While our primary interest was fiddling with the D-Spec Tokicos, we have to admit we had a blast (or two), peddling the boosted Mach 1 powertrain. With the deep-breathing cylinder heads and centrifugal blower, the top-end charge was stuff of freeway flyer legend. If following this path to power, however, our recommendation would be for more final drive gearing-3.73 cogs would be ideal (and were installed two weeks after we drove the car). As it was, the stock gears let the car pull famously as long as the tach was approaching 4,000 rpm or higher, but below that the response was the comparatively soft Four-Valve stock. In the real world, this can be put to good use, as this flashy Mach ran town errands and commuting with stock fuel economy and driveability, but would fly on downshift demand. The trade-off is you must be in a low gear and be ready to make big rpm when you want the power, similar to nitrous. The addition of steeper rear axle gearing will bring the power hit on line quicker, likely without a downshift.
We found the firm spring and shock rates (we typically had the shocks adjusted to the firm end of their range), combined with what felt like performance handling alignment settings, gave responsive, eager steering and handling. Definitely tunable using the adjustable D-Specs, the steering response was certainly quicker than stock, for a delightfully eager turn in on twisty roads, and an almost nervous free-way gait that wanted some attention paid to it while cruising. This was not a sleeping chassis.
As expected, adjusting the shocks firmer-the single point D-Spec adjustment alters both compression and rebound dampening-brought on increased handling capability for corner carving. Launch action, which is so useful at the dragstrip, naturally favors weight transfer to the rear, in which case turning the front struts all the way to soft was unmistakably helpful. It certainly would be no extra work to adjust these shocks while disconnecting the sway bar and fitting skinny front and slick rear tires.
The D-Spec's big advantage is its huge range of adjustment provided by a triangle-shaped window in the valving mechanism. Many adjustable shocks provide small, often just perceptible, changes in dampening, but not the D-Spec Tokicos. When you turn them down, it's the next thing to turning them off, and turned to full firm, they are nearly racing stiff. Tokico says the D-Spec's triangular window has added more ability to soften the shock than stiffen it-performance shocks are typically stiff enough for the street anyway-so the D-Spec's largest advantage is providing an easy street ride rather than stiffening into Formula 1 levels of suspension control.
To which we agree, but in the end we came to believe the D-Spec's advantage would be best paired with relatively softer street springs. Why? Because you can turn down the D-Spec shock, but you can't turn down the spring rate. If you're motoring around on the street with track-oriented spring rates, such as Bud's car, even with the D-Specs turned all the way down, the suspension will only be so compliant because the spring rates are still stiffening everything up. Bud's car ended up with sort of a baby-buggy ride with the shocks turned way down. It wasn't evil, but it was clear the spring/shock matching was diverging off the chart, leaving the springs to give an extra bounce when worked over by potholes and bumps while the shocks were turned down.
Screw in the adjusters to the stiffer end of the scale and the spring/shock balance felt great and the car really handled. The ride was definitely stiff and jiggly, as a sport suspension would be, but the handling balance was good.