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Old 10-19-2018, 04:17 AM   #1
JDwhiteWRX
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Default Time Attack BRZ

Hi Guys,

I was posting some photos of this project a while back in the "home made aero" thread but then photobucket died and I lost interest in posting photos on forums.

Anyway things have moved on, here are a bunch of photos to bring you up to speed.

Just so you know this is a low budget project I am building on my own in my garage, progress is slow at times as I have 2 children under 5 to keep me busy amongst other things.

You can also follow me on Instagram: @brzdiy



I built a jig of the rear suspension



It locates in the OEM bolt holes but I lifted it up a little to lower the chassis whilst keeping the correct geometry.



Mocked up a design after doing some reading on triangulation etc.



A friend of mine does FEA for a living and offered to validate my design, so I had to measure all the distances for him with a plum bob.



I started building the roll cage





Then I started to build my rear suspension design





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Old 10-19-2018, 04:17 AM   #2
JDwhiteWRX
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Then some more mock up to make the shock mounts



Making the shock mounts



Completed the shock mounts and removed the wheel tubs and frame rails



Boxed off the chassis rails







and just yesterday I finished most of what I want to do for now on the rear suspension.





This whole project has been a huge learning curve for me, I only started welding 2 years ago this month and have never bent any tube before either. I really enjoy the whole design aspect of putting a race car together, I do a bunch of research on each aspect before I lift a tool. The main goal though is to go as fast as possible without spending a fortune.

So far I have only just spent slightly over $3k AUD but obviously there are lots more parts needed to complete this build but I will be making a lot of things by hand to save money.
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Old 10-19-2018, 04:28 AM   #3
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This is completely fascinating to me. Thank you for sharing! Looking forward to future updates.
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Old 10-19-2018, 05:19 AM   #4
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sweet ride! would love to see more
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Old 10-19-2018, 12:29 PM   #5
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When did you start this project? These pictures look really familiar to me but I think it was years back I'd seen this.

Still looking great.

I'm finally buckling down on my long overdue projects. I think the Carcaine episode of Hoonigan's struck a chord

Last edited by Homemade WRX; 10-19-2018 at 05:40 PM.
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Old 10-19-2018, 01:10 PM   #6
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The thread title peaked my interest, then I open it up and wow, amazing work in here. Very much looking forward to your progress, as your time allows (I get it, have 2 kids under 5 myself).
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Old 10-19-2018, 07:25 PM   #7
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I picked up the shell in December of 2016 but I did not start working on it until May the following year as I was still learning to weld and confident enough to start working on it straight away although I knew what I was going to do.
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Old 10-29-2018, 04:27 PM   #8
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Quote:
Originally Posted by Homemade WRX View Post
When did you start this project? These pictures look really familiar to me but I think it was years back I'd seen this.

Still looking great.

I'm finally buckling down on my long overdue projects. I think the Carcaine episode of Hoonigan's struck a chord
Phoenix BRZ (?) I think was what I saw as well? I vividly remember the chassis being yellow. I want to say I still follow the page on Facebook?
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Old 10-29-2018, 04:52 PM   #9
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Interesting.
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Old 10-31-2018, 06:55 PM   #10
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I have started on the control arms, just measured everything and thinking about what I need. Basically I want each arm to be adjustable and I want to remove all rubber bushings so all the joints are either rod ends or spherical bearings. I will modify some of the factory arms and possibly build some from scratch.

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Old 11-05-2018, 05:37 AM   #11
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Looks great! Looking forward to seeing more.
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Old 11-05-2018, 04:05 PM   #12
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In on this. This build looks great and I may be able to learn a lot from you as I also picked up welding and pipe bending in the last year or so.
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Old 11-05-2018, 09:19 PM   #13
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Outstanding. Look forward to seeing more.
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Old 11-06-2018, 03:02 AM   #14
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And now following! Love the custom fabrication.

You planning on attending WTAC next year?
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Old 11-07-2018, 03:35 AM   #15
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Originally Posted by Eww Evo View Post
And now following! Love the custom fabrication.

You planning on attending WTAC next year?
Thank you, Yes I have been attending every year since 2011 as a spectator and will continue to do so as it's a great event.

Even though I am building this car to the WTAC rules there is a good chance I will never enter the event as a competitor. I just wanted to build to a set of rules as a way of future proofing the project.
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Old 11-07-2018, 04:10 PM   #16
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I've always wanted to do a chassis up build, definitely looking forward to seeing it it all come together on the track!
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Old 11-08-2018, 04:24 AM   #17
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Nice work!
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Old 11-15-2018, 01:00 AM   #18
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Not much happening right now, I'm ready to order everything I need to build the rear control arms but I want to order the parts for the front as well to save on shipping.

The problem is I am undecided on how I want to do the front, part of me wants to convert it to double wishbone so I'm looking into that and have done a lot of research over the past couple of weeks.

The current plan if I do decide to move forward with this is to use knuckles from a car that comes standard with this suspension type. From my research there are many options but once you mandate a 5x114.3 stud pattern this list gets smaller.

Some options are late model Mazda MX5, Honda S2k and Mazda RX8.

From these options the RX8 has the most similar dimensions to my BRZ. In fact I have been able to figure out that the HKS TRB-03 is in fact running the RX8 factory lower control arms, I have not been able to find photos showing the knuckle they are using but I would not be surprised if it is also from the RX8.



I have found some rough dimensions of the control arms and knuckles on Locost forums although I will most likely fabricate my own control arms and only use the knuckles from the RX8 ideally to keep the standard track width of the BRZ and build in some extra adjustability.

The tricky part for me will be the upper control arm length and mounting them in the optimum position. Working this out using some measurements and software is where my skills are lacking.

I'm guessing the procedure would be to use the dimensions from the current suspension and then feed them into the "double wishbone" setting of a software program such as Vsusp and play with the upper arm length and chassis mount points until you get the desirable camber change with roll etc. all within the size constraints of the chassis?

The Mazda RX8 suspension is actually all built into a removable crossmember so maybe I am better off purchasing this as a whole unit and using it as a kind of jig?

Any input welcome.
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Old 11-16-2018, 09:44 AM   #19
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This is a good cursory look into suspension design before you get into the tech books, start running heavy calculations, etc. Start at the tires and work your way back. You're going to want to define your track widths, and scrub radius before you start picking out control arms. You'll see where your roll rates starts to define what camber gains you'll want and that using a particular spindle might also box you in a bit. I'm currently looking at using Pontiac/Saturn Sky/Solstice spindles and hubs.

https://willmartin.com/suspension/

Also there's some free suspension software floating around, so that should help you dial in as well, if nothing more than give you nodes for setting up fixtures. If you have CAD, then you can run a kinematics model.
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Old 11-17-2018, 05:28 PM   #20
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I seems to me an easy way to do this would be to purchase the complete front subframe and suspension from a Mazda RX8.



The RX8 is a very similar dimension to the BRZ, the track width is only 19mm less than the BRZ. I can purchase this suspension assembly and then take measurements of everything and feed them into some software for analysis of how this track change may affect it.

What one guy was doing on the locost forum was to make a jig of the subframe similar to what I did with the rear suspension of my car and then using the jig to locate the control arm mounting points into a different chassis. I think the hard part would be working out the height to do this so it works with what I have done in the rear. I would also need to do the same triple hole tabs for the control arm mounts, not hard to do.

Another plus with the RX8 is I get 5x114.3 bolt pattern and there are lots of options for big brake kits. The cost savings on the PCD change should cover the cost of this whole conversion if I can get the RX8 front suspension cheap enough.
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Old 12-02-2018, 07:12 AM   #21
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Decided to jump in the deep end and convert the McPherson strut front suspension to a double wishbone. It's something I have been thinking about since I bought the shell but the whole idea seemed very daunting and information specific to a conversion was not really available. The only way was to focus my research on designing a double wishbone suspension from scratch and then adapt it to my car.

So I picked up a pair of RX8 uprights for $200 complete with wheel bearings and tie rods.



It would have been nice to buy the entire RX8 front suspension including the subframe but unfortunately I could not find one for a reasonable price. luckily the guy I bought the uprights off was kind enough to let me measure all the factory control arms.

Next step was to make a jig to position an upright in the correct position in space that it would sit if it were mounted to a 18x11" wheel with a 295/35/18 tyre on it.



With the upright in the jig I was then able to accurately measure the ball joint and steering arm locations, these are your "fixed" points that you can not alter. The arm lengths, angles and points at which they attach to the chassis are all the points you have freedom the play with.



I spent the majority of Saturday night and most of today measuring everything and plugging the numbers into some software I got off the Locost forums. I have tried to stay as close to as possible the Mazda RX8 geometry as it is considered to be very good. The software takes a bit to get used to but basically it just plots everything in X,Y,Z coordinates and allows you to see what the camber and roll center is doing in bump and roll or both.

I then lowered the shell back to its planned "lowest" ride height and positioned the jig inside the front wheel well such that the face of the wheel bearing is in the same position as it would be on a stock BRZ.



Now I was able to take my arm lengths and angles and see where the inner pivot points would land on the chassis. The RX8 has longer arms than the BRZ since the engine bay is not as wide so the stock RX8 arm lengths would require major surgery to fit to the BRZ.

I then went back to the computer with my shorter or more appropriate arm lengths as measured to see what effect shorter arms would have on the geometry. The results were good, I am seeing a 1.4 degree gain in camber with 2 degrees of roll. With 1" of bump I am gaining 0.5 degree of neg camber and combing both I am seeing 1 degree positive camber. Roll center migration is very minimal at less than 1 degree under 2 degrees of roll. The results are actually very similar to the stock RX8 arm lengths once to change the angles around to suit the shorter arms.

I have not yet factored in the steering other than doing my "fixed point" measurements with 7 degrees of positive caster in the upright. Ideal positioning the steering rack is not too difficult to work out however there is the chance of something being in the way of the ideal position and then I have to get creative.
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Old 12-02-2018, 02:55 PM   #22
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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.
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Old 12-02-2018, 07:12 PM   #23
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What I may do is extend my existing jig such that it locates the pivot point on the chassis. That way it can be checked on the bench and will keep both sides the same.
I also want to bring the roll cage through to the strut towers but I may also tie it into the control arm mounts somehow.

I've still got lots more thinking to do.
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Old 12-02-2018, 10:05 PM   #24
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Measure a million times, cut once for each of the one thousand prototypes, I say.

All joking aside, I really enjoy reading your progress. I'm enjoy learning, even though it's something I'll never invest in. Passion projects are always fascinating! Thanks for the updates!
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Old 12-03-2018, 12:32 PM   #25
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Quote:
Originally Posted by NSFW View Post
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.
Yeah, chassis are usually crap for repeatability. Had a stint doing design engineering work for bolt on kits to Hilux's, LC79, and some other vehicles. Chassis points can wander a lot. Every bolt was slotted for adjustment.

However using known pick up points and lots of measuring is better than nothing.

Last edited by Homemade WRX; 12-06-2018 at 10:07 AM.
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