The trickiest part of making a car both track- and street-worthy is the suspension. This is the double-edged sword because you want something soft enough to be comfortable and offer sufficient suspension travel on the street, while being stiff enough to handle all the loads generated on the track. We want to be competitive with a dual-purpose car, so we're going all out with Project Z's new suspension. Although the Nismo S-tune suspension the car came on was quite good on the street, it won't give us the competitive edge needed at the track because the spring rates are just too soft to support loads from such a heavy car and the grip generated by the Nitto NT05 tires we've mounted.
Instead of trying to get our suspension to simultaneously fill both needs, we decided to go with a different strategy. Just like real race cars, we'll be using different spring rates to adjust for differing grip conditions. This way, we'll have a set of race springs and a set of street springs that we will swap out between track weekends and our daily commute. With that in mind, we'll be using a coilover suspension setup to make spring swaps a little easier.
There's a problem with our strategy, though. Because of the drastic difference between springs rates used on the street and on the track, we needed a damper that can provide the right amount of damping in both configurations. In most cases, off-the-shelf coilovers are designed and calibrated (in terms of damping force and stoke length) for use with the springs that it came with. Some adjustable dampers can be fine-tuned to use slightly stiffer or softer springs, but not huge increases in spring rate like what we have in mind.
To fit our dual-purpose needs, we looked at some top-end, race-quality coilovers designed for use with multiple spring rates. Race teams change springs on their race cars from track to track, so race dampers/coilovers typically don't come with springs. It's left up to the discretion of the end user to determine the spring rate and spring length needed. And because of this, race-quality dampers often have a much larger range of damping force adjustment so that the dampers can be tuned to match the spring rate used.
While most street tuners are more familiar with brands like TEIN, KW, Koni or even the more rare JDM brands, those in the world of racing will know the name Moton. Manufactured in the Netherlands, Moton is synonymous with true racing suspension. The company's products were on 30 percent of the starting grid at Le Mans in 2000 and had since become very competitive in most forms of professional sports car racing all over the world. Moton's newest product, the Clubsport, is designed for the serious club racer at an affordable price.
Since our Z is by no means a race car in terms of weight, grip, aerodynamics and suspension travel, the Clubsport would be the perfect fit for us. The Moton Clubsports use an external reservoir monotube damper with independently adjustable compression and rebound damping, unlike more expensive race variants that have high- and low-speed adjustability for both compression and rebound. Internally, the Clubsport construction is similar with top-end race variants using high-quality aluminum for the damper body and an extremely large 22mm piston rod. This means the Clubsports are extremely light and provide finer damping control because the larger piston rod displaces 300 percent more damping fluid for the same motion than normal. Unfortunately, we needed to find springs and upper mounts for the Clubsports because they're made for racers-a minor trade-off for superior suspension.
After talking to our friends Steve Mitchell (with the M-Workz time attack Z) and the guys at SPL Parts, both of whom campaign time attack cars on Moton Clubsport suspension, we decided on using a 1,100 lb/in (20kg/mm) spring in front and a 1,000 lb/in (19kg/mm) spring in the rear. Normally, we would use the same spring rate for the front and rear, but because of our stiffer Nismo antiroll bar in the rear, more spring might cause the car to rotate too much, which is not good for a car this powerful and fast.
Eibach offered a wide selection of springs to choose from in its ERS line and we opted to use 2.5-inch inside diameter springs in 6-inch lengths in front and back for the race rates. We also added a softer tender spring in the front to help absorb minor wheel movements. A tender spring is an auxiliary spring that many coilovers will use to help the suspension extend under droop, but also absorb small suspension movements. Tender springs are different from helper springs seen on most coilovers because they're stiffer, have differing linear and progressive spring rates and are not fully compressed under the car's weight. Helper springs come in only one spring rate and are fully compressed at static ride height. Eibach also supplied a set or street-rate springs that we spec'd out to half our race spring rates. To compensate for not over-lowering the Z on the softer street springs, we increased the front spring length to 8 inches and the rear to 7 inches, as well as eliminating the tender spring.
The last part of mounting coilovers on a 350Z is finding a way to mount the rear springs. Nissan went to great lengths to move the rear spring inboard of the shock to reduce unsprung weight as well as sticktion in the rear suspension. While we could just pull out the old springs from the stock rear mid-link and use the adjustable perch on the Moton coilovers, the rear upper mount wasn't designed to support the vehicle's weight and we'd be undoing all of Nissan's handiwork. Instead, we opted to replace the stock rear mid-link, that the rear spring sits in and use a lightweight CNC-machined replacement link from SPL Parts. The link comes with an integrated treaded spring perch sized for 2.25- or 2.5-inch coilover springs as well as an aluminum upper spring seat and monoball outer pivot that replaces the stock rubber bushing. Bang for buck, this is the best way to update the rear suspension for coilover use as it maintains the same light weight without using heavy tubular steel control arms, eliminates the rubber bushing that plays a critical role in unwanted rear toe change under heavy loads and also has a secure method of holding in a coilover spring. The mid-link also integrates in SPL's hybrid adjuster for a more wider range and precise toe and camber adjustments in the rear suspension. SPL also came to our rescue with its pillow ball upper mounts for the Z that fit our Moton coilovers because they sell the entire kit.
With our new suspension installed, we headed over to Driftspeed in Lomita, California, to help us out with a preliminary alignment on the company's bells-and-whistles laser alignment rack. A laser alignment rack can be as accurate as stringing up a car (depending on the mechanic) and quite a bit less work. For now, since we don't know the final weight of our car in track trim, we passed on corner balancing and just leveled the ride height and the alignment settings for our current height. As recommended by Steve Mitchell, we started off with a zero toe setting in the front. For more aggressive track use, we will add in a bit of toe out later for better turn-in. Unfortunately, the Z doesn't come with camber or caster adjustments in the front suspension. This means, in order to keep an appropriate level of camber to get around on the streets while we build this car, we'll have to adjust the camber according to ride height. For now, we'll keep the car just slightly lower than stock in order to prevent excess tire wear from too much camber. We have some tricks up our sleeves, but will wait to address front camber and caster after we have the car at its final weight and respective ride height.
Our rear suspension wasn't as troublesome. With the added adjustability of the SPL rear mid-links, we were able to get about 1.8 degrees of negative camber and about 8mm of total toe-in in the rear. The idea behind these settings is more rear stability through the corner with the toe-in and more straight-line acceleration traction (with less camber) once the car exits the corner so that we can actually use all the power we're making.
Even with springs over twice the stiffness of our original S-tune springs (which translates to a wheel rate of roughly 560 lb/in in front and 275 lb/in in the rear), our Z with the Moton suspension actually still rides smoother over small bumps and highway expansion gaps than the Nismo setup. Obviously, over big bumps it's harsh, but the Motons are hard to beat when it comes to controlling wheel and body motion.
Next time, we'll look at ways to help our engine survive the track beating to come.