Josh18_2k

iTrader: (3)

I picked up a used double adj Koni setup over a year ago with the intent of dialing the car to my liking, dyno'ing the shocks, and then building Bilsteins to match (since theyre much cheaper). This didn't really pan out as I had hoped. Turns out I pretty much suck at tuning by the seat of the pants, not to mention its extremely difficult to positively identify changes when the race itself is constantly changing (autox is anything but repeatable). Tire wear seemed to change the car faster than my shock tuning process. I spent all of last season just playing with rear rebound. While pondering how long it would take to get all 4 adjustments dialed, an opportunity came up- some guy with a seriously competitive STS RX7 offered me 2k for my setup, so the Konis went by by.

In the meantime I had learned as much as I could about damping. Probably the single most informative website is this guy- http://farnorthracing.com/autocross_secrets19.html
He's not technically an expert, but he is a data aquisition nerd so has a lot of good stuff to say. Between his writings and a lot of FSAE/racecar related reading on suspension, here's what I've gathered:

For rebound, you want a damping ratio somewhere between .5-.75 Anywhere in that range will sufficiently damp body movement, and the spectrum ranges from better grip (soft) to better body control (hard). any softer, you get too much movement (wobbling?), stiffer makes for a more responsive chassis at the expense of grip. Damping ratio = 2*sqrt(M*K) where M = sprung weight of the car and K = spring rate (taking into account motion ratio, all units have to match, blah blah))

While rebound is straitforward, I still havnt figure out the best way to calculate ideal compression- this seems to be the real black art. From what I can tell, it comes from a more complicated 2 degree of freedom system involving both sprung and unsprung masses, as well as tire and chassis sprung rates. Generally, more compression = more grip, but feels worse when you hit a bump. From my experiance, I believe the harshness associated with coilovers has more to do with poor design than the actual valving.
Most cheap coilovers have too little compression (attempt to keep the car somewhat comfortable) and too much rebound (makes it feel like its on rails). Looking at dynos of real race shocks, you'll see the opposite.

Anywho enough of that crap. If there are questions, ask away. I have strut bracket drawings if anyone wants to replicate them.

Josh18_2k

iTrader: (3)

FRONT

Nissanroadracing.com has been a great source of info for Bilstein/Koni setups. Someone a long time ago discovered 3000GT inserts are valved appropriately for lighter/stiffer cars, and several people have used them successfully. They also happen to be the right size. I picked up a set, and designed my strut housings around them. I had Ground Control make me a set of camber/caster plates to match, since the Bilsteins use a unique diameter pillowball up top.
I designed the housings based of my Koni setup, modifying them a bit for more camber and better wheel clearance. Basically, I pushed the strut in as close to the swaybar endlink as I felt comfortable. I ended up with an available 4* of camber, and a little but more room on the inside. I cant compare tire clearance with this setup to any common coilover unfortunately, since my Koni housings were also custom.

Struts: Bilstein B36-5022-H0 ($100 each)
heres a site with insert measurements http://ryanizer.blogspot.com/2008/07...-for-s14s.html

Housings: Made by a friend from 4130 Stainless. I dunno what thickness the tubes or strut plates are, but he makes a ton of custom struts so I'm assuming they're fine. I paid $150 for the pair, powdercoating included.

Picked up a pile of used coilover sleeves/collars on ebay from some circle track team for $40. There were about 5 usable sleeves in teh mix, so that's plenty.

Pair of 8" long 600# used Eibach springs for $60 shipped.

Ground control plates were $300 plus shipping. I sent them a drawing of the top of the strut and they modified the plates to fit free of charge. I highly recommend these. They are the only plates that I'm aware of that actually allow the strut to articulate properly. They have a specially designed torrington bearing seated in a spherical top hat thingy. Simply put, they're the best.

Total cost = ~$750

REAR

This is where it gets tricky. Bilstein makes FC rear shocks, but they're too long (for me anyway). Bilstein does cheap revalving, but pretty much everyone complains about their valving. If you spec it out to them, its no prob, but I didnt want to rely on myself here. While on the phone with Bilstein attempting to find a good 'valver,' the guy referred me to Dick Myers. A little googling revealed he's a Chrysler engineer, and headed the factory Viper GTS-R race program. And now runs a small shop that build Bilsteins. Perfect! Gave Dick a call (http://ramengineeringmidwest.com/). Super nice guy, spent over 30min on the phone with me asking about my car and driving and whatnot. Unfortunately, he only builds "take apart" shocks, and by this time I was getting frantic (car had been down for tooo long). So I did my measuring and ordered a pair of 6" stroke SN's http://ramengineeringmidwest.com/ind...id=4&Itemid=38 ($250 each with coilover kit). Dick valved them for free, so that made it worthwhile IMO.
Now I had to figure out how to attach a 1/2" rodend NASCAR shock to my car lol. Turns out its pretty easy.

The FC's rear lower shock mount is a 20mm stud with a 12mm bolt. 12 is pretty close to 1/2"... I took a 1/2" OD nylon spacer (to properly center the rodend over the bolt), drilled and tapped the inside to 12x1.5, screwed it onto a Grade 12.9 cap screw, and there you have it.
By big concern of course was "Is a 12mm bolt strong enough to hold up a car in single sheer?" To be honest, I'm not totally sure. I did the maths a while ago. I don't remember my exact number, but a 12.9 12mm bolt in pure sheer, based on 9.1mm root diameter, should take something like 9k lbs to break. On top of that, the bolt is torqued to 90ft.lbs, so there is an additional clamping force between the shock and the stud. The total load ability of the bolt should be plenty, but a bigass hit to the wheel might still break it. Guess time will tell.. If it does break, the car will just drop onto the tire, so the worst that will happen is I'll probably mess up the tire a bit. And maybe crash lol.

For the top, I bought a pair of 1/2" mounts off ebay for $12 shipped, had my strut housing buddy cut upper plates out of 3/8" aluminum plate, and then just bolted the shock mounts to the plates. easy peasy.

I reused my 7k (400#) springs for the rear.

Total cost = ~$550

Josh18_2k

iTrader: (3)

Now onto the valving, since thats what counts. This is pretty much my baseline get-the-car-going setup, and fuure revalves will be cheap. thats the beauty of bilsteins In fact, I can convert them to single or double adjustable if I want, just gotta buy the shafts/canisters. Theres the big downside to Konis- you pay out the *** for revalves, and they're not nearly as reliable.

I decided to leave the fronts on OEM valving, mainly to keep initial cost down, and also because everyone seems to like them as is. I took them to my local shock dyno anyway just to have a look.



Unfortunately I didn't get a dyno for the rears (he doesnt have his dyno computer hooked up to any kind of transfer media apparently... no internet, printer, nothing). But he told me over the phone that they are linear, they make 28lbf at 1ips on both Comp/Reb, and at 10ips make 190C/290R. According to my damping ratio calculations, this puts rebound at .55 which is on the soft end of the spectrum. I told him my autox's were a bit rough, and I was mainly looking for maximizing grip in the rear, so this makes sense. I tried to reverse engineer his compression valving, but I still can't figure it out. I could proabbly just ask him, but It seems kinda wrong considering thats what he does for a living (you dont ask Coca Cola manufacturer what the recipe is).

And now for pics.

I wasn't able to run the rears inverted as they are designed- the spring hat is too close to the trailing arm. So they are upright




and FWIW, these go plenty low. I designed them for max tire travel. In front, the tire hits the framerail about the same time the shock hits the bumpstop (internal), and in the rear, theres about 1/2" of travel into the bumpstop before the tire bottoms out. I do have relatively tall tires, so people with much shorter tires (15's for example) may still run out of travel in the rear, in which case you'd have to run even shorter shocks. the fronts have room to go subterrainian.

Josh18_2k

iTrader: (3)

since its always cheaper the 2nd time around, the best budget option IMO is to run a simple 46mm circle track shock, valved by Bilstein to the specs you want. I just didnt know what I wanted, so I paid more. Sealed shocks can be had for <$150 valved, but then you have to add a coilover kit.

The best 6" coilover setup I've found is the B46-0205OR, which is an offroad shock designed for VW's. These are built to order at the factory tho, so Dick couldn't do it.



And now my review. I'm utterly amazed at how smooth these are!! I didn't know what to expect from the front struts. Bilsteins seem to have this harshness reputation, and they were designed for a 3kgt, and the rears are race shocks valved by a race shock builder for racing. These seriously ride about as good as stock, its unbelievable. Noticably more confortable than the Konis, and worlds beyond stance/megan/PBM/etc. This with 11/7 spring rates. Obviously the car moves when you hit a bump, its no cadillac, but theres NO harshness to speak of whatsover. I'm happy flying over railroad tracks.

I did my first autox in these a week ago at my usual location. I immediately noticed the car was more composed, and I didnt feel hardly any of the bumps I knew were there. The only time I noticed the car not just "driving along" was over a decent sized crest, but obviously anyone's gonna feel that. Unfortunately my rear tires were toast, with near new fronts, so the car didnt exactly act right. front grip seemed infinate compared to the rear, so I cant give a fair review of they car's handling charecteristics. I can say however that when the rear did step out, it was much more predicatable and easier to catch than before.

Next event will have fresh rear tires, and a bumpier surface, so we'll see how that goes.

Narfle

iTrader: (16)

Great review here. Thank you for the info.

MaczPayne

iTrader: (5)

Very interesting! Will wait for your future review on proper tires

You thinking about putting these together for others? :nudge nudge:

Josh18_2k

iTrader: (3)

not really any point in me trying to sell a complete kit. i would be amazed if enough people were interested to make it worth my effort.

the guy that made my housings makes tons of housings, so I should be able to get them made for people at a little higher cost. He makes shitloads of S13 and B13 housings ATM, and I think charges ~250/pair. he's also done a pile of one-off stuff, like volvo, subaru, mustang, etc.
The housings are really easy to make tho, so its probably best to just do it yourself if possible. Unlike Konis, bilsteins dont need gland nut threads, so its just simple fab.

the rest should be easily doable by the end user. my rear shock valving should be fine for most people, so it could probably just be spec'd out to Bilstein as is on whatever shock you choose to use.

project dc2

iTrader: (2)

i'd love to 100% replicate this type of suspension setup. i've been searching through AWR and ITC rx7's to see what type of suspension they use to have a smooth suspension such as the one you speak of.

HotRodMex

iTrader: (3)

So the off-the-shelf 3KGT front Bilstiens are handling the 600lb springs ok? Or rather, exceedingly well?

Josh18_2k

iTrader: (3)

yep! whoda thunk. well, it makes sense tho. half the weight + twice the spring = same valving.

they're probably a little bit underdamped for racing, but they feel amazing on the street. definately not underdamped like a blown shock would be (bouncy). i'll most likely get them revalved down the line, i just wanted to get my car back on the road and see how they felt. and not spend more money lol

GodSquadMandrake

Josh is it really that bad to get the Koni's done? I've been seeing them for pretty cheap and then you can just get the ground control coilovers in whatever spring rate you want to slip over them. How much would it actually cost to get the Koni's done proper?

From my point of view you went to pretty extreme lengths for a really good suspension. The price is really good for what you got and I really like the creativity in your research and using 3000GT shocks. But you ended up going with something other than Bilstein for the rear anyway? Are your rear shocks twin tube?

I'm just trying to learn because you seem to know more a lot more than I do.

Josh18_2k

iTrader: (3)

my rears are Bilstein race shocks - http://www.bilsteinus.com/products/c...ble-steel.html

good konis (8610/8611) can be done up front but they're gonna cost more. same parts involved, but the insert costs 3x as much and you have to thread the housing for a gland nut.
in the rear you're stuck with yellows unless you want to make a housing for another 86xx. The 86 setups are popular with nissan guys (not drift..), and cost at least 2k to build. I'm only aware of one guy running the exact same setup as me, in a dedicated autox car.
I sold my used 8611/DA Yellow setup for 2k without springs.

I went Bilsteins for several reasons - cheaper initial cost, cheaper to revalve (anyone can do it, Konis can only be serviced at authorized locations), more reliable (people blow konis all the time), monotube. only downside really is they're not adjustable, which really isnt a big deal if theyre valved right.

I had 8611/yellow setup before this, and I like these better so far (more comfy despite more spring).

I wouldn't call this extreme lengths really. Its just more work with less money. There really is no off-the-shelf good suspension for FCs, so we gotta get custom.

Also, it should be known that Yellows are not race shocks. Their internals are pretty different from 86's or Konis higher end stuff. The guy that bought my old setup was on GC revalved yellows, and seems to like the 86's a lot better.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/john-vs-sts-gtus-build-thread-871641/page19/

frijolee

iTrader: (1)

Yo Josh,

Nice work and many a thank you for posting up your findings. I give props to anyone who's out pushing the development envelope via science and logic.

I have to say that your lower rear mounting makes me pretty nervous. The bending moment of intertia for a circular shapes is Pi*r^4/4... Roughly eyeballing, the OEM mount looks like it's give or take double the diameter of the 12 mm bolt. That means it's 15 times stronger than the bolt for a given area (2^4=16 less 1 for the center section). Yes, the tensile strength of a 12.9 bolt is going to be high, but not high enough to cover the spread due to geometry. Obviously the shock was designed to work with this size hardware but I'm guessing it would normally be run in dual sheer instead of single. Any way to check that with the manufacturer?

The problem is that we don't know if you're compromising fatigue life and you already pointed out that if it lets go you trash a rear tire and likely lose control (and what happens next is up to the Engineer in the sky).

Just curious, have you measured bump steer in your car? We're both running quite a bit of tire while being pretty low slung and I'm curious if there are any improvements to be had in the suspension geometry area.

Josh18_2k

iTrader: (3)

Ya I'm pretty unsure about my rear mounting, I was kinda hoping you'd chime in lol.
The stud is 20mm OD, and the 12mm hole is only as deep as the stud is long. I dont know what it looks like once it enters the control arm. In regard to bending, I would assume its failure point would be at the root of the hidden threads.

The 12mm bolt shouldnt be in any bending, just sheer. Its torqued to 90ft.lb, sandwiching the bearing againts the stud, but I know the clamping force alone isnt enough to hold the car. I'm just hoping the sheer strength of the bolt + the clamping force friction will do the trick.

I didn't think fatigue would be much of an issue. its not a reversed load, and the I imagine the stud's SF is pretty high (for OEM mounting). I'm not certain, but I think a lot of ITS teams mount rear shocks the same way. I know ISC uses 914 rears with an adapter stud, but I'm not sure if the stud replaces the OEM one, or just screws into the end of it (never seen a pic).

I asked the shock builder if its OK to mount in single sheer, and he said people do it all the time, but it occured to me later on that most circle track guys dont use coilovers.
If you could to do some proper calcs it would be much appreciated. I'm still just a student, so no real world intuition lol

I havn't checked bumpsteer. I'm lazy! Is there even a way to fix it? I'm gonna build front roll center correction this summer as well, paired with SPL S13 tie rod ends. The 240 guys say it transforms the car, so it seems worth a try.

Josh18_2k

iTrader: (3)

ookay lemme know if i screwd this up..
12.9 M12x1.5:
Yield strength = 1100MPa
Sheer strength = 0.6*Yield = 660MPa
Root diameter = 9.93mm
Area = 7.74x10^-5 m^2

Sheer Force = 51.1kN = 11,490 lbf + clamping force (dunno how to calculate that)

What I don't know (remember) is if sheer+tensile combine for a resultant strength, or if they're independant. My machine design teacher was the worst teacher I've had, in probably the most important class. I was frustrated to say the least.

frijolee

iTrader: (1)

I prefer math over intuition myself. Let me grab a text book and get back to you. The one I want isn't handy. The short version is that both bending (for any newbies, this means compressive stress on one side and tensile on the other) and shear matter. We need to figure out the resultant principle stress and evaluate fatigue with notch factors for the threaded fastener. The load isn't fully reversing but it is definitely alternating so evaluation against a modified Goodman diagram is in order.

In terms of bump steer I still need to grab Prepare to Win by Carroll Smith. He talks a bit about bump steer measurement in Tune to Win (the second book in the series that I'm apparently reading out of order). Tune to Win has a lot more vehicle dynamics than pure setup and prep (the focus of Prepare). The section in Tune to Win on bump steer basically ends with "for details on adjustment read Prepare to Win as I don't want to restate myself."

That said, they're GREAT books and I've been enjoying the heck out of the read.

-Joel

PS Saw you co-posted this on norotors. I'll get back to you over there.

GodSquadMandrake

It's pretty hard to fathom getting on the level you guys are at with the math and tuning. I want to tune my car to be fast. But I dunno. I get spring rates and custom valving and that it's necessary but I just don't know how to do it myself.

Josh18_2k

iTrader: (3)

SCCA Autox today. My driving was subpar as usual lol, but the car was great! I'm loving these shocks so far. I finally beat my rival in XP- 1,795# 320whp STi powered 914. I'm pretty sure hes having some setup issues, but whatever i'll take it. last year he stomped me constantly with his 220whp flat 6.

Took 5th overall, 1st in XP (out of 4). All drivers above me are multi-time national champs (NW has quite a few of those). FTOD was a SS Z06 somehow.. miracles in that run, i dunno. He raped pax and raw.

My driving always goes to **** over the winter, I could have definately gone faster. Gotta tighten the nut behind the wheel. Looking forward to this season :-)

I always wonder what I could accomplish on new hoosiers, instead of old V710 takeoffs lol

GodSquadMandrake

Hmm what would happen if you dropped %10 off your time? That's probably what you'll get from the hoosier.

j9fd3s

iTrader: (3)

my friend had a car on koni's and the ride, even with big springs is unbelievable. its such a surprise. i actually have a low mileage stock FC too.

87TIIFC

iTrader: (2)

thank you for helping the FC community get some quality suspension. i bought my stance GR+ pros 2 years ago thinking it would make the car faster only to find that sticky street tires made a much bigger improvement, so i knew my suspension was at fault. im subscribed to this thread so that if anything happens i know, once my stances blow im gonna see if i can do what you did, reuse my springs and see what hardware i can use from the stances. if you can get pricing for the hardware and labor neccesary to do this can you post it? my college student budget makes my car a really slow build...

jkstill

iTrader: (11)

I will attest to how much Josh's car has improved in the past year.
Last year I could usually beat him by a bit in an autox.

This year his car is putting down the power so well I now have to figure out how to catch up again.

This last weekend I got to watch both him and his codriver exit from a short sweeper, and it was quite impressive how composed the car was in the corner exit with a lot of power applied.

eage8

iTrader: (9)

Thought I'd bump this and add to it a bit after making a similair set myself...

First the 3kgt bilsteins have gone up in price a good bit. I found a set for $130 each, but they're probably more like $150-160 each now.

it was interesting getting the GC camber plates to fit on the R36-5022 bilsteins. Here is my final setup:


the 2 bottom spacers have a 15mm ID and the top one is 14mm ID (there is a blank 15mm stud that turns into an M14 threaded stud... and you need a lot of space for the upper spring perch.)

finished front strut:


for my rears I used AWR custom rear bilsteins with remote reservoirs. these are the same units AWR and mazdatrix run/ran on their EP cars... I somehow forgot to take a picture... but they look like this but the newer ones have stainless steel braided lines instead of rubber:


and he also makes custom studs to help wtih the 1/2" mounting hole:


The price of these went up too (bilstein increased prices on everything) so they ended up being $320 each + $45 each for the bilstein mounting studs.


I had my first auto-x of the season last weekend and they felt great. I don't miss the adjustability at all. the only problem I had was that the rear dampers are actually really short. I have them as high up as they'll go without preloading the spring and it's just about perfect, but I can't fit a tender spring on their like I had planned.

Josh18_2k

iTrader: (3)

let me know what your camber range is on that setup, it would be nice to verify the plate design (since its been so long and i dont really remember what i did lol)

err, i suppose the roll center kit might affect that a bit, if its the same length as stock. still would be good to know though.

eage8

iTrader: (9)

Right now I'm running -3.5* up front on both sides. one side is more or less maxed out, the other has a bit of room. that is with caster as high as I could get it (I only have 1 bolt in the back of the camber plate and it's in the middle of the strut tower circle)

the roll center kit probably takes a bit of camber out due to the angle of the stud...

I'm glad I went with the more aggressive of the 2 ear drawings