I knew that I wanted to add a strut tower bar (stress bar) to my M3, but I was not happy
with any of the commonly available designs.
It appears that most of the bars on the market are designed with aesthetics
as the primary concern, and strengthening the chassis as an afterthought.
Furthermore, I personally believe that aluminum is a poor choice as a material
for a stress bar. If for no other reason than the fact that aluminum
has an endurance limit of zero (i.e. it will eventually crack, no matter
how strong you make the part).
I wanted
a steel stress bar. I thought about designing one myself and having
my friend Sean McLean fab' it up. But the ends of the bar where it
meets the strut towers are a little complicated. So I purchased a
Sparco steel stress bar. It cost $96 and I got it from Rod Millen
Imports in Huntington Beach
(Sparco p/n 03677).
The Sparco bar is made from 1.5" tubing.
I estimate the wall thickness at about 0.050" based on the weight of the
bar (it is very light).
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Straight out of the box the Sparco bar did not fit my car very well.
This was probably more a problem with my car than with the stress bar.
In any case, it
was OK since I planned to modify it. The Sparco bar bolts to two
of the upper strut bearing studs on each strut tower. But the mounting
plates bend down over the insides of the strut towers. Then a hole
is drilled through the side of the strut tower and a third bolt is located
here. See the picture for a better description.
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Thus, as it comes
from the factory, the Sparco bar is not easy to remove. However,
Sean and I modified it so that I could take out the center portion with
a minimum amount of hassle. We added a pair of flanges near each
end of the bar (see picture). By removing the four bolts that go
through the flanges I can pull out the center section of the bar in about
60 seconds. This is helpful when the stress bar is in the way of
working on the engine. This is similar to the "hinge" design that
is employed on many of the alloy stress bars but it is stronger because
it still offers some resistance in bending as opposed to only in tension/compression.
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I am very happy
with the way the modified Sparco stress bar turned out. It is light,
convenient, and still very strong.
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