Coil Overs

How to convert your stock springs to coil over springs

Above is a suspension upgrade I performed on my C4. The shocks are HAL-Ds401 QA1's with 375 pound spring rate 10 inch springs. To allow for the lowering of the car about 2 inches it required that I move the sway bar forward about 7/8 of an inch. For most I suggest 350 -400 pound springs. Due to the angle of the springs and shocks the actual spring rate is only about .66 times the spring pounds per inch. (375 * .66 = 247 lbs/in.).

UPDATE---- I relocated the sway bar back in it's original position and picked up these Helms joints from Exotic Muscle, they were about $220...

This is an image of the rear shock, they are using the ds-401 QA1 shock with coil over springs. The picture shows a 300 pound Spring rate 10 inch spring. I suggest 300-350 for the rears. The spring rate at the wheel is about .95 ( 300 * .95 = ~285 lbs/in.). The top of the shock mount is from Van Steel, these are very nice adapters and only took minutes to install them onto the shocks. the half shafts totally clear the springs when the wheel is fully in a "bump" position. 

This is my current setup the part numbers are from Summit Racing:

Qty Part number desc.
(2) QA1-10CS300 300# springs (rear)
(4) QA1-SS110SDM Studs for top of all 4 shocks
(2) QA1-DS 303 shocks (front)

(2) QA1-DS 401 shocks (rear)
(2) QA1-BAR350K T-Bars for front bottom shock mounts
(2) QA1-10CS375 375# springs (front)
(1) QA1-T114W spring adjustment tool
My best ride was with the front springs at 350 to 400 and rear at 300 - 350 these are pretty much the minimum  I suggest going. Anything less you will be riding the rubber snubs. The ride height is adjusted for 27" in the front and 27 3/4" in the rear with a full tank of fuel. This is measured from the ground to the center of the fender wells, both front and rear. Lower than 26.5 in the front the steering gets very stiff and it seems like the tie rods start to bind in the rack , this would probably require buying the zero bump steer tie rod ends. In the rear as you drop the car the shocks start to lean towards the back getting closer to the half shafts, the car will only ride about an inch above the rubber bumpers when set that low.

I used the van steel lower rear shock mounts. The shocks require the metal bearing inserts to fit inti the top and bottom adapters. For those concerned about how they hold up; to date I have over 15,000 miles driving on some of the worst roads in the country, everything has held together great.

these are the van steel top front shock and the upper rear shock mounts, these are very robust and very high quality shock mounts.

Rough measurements show that at 26.75" inches in the front, the shock length is about 12.5 inches. The Ds401 is from 10.1 to 14.0 inches so it looks like there is still 2 inches of shock travel, since the wheel moves about 3 inches to 1 inch of shock travel.