Interchanging springs

[jonnyslick]

OPG has lowering springs for g-body Monte SS's ... but none for the Cutlass.

I'm wanting to know if I could use the Monte springs on my cutlass with no issues.

 

[85 Cutlass Brougham]

They will fit the car just fine, but if the engine is lighter or heavier than a Small Block Chevy, it will alter the height of the front end. I believe an Olds 260/307 is heavier than the SBC, so it would be lower with that engine. If you have a V6, it would sit too high and not look right.

 

[jonnyslick]

It's the 307 ... I called OPG back today to see what spring rates are and the OPG drop springs lower your car 1", 2" or 3" ... but they have the factory ratings and are no stiffer that stock according to OPG (although I find that a bit odd).

Anyway it seems that's another dead end. So now I'm back to looking at Global West stuff.

 

[85 Cutlass Brougham]

My advice is don't over lower the car. It will hurt the handling because you will loose compression travel which leads to undesirable and spooky handling in the corners. If you are on the bumpstops, the spring rate becomes essentially infinite ( like welding the wheel to the body) and any irregularities in the road will cause the wheel to skip across the road surface rather than let the wheel follow the irregularity. Also, do a little more research before buying anything. I am starting to regret some of my purchases and would have taken a different route if I knew then what I know now.

 

[jonnyslick]

Good point ...

 

[Tony_SS]

I still think you would be fine with the OPG 2" drops. I run the 3" drops up front and it is in no way comparable to a stock rate. I think the guy just told you that because there wasn't a number in front of him to read to you. If you lower 2" or more, I would suggest using a Bilstein or Koni shock to be able to handle a pot hole or bump in the road.

If I had to guess, I'd say my 3" OPG drops are around 700lb rates for the front.

I have seen way too many cases where people aren't happy with the 1" drop given by GW, Eibach and Hotchkis.

Although I did see a set of Hotchkis that sat an 81 Malibu right, but he was running a 406 with heat and air. And the Hotchkis springs my Dads 70 Monte absolutely perfect..but that's not a G-body..

Or you could always try the springs 85_SS is running. His stance looks good to me.

 

[85 Cutlass Brougham]

I have the Eibach's on my car, and there is only around 1 inch between the bump stop and the frame. Now, this does not mean that you only have an inch of travel. That is determined mathematically by figuring out the motion ratio and multiplying the space between the bump stop and frame by that fraction. I have been meaning to do it, but just have not gotten around to it. Basically, you need to measure the distance from the attaching point and the ball joint in a straight line on the LCA. Then, you need to determine the distance from the pivot point to the tip of the bump stop. Divide the distance to the ball joint by the distance to the bump stop, then multiply the distance to the frame from the bump stop by this number. Since these are both describing proportional triangles, you can use the proportional relationship of one side to determine another.

 

[Tony_SS]

Here's a set of Hotchkis springs set my Dad 70 Monte. The front end has since settled about .75 of an inch, plus its a 454 so there is some weight. For a big block car, its handles very well, and rides smooth even on KYB shocks. But I really like the stance and even more since it settled some. Not to say you'll see similar results on a Gbody though...

Surprisingly with my 3/2" drop I have yet to rub anything as far a the tires in the inner fenders or even the rear tires on the lip or inner frame and I only have a 1/4" of space between the rear tire and frame.

 

[jonnyslick]

Thanks for the input guys!

 

[85 Cutlass Brougham]

Okay, I figured out the motion ratio between the ball joint and the bump stop. I arrived at it using the following data points: center of LCA pivot bolt to bump stop is 10.5 in. Center of LCA to Center of Ball Joint is 16.5 in. Using the center of the ball joint as your data point, the motion ratio is approximately 1.57:1 (16.5/10.5=1.57). The motion ratio to the center of the spindle I am guesstimating requires another 1.25 in of length, so that ratio is 1.69:1 (17.75/10.5=1.69) . ( I rounded to the 2nd decimal place) I measured them laying under the car at night with a drop light and a tape measure, so the actual numbers may be a little different. I also did not use trig to figure out the precise arc length, etc. since using terms like "arc subtended" when I can't achieve absolute precision would be silly. Anyhow, the distance from the frame to the bump stop is 1.25 in on my car with no front fenders, header panel, or A/C compressor. If you want the max compression travel at the lower ball joint, it is 1.25x1.57=1.96in. At the approximate center of the spindle it is 1.25x1.69=2.11in. The actual number then is around 2 inches of compression travel with the Eibach springs which are rated to drop it an amount I forget. Anyhow, you can use the math I provided to get an approximation of the available compression travel with a variety of springs.

Also, remember that the Motion ratio does not only affect the bump stop, but the spring as well. To get the spring's MR, you would need to measure to the center of the spring. This is important since the spring rate is reduced at the wheel by the motion ratio. So, the spring rate on a SLA front suspension like this is not the same as the wheel rate due to the mechanical advantage of the LCA acting as a lever on the spring. The same is not true of a G body's rear suspension since the spring rides on the axle, giving it a near 1:1 motion ratio ( reduced by a small amount as the spring is not directly above the wheel.)