Front springs w/ BBC - Impala Tech
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post #1 of 6 (permalink) Old 11-10-2017, 10:34 PM Thread Starter
Join Date: Nov 2017
Location: SE PA
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Front springs w/ BBC

I have a 68 impala 4 door. It originally had a 327/PG. When I bought the car it had no motor and 400 trans. I have a 396 with cast iron heads. My question is, do I need to upgrade the front springs due to difference in weight of the two motors?


1968 4 dr Impala
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post #2 of 6 (permalink) Old 11-10-2017, 11:33 PM
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Only if you want to maintain the original height.

-Parting Out over 75 '58 to '73 Full Size Chevy Cars-


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post #3 of 6 (permalink) Old 11-11-2017, 10:46 AM
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Old springs sag with age so your car is now sitting an inch and a half to two inches lower now than when it left the assembly line. Adding a BBC adds 220 pounds of cast iron over the nose. New springs would help get the car off the ground and provide for more suspension travel (allows your shocks to dampen recoil with out bottoming out). That and I would replace every front end part that wears with age (ball joints, tie rod ends, idler arms and suspension bushings). Ripping it apart to replace the springs is a good time to do that.

Big Dave
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post #4 of 6 (permalink) Old 11-20-2017, 07:59 AM
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Location: Lewisburg, Ohio
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New front springs have been a topic of discussion on several websites. I have yet to find anyone that has replaced their front springs and was satisfied. Most are too stiff and the car sits on the suspension bumpers on the frame with no travel. I myself installed new springs on my 65 convertible 396 and had to remove them and cut one coil off the bottom. I've had them installed now for several years.  69
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post #5 of 6 (permalink) Old 11-20-2017, 10:02 AM
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I replaced front and rear springs on my '63 sbc, manual transmission, non-a/c, convertible. Used Moog 658a (409 spring) in front and 6041 (wagon spring) in rear. Front is about 1/2" above stock height, and rear is raise a few inches (which is what I was seeking). Didn't cut, or trim, or adjust/modify in any way. The ride is perfect. A least one satisfied customer to report.

Suspension is stock configuration and stock drum brakes all around.
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post #6 of 6 (permalink) Old 11-20-2017, 10:43 AM
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When I ordered springs for my car I had them custom wound by Eaton spring because a BBC was not an option in my year of production (hasn't been a BBC offered in a car body since 1973 due to California emission levels even though the book carried it as an option through 1974 on the Corvette and full size).

I weighed my car and upped the spring rate to 550 inch pounds because I knew I was going to be driving my full size as if it were a sports car. I wasn't disappointed.

Car sat at factory ride height as expected and was as stiff as a lumber wagon at slow speeds. But didn't float at high speeds, and was able to turn like a slot car on curves. I also used Bilsteien custom valved shocks for the weight of the car. All of this is based upon kinetic energy being equal to one half times the mass of the vehicle times the velocity squared. As speed increases so increases exponentially the forces you have to control with your suspensions. You build a car to drive it. How you drive it determines how you have to build it (limited by your budget). If you are building a static show car then anything will work, as you slide it on and off your trailer at a slow speed.

Big Dave
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