Rear Coil Over Springs

Ralphy · #1 (**permalink**) 10-29-2009, 11:09 PM

At what point should you're springs be compressed in a static load? I'm looking at 4 total inches of travel at the shock. My best guess is in percentages about 40%. So a 10 inch spring should be at app. 8.4 inches minus. Compressing 1.6 inches. I'm guessing less then 50%? Or maybe I should be at 50%?

Any help would be appreciated.

Ralphy

RICK LAKE · #2 (**permalink**) 10-30-2009, 02:56 AM

Ralphy You need to figure out the angles of the shock in the car. This will change the spring rates. What rearend are you running, Jag, 8.8, 9"? What is the weight on the motor? Is your motor all iron or all Aluminum or partial aluminum upper end? A 200 pound differents in motor alone. With out this info a guestamate is the best I can do. You want the front to back weight ratio of 48/52% with your body weight in the seat. 12" springs for the front with a 325-350 spring rate. A good set of QA1 shocks all the way around. 7/8-1" front sway bar. This will be a starting point. You really need the car togeather with everything in it, then look at the stance and start measuring. There is a different between 2 shocks and 4 shocks for the rearend of the car for spring rates. Sears sells an electric angle meter, this will tell you the "%" increase of spring rate to off set the angle of the shock. High the angle the more spring rate to holdup and control the car. There are 2 good suspension books to look at Herb Adams, Chassis Engineering and Don Alexander's High performance handling. Rick L.

Ralphy · #3 (**permalink**) 10-30-2009, 05:03 AM

Rick,
Not asking about spring rates. I have a fairly good idea as to what it should be. Please read my question again. I asked where the spring should be compressed to? There is another thread about springs unloading because the shock has more travel then the spring. As to my situation the angle is pretty much 0 degrees with the spring in front of the axle. Which will increase the lb's needed. I am maybe going to try and copy something I have found. I am running a Corvette C3 rear. The package they sell comes with 600 pound springs. Shocks would be QA1 dual adjustable.

I have a pic of a suspension at my page, yellow paint, red Wilwood.

http://www.summitracing.com/parts/HAL-DDR4855P/

scottj · #4 (**permalink**) 10-30-2009, 05:49 AM

Ralphy,

The question you are asking is related to the spring rate, not the shock length. You want the shock in approximately the middle of its stroke at ride height. That will determine your shock length and it is independent of the amount the spring is compressed at ride height.

Scott

Ralphy · #5 (**permalink**) 10-30-2009, 05:57 AM

Exactly, the shock is at center. Should the spring also be centered, less then centered or more then centered? When the suspension drops also the shock I'm sure should not bottom out. Just trying to find out if there is an ideal position of the spring?

Ralphy

bkozlow · #6 (**permalink**) 10-30-2009, 06:19 AM

Ralphy,

Where did you come up with 600 lbs.? That seem extreme to me for your setup. I run C-4 setups on the same chasis and the highest I have ever used in the rear was 410 lbs.

Bill K

scottj · #7 (**permalink**) 10-30-2009, 06:35 AM

The amount the spring is compressed at ride height has been determined by your spring rate. If the amount of available shock extension is greater than the spring compression, the spring will be loose at full extension. You can go with a shorter shock and have a greater amount of compression vs extension, or install 0-rate take-up springs. At full extension the shocks will be topped out, in other words, the weight of the suspesion will be hanging by the shocks. Is this C3? I thought E-M only made C4 chassis??

Ralphy · #8 (**permalink**) 10-30-2009, 06:38 AM

Bill,
Ok, this kit sold is a Corvette kit designed for a Vette. I am not saying I am looking to run a 600 lbs spring. The kit comes with 600 lbs. spring. This is why I am asking the question, my guess is I am needing somewhere between 400 to 500. The package is $1,600.00 plus. I have located the shocks and springs for about $650.00. I am a machinist and I work with about 30 aircraft certified welders. We have the ability to do! Looking to maybe save a grand.

63-82 Rear Coilover Conversion Kit - Big Block - Double Adj Shocks

* Offset Trailing Arms w/Poly Bushings - Powder Coated Black
* QA1 Double Adjustable Shocks
* 600# Hyperco Coil Springs
* 2 Upper Reinforcement Brackets
* Eliminates Rear Leaf Spring
* Spanner Wrenches
http://www.vansteel.com/index.cfm?fu...p=1971&ID=3176

Ralphy · #9 (**permalink**) 10-30-2009, 06:44 AM

Scott,
EM was not the only builder of EM's. I was just told this by EM. EM sold kits to other local companies that built and sold. I was told there were two in FLA. You can find EM's with 9" fords. I have seen more than one on the net. My understanding is that the new version is using T Bird rears.

Ralphy · #10 (**permalink**) 10-30-2009, 06:47 AM

Bill where are your shocks located? The C3 is forward of the half shafts. The further forward they move the greater the spring rate. Thinking yours are the same, yes?

Ralphy