LionZoo

Designing adapters for the front mounts to use 2.5" springs is going to be a bitch...

LionZoo

Adapters for both the front and rear have been designed. With these adapters plus the sleeves, you can convert any normal damper, Bilstein or otherwise, to use 2.5" springs and so you'll no longer be constrained by other manufacturer's spring choices. Sadly, prototypes have been behind schedule, but I'm hoping to get them machined in 2-3 weeks and have a set I can test on my car. Once the fitment is confirmed, it's just a matter of getting the Bilsteins revalved and putting everything together to do some testing.

It's been a long time coming, but there is light at the end of the tunnel.

LionZoo

By the way, I might design a spacer assembly for the adapters as well so that there is a way to change the ride height of your car without messing up the preload too much.

series7

Moar Pow3r!!

LionZoo

I test fitted a rough rear adapter in the rear over the weekend and found that were was some rubbing between the damper and adapter when the suspension is compressed about 1-1.5 inch from static. The rear adapter has been redesigned to eliminate this problem.

Because of the design of the front mount, the front adapter won't have the same issue.

MilesJ

LionZoo,

I am piecing together some parts to change up my suspension for next year and had some questions on the Bilstein HD's. Are they 46mm diameter shocks? Do they use a snapring on the shock body for the spring perch to sit on?

Thanks.

Great write up btw.

LionZoo

They're snaprings, but I currently don't have them with me to measure the actual diameter. I'll get them when I can.

series7

Moar Powah!

LionZoo

That's -10 points.

LionZoo

Dampers are getting revalved today or tomorrow. Top mounts will be machined this weekend. Then it's a matter of test fitting and making sure the mounting hardware all fits.

Judging by what EricMeyer says and my own personal feeling, we'll either be going to a stiffer front bar or possibly downgrading to a NC Miata rear bar.

swoope

iTrader: (5)

cool,

keep up the info..

beers

LionZoo

I received the revalved dampers today. The damping should work great with the proposed spring rates. The left and right dynos match up quite well. No pictures since they basically look like regular Bilstein HDs with a Schraeder valve on them.

Now I just need to figure out how to transport them safely from NorCal to SoCal over 400 miles of mountain roads...

c0ldf1ame

iTrader: (5)

on your stock springs!

MilesJ

Still kinda far off on my own custom, threaded perch, 2.5"ID race sprung, Bilstein shock setup but I was wondering what you thought of my proposed parts list.

OE tops and hardware F and R (thinking about upgraded bushings for the tops for the future)
Hypercoil Springs, (not settled on rates but thinking 400F 300R)
Goodwin Racing Delrin rear upper spring seats for 2.5" ID springs
Threaded perches: Nascar style (has upper and lower perches for 2.5"ID springs)or maybe FCM will make some for the NC/RX8 some day.
Hotchkis MX5 Sway bars.

Thoughts?

LionZoo

FCM should be able to provide all the adapters and perches necessary for a conversion setup. Right now I'm going to test 300/300 rates and preliminary calculations suggest that a 400/300 rate probably isn't the best way to go, but I'll need to confirm my choice when the kit is on the car. The prototype adapter machining keeps getting delayed; it's frustrating.

MilesJ

I assume you are talking about the rear upper spring perch adapters. Have you checked out Goodwin's delrin rear upper perches for 2.5"ID springs? If you are using the OE tops these look like they're the ticket for the type of springs we want to run. And they're not too expensive either. I would assume that the upper perches for the front are the same for any Bilstein shock, thus the current FCM upper perches for 99+ miatas should work right?

LionZoo

I'm actually designing new perch adapters for both the front and the rear for the RX-8 in conjunction with FCM. I've seen Goodwin's designs, but have a couple worries about them and so I'm making my own just to confirm that everything will be good.

LionZoo

After much delay the machining work on the prototype adapters have started. I need to do one more fitment test for the rears, but that'll be sorted out in the next couple days.

LionZoo

Did a rear fitment test again over the weekend with rear adapters that are bored out as much as I dare to go. The result is that the rear damper is still rubbing the adapter about 1" away from full compression. It looks like I'll have to design the rear to use a bigger spring; I'm thinking 2.75" (70mm) ID instead of 2.5", but spring selection decreases dramatically when you aren't using the 2.5". Sadly, I think that's a compromise I'm going to have to make to make sure nothing is rubbing and there is proper clearance everywhere in the suspension travel. I'm kind of torn on how to go and at this point would appreciate feedback and ideas to solve the problem of my rear adapter rubbing in the current design.

Now I know Goodwin Racing sells a rear adapter for the 2.5". I'm not sure if his rubs or not, perhaps it doesn't and perhaps it does, but it doesn't matter as he's using delrin. Regardless, my findings are showing that the rear is rubbing with Bilstein HDs and I'm not willing to accept that.

Blackroadster

You are correct. GoodWinRacing's delrin adapter does rub the Bilstein shock. I have it currently running with FCM revalved shocks right now and seeking solution to the rear rubbing problem. Brian said the rubbing was normal(hence he used delrin) and I respect him, but the rubbing has gone to a point that the yellow paints are rubbed off on my friend's setup.

my setup can be seen here http://forum.miata.net/vb/showthread.php?t=313330&highlight=fcm

I'm considering running JIC's rear coilover spring (7kg) for the rear if it fits my coilover sleeve. I need to know the ID of the spring and see if it fits at all.

I might consider machining a new adapter for the rear running 2.5" ID spring by having an outer rim guard/guide instead of inner, allowing full 2.5" bore for rear shock to pivot. I won't have time to do that till Sept the earliest, so I need to seek a temporary solution(I don't wish to go back to stock)

LionZoo

Okay, I know this thread is in dire need of an update. It might seem like I'm ignoring this thread, which might be true, but progress is still slowing moving forward.

I have six months to recap for, so here goes. The adapters work. I did a test fit and while the front needs some very small changes, everything about the concept is spot on. The rears are fine. Nonetheless, this might be a mute point as you'll see...

My spring rates and lengths were off. This necessitated sourcing new springs and hence slowed down my progress. Also in between I got laid off and so I no longer had the desire to pay through the nose for Swift springs. I have a set of Swifts now that if anyone wants they can get off of me.

Previously I was using 10" long 6 kgf/mm (336 lb/in) springs for both the front and rear. While that is pretty close in the front, the rear is far too long. I ended up switching to a 175mm long 5 kgf/mm (280 lb/in) with an 80mm long 1.6 kgf/mm tender for the rear. Tein also has a 70-90mm tapered spring that works great with the stock top hat which means that I don't need the rear adapter. The 70-90mm tapered spring will also work for the front, but I didn't discover that until recently. If using the tapered springs from Tein, adapters are no longer needed. I kept the Swifts for the fronts for now only because the Tein springs I wanted for the front are currently out of stock. I plan to go to a tapered front spring with a tender as well in the future.

So how does it all work? Well, the new rear spring combo yields a good ride height. You can lower the car a little more than an inch from stock without the springs unseating. The fronts with the old Swifts are at stock ride height and can't go any lower. I'll need to do a spring change in the front as well, but it wasn't as critical as the rears so I fitted them on and went to the track.

Right now my car is at pretty much stock ride height. The spring rate is 6 kgf/mm in the front and 5 kgf/mm with a tender for droop purposes in the rear. The tender fully collapses and under normal operations it shouldn't have any effect. However, when going through situations where you need a lot of travel like driveway ramps or big bumps, the tenders help keep the wheels on the ground in a way that short travel coilovers would not be able to.

The ride height itself is good. The car is definitely more taut, which is only to be expected considering how much stiffer than springs are compared to stock and the damping changes that are needed to control the stiffer springs. However there is never any harshness over bumps and in fact in that regard the car is actually superior to the stock combination in that regard. Nonetheless over normal bumps it is vibrating at a higher frequency than stock, but everything seems more buttoned down and controlled. The car stays flat, there is never any porpoising. I've ridden in RX-8s with the Tein Flex and the Koni/S.Tech combo at full soft and I have to say the ride quality of this setup is superior to both. The Konis especially had a jarring characteristic over certain bumps that I just didn't like.

At the track that car rides flatter and turns in quicker than stock. The delay between turn in and the car responding is completely gone. However, the car is now more oversteery than before, for good and bad. I'd say the balance has gone from slight understeer to slight oversteer at the limit. Also, whereas the stock car's rear end is practically glued to the tarmac under power, the car can now take various sets depending on your throttle position. It's very easy to gather the car back when it does start sliding though, and it communicates the slide earlier. Nonetheless, the balance is not what I want at the moment as I feel while being able to throttle steer is nice, there is a bit too much corner exit oversteer for my tastes at the moment. The car transitions much faster, but Horsethief Mile doesn't have good chicane complexes where I can really test out that characteristic.

My plan going forward is to do another bounce frequency test on the car to determine whether I should change either the sways or the springrates to take out some of the oversteer. If the frequency is in the ballpark of what I want it, then I'll be going to a bigger front sway. If the rear frequency is a bit too much higher than the fronts, I'll probably change to a 7 kgf/mm (392 lb/in) front spring (with tenders). There might also be tweaks to the rear damping. Nonetheless I'm quite pleased with the accuracy of what is essentially a first cut try. The overall product is good, it just needs some fine-tuning.

Special thanks to Shaikh at FatCatMotorsports for making this all possible. He's the one that also done all the damping work and has offered quite a bit of helpful dynamic suggestions. Also, thanks for reading this essay.

LionZoo

So based on my latest testing, it seems your 400/300 is well in the ballpark. My initial 300/300 estimate was way off and would've probably resulted in an even more oversteery car than what I have right now. My apologies for the misinformation.

bingo

subscribed

LionZoo

Dampers have been sent back to FatCat for adjustments, but before I did that I got some interesting data.

First of all, I removed the rear sway before a long run I did to test the balance without it. There was a bit of understeer, perhaps a touch more than stock, but towards the end of the run I still managed to get some (very controllable) on-throttle oversteer. I think part of the issue was tire heat though as the front tires were much warmer than the rears, due to them being worked much harder through the deletion of the rear sway. I have the non-Star Spec Sport Z1s and those tires have a reputation for requiring some heat to work optimally.

I also bounce tested the car. Now my bouncers are novices and so I'm not very confident in the numbers. Instead of counting bounces per 30 seconds, I video taped it and counted frames. The results were ~1.6 Hz for the front and ~1.75 Hz for the rear. The rears were reported to be noticeably harder to bounce than the fronts. I probably will go ahead and change to a 7/5 kg/mm F/R spring spread.

I also measured the front and rear installation ratios by hand to confirm the numbers. Through my super accurate tape measure method, I got a front installation ratio of 0.74 and a rear installation ratio of 0.85. I'd say those numbers are probably +/- 0.3.

One issue I have with pretty much every off the shelf coilover except the Mazdaspeed unit and the custom Konis is that they use the stock rear Mazda top mount. The rear top mount is horribly non-coaxial with respect to the bottom spring perch. With my 70mm springs being not fully pressed against the OD of the coilover sleeves, I'm hearing a lot of noise as the spring moves around on the perch through its travel. I'm thinking about cutting my own rubber gaskets for the bottom perch in the same vein as what Mazda does for the top perch just to prevent them from moving, but I'm wondering what's the lesser of two evils; no movement or the spring moving around through sudden snapping movements. The Mazdaspeed Eibachs of course have their own issues with durability and the Konis are full custom units.

So for now the dampers are back in NorCal. I'm probably going to bring the rear damping down a bit and bring the front up. I'll also be ordering some new Tein springs for the fronts along with the adapters.

TeamRX8

iTrader: (25)

https://www.rx8club.com/showpost.php...06&postcount=4