Duke's'72 Carbed KA project

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duke
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Re: Duke's'72 Carbed KA project

Postby duke » 27 Feb 2016 15:48

For the last 3 or so years I have been using a coilover setup that is woefully inadequate. The shocks were a set of old Carrera's that I received in a box when I purchased the car. They worked, but they had some issues. I had no clue what the valving was, they were mounted in the typical 510 fashion (poly bushing on the bottom and bayonet on the top) and one of them had recently started to leak. I decided to upgrade to a Koni 30 series damper, similar to what can be found in the Ground Control kit. I did this for multiple reasons, but the main one is that circle track parts have a very good industry support, so if I decide to upgrade/change valving in the future this should be pretty simple. With this though I wanted to make some changes. Where the coilover mounts to the control arm people typically use a poly bushing to slid over the stud. If you have ever looked at one of these bushings while the car is on the ground you can see that they deflect a pretty good amount under the weight of the car. I wanted to use a solid mount on this end. If you have ever measured the stud that the shock mounts to on the control arm you will find that it is about an RCH over 5/8”. I figured if I mounted a 5/8” spherical bearing on the end of the shock shaft (typically with circle track shock uses a 1/2” spherical bearing here) I could hone down the stock shock mount to fit. So I purchased a couple 5/8 spherical bearings and the associated weld cups and modified the normal Koni shock shaft mount to come up with this.

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For the upper mount I wanted to forgo the stock bayonet style mount and use the 1/2” spherical bearing on the Koni shock. To achieve this I cut out the old shock tower top and made a new one to accept a 1/2” through bolt.

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This all ended up taking a little longer than expected because I got into a pretty bad case of “while I'm in here.” I ended up stripping all the undercoating from the rear wheel wells, the paint from the trunk floor and rear seat area (both areas were pretty ugly), stitch welding the shock towers, and redoing the plumbing on the rear half of the fuel system. In the end though it was all worth it, and the rear interior area of my car is much prettier.

Back to the coilover install. My initial impressions are very positive. I have the shocks set at the softest of their 4 settings and the car feels very well balanced. Mid-corner bumps have a much smaller affect on the attitude of the car in it feels much better in transition. I was also a bit concerned that the solid mounts would be a bit clunky, but things have been silent so far. I'm looking forward to seeing how these perform at the first auto-x of the year in about a months time.
Duke Schimmer

'72 2-Door 510
"Simplify and add lightness."

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Byron510
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Re: Duke's'72 Carbed KA project

Postby Byron510 » 28 Feb 2016 02:45

Duke, I've been looking at a cool over solution for the back of the Bronze for years, mostly to achieve a better shock set up as my current set up is too stiff and I have no way to adjust it. I run a wheel rate of 270 lbs/in and like the spring rate and would shoot for something similar.

There are a number of set ups out there, What made you go this route with the Koni set up vs what's already on the market?

I look forward to hearing your road impressions.

Byron
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Re: Duke's'72 Carbed KA project

Postby Sleepys-14 » 28 Feb 2016 07:45

I love the idea of the upper strut mount. That is very close to what i had in mind for the rear shock mounts! Nice execution!
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Re: Duke's'72 Carbed KA project

Postby duke » 28 Feb 2016 11:24

Byron510 wrote:Duke, I've been looking at a cool over solution for the back of the Bronze for years, mostly to achieve a better shock set up as my current set up is too stiff and I have no way to adjust it. I run a wheel rate of 270 lbs/in and like the spring rate and would shoot for something similar.

There are a number of set ups out there, What made you go this route with the Koni set up vs what's already on the market?

I look forward to hearing your road impressions.

Byron


Byron, the reason I went with this setup was for a couple of reasons. Price was a major consideration. For a pretty decent shock these aren't very expensive. I also already had many of the components that I needed so a kit didn't make much sense to me. Also, because my car is so low (most likely lower than optimal :? ) I was pretty sure that most of the off the shelf setups available wouldn't work. Another big reason was support. Circle track racing is one of the most popular forms of racing in the US so using parts that are typically circle track parts opens up a huge base of aftermarket support in terms of shock revalving, etc.

Sleepys-14 wrote:I love the idea of the upper strut mount. That is very close to what i had in mind for the rear shock mounts! Nice execution!


Thanks!
Duke Schimmer



'72 2-Door 510

"Simplify and add lightness."

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Re: Duke's'72 Carbed KA project

Postby defdes » 28 Feb 2016 13:23

I went with the circle track struts on my coilovers for the rear too for the same reason. Mine came with a spherical connection option for the bottom, the top is stock with very hard bushes.

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Re: Duke's'72 Carbed KA project

Postby Sleepys-14 » 01 Mar 2016 06:14

What do you have for rear spring rates now? Im at 250 now, but I will be adding a large rear wing this year, so I might have to go back up into the 300's.
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Re: Duke's'72 Carbed KA project

Postby duke » 01 Mar 2016 07:44

Sleepys-14 wrote:What do you have for rear spring rates now? Im at 250 now, but I will be adding a large rear wing this year, so I might have to go back up into the 300's.


I'm running 350's in there rear. They are a good match for the autocross tires I run, but are a little to stiff for street tires.
Duke Schimmer



'72 2-Door 510

"Simplify and add lightness."

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Re: Duke's'72 Carbed KA project

Postby Byron510 » 01 Mar 2016 17:11

Duke, what is the part number for the units you used, and do have the dimensions at full extension and compression?

I'll assume these are fully adjustable for compression and rebound, yes?

defdes wrote:I went with the circle track struts on my coilovers for the rear too for the same reason. Mine came with a spherical connection option for the bottom, the top is stock with very hard bushes.


John, I have to ask the same question, since yours were a different configuration, what was the part number?

I definitely want to go this route as I have to address the shock issue on the Bronze. Mine are simply too stiff. But the wheel rate at 275# will remain the same.

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Re: Duke's'72 Carbed KA project

Postby duke » 01 Mar 2016 22:43

They are Koni 30-7436. They are only rebound adjustable. 7" steel body, 12.75" min length, 19.75" max length. If I were to do it again I would go with a shorter size. Here is the info page for Koni 30 series shocks: http://www.koniracing.com/oval30.cfm
Duke Schimmer



'72 2-Door 510

"Simplify and add lightness."

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Re: Duke's'72 Carbed KA project

Postby duke » 20 Mar 2016 23:27

The first autocross of the year was this last weekend. The car performed awesome, but I can't say the same about the driver. It took me a few runs to remember the limits of R compound tires, and once I did, I couldn't get a clean run to save my life. On the plus side the new rear coilover setup felt much better than the old. The venue where we run has pretty horrible pavement, and the car was much more settled when going over the rougher areas.



Here are some pictures from the event courtesy of Bob Jenkins.

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I've got some more things happening with the car so there should be a few updates within the next few weeks.
Duke Schimmer



'72 2-Door 510

"Simplify and add lightness."

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Re: Duke's'72 Carbed KA project

Postby DADZSUN » 22 Mar 2016 14:41

Damn look at all the green in the background! It looks like summer... there's still snow here. :(

It usually takes me a good 2-3 events to shake the rust - and that's without changing the setup as you have in the rear.

Good call on the Konis, I've always been a fan of the yellows and will make my next change back to them.
'72 Datsun 510 - KA24E/R1 carbs/EDIS 4 Megajolt
'76 Datsun 280z

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Re: Duke's'72 Carbed KA project

Postby defdes » 22 Mar 2016 18:29

Byron510 wrote:
John, I have to ask the same question, since yours were a different configuration, what was the part number?

Byron


I can't remember, I'll have to have a look under the car to see Byron.

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Re: Duke's'72 Carbed KA project

Postby duke » 26 Apr 2016 13:51

What's the saying? If it ain't broke, build a better and lighter one to replace it...I'm not sure if I got that one right…

On that note I recently built a new set of lower control arms and T/C rods. My main motivation behind this was basically that I wanted to make something, and these seemed like a good candidate for redesign. My secondary motivation was that I wanted to try and use the 280zx steering arms that I had laying around to see what kind of a difference they would make with steering feel. The whole project kinda snowballed, as they often do, into a fairly comprehensive front suspension rebuild.

For the LCA I wanted to build a full tubular setup that used a 5/8” spherical bearing in place of the stock ball joint and eliminated the sway bar mount (if you recall my sway bar is now mounted to the strut tube) and moved the T/C rod mount outward to better triangulate the forces on the control arm. The inner pivot is the same 5/8” rod end from my previous setup. The main tube is 1”x.083 wall DOM tubing. The T/C bracket is made from 1/8” flat bar. The T/C rod mounts on a single 3/8” AN bolt. The single mounting point of the T/C rod allows it to pivot when the LCA's are lengthened, eliminating the binding that can happen with the stock setup. For the T/C rods I used 3/4”x.188 wall DOM, drilled and tapped on the end to accept the M14x1.5 inner tie rod end that I use as the T/C pivot.

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You can see how much simpler they are when compared to the stock arms. I never did weigh them, but feeling them side by side there was a noticeable weight difference.
Duke Schimmer



'72 2-Door 510

"Simplify and add lightness."

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Re: Duke's'72 Carbed KA project

Postby duke » 26 Apr 2016 13:52

For steering arms I have a couple of options. The first is a set of stock 510 arms (thanks Icehouse!) that I reamed out the stock tapers to 5/8” straight for the ball joint and 1/2” straight for the tie rod. I did the same with a set of 280zx arms, but because of the larger holes for the ball joint and steering arm, I had to partially weld up the holes before reaming them. My reason for going to straight holes vs tapered is that I can easily adjust roll center and bump steer by adding or removing spacers between the steering arm and LCA or tie rod end. Being able to adjust bump steer is really just in preparation for installing a rack and pinion in place of the stock steering box, something I have planning on doing for quite some time now. The outer tie rod is a 1/2” female heim joint with a turnbuckle that attaches it to the stock tie rod. The turnbuckle setup was used anticipating the future rack and pinion setup.

Reaming the steering arms.

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Duke Schimmer



'72 2-Door 510

"Simplify and add lightness."

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Re: Duke's'72 Carbed KA project

Postby duke » 26 Apr 2016 13:52

When disassembling the front suspension to install the new LCA and T/C rods I ran into a nasty little surprise. Both of the Tokiko Illunina inserts that I had been running for the last 4 years or so were completely blown. One had lost it's gas charge and the other had a sticky rebound valve that caused about an inch of dead movement before the rebound damping engaged. I knew that my front dampers were a weak point in my suspension setup but I didn't think they would be this bad. I don't know why these failed, but I can tell you I don't think I will ever run Tokiko's again. Koni to the rescue. I went with a set of their adjustable race inserts, which should compliment the new rear shocks nicely. Then it was just a matter of getting a new set of 280zx strut housing (thanks Yenpit!) and building up a new set of shortened struts. I don't have any pictures except for this gratuitous shot of welding on the coilover sleeves.

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Duke Schimmer



'72 2-Door 510

"Simplify and add lightness."


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