My next project
 

In typical Pipefather masochistic style, I have decided to inflict upon myself a new challenge: Build the ultimate DIY coilover setup for a miata.


Why?

I got tired of looking for a decent used set of miata-specific shocks and decided to build my own for 1/10 th the cost. The goal is to match the performance of high-end shocks like the Tein Flex and FM AFCO, particularly the latter, as the (claimed) suitability to road racing + street use is intriguing.

The primary ingredient is this:

http://img213.imageshack.us/img213/9897/dsc00535vw8.jpg

These are a set of non-adjustable Carrera shocks used in circle-track asphalt racing (basically a NASCAR feeder series).

They are a twin-tube design and have an aluminum threaded body. Travel is 9" front and 7" rear. Weight is 3-4 lbs each. The shock bodies are almost a perfect match for the miata (0.5" shorter than OEM in front, and 1.25" longer in back). The ends have 1/2" heims so custom mounts will be needed.

Oh, and did I mention that the shocks are revalveable at home??

The price I got them for is jaw-dropping: under $180 shipped for all four. Obviously used but that's killer anyway you look at it!

The next 3-4 months will be spent calculating and street-testing optimum spring rates, bumpstop rates, ride heights, shock valving etc. Track testing will be done next season when I prepare my car for NASA TT competition.

I am no expert on this, so I hope the gurus here can give me some food for thought. All comments/jabs welcome.

what kind of spring rates are these designed for? are perches setup for 2.5" or 2.25" springs?

Very interested in your progress. Good luck!

Thanks. I have no idea what they are originally valved for, but the guy I bought them from had 300/175L and 300/185R. I dont intend going above 300/225 if I can help it. Perches are setup for 2.5" which means there's a motherload of springs out there to choose from.

street duty first, then track - correct? Because your street spring rates will hurt you on the track IF you plan on competing seriously.

Since you're going to all the trouble, you need to work out flipped mounting (body mounts to chassis, rod mounts to control arm) so you can minimize your unsprung weight. Did you get a cheap MIG yet? ;-)

Carrera was popular way back when I started racing with the IT crowd. AAMOF a pal of mine had inverted mounted carreras (looked just like yours) on his ITA crx.

No but I got a job as vehicle test and development engineer starting september. The proto shop there has every imaginable piece of equipment you can think of. 5-axis mill, CNC lathe, press, MIG, TIG, spot welder, plasma cutter:fawk:, shear brake, you name it its there. I only need to learn how to use the welding equipment.

500th post BTW :D

Good to know they were used in road racing. Gives me some confidence. My level of seriousness with competition is more to develop myself technically, not to win the race. I want to eventually build and race my own DSR / B-Mod car.

Flipped mounting, hmmm. They're quite light already, will that make THAT much of a difference on a 2000 lb car with an already low unsprung weight? Because they have 1/2" shafts which can be easily adapted to stock upper mounts, which, IIRC, are 12 mm??

definitely interested in your progress since i don't really understand valving, fluid, damping, rebound, and how they all interact together in a practical way.

On the inverted mounting- my assumption is that the body weighs in at more than your rod. Which I'll be it does. Given your new work environment and tool set, it would practicably be irresponsible of you to NOT mount them that way IF it's the proper way to mount them for a competitive advantage. Not so much for you to win the event, but for you to fulfill your duty as a vehicle test and development engineer. :D But alas, they're your shocks and your project.

Eager to see where this goes in development... ;)

inverted mounting a twin-tube shock is a bad idea. the passages to the outer tube are usually in the bottom of the body (near the mounting point) and if you invert it, you'll have air near the passages and it will suck into the main body area and turn the oil to nasty, worthless foam.

http://static.howstuffworks.com/gif/...spension-8.gif

from: http://auto.howstuffworks.com/car-suspension2.htm

Edit: plus Pipe's shocks are aluminum. they already weigh about half what a stock shock weighs I bet.

not to mention it would probably be easier to cut off the brackets and weld on body mounts to the body of the shocks....

I have some 225 10" 2.5 diameter springs that would work very well on the rear of that setup by the way. I'll sell them cheap to get them out of my overcrowded basement. They're Suspension Spring Specialists brand.


http://www.bluecoilspring.com/

Matt

Ok, missed the twin tube part. OPM/Carrera modified the shock to work inverted- which was probably a monotube in this case. It wasn't a threaded body either, since they're illegal.

The point of inverted mounting is taking advantage of an installation at "no" (or little) additional costs for a benefit. It's the cumulation of those efforts that pay off IMO.

there may be a minor advantage but the best thing to do is to weigh both ends with the spring in place.

I recall from my Advance Design days that the aluminum shock itself was very light compared to the spring and steel NB top mount. even with oil.

y8s is right, carrera do not recommend mounting these shocks inverted. i'm thinking i'll just slap on a set of bored-out stock top mounts, shim the bottom heim down to 12 mm (control arm bolt IS 12 mm, right???) and be all set to throw them on there.

i will end up buying those off of you. give me a few weeks, i am moving to my new "life" (house in the suburbs, job, dog etc :D) so I dont have a stable address right now.

no sweat, they aren't goin nowhere.

I had a set of these on my corrado and they were awesome. I might do this in the future after you do the hard work.

why not take a stock mount and weld in something to mount at the heim joint, through the body of the car, and win at life? I really like where this is going. You could even make the heim mounting assembly off the stock mounts, and put the mount under the car, but the bodies are probably too long for that.

After riding in cars with tein and moton dampers using 550/400lb springs, if the valving is right you can be comfortable on the street. Good luck figuring that out, but you can probably steal data from FCM.

Where can you get valves?


wow, if we could figure out which valves to use, this could be really, realy cool.

edit: search on ebay for "shock body" and tons of cheap stuff comes up. I don't see why a little fab work can't save us thousands. I was trying to prepare myself to buy the Afco's or something in that caliber, but I might save a ton of cash.

Afco has cheap close-out shit too:
http://www.afabcorp.com/AFCO_Dynatec...ode=cs_springs

+1 M2CupCar...

At that price grab 2 sets!

thats exactly what i might end up doing if i cant get them on to the stock mounts (with upper heims removed of course). The rear MIGHT need a custom mount to maximize travel as the body is already 1.25" longer than stock, which is itself travel-limited.

there's several places that revalve circle track shocks. i will contact one of them with an appropriate miata-specific dyno curve and ask if they can replicate it for me.