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Old 11-15-2018, 03:06 PM
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coil over kit

I am thinking about installing a QA1 coil over conversion kit on my 67 chevelle, there is different spring rates available as well as different length shocks, figuring out the shocks extended and compressed lengths that i need seems easy enough to determine but what about the spring rate? with the rear springs and 3 way adjustable shocks that are on it now it seems to almost bottom out when i launch hard, i am not overly concerned about ride quality since it is not a daily driver, they list the spring rates from 100 lbs up to 175 lbs per inch, with the 175 per inch it suggests a rear weight of 1500-1800 lbs, not sure if that is sprung or unsprung weight, any advice would be great,
Scotty

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Old 11-15-2018, 05:33 PM
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Coil overs bolted to stock shock mounts can be a real problem, the shock mounts are not built strong enough to actually carry the weight of the car and will crack and break.

You'd be better of to use the shock from a coil over type(or just buy a good adjustable non-coil over shock), without the spring on it....that way you can get the adjustable compression and rebound settings if you want(single or double adjustable), and then use a common stock type coil spring on the stock mount....you can get almost any rate imaginable from circle track suppliers, used in classes that won't allow coil overs.

When coil overs are used an race cars, the axle housing mounts and the frame or body mounts for the shocks are built to carry the load.

Spring rate on a Chevelle rear can range from 110 lbs/in to 300 lbs/in depending on what you are doing with it...110 would be a lightened drag car(fiberglass bumper and deck lid, no interior) to 300 lbs/in + for road race, and even more for the right side on Bomber dirt track cars.
The stock spring in an SS Chevelle would have been in the 175-300 lbs/in range.
A friend of mine has 130 lb on the rear of his '67 ElCamino drag car. Close to stock rear weight.

That 1500-1800 lbs weight figure is referring to if you drove just the rear tires onto a scale, and weighed how much is resting on the rear tires in ready to drive/race condition. That means both sprung and unsprung weight.
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Old 11-15-2018, 06:03 PM
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thanks Eric, so as of now the ride height is right where i want it so if i go to a good adjustable shock as you suggested will that allow me to keep the height where it is and still stop the rear from squatting on hard launches?
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Old 11-15-2018, 06:49 PM
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Quote:
Originally Posted by scotty57406 View Post
thanks Eric, so as of now the ride height is right where i want it so if i go to a good adjustable shock as you suggested will that allow me to keep the height where it is and still stop the rear from squatting on hard launches?
Yes, with a shock having adjustable compression settings, you can tighten the shock so that is resists compressing the suspension as fast as it does now, which should also limit how far it will compress before it recovers.

Part of the squat problem is the orientation and angles of the stock rear suspension arms....have to done anything to alleviate that??
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Old 11-16-2018, 06:15 AM
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all that i did to the rear suspension so far is box the upper and lower control arms and changed to urethane bushings in the rear and the front suspension as well, i also have air lift bags inside the rear coils.
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Old 11-16-2018, 03:07 PM
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For the stock housing and arms, I'd recommend a set of No-Hop bars....they bolt to the upper ears of the housing and raise the connection point of the upper arm to get suspension geometry that eliminates squat and uses the orque reaction to press the tires harder to the pavement...when the suspension is moving to a squat position, you actually have a big decrease in traction while it is doing the squat move.
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Old 11-17-2018, 02:37 PM
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Eric i checked out the QA1 no hop bars on the summit website, the price was a lot more reasonable than i expected it to be, it says can be used with the stock arms but sorta suggested going to the adjustable QA1 ones, with using the stock arms will the angle still be alright?
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Old 11-17-2018, 02:57 PM
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Yeah, they can still be used with stock arms, and the angles that result will be fine until you get to a real high power point that causes the increase in anti-squat gets so high that they really pound the tire into the track, getting too violent and crushing the tire sidewall down, distorting the tire contact patch. When you get into the mid 10 secong 1/4 mile roughly 600+ HP level they can then cause too hard of a hit off the line, but they work well on typical street driven cars that see some strip time and don't want huge suspension modifications.

I don't remember who first manufactured these, whether it was Competition Engineering or Genuine Suspension or maybe even Lakewood....but they were designed originally to fit stock boxed arms, aftermarket adjustable stuff didn't exist back then(40+ years ago).

The main advantage to adjustable upper arms is the ability to change the pinion angle to experiment with the best setting for your vehicle, tire size, gearing, and engine power.....more of a frequent track goer thing than a street driver thing.
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Old 02-21-2019, 02:40 PM
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i finally scraped up the cash to buy my QA1 anti hop bars, i installed them but i
definitely have to change my upper control arms, pinion angle is way out, so my game plan is to shorten my existing ones, so i did my measurements and came up with these results,
transmission yoke is -2.8*
driveshaft is -3.5* which only gives me .7* working angle
pinion will be set at +2*
driveshaft is at +3.5* which gives me a 1.5* working angle
does this sound like it should work alright?
i have not re welded my existing ones yet as i wanted to get opinions on my measurements first, thanks
scotty
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Old 02-21-2019, 05:25 PM
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Sounds right...if it is a higher powered car(500HP+) setting the pinion at just +1 might be better to allow for pinion climb.

I probably should have worded a previous post differently, the arms typically don't need modifying if the ride height is still the stock rather high SS ride height..as the car sits lower the upper arms tip the pinion more.
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Old 02-21-2019, 07:31 PM
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thanks Eric, i will set pinion angle to +1
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Old 03-13-2019, 06:17 PM
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well i cut my rear upper control arms for my 67 chevelle, got the length that i need for proper pinion angle and am ready to weld them, BUT before i do i wanted to run this scenario by you experienced suspension guys, ever since i have had the car, 30 yrs, and the few times that i have had the 12 bolt rear end out it was always a fight to get the uppers back onto the bushings on the rear end, it was easy to get them into the frame without problem but they had to be forced over with a prybar to get them close enough to go over the ones on the rear, then it seamed that they were binding and not moving freely, the problem was compounded with the urethane bushings since they are a lot stiffer than the old rubber ones, Question, can i weld them offset the amount needed so that they fit properly and without binding, when looking at QA1 adjustable ones they have a swivel end to compensate for such misalignment, any thoughts ?
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Old 03-13-2019, 10:34 PM
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Yeah, definitely you can change the angle of the end to make it fit better. Doing it will only make the suspension work better. Any binding is not a desirable thing.

By chance, was this originally a 10-bolt rear car and has had the 12-bolt swapped in?? I know there are slight differences in the arms, and GM used to catalog about 12 or 13 different upper arms across the various divisions A-body's depending on year, rear axle used, and brand(Chev, Pontiac, Buick, Olds)
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Old 03-14-2019, 06:16 AM
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Hi Eric, yeah it was a 10 bolt car, the rear came out of a 68 GTO,
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