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PostPosted: Mon Jul 09, 2018 3:43 pm 
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Very cool. Looks like the front matches the rear quite nicely.
They look like big brakes under the fronts. I assume R33 disks?

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1972 Datsun 1600, S14 SR20DET Engineered (190-210kw @ 15-16psi.)
http://www.ozdat.com/forum/viewtopic.php?t=6579
M35 Axis Autech


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PostPosted: Mon Jul 09, 2018 4:28 pm 
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Location: CRACE, ACT
Currently Z32 / R32 but I have a set of 296mm Exige rotors to go in with R33 calipers modified to fit 26mm wide rotors, all on my own design alloy hub. Slightly bigger, but a massive 3.5kg lighter per side ... compared to std R31

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Last edited by AlanDatsomefun on Mon Jul 09, 2018 4:36 pm, edited 1 time in total.

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PostPosted: Mon Jul 09, 2018 4:32 pm 
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3.5Kg is massive.

I've always wanted to get an aluminium hat floating version of the R33 rotor I am currently using on the front of my car.
Unfortunately DBA don't make them. Plus they would be too expensive I think...

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1972 Datsun 1600, S14 SR20DET Engineered (190-210kw @ 15-16psi.)
http://www.ozdat.com/forum/viewtopic.php?t=6579
M35 Axis Autech


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PostPosted: Mon Jul 09, 2018 4:45 pm 
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Earlier, I included a photo of rotor, hub and alloy spacer plate under the thread "Brakes Upgrades Performance and Weight".
The R33 calipers look no different, they are just 4mm narrower: no real saving here.
The 296mm diameter x 26mm thick DBA bolt-on rotor for the Lotus Exige is heaps lighter than the Nissan R33 rotor which also incorporates a cast "hat", overall making it as heavy as a boat anchor.
The alloy hub is very much lighter than the Nissan Z31 Californian 5-stud one, not surprisingly.
Whilst the design replaces cast iron with aircraft grade 6061-T6 alloy, the whole assembly contains much less metal.
Unfortunately, this worked out to be a very expensive modification. Titanium bolts have to be used to fit the rotor.
Hubs have a design life of 80,000km.
This was quite difficult to design and tricky to build, particularly from the viewpoint of installing the bearings without damaging the hubs.
... but exciting to do.

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PostPosted: Thu Aug 09, 2018 7:00 am 
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Cool thread!

I enjoy daily driving my 510 with rack and pinion, hope you guys get to do the same.

Baz less then 3 turns lock to lock isn't bad on the street, although in our enduro car it's enough to wear you out. It has 225's all the way around, which is some serious grip!

[ img ]


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PostPosted: Thu Aug 09, 2018 10:22 pm 
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Hi Icehouse, can you post some more pics and info on your car.
What rack and cross member did you use for your conversion?

Cheers
Mick


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PostPosted: Fri Aug 10, 2018 2:27 am 
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Coz22a wrote:
Hi Icehouse, can you post some more pics and info on your car.
What rack and cross member did you use for your conversion?

Cheers
Mick

Me and a few of my buddies make these JBcoachwerks.com We've only done a few of each version, but I enjoy one of each in my many cars. It took us a few years of 3D modeling and prototypes to get where we are. I think it was all worth it though. Like you guys we heard all the different "rules of thumb" and it was cool to see what actually effects roll, bump and ackerman without having to change a test jig. As you know, over here we like our cars super low. So it's really cool to have a car that tracks well through the rough roads while avoiding bottoming out.

One tidbit that blew my mind when figuring out what effects bump. I saw the earlier post about LCA's neeeding to being the same length as tie rods. That is actually wrong. Imagine if you will, the strut at max droop then max compression. Notice any odd changes? Since the strut has caster the more compressed it becomes the more caster that is added. This rotates the outer tie rod down effectly giving it a different arch then the LCA. There is even more to it then that but I'm bad at explaining things through typing. It's a fun thought experiment though.


How do I post a picture that isn't so big?


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PostPosted: Fri Aug 10, 2018 9:14 am 
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Location: Blue Mountains, NSW
This thread is still going then! Looks good. I'd resize the images and host them on this site rather than photobucket or another party?

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Ongoing Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
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Previous Car: Restored Green 1972 Datsun 510, Hot L18


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PostPosted: Tue Oct 30, 2018 12:50 pm 
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To Icehouse ...

I think you misread this ... it was not suggested that the lower control arms and tie rods be the same length. In the conversion that I have built and I described in this thread, the tie rod (centre of rack rod end ball joint to outer tie rod ball joint) is 50mm (2 inches) shorter than the lower control arm (pivot point to centre of lower ball joint): see drawing posted earlier. For a bunch of reasons these two components have to be of similar length, and the tie rod is [generally] going to be shorter and the steering arm angled inboard somewhat. Further, the length of the steering arm and the extent to which it is "bent" have to be taken into account along with the effective height of the outer ball joint (on the steering arm) with respect to the lower ball joint, and etc. Changing the steering arm so that it is either a different length or the tie rod ball joint is either higher or lower will change the bump steer. I have discovered that Nissan Datsun produced three or four slightly different steering arms during the production of 510s: each will produce slightly different amounts (more or less) bump steer, and depending on their length and height of the outer tie rod end relative to the LCA ball joint.

Also, whilst the LCA ball joint and tie rod end ball joint both move up and down in an arc in the vertical plane, the tie rod end ball joint also travels in a plane +/- 25-30 degrees to the horizontal in an arc about the LCA ball joint. In effect (ignoring compression or drooping of the suspension for the time being) the tie rod end ball joint on one side of the vehicle is doing much the opposite to that on the other side of the vehicle that the outer tie, producing simultaneous large amounts of toe-in / toe-out we know as Ackerman steering. For example, turn the steering wheel left and the left hand road wheel turns heaps and the right hand one not so much: the inside (left) has to roll through a tight arc and the outside (right) has to roll through a larger arc.

Here's the thing: a really good start point is to try to ensure that the length of rack (measured at the centres of rack rod end ball joints) and distance between LCA pivot points are (as close as possible to being) the same, and that these are to be in the same horizontal plane. Of course, any guide is a simplification which is mostly true but sometimes wrong, at least in some respect. Having quickly checked the photos on your website, this appears to be EXACTLY what you have done!

Consider the position of one roadwheel: for any given steering wheel position, as the suspension moves from full droop to full compression the outer tie rod end ball joint (effectively the end of the tie rod) and the ball joint at the end of the lower control arm (effectively the end of the LCA) must travel through parallel arcs otherwise there will be unanticipated toe-in or toe-out: indeed the condition know as bump steer is the unintended change in direction of the pointing of the roadwheel as a consequence of these arcs not being parallel. As the position of the steering wheel is changed the distance between these two arcs will change: when the steering wheel is in the straight ahead position, the distance between these two arcs will be at its least and when the steering wheel is at full lock the radial difference between these two arcs will be at its greatest: this is one of the essential conditions to create Ackerman steering. Further, if the suspension on one side is compressed whilst the other side is drooping, say under conditions of hard cornering and body roll, it is quite likely that the changes in pointing of the roadwheels could result in toe-in or toe-out or a compound form of bump steer. Throw a pothole in for good luck and there could well be excessive bump steer on one side combined with toe-in or toe-out.

Early contributions to this thread indicated that determining what might work and what could produce dynamic changes in geometry (bump steer, for example) involved doing lots and lots of measurements along with modelling of the steering geometry to determine turning circle, Ackerman steering geometry, changes that occur from full droop to full compression, and so on. ... which is what you are saying (I think) ... and I have said it too ... doing a rack-and-pinion steering conversion is not simply a matter of grabbing something that looks like it will work and with mechanical surgery transplanting it into the chassis and expecting that it will work.

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