It's been a long while since our last update on Project Z. If you consider 16 months a long time, that is. The problem with long-lived project cars is once you get to a certain point, it's hard to find new things to do. We knew there were issues with the car's ability to go straight with all of its power (560 hp at the wheels as of the last installment), and driveability problems from the new JDM front end causing turbulence in the mass airflow meter, but what to do about it? We were beyond simple bolt-on, off-the-shelf solutions. Everything from now on out had to be sought after, researched, or fabricated. In some ways, it's just business as usual as Project 300ZX breaks new ground.
SPL's adjustable link features an easy-to-turn screw collar to adjust camber and very low-friction, sealed-pivot ball bearings. This is much easier to adjust and has less slop than our previous adjustable upper link.
In the six years since this project started, there are new developments in the Z community as well. Like improved exhaust manifolds that allow Zs to make more than 700 whp and still be streetable. That's not quite Supra territory, but it's impressive nonetheless. There are new, affordable big brake kits from StopTech and Fastbrakes. And in 1998, we hadn't even heard of Tein or JIC. So keeping up with the changing world of the Z has been keeping us busy for the last year and a half. Here's what we've been doing.
Minor tuning
We reported in January 2003 that our first dyno test, just 500 miles and one oil change after MS Performance assembled it, was 560 hp and 549 lb-ft of torque at the wheels. We drove a few more months, put larger water jets (up to 0.8mm from 0.7mm) in our Aquamist water injection system and advanced our timing from a conservative 13-degrees base timing to 15 degrees.
The link as bolted into the car. It's much easier to access the adjusters of the narrow SPL part.
During that January test we also tried making some impressive quarter-mile times, but were thwarted on the big end by a mean misfire caused by air turbulence blowing across our filters. This turbulence confused our hotwire Mass Airflow Meter (MAF). This was only a minor problem on the dyno, but it was disastrous at more than 100 mph. We had a friend fabricate a carbon-fiber airbox to protect our JWT Twin POP filters from a direct air blast and subsequent MAF turbulence. The misfire seems to be totally eliminated.
The result of these minor tweaks is a whopping 574 whp and 549 lb-ft of torque at the wheels. Although some Zs now have considerably more peak horsepower, ours has the broadest powerband, the most torque and best low-end of the higher powered Zs we know of. We did lose a little power at lower rpm and we intend to address this with some more ECU tuning at a later date. Even with "only" 574 hp, Project Z is rather terrifying to drive, even in a straight line. We're doing some things to address this.
The SPL front lower control arms look pretty out of the car. The stiff tubular construction and the spherical bearing is easy to see here.
SPL suspension
Although our suspension was state-of-the-art at our last installment, since then, the art has advanced. Previously our suspension was converted to full adjustability and we got rid of the numerous squishy rubber bushings, replacing them with hard rubber Nismo bushings. Even with those mods, Project Z's suspension still exhibited some suboptimal handling characteristics, and at these kinds of speeds, you don't have time to drive around little problems.
The first problem was a tiny amount of wheel hop. This was merely an annoying pittering compared to the parts-breaking, earth-pounding Michael Jordan rear-wheel dribble the car used to have, but even this small hop prevented us from getting optimal traction. Plus, with this much power, that little dribbble is hard on the drivetrain.
As installed in the car, you can see how you can adjust the angle of the arm and thus the roll center with spacers placed between the spindle and the spherical bearing (on the right). The SPL T/C rod controls for-and-aft movement and allows the caster to be adjusted.
When launching at the dragstrip, the car also had a disarming tendency to turn left. Most disturbing, though, was the rear-end twitchiness and tendency toward wheelspin in first, second, third and sometimes fourth gear. This twitchiness could elevate to nearly uncontrollable tankslappers down the track as the hapless driver (yours truly) chased the rear of the car from side to side.
Most of these undesirable characteristics could be traced, we guessed, to the small amount of flexibility remaining in the NISMO bushings. Our powerful engine and our 2-inch-wider-than-stock tires put more load into the suspension than any NISMO engineer probably ever dreamed of.
Searching for the latest in Z trickery, we stumbled upon Texas-based SPL. SPL sells many specialized parts for the Z, S13 and S14 240SX, Skyline GTR, 350Z and G35. The SPL Web site had us drooling over super-trick and esoteric Z parts way beyond the basic bolt-ons. The fact that the Z shares nearly all of its suspension components with the popular R32 Skyline GT-R and S13/S14 240SX/Silvia probably helps.
The rear upper traction arm and camber adjuster arms are works of art.
SPL sent us its entire array of fabricated tubular heim joint and spherical bearing equipped suspension links. These parts are pure racecar stuff, and they replace both the rubber bushings and the stamped-steel links that, at these loads, are probably starting to flex a bit themselves.
Starting with the front suspension, the upper link is adjustable in length, giving camber adjustment. The link is cut from hex stock aluminum with two locking collars held with Allen bolts. Just loosen the collars and turn the arm by hand to quickly adjust camber. This is by far the simplest and easiest-to-adjust camber adjuster we've seen for this car. The arm pivots on sealed ball bearings for low friction and absolutely no flex at all.
SPL's T/C rod is beefy 4130 chrome-moly tubing with steel adjusters. Not much chance of this failing. The bearing eliminates Nissan's big, squishy, silicone-filled rubber bushing and the rod is adjustable for length to change caster.
The lower control arm is fabricated from tubular chrome-moly tubing and is heavily gusseted for strength. Not only does the Z's lower control arm have to support the lateral cornering loads, it also has to absorb longitudinal loads from the tension/compression (T/C) rod. Hit a bump or clamp the six-piston AP binders and the front wheel tries to move backward. The only thing holding it there is the T/C rod, which bolts to the middle of the lower control arm. That arm, then, has to be beefy. This arm, too, attaches to the chassis with a spherical bearing, which allows movement on any axis to avoid binding. No squishy rubber or even polyurethane here. The ball joint has been replaced with another spherical bearing with a long shank attaching it to the spindle. This relocates the control arm lower, which raises the front roll center back to nearly its stock location.
The roll center, by the way, is the imaginary point in space the body rolls about in a turn. When the car is lowered, the roll center is lowered as well. The distance between the roll center and the car's center of gravity is called the roll moment, and the roll moment is basically the lever arm Isaac Newton used to make the body roll in a turn. When lowering a multi-link car, the roll center usually drops more than the center of gravity does, which makes the roll moment longer, causing more body roll. Even though the overall center of gravity is now lower, the torque making the car lean in a turn and causing weight transfer to the outside wheels is greater. Since the SPL lower arms raise the roll center back up, they reduce the roll moment, reducing roll and weight transfer to the outside wheels. Pretty cool, huh? This goes a couple of levels beyond your typical bolt-on suspension kit.
These bearings from SPL press into the aluminum spindle and eliminate the squishy rubber. The bearings also reduce friction in the suspension. They do transmit a bit of road noise, but the price of glory is high.
Remember that T/C rod we were talking about? SPL makes one of those, too. Naturally, it's fabricated from tubular chrome-moly steel and is adjustable for caster. It has a solid heim-joint bearing as a pivot point, reducing friction and any geometry-spoiling flex. After the SPL treatment, the front suspension has had its friction reduced, flex of bearings and components basically eliminated, and had its geometry corrected for best handling.
The SPL rear suspension components have a similar level of construction. Eliminating the flex and rubber is especially important on the wheel-hop-plagued Z. The compliance of the rear suspension's numerous bushings are so great the suspension hops like a horny bunny on Viagra when stock. We were hoping the SPL full race parts would completely eliminate this hop. The rear upper link is made of chrome-moly elliptical tubing for additional stiffness. It pivots on heim joints and is adjustable for camber. The forward-facing trailing link is also made with this type of construction to eliminate flex and bushing squish. Both upper links are adjustable for length for the obvious reason of camber adjustment. Not so obviously, with some careful adjustment, the relationship between the two top links can be adjusted to reduce toe changes under roll.
The SPL lower shock bearing directs 100 percent of the rear suspension movement into the damper by getting rid of a big squishy rubber bushing that is pressed into the spindle.
The SPL lower arm is fabricated from elliptical tubing and pivots on heim joints. A spherical bearing and a long shank replaces the ball joint at the spindle attaching point and, similar to the front arm, raises the rear roll center. One problem we had was Project Z's extreme 52mm rear offset and 10-inch wide wheels. The arms were designed for a 9.5-inch wide wheel with a 35mm offset. We had to modify the lower arms for clearance, which involved cutting and welding. SPL is working on a new design, which will probably be available by the time you read this. If you have narrower tires and wheels with a smaller offset than us, this won't be an issue.
To eliminate the rubber bushings in the rear upright hub carrier, SPL has spherical bearings mounted in aluminum carriers that replace the bushings. These bearings replace the lower shock mount bushing as well as the mounts for the control arms. SPL is the first company that we know of that addresses the squishy spindle bearings. These bearings and most of the rear suspension stuff will also work in a S13/S14 Silvia/240SX and a Skyline R32 GT-R if you're inclined to need razor-sharp handling.
The theme for SPL's rear lower arm is stiff. All the better to control our fat sticky tires and nearly 600 hp.
We had previously installed a set of Nu-Tech endlinks on our rear anti-roll bar and were pleasantly surprised how much more effective they made the bar. The bad thing is that Nu-Tech went out of business shortly after our article was published. Thankfully, SPL has recreated the Nu-Tech parts and has again made them available. The SPL parts take the mushy end links that come stock or with the Suspension Techniques or Stillen bars, and replace them with heim joints so the anti-roll bar coupling is immediate. Believe it or not, this makes such a huge difference that typically you have to soften the anti-roll bar adjustment a notch. We had to go from full stiff to medium when we installed the links. With the rear bar adjustment centered, we now have greater latitude for adjusting our suspension.
An item not to forget if you're going to an all-solid-bearing rear suspension, is that you must eliminate the HICAS four-wheel steering that all twin-turbo Zs are equipped with. HICAS relies on bushing compliance to work without binding and if you replace the bushings with bearings and still have HICAS, the hydraulic steering ram will try bending things instead. SPL has a well-engineered HICAS eliminator kit but since we already have a Stillen unit, we opted not to use it. Eliminating the HICAS is a good thing. We feel that getting rid of it makes the car much more predictable at the limit, especially in the pre-'94 cars, which had a slower reacting system.
SPL's endlinks eliminate squishy rubber and couple the anti-roll bar directly. The adjustable length also allows you to eliminate preload from imperfect bars.
To reduce chassis flex, we installed some of SPL's front chassis braces. These install under the front fenders and brace the front shock towers to the door hinge bolts on the A-pillars. These braces perceptibly stiffened the chassis to the point where it understeered noticeably more in corners, enough that we had to change our anti-roll bar a little to compensate. That's a far greater effect than what bolt-on braces typically do. We previously noticed that if we jacked up the car from one corner it would be harder to close the doors. With the braces installed, the doors didn't care how we jacked up the car, a sign that the chassis was much stiffer. The on-the-road feel is much better and the ride actually improved some as well, additional signs that the chassis is stiffer. We had to remove our front fenders and part of our deactivated AIV system to install them but the installation was only mildly difficult. The braces were so pretty it's a pity we had to cover them up with the fenders.
SPL's front braces triangulate the A-pillar to the shock towers under the front fenders, bolting to the door hinge bolts. These braces make perhaps the biggest difference of any frame stiffening measures we have done so far.
The problem with all these adjustable pieces is that you have to adjust them. More accurately, unless you have a laser alignment rack in your garage, you have to find someone you trust to do it for you. We took Project Z over to Westend Alignment in Gardena, Calif. Westend specializes in high-performance street and racecar chassis setup. Not only did Darren Nishimura at Westend do the alignment, he helped press the bearings into the rear uprights and corner weighted the car as well. Our current setup is -2.5 degrees camber in the front with 9 degrees caster and zero toe, and -1.25 degrees camber with 0.125-inch toe-in in the rear.
As far as we can tell, the SPL suspension parts made a good package even better from a performance standpoint. We were worried the ride would get harsh but it wasn't as bad as we had anticipated. Much more road noise is transferred to the interior of the car and you do feel every small bump in the road, but this same feel also leads to very good road feel through the steering. Hey, the F40 has a pretty harsh ride as well, and you don't hear much complaint from Ferrari owners, do you?
The bearings reduced friction and bind in the suspension, allowing it to move more freely and making it more responsive to bumps. The reduced friction allows the shocks to work better as well. As much as the lack of compliance hurt the ride, the reduced friction improved it. Due to the higher roll centers, the car now rolls less in turns and responds more quickly to steering input. The improvement in steering response as well as the total elimination of wheel hop was great. Spinning the rear wheels is now smooth and more predictable without the annoying, nibbling hop we were getting before.
The trouble with Project Z is that the car's limits are getting so high, it's impossible to experience and evaluate them safely on the street. We plan to go to the track to get more feedback soon.