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Hi, I would like to know how I could do this. I'm planning on getting MSA springs but like my ride to be lower then what they have. I read that to do it properly without having to cut the spring I would need to section my struts. First of all how in the world do u do that? Does it mean I have to cut my strut casing and then re-weld it back together after removing some off? How do u align it all together? Anyone, have a sight or detail descriptions of the process?
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I've never heard of anyone section struts and using the stock diameter springs and spring perches. Doesn't mean it can't be done, but its would be a lot of work.

Strut sectioning means cutting out a section of the strut tube and welding it back together. This is done on a lowered car to gain back some bump travel in the suspension. Wayne Burstein wrote up a good description of this for IZCC and its reprinted below with his permission:

Let's start by defining the task at hand. We want to lower the car in order to lower the center of gravity. I'll skip all the analysis on why we want to do this because there are lots of good books on the subject, and confine my comments to what you might run into in performing this on a Z.

First I need to define a couple of terms:

Bump -- suspension travel in the compression direction (i.e. the result of hitting a high spot in the road).

Rebound -- suspension travel in the opposite direction (i.e. the result of going over a hill and the wheels leaving the ground).

The first problem we run into is that when we shorten the springs, we are reducing the available bump travel in the strut cartridges by the same amount we lowered the car. With all the travel available in a stock Z, this is not too much of an issue when we lower the car only an inch or so. For those of us who are racing our cars, we often lower them much more; for instance, in the SCCA's IT class, we are allowed to lower the car until the rockers are no lower than 5" above the ground. This causes a problem because the suspension is almost fully compressed when the
car is sitting at rest. When you hit a bump, the suspension quickly bottoms out (hopefully on a bump stop of resilient material). This is a real problem because in effect, the spring rate increases very dramatically and negates all of our efforts to drive the car smoothly. When driving at or near the limit, this often is the beginning of a very impressive crash.

Well, we now have the car at the desired ride height, but need to increase the travel in bump. The way to do that is to shorten the struts. Now things get pretty messy. Don was correct in stating that this is dependent on the length of the struts; however, this is only partly true. The struts need to be long enough to insert the cartridges of choice. For racing, the ones that I would recommend are Carerra, Koni, or Tokico, in that
order ( this should cause a bit of discussion on its own). If we automatically shorten the strut to exactly fit the cartridge, we might actually shorten it too much. This leaves us without adequate rebound travel. Just in case this does not scare you, it should. I learned my lesson the hard way when
I had the rear wheels pick off the ground while cresting a hill that had a slight turn to it. That made for a looooong full lock slide at 100 MPH!

Ok, now we need to decide just how much we want to shorten the strut housing. The desired end result is to have about equal bump and rebound travel. In other words, when the car is sitting at rest, we want the struts half way compressed. On a street car, this is fairly easy to do, because we generally set the car up once and never play with it. Race cars are another situation entirely. First of all, different tires require different ride
heights -- for instance, switching from 60 series to 50 series tires lowered my car by .75", causing me to have to raise the car by the same amount. We also play with spring rates, and assuming that we are using coil overs, need to keep the spring collar low enough on the strut housing to avoid it interfering with suspension travel. The bottom line is that before cutting anything off your struts, you should carefully think about what you
anticipate doing to the car over the next few years as far as tire/wheel, strut, spring or ride height changes, and then come up with a compromise that works for you.

FWIW, most people shorten struts 1-2". If you figure out that you want to go more than this, recheck everything before cutting. Yes, you can add a section, but speaking from experience, it is much easier to remove than to add. I almost forgot to mention this, but if your strut housing is longer
than the cartridge, you need to put a spacer below the cartridge inside the housing -- typically, these are just pieces of tubing that is slightly smaller in diameter than the inside dimension of the housing.

Just a couple of tips to consider:

1) The best way I have figured out to cut the struts is to use a large pipe cutter. This gives a fairly straight cut with minimal cleanup -- you need to grind the burr off the inside of the housing and bevel the outside edge before welding them together. Be careful not to make the cut
so high on the strut that you hit the threads for the gland nut!

2) To remove the original spring perch, the quickest way I have found is to cut through it just above the housing with a grinder or cut-off tool, and then grind the remaining metal off. I found it much easier to do this before cutting the strut because even though I was not cutting the section with the perch off, it did interfere with the cutter.

3) After lowering the car, you need to align the suspension because you have added negative camber at both the front and rear wheels. Of course, you should probably do this any time you remove suspension components anyway.

Wayne Burstein
WDCR SCCA ITS #10
IZCC #214, NVZCC
[email protected]
www.mountainmotorsports.net

- John
 
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