcement, while the stainless lines that I have used have a very thin teflon tube reinforced with stainless braid. The EPDM is thicker and more compressible than the teflon, and the rayon is somewhat more elastic than the stainless when cold, and moreso when hot. Combined, those factors result in a difference in volume change under pressure that is measurable in the lab, but is unlikely to be noticeable in any but the most extreme driving conditions.

In addition to the real benefit of changing the fluid is the placebo effect. of course the new super-performance brake lines are carbon fiber reinforced.....
 

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@JohnWR I never paid much attention to materials and you're correct in that they are different, at least in the smaller sizes. Larger hydraulic hoses still look like they might be the same, or much more similar at least, but you probably don't use a lot of -8 hose on your car.

I just red-neck slapped some calipers across a rubber line and an off-the-shelf braided line with and without someone standing on the brake pedal and concluded that the difference in expansion was well within the margin of error in my set-up, and assuming you stay within the safe operating temperatures of everything involved.

Ironically, the lines we use at work now have an additional black PVC sheath overtop of the stainless weave, so once again actual "race car" components look more like regular OE components and less like an expensive, shiny object.
 

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@JohnWR I never paid much attention to materials and you're correct in that they are different, at least in the smaller sizes. Larger hydraulic hoses still look like they might be the same, or much more similar at least, but you probably don't use a lot of -8 hose on your car.

I just red-neck slapped some calipers across a rubber line and an off-the-shelf braided line with and without someone standing on the brake pedal and concluded that the difference in expansion was well within the margin of error in my set-up, and assuming you stay within the safe operating temperatures of everything involved.

Ironically, the lines we use at work now have an additional black PVC sheath overtop of the stainless weave, so once again actual "race car" components look more like regular OE components and less like an expensive, shiny object.
Absolutely correct about the different construction for different hoses intended for different applications. Aeroquip currently lists 41 different hose constuctions with a variety of liners, reinforcements, and jackets in various combinations. And we definitely don't need -8 for brakes!

Agreed. For anything but the most extreme use, the teflon/stainless is overkill.

That would be the difference in specifying materials for performance rather than bling. The sheathing protects the braid from damage, and protects you and everything else from being damaged by the braid.
 

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Discussion Starter #59
2021.03.13: Seat

Been working on a seat for a couple weeks now. I got a Sparco QRT-R seat, which is narrower than the seat from my Trans Am (an EVO2 L) and that was way to big for the Sky, too wide at the front, and the shoulder wings way too wide too. I lost some weight last year (about 30 pounds via controlled fasting, I highly recommend this book and method) so I can have a slightly smaller seat. The QRT is better up front and shoulders, but still not perfect. For autocross I like to be seated a little more forward... so I still had to trim the front of the seat edge where it contacts the transmission tunnel.

The seat brace itself was 1.25 inch L 1/8 inch, with 1/8 "feet" and 3/16 x2 inch for the cross bars, with some lift under them, welded. Because of the position of the Sparco seat frames, I had to cut an "access port" to get to the seatbottom bolts. Not ideal, it's quite a careful process to put the seat in and bolt it down. Obviously there's no access to anything on the tunnel side. The part sticking up you see is the extender to put the stock seatbelt reciever at a place I can use it to be legal. I don't have a full metal shop or I might have tried to construct something simpler and lighter. But such is being constrained with standard hand tools. I did buy a drill press and that was a great help for punching 1/2 inch holes and others in that thick stock, the hand drill would have taken forever and dulled up a lot of bits.

As for the QRTR seat itself, it leans back more than the EVO or Pro 2000 which were my other choice. I thought the 2000 sat too upright, but if leaned back maybe it wouldn't be bad. I might have really preferred the EVO, as I find the QRT seating angle to be not quite perfect for me. It's a little bit of a compromise for arm length vs leg length and angle (for me, maybe you're built different). The giant blob under the ignition switch is super unfortunate as it really gets in the way if my legs are very angled. So dumb. Anyways I can fix some ergonomics with extra foam (good upholstery foam not cheap soft stuff). I do need my legs a little straighter so I can avoid the ignition blob, but that puts my arms/torso back a little too far. Again fix with foam and special foam carving with a turkey carver. The seat shoulders do just fit inside the door if the the seat is angled a little.

I'm wondering if it would be wise to put any holes to lighten this a bit and if so where would be acceptable. Suggestions welcome.
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Had to cut the rolled edge so it sits tight to the tranny tunnel.
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Discussion Starter #60
2021.03.13

I got my 315s about a week ago. 🤩 Waiting on rims.
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