Gear Monkey
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| posted on 9/12/11 at 08:39 PM |
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Chassis Design to accommodate RX 8 back end
Hello,
I've managed to secure something of a bargain on Ebay
eBay - The UK's Online Marketplace
It's an entire RX8 back end complete with LSD for only £51 
However I need a way of building a back end to either accommodate the entire RX8 cradle or do I fabricate a framework, brackets etc and transplant all
the components. If anyone could give me any pointers before I break out the saw it would be much appreciated.
Thanks
GM
[Edited on 9/12/11 by Gear Monkey]
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mark chandler
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| posted on 9/12/11 at 09:28 PM |
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I would discard the carrier and make a set of bones up, lightness is key.
If you have a look at pictures of the rear of the frames you will see plenty of examples, you could also carefully measure the pickup points and
transfer across.
As an RX8 revs very high what diff ratio is that?
Looks ideal BTW, and a bargin
[Edited on 9/12/11 by mark chandler]
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austin man
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| posted on 9/12/11 at 11:23 PM |
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as before make wishbones and carriers
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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Simon
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| posted on 10/12/11 at 01:14 AM |
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Basically, as Mark and Austin Man say. You don't need the carrier, trailing arms etc. Make your own wishbones to suit a) your inner chassis
mountings and outer hub carriers both of which you'll need to design and brackets on the chassis to carry the diff, adapting as necessary to
allow provision for 1) handbrake, 2) brakes and spring/shocks.
You may be able to utilize the top "wishbone" that mazda made. Can't see what's at the bottom, but if it's another bone,
you may just need to transfer the carrier pivot points onto your chassis - making chassis the appropriate width (and all the aggro that will entail -
such as one-off bodywork )
Cheers
ATB
Simon
[Edited on 10/12/11 by Simon]
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Dusty
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| posted on 10/12/11 at 09:09 AM |
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What a shame you can't just bolt that lot straight onto a modified chassis, couple up the prop and brakes and Bobs your uncle. Apart from the
weight is the design so poor that it would be useless?
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mark chandler
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| posted on 10/12/11 at 10:00 AM |
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You can probably utilise the bones, the shocks and springs and carrier all go back on ebay
This is all designed to support a car of twice the weight.
If you have a look in speedyxjs's archive he did the same thing with a Jag rear end.
Regards Mark
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Gear Monkey
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| posted on 10/12/11 at 07:03 PM |
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Here are some pics of the chassis and RX8 back end. The chassis is based on the 2nd edition or Ron Champions book and was started back in 2005 and
only just res-erected. Despite living in a ultra dry barn this past 6 years it's gone a little rusty but it's very light surface rust
which will easily vanish with it's pre powder coat shot blast.
 
As the Ron Champion chassis is 4" narrower the more modern Haynes roadster the rear wheels are going to stick out quite a bit.
The RX8 back end weighs around 80kg (170lbs) so I'll take everyone's advice and ditch the cradle
Fancy and incredibly light carbon fiber prop is far too long....Such a shame 
The discs are huge so I'll need wheels from an RX8 to cover them. This pic shows the upper links which I'll look to restore and retain.
The bottom links I'll also keep once cleaned and painted. Anyone think I'll need or would benefit from the anti roll bar?
Some mods I'm making to increase overall stiffness. I've got quite a few ideas which I believe will make the chassis unique and super
stiff.
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PSpirine
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| posted on 10/12/11 at 07:09 PM |
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I think it's a great project, but honestly, why not consider selling the diff/cradle for £150 which will get you a sierra LSD disc braked rear
axle which would be far easier.
Otherwise you're into a world of complications, plus you'll need either hub adapters or different wheels front and rear (different stud
arrangement).
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Gear Monkey
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| posted on 10/12/11 at 07:25 PM |
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I'm hoping (maybe someone can help me here) that MX5 front uprights are the same stud pattern as the RX8 and if so I'll get myself some
fat RX alloys.
Regarding the complications, which I'm no doubt going to be up against, I love an engineering challenge and I'm keen to create something
totally unique.
GM
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stevebubs
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| posted on 10/12/11 at 07:54 PM |
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Yes -
http://forum.miata.net/vb/showthread.php?t=205820
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stevebubs
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| posted on 10/12/11 at 07:59 PM |
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Ratio looks interesting 4.444 or 4.777 ...very high ratio....
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gazza285
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| posted on 11/12/11 at 01:35 AM |
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quote:
Originally posted by stevebubs
Ratio looks interesting 4.444 or 4.777 ...very high ratio....
Low ratio?
DO NOT PUT ON KNOB OR BOLLOCKS!
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tomprescott
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| posted on 11/12/11 at 04:10 AM |
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I had exactly the same, I got the complete rear end from a lsd 200sx, then looked at how much wider it was than the chassis and how much weight there
was in the cradle.....in the end I decided to sell the chassis (although haven't got round to shifting it yet) and starting something new....
Not sure if it will be the same for you, but the offset of the diff and the total dimensions meant it would be utter ball ache to modify the champion
chassis to fit - would also have left me a small driver seat width (which would have proved a logistical problem given the size of my ar$e)
Good luck!
A bird in the hand....
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