74_5.0L_Z

Think of it this way: If you set the coil-over so that the collar just takes all of the slack out of the spring (zero pre-load), the spring will compress enough to support the weight of the car when installed. For the sake of example assume 250 lb springs, no pre-load, 600 lbs on the corner, and a motion ratio of 1. When installed and the car is resting on the tires, the spring will compress 600/250 in (2.4 inches). Now, if you pre-load the spring before installing it by turning the adjuster collar up one inch, the spring will be pre-loaded by 250 lbs. Once installed, you would have to apply 250 lbs to the strut before it begins to compress. With the same 600 lbs on the corner, the car will now only compress the spring an additional 1.4 inches. The spring itself will still be compressed 2.4 inches, but 1 inch of that was before installation. The car will sit 1 inch higher at rest. Now, take an extreme example. If you pre-load the spring 2.4 inches, then you would have 600 lbs of preload. When installed on the car, the suspension would not compress at all under static conditions. You would have raised the car 2.4 inches above the zero pre-load condition. When I ran the 250 lb springs on my car, I ran a slight preload (somewhere around an inch). Pre-loading the springs using the collars isn't easy unless you have bearings between the springs and the collar. Do yourself a favor and install these between the spring and collar. http://www.speedwaymotors.com/QA1-7888-109-Coil-Over-Thrust-Bearing-Kit,6001.html

I have one that you can have for free. Just come get it. It is not perfect, but is solid. http://forums.hybridz.org/topic/124327-centerline-wheels-koni-shocks-triple-weber-dcoe45-eibach-springs-bumpers-wipers-and-misc/

When I designed and built the headers for my car, I contemplated making 180 degree under the pan headers like you are doing. In the end, I decided that the added complexity wasn't worth the effort. One thing I found necessary was to angle the collectors inboard so that the exhaust pipes converge toward the center of the car.

I just looked at the Eibach catalog, where they publish all the spring information. http://eibach.com/sites/dedevperformance-suspension.eibach.com/files/download/ers_catalog_global.pdf The load at block height for a 10 inch, 150 lb/in spring is 972 lbs and it total travel from free length to being fully compressed is 6.48 inches. With these springs you will only have ~2.5 inches of travel before the springs stack. For a 12 inch, 150 lb/inch spring the load at block height goes up to 1171 lbs and the total travel increases to 7.71 inches. With these, you will have ~3.75 inches before the springs stack. For a 10 inch, 250 lb/in spring the load at block height is 1569 and the total travel is 6.28 inches. With these, the springs will compress about 2.4 inches for the 600 lb static weight per corner. You will have about 3.9 inches of travel before the spring stacks.

The 10 " inch, 150 lb/in springs may cause you a problem as well. The sprung weight per corner is around 600 lbs, so the springs will compress about 4 inches with the car sitting in the driveway. When you hit a bump you will try to compress the springs an additional 2 - 4 inches. Unfortunately, the springs will stack solid before you can get that much more travel. The free length that you need is related to the rate of the spring. The stock springs were about 100 lb/in and had a free length of about 15 inches. When I ran my car on the street, i had 250 lb/in springs with a free length of 10 inches on the rear and 200 lb/in springs with a free length of 12 inches on the front. Currently, I run 500 lb/in on the front and 400 lb/in on the rear with an 8 inch free length (no longer a street car). If you want to stay with 150 lb/in springs, you should try for at least a 12 inch free length. BTW, I have my old 250 lb/in springs (2.5 diameter coil-overs) for sale cheap.

The structure of the front of your chassis was probably flexing significantly prior to adding the front bracing. A flexing chassis acts like a spring in series with the springs on the struts. By stiffening the chassis you effectively raised the front spring rate. If the car was neutral before the added bracing, the car will now understeer. So, either decrease the rate of the front springs, go to a smaller diameter front sway bar, or increase the rate of the rear springs.

So, where are you acquiring these 3D engine models? I would love to get a decent 3D model of the old 87 - 93 5.0L Ford engine.

One of fellow members here (erikr) really stepped up and has helped with improving our dimensional knowledge of the S30 front suspension. He measured two 240 Lower Control arms using a coordinate measurement arm. Attached are photos of the set-up and the results. We can say with great certainty now that the center to center distance of the LCA is 11.2 inches I would like Erik to describe the process. Also, I invite others to help us out.