So I just order a set of Koni yellows that I plan to "convert" to coilovers. I find it very strange that GC kit for the FD is $599 when a GC kit for a Honda is only $339! http://www.ground-control-store.com/...ion.php?II=508

What the heck is the difference?

Is their anywhere else to get such a kit? Are they $599 all over the internet? Can I order the Honda kit (only half serious) and install on the Mazda?

Also, I would prefer to run swift or hypercoil springs rather than eibachs. How do you all recommend I piece this kit together from?

What would be the ideal spring lengths if I had the ability to choose my own length?

Lastly, I am thinking of running 500 lbs/in (9kg/mm) front and 450 lbs/in (8kg/mm) rear. Can the OTS koni valving take it? I don't want to get a revalve.

-Jake

 

Don't hate on the ERS's. They really are fine.

Price difference is all supply and demand. They sell lots of Honda kits, hence they are cheap. There are probably some differences between the kits as well.

I've heard of OTS Koni's on 700lb springs (on a miata) and they held up quite well. 500/450 should be well within their range. I was planning on still using mine for the season when I go 600/500 this summer.

 

I don't know for sure, but I would tend to think that yellows are not valved equally between models and makes.

 

500/450 will be fine with the Koni's "as is". That's a common GC spring setup for the FD.

 

Yep. Search on posts by ptrhahn and crispyrx7 who use/used the Koni GC kit (as do I).

 

Alot of cars use the same part numbers though. This is why they aren't "drop-in" for everything.

 

Seems to me that the only difference across gc kits across makes would be the spring length, and collar diameter (and possibly the upper spring perch shape).

Also, I probably wouldn't be able to tell just from driving a car if it was underdamped. I hope some of these people who have done it with "no issue" are sensitive enough to shock tuning where they would be able to affirmatively sense a miss damped shock if it were present.

 

I know I would. Its pretty easy to tell that you are "under damped" when you feel it. Difficult to explain though...

 

You want to be underdamped to a point... overdamping is slowing down the reaction time of the chassis.

 

By definition the point you are referring to would be "properly damped". Softer than ideal (or what you want) would be underdamped.

 

^what he said. You want the dampeners (aka shocks) valved to be able to control the springs and their rate of movement (compress/uncompress).

 

See how the higher damping ratios slow down the rise time to steady state? You want the system to be slightly underdamped (I recall reading .6 as the ideal value for automotive applications, but I may be a bit off). The lighter damping speeds the response at minimal penalty of overshoot. Look how much quicker the .7 ratio rises than the 1 (which is technically "proper" damping).

 

I read somewhere (autox to win , possibly) that 0.6 "critical damping" is a good rule of thumb.

So has any rx7club member ever measure the "critical damping" of Koni sa shocks with 500/450 springs in all of the shocks adjustment range?

 

I would like to piece together something a little different than you regular GC kit.

Does anyone know the dimensions of the GC sleeve designed for FD Koni Yellows? (specifically the inner/outher diameter, the length, and the thread design) Wonder if GC will sell this sleeve, lower perch, and upper perch without springs. If I know the dimensions, than maybe I can see about sourcing from a different application.

 

I doubt you'll find that kind of data here. You might have luck on some of the racing forums (NASA, SCCA) looking for data like that but I doubt it.

Do you just want different spring rates than the standard rates of the GC kit?

 

What are the standard GC rates? They are not advertised on the many vendor listings for FD FC kits. I would like to run hypercoil springs (personal preference). Also, I would like helper springs so I don't have to worry about anything raising and lowering the car.

 

I believe the default for their FD kit is 500/400 (i.e. if you don't require different rates). Could get different rates with the kit, and them sell them individually. Keep the sleeves and then purchase the springs you want. The reason for different rates as someone who already has a GC kit is not going to buy the same springs they already have.

 

Good point.

 

The GC kit uses one of a variety of universal threaded sleeves, with a Koni-specific machined spacer that sits on the regular adjustable perch e-clip, and then an FD-specific upper mount and bushing.

I'm not sure if GC has a standard set of rates, you specify, but most common is 550/450 as originally spec'd by M2 when they offered a rebadged version of the GC kit. 500/400 is a good set up too.

I'd just buy the GC rather than trying to reinvent the wheel to save a couple bucks. It's not worth it.

 

Sold... No seriously, thanks for the reality check. But are there any draw backs to the GC kit?

Also, back to the original question... Where is the best place to buy GC kit?

 

I think you can just get it from GC... that's all anyone else will do. I can't think of any real "drawbacks" per se. It's a pretty tried and true budget solution.

 

Do the springs get all loose off the upper mount when the car is jacked up in the air?

Also, has anyone ever had the sleeves move, slip, or go off angle relative to the shock body?

 

if you're willing to generalize the weight on a corner, you could actually compare for critical damping pretty easily if someone knew the damping coefficient of each click of a particular shock absorber.

unfortunately i don't know how to solve for damping coefficient off the scant info we have for any particular shock. in college, we only solved for it experimentally. and based on how non-uniform shocks are, you'd probably have to put one on a dyno to get an accurate value for the coefficient to make a good comparison anyway. that's a bit overkill for an off the shelf solution.

 

Honestly, on jack stands yes, but who cares? You'll never have the car in the air long enough in driving conditions for that to happen, or if you do you've got bigger problems. FWIW, they'll only do that if you get the whole car up in the air, if you just jack up a whole side, the way bars won't allow enough droop to make the springs loose. Non issue.

 

Order direct from ground control. FYI If you ask nice you get 10% off.