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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Thu May 04, 2017 8:27 am 
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Joined: Mon Aug 25, 2003 12:00 am
Posts: 3493
Location: Brisbane
Its pretty strange to have such a low rate spring in the rear, the biggest downfall of the gti is diagonal squat coming out of corners, with a low rate rear spring the outer rear wheel squats and the inside front wheel losses traction as it lifts.Circuit racing is a different game but the principles are the same and typical spring rates for circuit are 300-350lb front with 600-750lb rear ,thats if the rear springs are in original mounting point(if they are coil over rears the rate is lower ,more like 300-350lbs in rear),so for rally I would be trying something softer than above but keeping the front to rear balance the same.Typically for circuit we run a heavier than std rear sway bar and keep the std gti front bar.I dont think ride height will be a issue in your case as you will be running a fair bit of clearance in the front, but it is important for roll centre to have the front lower control arms pointing upwards towards centre of car, if they are flat or downhill then its totally wrong and spring changes will not have effect as they should.

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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Thu May 04, 2017 3:45 pm 
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Joined: Tue Feb 23, 2016 5:38 am
Posts: 131
Location: Christchurch
Thanks Dave.

I was surprised at the spring rates given this was a tarmac setup. I could understand the fronts at 325 but not the rears at 100 given it's coil over in the rear.

The front control arms are flat but like the rear changing that will not be straight forward. The platforms are as low as they can go. I did measure the difference in height between the Gaz Gold ( what the car currently has ) and my Koni tarmac setup and from memory it was something like 75mm. That is, the Gaz was 75mm longer from the lower strut mount to the top of the fully compressed strut. This was simply because the lower mount was welded on further down the tube than on the Koni. They probably need to be longer and therefore higher than the Koni but somewhere in between the Koni and where they are now.

I have a set of 175 springs for the rear that I could try but I was thinking that might be a little on the high side and had intended starting at 150 for gravel.


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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Fri May 05, 2017 8:05 am 
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Joined: Mon Aug 25, 2003 12:00 am
Posts: 3493
Location: Brisbane
If your going 225 in the front and the rears are coil over ,175 would be an ok starting point in the rear (possibly a bit on the soft side).
So if your front platforms are as low as they can go ,raising the ride height by screwing the platform up will help correct the roll center ,it is more important to get the front roll center correct than to worry too much about the ride height.If you cannot achieve the lower control arms pointing upward towards center of car a couple of years ago i came up with a mod that achieves this (search front roll center correction kit)by using modified front uprights from a late model swift coupled with a new type lower ball joint.

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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Fri May 05, 2017 9:20 am 
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Joined: Tue Feb 23, 2016 5:38 am
Posts: 131
Location: Christchurch
Yes sorry, of course the roll center won't be a problem given we can raise the front platforms. Fully down has the control arms flat so going up 25-30mm should have the desired effect.

I have the rear struts out so I'll fit the 175's and give them a try.


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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Tue May 09, 2017 6:47 am 
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Joined: Tue Feb 23, 2016 5:38 am
Posts: 131
Location: Christchurch
Ready for testing again.

I've dropped the rear strut clamping position. This wasn't as straight forward as I hoped. The strut tube had been turned down to fit the clamps so I needed to turn about a 1mm off the tube then cut a new locating groove.

Attachment:
IMG_4242.JPG
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The original locating groove has been cut with a lathe ( ie full circle ) but I wasn't keen to do this with the new higher position as I wasn't sure what effect it might have on the strength of the strut if I decided to use the original location again. I just cut a groove with a file using an old clamp as a guide.

The end result looks pretty good and I can now use the platforms for useful height adjustment.

Attachment:
IMG_4249.JPG
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The setup now is 225F and 175R. I'm running a 20mm bar on the rear and no front bar. I'll also run DMack DMG3 tyres instead of some 20 year old SP82's that I had been using. Too many changes at once really but it's a bit hard to do any useful testing outside of an event.


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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Tue May 16, 2017 7:16 pm 
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Joined: Tue Feb 23, 2016 5:38 am
Posts: 131
Location: Christchurch
The setup was definitely an improvement, a much nicer car to drive. More stable and more predictable. We're still 2s/km off the pace so an improvement but more is needed. In hindsight the rear is probably too low in relation to the front. The last 1/3 of the road for the last rally sprint was steep uphill and I'm pretty sure that's mostly where we lost time lacking traction. We're also under steering a bit in the slower corners but it was doing that prior to changing the spring rates as well.

I think for the next event I'll leave the spring rates as they are but I'll raise the rear on the platforms and maybe drop the front a little.


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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Thu Sep 07, 2017 7:19 pm 
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Joined: Tue Feb 23, 2016 5:38 am
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Location: Christchurch
After following swift12's process of discovery with roll center correction I decided I'd better get on with my own project. After going around in a few circles with the best way to do the LCA's I've decided to stick with the original plan which was to use Mazda Astina bolt-in ball joints.

The process will be to create a jig from box section that gives the original location of the ball joint. Next, cut off the existing ball joint and fold a piece of plate to locate the new ball joint. Then use the jig to locate the position of the ball joint and the plate and tack the plate in position. Bolt the ball joint in position and then complete the weld.

Hopefully this won't be a journey of discovery but in case it is I've sourced two sets of used LCA's rather than remove the current set from the car.

So far step one is complete with jig made using a pair of existing GTi LCA's as the template.
Attachment:
IMG_4292.JPG
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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Fri Sep 08, 2017 3:22 pm 
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Joined: Tue Feb 23, 2016 5:38 am
Posts: 131
Location: Christchurch
Now the old ball joints have been cut off directly behind the ball joint using a power hacksaw. I've had a trial fit and we're ready to fold the plate that will locate the position of the bolt-in ball joint.
Attachment:
IMG_4293.JPG
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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Wed Oct 18, 2017 12:51 pm 
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Joined: Tue Feb 23, 2016 5:38 am
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Location: Christchurch
Some info on mounting Wilwood brakes for Zero_Cool_1983.

Firstly what it looks like:

Attachment:
IMG_4316.JPG
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The mounting bracket looks like this:

Attachment:
IMG_4320.JPG
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The mounting holes for the upright are 140mm center to center. The mounting holes for the Wilwoods I'm running are 152mm center to center. The bracket has been milled from 25mm alloy. The caliper is radial mount. The caliper mounting holes are centered in the bracket but the bracket has been recessed where it mounts to the upright. The bracket is 15mm at the mount. This means that the bracket sets the caliper back ( inwards ) by around 2.5mm.

Whether this is correct for your installation will depend on your caliper and the brake bell that you're using. It might be a good idea to grab a piece of alloy angle and cut it to length as a dummy bracket then drill mounting holes and pack them with spacers or washers to get the caliper in the correct position. Once you have checked the installation with the dummy bracket you can measure the set back and get a machine shop to mill the real thing.


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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Wed Oct 18, 2017 8:23 pm 
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Joined: Mon Aug 25, 2003 12:00 am
Posts: 1526
Location: Londoninium
Adding to Sam7's post
These brackets are for a Justy or cino hub and a 282/5mm rover disk.
the mounting lugs on the hub are 10mm closer to the axle centerline than a GTi.
I have tried these on a GTi hub and they do bolt up but without modification will require a 305mm disk and 16 inch wheels. But the image give the key dimensions ready for you to amend.
Attachment:
wilwood.JPG
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the Bracket bolted into place.
Attachment:
Willwoods 2.JPG
Willwoods 2.JPG [ 49.35 KiB | Viewed 13 times ]


All bolted together

GTP


Attachments:
Justyfrontbrakes7.jpg
Justyfrontbrakes7.jpg [ 63.22 KiB | Viewed 13 times ]
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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Thu Oct 19, 2017 3:49 am 
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Joined: Tue Feb 23, 2016 5:38 am
Posts: 131
Location: Christchurch
I'm guessing the discs on my car are smaller than that as we're running 14" wheels. I'll measure and let you know.


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 Post subject: Re: Swift GTi Tarmac Rally Car
PostPosted: Thu Oct 19, 2017 12:10 pm 
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Joined: Tue Feb 23, 2016 5:38 am
Posts: 131
Location: Christchurch
The disc is 262mm so probably the same kit as Garndi was using. Looking at the post from years ago it looks like he gave the DXF file to bzchi so it might be worth sending him a PM to see if he still has it and is willing to send it to you. Garndi had said he didn't mind it being used but didn't want to produce the brackets for sale.


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