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So i broke down and bought a set of QA1 front coilovers with the 450# spring rate. There isnt any other threads that i can find relating to my inquire other than one from 2018 that mentions rates, but the answer is to vague to make a judgement call. Is 450# sufficient for a stock 400 with PS/AC (vintage air) or should i request the 500/550 variant?

 

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So i broke down and bought a set of QA1 front coilovers with the 450# spring rate. There isnt any other threads that i can find relating to my inquire other than one from 2018 that mentions rates, but the answer is to vague to make a judgement call. Is 450# sufficient for a stock 400 with PS/AC (vintage air) or should i request the 500/550 variant?

Hmmm, may ride a little stiff unless you can adjust them? 450# is more in line with the 1970 454 Chevelle spring rates if I am correct.

Factory GTO front's 305# per in. and rear 122# lbs per in. GTO specs are the far right - other specs for Tempest/LeMans. I don't see any mention of a heavier spring for AC.

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Jim,

Thanks for your input. Below is the link to the set I purchased, BUT may change based on others input as I'm clueless when it comes to coilover rate on a car.

OK, I am not a lot of help with suspension mods, but can wing-it. They are adjustable shocks. I think the 450 lb rating would be better than 550 as it may be too stiff - keeping in mind that sway bar size can have some bearing . However, the UMI rep at the Chevelle sight says their 530 lb fronts are OK, but a little stiff, but not uncomfortable. You have to be careful not to make things overly stiff or you will feel like riding in a car whose suspension is bolted to the frame - and why I don't like a Corvette because they handle great, but ride harsh.

When I had my '68 Lemans on the road, it still had its factory front coils. I used a taller 15" rear tire and shorter 14" in front so it pointed the nose down, was closer to the ground, and also shifts the weight more to the front. I installed a 3" exhaust system that hung a bit low. When I hit any good bump in the road, the front end did bounce and I would scrape the exhaust. I had new gas shocks, but they seemed weak. I went with a set of drag race type 90/10 shocks that they say not to use on the road - I don't listen very well. The 90/10 shocks did the trick. The car would bounce up, and then settle down very easy & slowly - which is the purpose of the 90/10, raises up easy to shift weight back on the rear tires when you mash the gas, and then settles down gently. Problem solved and there was no issue street driving. Put 20K miles on the car like that. So if you might raise the back end any to get the 70's look, then keep in mind you are shifting weight forward to the front suspension and then the higher rate springs may be better.

The Vintage Air doesn't use the real heavy factory type compressor so that is where most of your weight is along with the brackets.

Often times you can find an answer looking at the Chevelle guys who have the same year. They are basically the same as the GTO and there are more Chevelles and guys who tweak them. It seems a toss up on the 450/550 choice. I found this on the Chevelle forum:





 

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Give QA1 a call. they are super helpful, I asked this same question and the 450 is what they recommend for the street version the road race version is stiffer. He told me it would be a good ride and handle well but not be too stiff.
 

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1971 GTO resto mod. Modified 428 HO, 4 sp (built by midwest muncie) Dana 60, 3.55 rear
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Johnny,
Originally the front spring rates on my 1971 AC/PS/PB GTO were roughly ~380 # per inch rate.. Decent enough smooth ride but it was not so much a corner hugger. I upgraded several years ago to Hotchkiss 1" drop springs with a rate of about 515 # per inch..
Those put the car into a completely different driving pattern.. Felt more like a newer cornering car than an old time muscle car. I've also made other upgrades through the years like bigger front/rear sway bars and Detroit Speed upper/lower control arms with 2" drop spindle which changed the front end tire geometry and alignmen, all for a vast handling improvementt.. Hope that info helps..
 

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Discussion Starter · #8 ·
I think there's going to be some trial and error, and you may find that you need to change springs later. If you have 18" rims and lo-pro tires, then a stiff rate will make the car very twitchy and harsh... So as a guy who does a lot of GTO suspensions, I'd lean toward the softer rate.
The plan is to go with a 17in wheel combo. Not entirely keen on lo-pros on a muscle car. I picked the 450#'s. I plan on doing what Jim mentioned regarding the rake.
 

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Cameo Ivory 1967
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The plan is to go with a 17in wheel combo. Not entirely keen on lo-pros on a muscle car. I picked the 450#'s. I plan on doing what Jim mentioned regarding the rake.
Most of the old-skool guys here, want sidewall showing, on our muscle cars...

A 17" wheel will not allow you to have much meat on the tires, since you're now loosing two inches to the rim. If that's the look you're hoing for, then so be it, but IMO, if you're going with 17's, then you're in the low-pro club, already!

That creates two considerations:
  • The subjective one, aesthetics. It's your car, do as you like.
  • The Scientific one, you're car will now handle better, but be twitchy and ride harsh.
If you're not 100% sold on the low profile look, and you're looking for opinions on it, here's mine:

IT SUCKS!
 

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Discussion Starter · #11 ·
Here you go ma
Most of the old-skool guys here, want sidewall showing, on our muscle cars...

A 17" wheel will not allow you to have much meat on the tires, since you're now loosing two inches to the rim. If that's the look you're hoing for, then so be it, but IMO, if you're going with 17's, then you're in the low-pro club, already!

That creates two considerations:
  • The subjective one, aesthetics. It's your car, do as you like.
  • The Scientific one, you're car will now handle better, but be twitchy and ride harsh.
If you're not 100% sold on the low profile look, and you're looking for opinions on it, here's mine:

IT SUCKS!
There you go making sense! I've never ridden in a goat with anything other than 15s so I cannot give my opinion.

If any of you guys are at Barrett Jackson I'm here all week! There are a few beauties here
 

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If you stay on a 28 diameter tire it doesnt look to bad.

225/75R15 6.5 side wall

225/65R17 5.8 sidewall
255/55R17 5.5 inch side wall
these work on 17x8 if they fit on your car.

I use tire size for comparison.



I run 215/70R15 on Rally 2 which is 5.9 side wall in 27 in diameter
 

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Cameo Ivory 1967
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Here you go ma
There you go making sense! I've never ridden in a goat with anything other than 15s so I cannot give my opinion.

If any of you guys are at Barrett Jackson I'm here all week! There are a few beauties here
Hard to argue the point, since many of my best buddies here, run low profile tires... but I own a 60's muscle car, because I want to look like a 60's muscle car. Big fat tires, dual exhaust, and a hood scoop!
 

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Discussion Starter · #14 ·
If you stay on a 28 diameter tire it doesnt look to bad.

225/75R15 6.5 side wall

225/65R17 5.8 sidewall
255/55R17 5.5 inch side wall
these work on 17x8 if they fit on your car.

I use tire size for comparison.



I run 215/70R15 on Rally 2 which is 5.9 side wall in 27 in diameter
Thank you---the plan is to go 15x8 rear and 15x7 front.
 
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