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Old 12-05-2018, 03:50 PM   #26
lockheed
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I salute you for taking on the challenge.

If it was me - and keep in mind I've never done this - I'd want to attach that jig to the chassis somehow, and probably attach the knuckle's steering link to the jig, and then re-measure everything about ten times just to be sure. Then put the pivot points on the chassis (and re-measure another ten times). Then the knuckle + pivots basically becomes a jig for the wishbones. Though I guess it might get crowded in there.
do this , im familiar with the auto robot jig repair system. you must keep accurate datum points and maybe create a measuring system.
I love your thread keep it up
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Old 12-05-2018, 04:47 PM   #27
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Looks fast and expensive
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Old 12-09-2018, 04:48 AM   #28
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I spent the afternoon measuring all the pivot points in the rear suspension so I could enter them into my software and see how it compares to what I have designed for the front.



The car is super low in this photo but you wouldn't know it from the angles on the control arms. This is at my lowest possible setting but I found the roll center and camber gains where much better with the car raised about 20mm from this position. Actually the camber gain numbers almost mirrored my front design but the roll center was slightly lower.
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Old 12-16-2018, 05:59 AM   #29
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So I did all my measurements of the rear suspension to see what the camber is doing in roll, bump or both which is basically what happens in a corner.

With the car sitting at my lowest ride height it was giving a fair amount of camber gain in bump which is probably not ideal. What I found though was that at this low ride height which is like super low (90mm to the pinch welds under the sills) is that my drive shaft angles for the diff would be a little extreme and maybe at risk of fouling on the frame.

Luckily I built the diff mounts with the ability to raise the diff 25mm if needed. So with the diff raised and the ride height lifted about 20mm everything was looking perfect again.

This is an old photo to show how removing one spacer allows me to raise the diff.



at the rear mounts it simply moves up one hole.



So here it is with the slightly lifted rear ride height and the mock up drive shaft showing zero degrees at the position it would be in with the diff lifted.



With the new ride height I re-measured the inner pivot positions and put them in my software. The camber gain is now much better.

Moving to the front of the car now.

I have been going round in circles with my suspension design for many weeks but I am now at a point where I think I am happy enough to start with the fabrication side of things. I will build enough adjustability into it anyway so I can fine tune it later. Similar to how I did the rear end.

Today I measured where my tyres would be sitting and begun removing metal that would foul on the tyres. Under the rules I must retain the strut towers but I am free to remove material for tyre clearance.

In this photo you can see black dotted marks where the tyres would hit on the left of this line.
Note everything in front of the strut towers will come off at a later date and be replaced with tube but I need to keep it for now so I can mount the standard panels and make fiberglass molds.



After lots of cutting and drilling of spot welds.



Side view.



With that gone it will be much easier to work on as I make the new control arm mounts. The plan is to run tube from the roll cage up to the strut towers and back down to the main chassis rails to triangulate everything.

This will also help with venting the wheel wells for better aero. I will be doing a bit more trimming around that area to create some smooth transitions for air to escape.
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Old 12-18-2018, 06:50 AM   #30
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Awesome project.

Look into the Griggs setups for Mustangs on SLA setups / conversions for strut cars. Some other companies make kits as well.

There was a NASA national winning FC RX7 with a super home brew double wishbone setup. There was some info out there on it.
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Old 12-18-2018, 10:43 AM   #31
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Sub'd this is awesome! Blessed to have such skill!
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Old 12-18-2018, 07:39 PM   #32
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What an incredible build! Can't wait to see more updates!
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Old 12-19-2018, 11:12 AM   #33
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Keep up the great work!

Curious as to what your threshold was for too much camber gain in the rear and what is typically considered an ideal range/rate. I know this is highly setup dependent, but considering the similarity of production cars that most of us normal people race and the shrinking performance gap of 200TW "street tires" to race rubber, it'll be helpful.

The car I race (S14 240) is notorious for what many people say is excessive camber gain in compression in the rear.
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Old 12-20-2018, 03:21 AM   #34
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Keep up the great work!

Curious as to what your threshold was for too much camber gain in the rear and what is typically considered an ideal range/rate. I know this is highly setup dependent, but considering the similarity of production cars that most of us normal people race and the shrinking performance gap of 200TW "street tires" to race rubber, it'll be helpful.

The car I race (S14 240) is notorious for what many people say is excessive camber gain in compression in the rear.
Thanks,

I don't know the answer to what is considered ideal but I did some looking at published figures I found online for some sports cars considered to have good suspension. For example the miata has 0.91 degrees of camber gain for 1" of bump at the front suspension but I did not find anything about the rear suspension. Further reading suggested they should have more camber gain in the rear to aid traction on power down corner exit but I learnt this after writing my comments above in the previous post.

From my estimates the BRZ rear suspension has about 1.2 degrees of camber gain for 1" bump.
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Old 01-05-2019, 08:27 PM   #35
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Happy new year to you all.

Not a lot has been happening with the car with Christmas and all that but yesterday I did manage a full day of work on the front suspension.

After lots of back and forth on the design I finally came up with a method to attach the inner control arms to the chassis. Similar to the rear I wanted to be able to adjust the geometry as much as possible.

I started out with cutting up some 75mm x 50mm x 3mm rectangular box steel.



Then I cut out one face of the box. There are 8 in total which is enough to do upper and lower control arm mounts on both sides of the car.



Then I had to cut out 16 squares from 3mm sheet to box in the open faces.



I then tig welded them all and it took a really long time! I calculated after I had finished that I had welded 2.8m in length. Anyway it was really good practice and by the time I welded a couple my settings were dialed in perfectly and my welds were very consistent.



I also beveled both faces before welding for maximum penetration.



So this is the finished product before it gets welded into the chassis. The rod end is just an old one I had from my wrx to show how it works. I will be using one size smaller than this when I do my bulk order for all the control arms.



They will be mounted in the chassis with the bolt running vertical so the rod end is sitting horizontal. This will allow me to use spacers to position the rod end on the bolt at different heights to adjust the pivot height which changes control arm angles for camber gain and roll center.

Using the rod ends also allows me to adjust the length of the arms for static camber and caster adjustment.
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Old 01-09-2019, 01:14 PM   #36
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This is intense! Good luck with your build and have some fun ripping when it's done!
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Old 01-13-2019, 07:42 PM   #37
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Coming along nicely Joel
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Old 03-03-2019, 06:30 AM   #38
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Alright some big news for those not following on Instagram, the engine for this project has been selected, purchased and collected.

After a lot of consideration I decided to go with a Honda K24 which will be turbocharged. Bang for buck you can not beat this engine especially here in Australia where these motors are dirt cheap and readily available. I paid $450 for this engine with only 90k km's on it at a wrecking yard.

After getting it home I removed the intake and exhaust manifolds and gave it a pressure wash.



Under the WTAC rules I am building to the engine is allowed to be moved back so that the rear of the engine is no more than 50mm rearward of the original firewall.



So to make the most of this rule I basically cut the original firewall out and once the motor is in its final position I will have to make up a new firewall from sheet metal.



With that done I then slid the engine into its intended final position.



I am really happy with where it is sitting, most of the weight is behind the front wheels and there is loads of space for a really well ducted intercooler/radiator combo. It will also leave me enough space for the steering rack to sit in front of the engine.



The reason I have purchased the motor before finishing the front suspension is that the lower control arm mounts will be part of the front cross-member which will also contain the engine mounts. So I basically had to buy an engine to get that finished.
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Old 03-03-2019, 07:42 AM   #39
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Great choice on the motor. Which K24 did you end up with? I’ve had a couple of K powered cars and they are incredibly stout engines even in stock form.

Last edited by Turpid Porpoise; 03-04-2019 at 07:07 AM.
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Old 03-03-2019, 03:54 PM   #40
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Quote:
Originally Posted by Turpid Porpoise View Post
Great choice on the motor. Which K20 did you end up with? Ive had a couple of K powered cars and they are incredibly stout engines even in stock form.
Thanks, this is a K24A3 which I don't think you get over there but its essentially the same as what comes in the Acura TSX.
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Old 03-07-2019, 07:05 PM   #41
Norm Peterson
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Couple random thoughts . . . Ford Mustang wheels use the 5 x 114.3 bolt circle which should open up the choices in 11" or wider . . . 1.2/inch implies a rather short front view swing arm length.


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Old 03-14-2019, 12:43 AM   #42
JDwhiteWRX
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What I am struggling with now is the location of the steering rack, I have not purchased a rack yet but I do have a electric motor that pumps the fluid out of an Opel/Holden Astra.

At the moment the steering rack needs to sit about where the front of the crank pulley is and I still need to add a small pulley to the front of the crank for the dry sump.

I have two ideas at the moment to solve this but am open to suggestions from you guys.

My first idea was to use those rack offset spacers that drifters use to step the rack forward but still keep the tie rods where they need to be, this will gain me about 25mm.



The other idea is to move the front wheels forward i.e. extend the wheelbase. This will obviously move the tie rod connection point on the knuckles forward buying me some more space for the steering rack. I am not sure if I am overlooking any downsides to extending the wheelbase though? Normally that would be rather extreme modification but since I am already re-designing the whole front suspension its actually very easy for me to do. Also I have noted in a video on youtube that the Subaru GT300 BRZ extended their wheelbase by 35mm for the 2017 season.



The orange string line in this photo shows where the rack needs to be.


Last edited by JDwhiteWRX; 03-14-2019 at 05:44 AM.
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Old 03-24-2019, 10:48 PM   #43
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I have made some more progress on the front cross-member and double wishbone conversion. The lower control arm mounts are now finished.

Once I had worked out the control arm pivot positions I moved the pieces I had made previously onto the bench to get everything measured up and square. I then tack welded some scrap metal to them to hold them in place.



Then I had to position it in the car in the correction spot and take some measurements for the tube required to join it together.



Then with a bunch of tube notching, these are very short so I had to do a complete cut notching two pieces in one go. Usually I do one end at a time to the hole saw is not working so hard.



These then join to the parts I had made previously which bolt into the factory front cross-members mounts on the chassis rails.



I then tacked it all together on the car before taking it back out so I could weld it on the bench.



I also added some captive nuts to make adjustments to the geometry easier.



Even though I will be adding to these pieces later I decided to cold gal them to keep the surface rust away. I hate cleaning off surface rust.



Back on the car.



The rod ends will be mounted horizontally with spacers or varying thickness above and below. This allows me to change the inner pivot height over a reasonable range to tune the camber gain and roll center to my liking.



Next job will be the upper control arm mounts.
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Old 03-25-2019, 06:59 AM   #44
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Really good project, I hope you achieve it
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Old 03-25-2019, 07:48 PM   #45
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You'll definitely want to tie them together and/or due some triangulation. Flex city there!!

Thinking of the lateral load path, boxed/rectangular tubing might have been better for the horizontal bar.
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Old 03-25-2019, 08:28 PM   #46
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Originally Posted by Homemade WRX View Post
You'll definitely want to tie them together and/or due some triangulation. Flex city there!!

Thinking of the lateral load path, boxed/rectangular tubing might have been better for the horizontal bar.
This is just the start of what will be the cross-member, plenty more tubing to be added yet.
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Old 03-26-2019, 09:55 PM   #47
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Originally Posted by Homemade WRX View Post
You'll definitely want to tie them together and/or due some triangulation. Flex city there!!

Thinking of the lateral load path, boxed/rectangular tubing might have been better for the horizontal bar.
With how short and wide those tubes are I doubt there will be much flex, that stated, might as well just add a thin steel sheet on either side for minuscule weight increase and huge strength and stiffness increase.
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Old 03-26-2019, 10:22 PM   #48
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With how short and wide those tubes are I doubt there will be much flex, that stated, might as well just add a thin steel sheet on either side for minuscule weight increase and huge strength and stiffness increase.
I'm expecting the chassis' thin sheet-metal to flex and probably fatigue to failure. I do agree on the sheet metal to gusset.

But he says it's the start of the actual X-member, so I'll grab my and shut up.
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Old 03-27-2019, 08:23 AM   #49
Norm Peterson
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Originally Posted by JDwhiteWRX View Post
This is just the start of what will be the cross-member, plenty more tubing to be added yet.
Can I assume that this will include something to tie the rear LCA pickup points off to basic car structure? Longitudinal loads at the contact patch resolve into fore-aft and longitudinal loads at the control arm chassis-side pickup points. I'm thinking more in terms of alignment in operation and fatigue rather than outright strength here.


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Old 03-27-2019, 11:54 PM   #50
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Originally Posted by Norm Peterson View Post
Can I assume that this will include something to tie the rear LCA pickup points off to basic car structure? Longitudinal loads at the contact patch resolve into fore-aft and longitudinal loads at the control arm chassis-side pickup points. I'm thinking more in terms of alignment in operation and fatigue rather than outright strength here.

Norm
Hi Norm,

Yes, in the photo below I have included a green arrow to show where there is another chassis mount for the OEM front cross-member.
I intend to use this mount to connect some more tube that will run diagonally forward to where the steering rack is located and from this tube another tube will come up and connect to the rear of the rectangular box that is the rear control arm mount. The engine mounts will also be supported by this tube.

In front of the engine I plan to make some type of bolt-on tubular X-brace that ties the steering rack to the strut towers.

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