Trying to help a friend. He had a shop do a lot of work on his car; 71 Cutlass Supreme SX Convertible, 455 TH400, 265/40 18 on front and 275/40 18 rear. Has unknown tubular front upper and lower control arms, Moog 5450 front springs and Moog CC501 rear springs, KYB shocks front and rear; KG4513 & KG5504. Car Sits too high and rides like a truck! 11" 1 inch behind door pillar and 11 1/2" 3 inches before rear wheel opening. I would like some input please, before trying several different springs to get it right. Car does have headers. Right not there is 6 1/4" ground clearance at headers. I have been reading some of the other threads, but gets confusing. Figured I would start a new thread.
Thank you all so much for help in this matter.

 

Car was factory air but all components were removed and now has Vintage air installed. All suspension components have been in for a few years.

 

The rear tire diameter is a bit small at 26.6" diameter vs the 28" that most of us run. Can't help on the front springs because you're using aftermarket control arms, but I put a link below to search and compare spring specs, it can be sorted in multiple ways by column.
Moog Coil Springs | Moog Suspension Parts (moog-suspension-parts.com)

As far as riding like a truck, the low profile tires will cause that.

 

Are the springs indexed correctly? Only asking because I just went through this on my '69. Nose high, and super stiff.

 

As said the aftermarket control arms may change things, but look at the Suspension sticky to see what others are using. Most are like me with factory control arms.

 

I don't know if they are indexed correctly, I'll have to look and see. I didn't put them in. It is hard to see in the bottom of the tubular arms. It would make sense if they are not. Front is very stiff.

 

Look up the specs for those springs. From what I recall, they are not overly stiff. My car has 5536 that are advertised as 488 lbs/in whereas the 5450 are 454 lbs/in and my car rides very similar to when it had 40+ year old worn out springs. Much firmer handling but still comfortable ride.Not stiff or uncomfortable at all.

 

I just started shopping for new front springs for my 66 442. On Eaton site they have “standard” and “heavy duty” versions…maybe they put heavy duty versions in?

I’m going with Eaton standard….hopefully those workout. On those Moog springs…do you know which model number is standard spring rate for 1966.

 

Ride height similar to 40 year old car right? Not “feel” of 40 year old springs?
I want that.

 

Correct, similar ride height due to the shorter 5536 springs, but firmer handling due to the stiffer spring rate. Firmer but still comfortable.

 

It looks like the body is sitting really high on the frame in this photo. Could just be the angle. Did the shop replace the rubber body mounts with solid mounts? There are companies that sell solid aluminum mounts like the ones seen below. If these or something similar were used, you will get a lot more "road feel" as there is no isolation between the body and the frame. This could be a cause of your freind's problem along with changes in the suspension and tires.

 

I don't know if this helps but I have a '72 ragtop with Vintage Air - it's a 350 / TH350 which was somewhat further lightened by use of an Edelbrock aluminum manifold in place of the factory cast iron - it's riding on factory control arms up front with Moog 5536. I'm running 245-50-R17 tires on 17x8 American Racing Torq Thrusts (4.5" backspace) all around.

I've tried a few different rear spring sets, currently 5379 in the back which basically levels the car just about even with the front 5536 springs. You might also want to look at the Moog 5385 springs as a companion to the 5536 up front (or as another potential index to where you want the car height to be so that you can determine if something else up front is needed for a better match.

Keep in mind there are a number of older Moog spring part numbers that are no longer made (you can google older threads to pick up some of that info) Point to this is a company named Mevotech makes a line of coil springs off the Moog specs, to include several that Moog no longer makes. So if you find an older spring set of interest that Moog no longer makes, Mevotech probably does. Summit, Amazon and others carry them.

 

Those tires actually aren't terribly undersized. The rears are 26.6" OD, the fronts only slightly smaller at 26.3". That's not very different from the OEM tire diameters. The car rides like a truck because your 4" sidewalls don't absorb any road shock the way the 6" sidewalls on the OEM tires would have. It's kinda the problem with bigger wheel diameters. The car is definitely high, but you should verify ride height using the factory measuring points at the rocker per the Chassis Service Manual. Look into spring installation, especially where the upper end of the front springs fit into the spring pocket in the frame, This is a blind installation and it's really easy to get the spring off center, which causes it to sit on the locating feature instead of around it. This causes at least an inch increase in ride height. Also, did the control arm bolts to the frame get torqued at ride height or with the control arms hanging down while the car was on a lift. The latter will also cause excessive ride height.