It seems that Coilovers are always a debated topic for one reason or another. I decided to switch over to coilovers for 2 reason.
1.) The cost in reference to a new leaf spring
2.) Ride height adjustability

So Ill start with a cost breakdown, then I'll go into selection, and lastly installation

Cost Breakdown:

(2) QA1-DS304: $327.94
(2) QA1-BAR350K: $43.94
(2) EIB-08002500450: $119.94
(2) QA1-SS200SD: $33.94

Total Cost: $525.76

Cost if I kept Monoleaf and just changed shocks

(2) QA1-TS511: $297.98

So, the cost difference to go to full coilovers is: $227.78 whereas a new leaf spring is $500+. You also have the capability of changing springs for roughly $50-$60 per.

Selection:

Bilstein Factory specs:
Extended: 13.56''
Collapsed: 10.18''

Now, QA1 makes all of their custom mount shocks with eyelet ends. The problem being the factory upper mount is a stud style. They make a stud style adapter to remedy this problem but I dont like the idea of how the force is applied to that stud as the suspension goes through it's motions. To solve this I used the QA1-SS200SD which convert the eyelet into a stud mount utilizing a clevis style setup. This eliminates the rotating motion on the stud. This adapter also adds roughly 1'' to the lengths on the shock so I had to take that into factor.

As previously stated all of the coilover shocks are eyelet mount so I also had to convert the bottom to a T-bar (this maybe adds 1/8'' to total length) using kit: QA1-BAR350K

So this narrowed it down to one shock
DS 304:
Extended: 12.625 (to roughly 13.625 w/ adapter)
Collapsed: 9.5 (to roughly 10.5 w/ adapter)

At first I though the added 3/8'' of collapsed length compared to the bilstein shock would be a problem but the factory front shock qa1 sells for it has a collapsed length of 10.625 so I figured I'd be alright.

Ok, so now I have my shock selected, my adapters selected, all that is left is which spring.

Spring Selection:

I decided to look around at other kits IE DRM and Van Steel to see what rates they use. This lead me to choosing a 450 lb spring. I also took ride frequency into factor which came out to be roughly 1.93hz. So not too bad for a street/track car. I could write a huge post on all that I looked at for this but that isnt the point of this post

The best part:

Installation

I took some pictures for reference but the procedure is as follows:

1.) Jack Up Car
2.) Remove Wheels
3.) Remove original shocks
4.) Separate lower ball joint from spindle
5.) Remove (4) monoleaf mounting bolts
6.) Remove monoleaf (Its a pain!)
7.) Reinstall mounting brackets without the spring (this will makes sense when you get there)(I put the back on because the bolts go through two pieces of the car that are welded together and will hopefully help the two pieces stay together. Maybe it wont ever matter but I was already there so why not)
8.) Clearance Sway Bar Linkage
9.) Slot sway bar mounts to push forward roughly .25''
10.) Reconnect lower ball joint
11.) Install Coilover shock
12.) Put wheels back on
13.) Set ride height

That list a rather vague but it's just the general idea of what goes into it, it took me roughly 6 hours from start to finish but I was in no hurry and took my time.

You can have a thread like this without pictures!!!
I didn't go too crazy with photos, only have a few and my phone rotated them 90 degrees but you get the just of it. Also, my suspension is not not spotless haha, I try to drive it atleast once a week

Sway Bar Linkage Clearance: ( I worried about the strength of the bracket after cutting on it but, that section still has a larger cross sectional area versus factory sections so I didnt worry too much about it)



Installed!:


Installed:


At factory ride height there is about 2 inches of travel in the shock left which correlated to 6ish inches at the wheels so I'm not concerned.

If you have any questions feel free to ask here or PM me!

Thanks!
Colton

 

Great post!

 

Great information-Thanks for sharing!

 

wow great post. question: if you lower the car to say 1" lower than stock, will that affect shock travel?

 

You would lose roughly 1/3'' to 1/2'' of shock travel. I'd have to adjust and see how it changes it. You would still have quite a bit of wheel travel left.

 

What year is your c4?? I am going to do this on my 1987 C4... it seems it is the one year no one lists a coil over for.. thanks, gary

 

I think that a lack of coil overs for the early C4's is because the upper shock mounting bracket is too narrow. You would have to cut that bracket off and weld in a wider bracket to clear the upper part of the spring. The later C4's already have a upper shock mount that is wide enough.

That shouldn't be a reason to not go with coil overs, just some extra work involved.

 

if it lists for 86, i think 87 is the exact same. id go for the 86 setup.

changes were made to suspension configuration for the 88 year is my understanding.

 

It's a 94. Ive heard you can do it on the earlier years but you have to flip the coilover so that it clears the shock tower.

 

Looks great. Are you planning on doing the rear as well?

 

what yeat starts the wider upper mount? Mines an 89

 

88+ is the wider towers.

I cut my tower off and did the same with QA1's on my 85. Wont ever go back.

 

I will hopefully do the rear this weekend if time allows. I basically doubled the wheel rate in the front in comparison to the factory one. With keeping the shock on their lowest setting it rides smoother than the factory setup ever did. That being said, there is not near as much body roll going around corners. That's due to the spring rate. I can't really judge how the entire car handles since the rear spring is still the factory one. Right now there is a large gap between the wheel rate from front to rear. So I will be able to give a good writeup on the difference once the rear is on and I can drive it for a while.

Colton

 

450 lb springs are pretty light really, Im running 600 lb front coil overs with 326 lb Z51 rear leaf.

 

The highest wheel rate GM put on the front of C4's (challenge cars and z51) was 30.8 N/mm or 175lb/in. I went up to a wheel rate of 250 lb/in. I didn't want to go too high and cause the car to bounce all over the place on bumpy roads. I think I could've gone higher but it rides nice on the street. I'm going to run 300lb wheel rate on the rear. This is a pretty close ratio front to rear as the challenge cars had.

 

That is pretty light. I am on 375/400s

 

My spring rates are 450 front and 300 rear. That correlates to my wheel rate of 250 front and 300 rear

 

You might be getting too hung up on the wheel rates,
GM made the later Z51 / Z07 and R9G's with 659 lbs front and 326 lbs rear and that seemed to work !

 

The wheel rates are what really matter. I could have a 1000 lb spring but the spring is at such an angle and motion ratio that it only relates to a wheel rate of say 100 lbs. The spring rates themselves are directly comparable but a 450lb coilover doesn't equal a 450lb monoleaf because of the way the spring is mounted to the car. The wheel rate is what the tire/you experience driving down the road. That's my understanding of it haha

 

I did all the measurements and weights (including sprung and unsprung suspension)of my car, being an early c4, and took them to someone who does suspensions. His calculations (taking into account street tires/no aero, size of wheels/tires) was that the ideal coil spring rate was 550 lbs. He suggested an extra 50 lbs to compensate for a rough track.

I did a bit of research beforehand and found that most people were running 450 lb coil springs on road cars, mainly because that what was what the kit suppliers were supplying. For track cars most people were around 550 - 600 lbs (sticky street tires/no aero)

I had bought some 450 lb springs to use on the street before doing the measurements etc to decide on a track rate. I didnt tell the suspension guy what other people were using as I was interested as to what he would come up. Obviously most people are using the same mathematical formula.

The interesting thing was I then took my 450 lb springs off and replaced them with the 600 lb springs when they were made, and guess what, on the street I couldnt even tell the difference. I did have my double adjustable shocks set on soft settings, so that probably helps. It doesnt "bounce" around.

But tracking my car with 600 lb coil up front and 326 lb leaf at rear it handles well.

and yes a straight up coil is more efficient than a transverse leaf.

Are you saying that you dont want to go greater than 450 F and 300 R split because it will be too "bumpy" ? If so I think that a lot of people over a lot of years have done front / rear splits similar to mine without any issues on both street and track.