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Thread: Which Rear springs for c4 IRS
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01-12-2007 #1
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Which Rear springs for c4 IRS
I have a 1968 fire bird convertible and am installing a wayne due c4 kit with dana 36 IRS.I need to purchase the coil overs (Dr5855B) and springs (2.5 ID12 I believe) for the rear. However there appears to be springs ranging from 80#'s to 600#'s . How do I decide which spring? Any help would be appreciated.
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01-12-2007 #2
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somewhere between 120 for stock ride, and 175 for performance, that's the rate leaf springs for your car use. But because you don't get any anti-squat with independent rear suspension, maybe a bit higher rate is needed.
Just a rough guess, so don't hold me to it.
DavidDavid Pozzi http://www.pozziracing.com67 Camaro RS that will be faster than anything Mary owns.
01-12-2007 #3
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We installed 550's on ilovefirstgen's 68 coupe. They were 10" tall, I think. That should be close to what you may need, but that also depends on what front springs you're running.
Allen Ortega
Meanstreets Performance Fabrication
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01-12-2007 #4
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i concure. Thats pretty good for an old guy...you must have one of them, what do you call it? Ahh er ponographic memories.
Due to cosine effect the rate is in fact higher...stock C4 is 600 range. im told.MrQuick ΜΟΛ'ΩΝ ΛΑΒ'Ε
01-14-2007 #5
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Running GMP14 coil overs up front with BRP modified front subframe and ls1 / t56 combo.
01-15-2007 #6
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So they were 10" and not 12"....
01-15-2007 #7
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Yes, they were 10" springs. He originally had 12" springs on there, but we couldn't lower the car to the ride height we wanted it at. It wouldn't go low enough.
Allen Ortega
Meanstreets Performance Fabrication
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Vegetarians are the reason for global warming
01-16-2007 #8
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Wait... huh? Why the big discrepancy between C4 coilover conversion spring and stock Camaro leaf spring rates? Since the coilover is attached directly to the knuckle spring rate is about equal to wheel rate depending on the angle. Leaf spring rate is equal to wheel rate so what gives? I know I am wrong here somewhere, but where?
I wish I could find that Fred Puhn "how to make your car handle" book.
Mike
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