coil spring rate on SB and BB
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
coil spring rate on SB and BB
I'm rebuilding the front suspension on my BB 68 convert. While the springs are out, I would like to confirm they are actually for a big block car. The engine has been switched- 454 not 427- and the car has a long style BB hood with "427" emblems. But- BB cars were supposed to have rear sway bars in 1968. Mine has none, not even the attachment points for the ends, so I do not know if the car is a BB or SB suspension. Do the coil springs have a part number or any identifying mark on them to tell which they are? I have four sets of springs for my RX-7 and they all have the spring rate stamped into the ends. With that boat anchor motor I would prefer to have the correct springs.
RA
RA
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
How does the front of the car sit? Too high? Too low? Are the springs too stiff? Too soft?
Fwiw, I have a big block and am using the small block springs. It sits where I want it too and doesn't ride too harshly.
Fwiw, I have a big block and am using the small block springs. It sits where I want it too and doesn't ride too harshly.
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
springs
bashcraft- car height and ride is OK. but I would still like to know if it is OK because the correct springs are installed or not. I suspect there is a part number somewhere on the spring under 50 years of dirt and rust. After I get some of the more pressing issues fixed on the car I will start fooling with fine-tuning the suspension. RA
Melting Slicks
Joined: Jun 2003
Posts: 2,802
Likes: 241
From: Niles, MI
The spring rates for all of the 68-71 350 coil springs are as follows:
327/350 (no AC) GM #3931823 (331316) - HS- 250 lbs/inch
327/350 (w/AC) GM #3931824 - HT------------- 264 lb/inch
427/454 (no AC) GM #3931825 (331318) - HU- 284 lb/inch
427/454 (w/AC) GM #3931826 - EA------------- 325 lb/inch
GM #3832518 (F-41)----------------------------- 550 lb/inch
These are all variable rate springs so I'm not sure if the spring rate given is for the stiff or soft end of the spring. I don't think there is any identification on the springs other than the tags which are probably long gone.
Edit: Spring rate for a variable rate spring as in other springs is for the first inch of compression so the soft end is the primary factor since it would compress more easily than the stiffer end. Hope this makes sense.
327/350 (no AC) GM #3931823 (331316) - HS- 250 lbs/inch
327/350 (w/AC) GM #3931824 - HT------------- 264 lb/inch
427/454 (no AC) GM #3931825 (331318) - HU- 284 lb/inch
427/454 (w/AC) GM #3931826 - EA------------- 325 lb/inch
GM #3832518 (F-41)----------------------------- 550 lb/inch
These are all variable rate springs so I'm not sure if the spring rate given is for the stiff or soft end of the spring. I don't think there is any identification on the springs other than the tags which are probably long gone.
Edit: Spring rate for a variable rate spring as in other springs is for the first inch of compression so the soft end is the primary factor since it would compress more easily than the stiffer end. Hope this makes sense.
Last edited by Kid Vette; Nov 18, 2015 at 12:21 AM.
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
this might sound odd but do you know any short track stock car racers? or maybe a shop that caters to short track guys? most of them change springs all the time and have a spring (rate) checker, get what you have checked then you will know what the rate is.
Last edited by redvetracr; Nov 18, 2015 at 08:42 AM.
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Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
springs
With all of the other peculiar changes on my car with multiple owners, I can't assume anything about the car, except I'm pretty sure it is a GM product.
RA
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
springs
Pop Chevy- wow, 826 lb springs. Think I'll pass. I had 550 lb springs on the front coil over setup on my RX-7 for a while. It loosened my fillings ever time I hit a bump. I now have 250 lb front and 200 lb back and it rides better, but still corners well too. Your 826 lb would be good for track or autocross, but I'm looking for a weekend driver. RA
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
springs
redvetracr- I have been trying to find someone with a spring dyno, but no luck, so far. I actually have a way to manually check with my shop press, but can't find a scale that goes high enough to measure the weight if I compress exactly one inch. RA
Melting Slicks
Joined: Jun 2003
Posts: 2,802
Likes: 241
From: Niles, MI
Pop Chevy- wow, 826 lb springs. Think I'll pass. I had 550 lb springs on the front coil over setup on my RX-7 for a while. It loosened my fillings ever time I hit a bump. I now have 250 lb front and 200 lb back and it rides better, but still corners well too. Your 826 lb would be good for track or autocross, but I'm looking for a weekend driver. RA
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
sway bar
John- I put my micrometer on it and it is 3/4 inch, so I obviously do not have a BB sway bar. What rate the springs are is anyone's guess. I planned on replacing the front bar and adding a back one anyway. I think I will also order the correct BB springs. they are only about $80 a pair.
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
John- I put my micrometer on it and it is 3/4 inch, so I obviously do not have a BB sway bar. What rate the springs are is anyone's guess. I planned on replacing the front bar and adding a back one anyway. I think I will also order the correct BB springs. they are only about $80 a pair.
I have an extra factory 1-1/8 front and a factory 9/16 (with the links & most of the mounting hardware), if you or anyone else is interested send a PM
