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Chassis and Suspension Comments
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Here I will make various observations and comments on how the 3MZ-FE engine, transmission &c. function, and in some cases how to make improvements. New material will be added regularly, and eventually better organized. Click below to jump directly to an individual topic. |
Understeer?
1. stiffen up the rear bar bushings
2. battery in trunk
3. reduce rear tire pressure 5 lbs. |
Coil spring rate?
The lower the car is, the stiffer the spring must be to prevent accidental removal of the exhaust system.
Increase the lbs. per inch deflection rate also limits the total amount of travel, so the camber pattern is shorter.
The rule for spring rate (road race) used to be to get the car height where you need it for aero, downforce etc. then decrease the rate to where the car just touches the compression stops at the worst part of the course. If it never touches, the suspension isn't properly loading the wheels and using full suspension travel to prevent the chassis from being affected by road surface changes. Be very careful about moving the compression stops - when the suspension hits them, that spring rate goes to near infinity and the wheel has zero traction.
The only downsides to loose springs is excess camber change and bottoming. If it wallows, stiffen the shocks. Using heavy springs to control body roll isn't effective - play with your bars. |
MacPherson strut brace design
I’m not impressed with any of the strut braces I've seen (factory, TRD, etc.).
I’m sure they’re all better than not having one, and you don’t have a clean sheet of paper for the design due to the space/clearance limits under the hood, but all of them are missing the essential element.
What a strut brace does is not add strength (resistance to breaking), but attempt to keep the relative positions of the MacPherson strut (by the way - it’s a General Motors invention to save money, it’s not an advantage) upper mounts in exact alignment.
What happens under high engine torque, cornering, etc. is that the shock towers try to “skew” (twist out of alignment), and also move toward or away from each other. To prevent this the requirement is stiffness (resistance to bending), which is largely a function of the cross-sectional area of the beam, not the material (chrome-moly and steel are equal, both much better than aluminum) or wall thickness.
The easiest way to improve an existing bar is to use the shock mounting plates, and add or substitute a larger diameter beam across them. The shock mounting plates should be made longer (front to rear) by 2-3” and the beam should attach at 2 new points farther apart than the stock points.
The beam should be as tall as possible to just clear the hood, and as wide as will clear the engine covers, etc. The shape can be round, square, or rectangular - steel tubing is easy to find in standard dimensions. Wall thickness as thin as .059” is fine if the beam is large enough so there is no weight penalty.
The beam can be made in 3 pieces, with the 2 ends bolted to the shock plates (as current), and detach from the center section with a bolt pattern. The center section should be as wide as you need for engine service, etc. |
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