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First a quick tour of what Tim and the team were dealing with:
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| The front suspension is struts, but very lame ones. The lower control arm is just a lateral link. Fore/aft control, which would normally be provided by a tension rod, is instead provided by front sway bar. A sway bar, of course, lacks the necessary rigidity to control wheel position if there is more than 36 hp involved. |
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| The rear suspension was a leaf-spring solid axle. Notice the car is so small the springs actually stick out past the bodywork. |
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| After wasting a few weeks trying to figure out how the Z600's tiny brakes and suspension could be made to control a quadrupling of horsepower and a sudden swapping of drive wheels, a simpler solution was found. A bent, engine-less RX-7 GSL-SE cost $200 and provided a treasure trove of parts for the project. |
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| In case you're wondering what RX-7 parts will fit a Z600, the answer is whichever ones you weld to it. After welding in a brace to hold the strut towers in the proper relationship, the entire front suspension was taken out as a complete assembly. |
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| Though a first-gen RX-7 is incredibly narrow by modern standards, the whole assembly had to be narrowed by 6 inches just to get the strut towers under the Z600's hood. |
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| It almost looks like it belongs there, doesn't it? |
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Me: You welded the sway bar back together? Isn't it gonna snap? Tim: No, you just need to use a sleeve and TIG weld it with uber-expensive Weld Mold 880 Nickel/Chromium filler material that stays ductile on high-carbon steel without heat treating. Me: I'll shut up now. |
Just narrowing and welding in an RX-7 front suspension doesn't solve all the front-end problems. There's still the very big issue of steering. RX-7s had some kind of horrible, archaic, worm-in-nutsack steering box that was a carryover from the RX-3. Not only was it the single worst feature of the car, it wouldn't really fit in the Z600, even with a welder.
The Honda, on the other hand, actually had rack and pinion steering, though, like the rest of the car, it was a little goofy. The rack was high-mount, on the firewall, with the steering arms mounted high on the front struts. Amazingly, the front of the car is so short that even though the rack is on the firewall, it's front-steer. That is, the steering arms stick forward from the struts. Look back at that picture of the engine bay (the rack isn't installed in that photo) and notice the firewall is in line with the centerline of the strut tower!
Time to make Honda steering work on a Mazda strut.
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| First, the Honda struts were chopped to bits to free the steering arms. Then Tim took half an inch out of the arm in an effort to quicken the steering. |
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| Both arms chopped and ready to weld in place. But where to put them? Bump steer will be impacted by how high up the strut the arms are attached, and Ackerman geometry will be impacted by whether or not the arms are parallel with the wheels when the welder comes out. All options are on the table at this point. |
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| After much contemplation, the arms were welded in to give zero ackerman and as close to zero bump steer as possible, erring on the side of roll understeer (toe-out under bump). Luckily, the RX-7 struts had removable inserts, so its possible to weld directly to the strut tube without damaging the damper itself. |
With the front suspension handled, its time to stuff an RX-7 axle in the back. As you should expect by now, this was also far from simple. Turn the page.
