Coil Over Spring Rates

[duke]

Received my tires and wheels yesterday and took the Cobra off the jack stands. Even after turning the adjustment up as far as possible I can't get the front to a reasonable height. Oil pan is only 1" off the ground. Rear springs seem to strong and front to weak? Big Block engine, B&B 9" rear and tubular front, same OD tires as B&B rec's. Does anyone have a spring rate recommendation for running with a big block?

[Clois Harlan]

I am running 600 # springs on my coilovers with my B&B Carrera Coil overs. You may only get about 3 1/2" of clearance but that will be plenty. In seven years I have never hit anything on the highway or on occassion off the track. Just be careful with speed bumps at the shopping centers.


Clois

[JCoop]

Wow! 600lbs? I have 450# 12" on the rear and 475# 10" in front over QA1 adjustables and I thought they were too stiff. I have ordered a pair of 12" 175/350 progressive rate springs for the rear to test out as I've heard good things about them... We'll see...

[Clois Harlan]

Ray,

My street springs are only 500# front.

[JCoop]

I just installed a pair of 175/350 QA1 progressive springs in the rear. The ride is incredibly smooth. It required a lot of preload, however, in order to get the ride height up to the recommended 26.5" (fender lip to ground). I suspect I'll get some bottoming out in the big bumps. I think a 250/400 would be ideal.

[601HP]

duke,
I've gone through something similar to you, but after reading your statement, there are some things to consider before deciding on spring rate/s. Because I didn't follow steps 1 thru 4 as listed below, until recently, my collection of springs looks like I have a spring warehouse.

To separate the wheat from the chaff, find out the following:

1. Have you determined your desired ride height, front and rear?
2. Are your shocks the proper length for the desired ride height?
3. Are your springs properly matched to the length of the shocks?
4. And finally, what level of ride firmness are you looking for?

After you determine ride height, measure the distance between the center-lines of the shock mounting holes. Then go to a website such as this one http://www.carrerashocks.com/pdf_files/street_rods.pdf, and look for your proper shock. Shock compression and extension length is very important. Sites such as the one shown, also recommend a specific length coil for the selected shock.

Hope this helps.

David

[duke]

Thanks for the info. I found the Carrera technical paper last week and went through the calculations. I also bought a whole range of springs to try. A few other members sent me emails for much appreciated guidance.

I set the ride height and ground clearance, checked shock range, and then tried springs till they fit. Page 15 was a lot of help:

front weights:
Spring 1150 to 1324 1325 to 1524 pounds
Length
8" 450# 550#
9" 350# 450#
10" 275# 350#

With the big block the standard 8" 500# spring was to short at its compressed 8" length. I could compress it to get to the ride height but you lost spring movement. I then went to a 10" 350# spring and the height was perfect. Needed to compresss it slightly to install it. There was more suspension movement which should give a better ride. I am running a heavy sway bars so a softer spring should be fine.

Part Number for the springs I used were 10MB350 which are available but not in the catalog.

There are a number of spring options for the 2-1/2" ID bottom, and 3-1/2: ID top coil to try. Seems they were used on early GM cars.

[pmfranke]

more good info and have you tried out those brakes yet?

[BeasleyRB]

You mention 26.5" fender lip to ground height as recommended. I have one side 26.5 and the other 25.5 so I have some adjusting to do. What do you guys like for the rear? 15 inch wheels 50 series tires. Mine is higher in the rear an inch or two right now.

PM - I put a seat in the car and drove it last weekend a little by my house in the country. No Hood, No Trunk lid, no lights, one seat what a blast! Just a taste of things to come! My 11 inch disc brakes were fine. Steering great as well. Neighbors commented to my wife that there was some gray haired guy running up and down the road like a kid. Yep it was me!

[pmfranke]

beasly,make sure you get the corners weights correct (ie. weight on the tires) before you mount the body so the body height can be adjusted with shims for side to side height .