Sport Compact Car - January '98
Project 200SX SE-R
by Mike Kojima
[Put into HTML format by Ken Pratte]
We dial in our suspension and braking systems, and then go all-out with a Ground Control suspension.
PHOTOGRAPHY: Dave Coleman, Mike Stute
In our quest for higher performance we continue along the upgrade path for Project 200SX. In part one of Project 200SX SE-R (SCC, June '97), we attacked the suspension and brakes, adding GAB shocks, Eibach springs, Suspension Techniques anti-roll bars, and some huge brakes from SMC. At the end of that story, we promised to bring you up to date with any fine-tuning that might need to be done. Over the last few months, we have continued to tweak the suspension and brakes, first making small adjustments to make our modifications work right, and then, as usual, going overboard with more modifications. At this point, we are getting into the serious zone where the car would be a deadly contender in open-track time trialing, or slalom racing. Throw in a full roll cage and it could be competitive in wheel to wheel road racing events. We are still sticking to our original goal of maintaining a daily driven, commuter street machine. Through the careful engineering of some of our parts suppliers, the difficult to obtain goal of a streetable race car is becoming a reality.
Rear Brake Upgrade
After installing the unique SMC brake upgrade in part one of Project Nissan 200SX SE-R (SCC June 97'), we needed to do some additional work to make the brakes function as well as possible. As you will recall, we installed massive 11.7-inch cross-drilled rotors and Wilwood 4-piston calipers on the front, but only used cross-drilled stock rotors on the rear. The result was too much front brake bias causing the front wheels to lock well before the rear. Since most of the braking is done by the front wheels (especially in front-wheel drive cars), it's almost impossible to have too much front brake. But to get the most out of the system, all four brakes should be doing the most possible work to stop the car.
We also wanted to do something to improve the pedal feel of Project SE-R. The hydraulic system used by the brakes works like a liquid lever arm. The amount of force that your leg can provide is multiplied by the ratio of the area of your master cylinder piston to the area of your caliper pistons. If you have one square inch of master cylinder piston and ten square inches of caliper piston, the strength of your leg is multiplied by ten. The ratio of movement goes the other way. To move the ten square inches of caliper piston one inch you would have to move the master cylinder piston ten inches. This is why the brakes are a liquid lever, the force is multiplied by moving the master cylinder piston a greater distance. That is how you can stop a 3000 lb. car traveling 60 mph so effortlessly. This is the same principle as a lever arm or even a hydraulic floor jack.
The Wilwood 4-piston front caliper used in our front brake system has almost twice the piston area as the stock brake caliper. The effect of this is increased clamping force because of the additional surface area of the caliper pistons. One drawback is that the brake pedal now has a longer throw than previously. In our opinion, the brakes had a mushy feel and although very powerful, were difficult to modulate. What we needed was a bigger master cylinder to reduce the amount of pedal stroke and obtain a better pedal feel.
The SE-R's stock master cylinder has a bore of 7/8-inch. We searched Nissan's corporate parts bin and found that the Altima master cylinder has a bore of 15/16 of an inch. Although the difference in master cylinder bore seems small, 1/16-inch makes a significant difference in feel. We found that the Altima master cylinder is a bolt-in with a direct fit in the brake line ports. The 1/16 of an inch in piston diameter made a world of difference in the way the brakes felt. The pedal stroke was now only slightly longer than stock with a firm, easily modulated feel.
After doing some simple calculations and consulting with a brake system engineer friend, we determined that we probably did not need a brake proportioning valve. If this seems pretty radical, many British sports cars as well as some race cars do not have proportioning valves. If the amount of brake bias is correct, a lack of proportioning valve may only be a disadvantage on low coefficient of friction surfaces like snow, ice and slick dirt. Since we don't ever plan to drive Project SE-R under those conditions, we don't feel that a lack of a proportioning valve is a significant disadvantage.
SMC products removed the proportioning valves from the Altima master cylinder. This is fairly difficult to do correctly, as part of the valve must be o-ringed to avoid fluid leakage. With the proportioning valves removed, we calculated the front brake bias at 86 percent. Even with no proportioning valve at all, the front brakes would still lock way before the rears would even think about locking.
To increase the braking power out back, SMC products modified a set of rear brake rotors from a late model Maxima SE. The Maxima rotors are just less than 11 inches in diameter versus the stock 9.2 inches. The Maxima rotors are also thicker, at 11 mm thick versus the stock 9 mm. SMC redrilled the Maxima rotors to the 4x100 mm bolt pattern of the 200SX. SMC also cross drilled the rotors and applied some gold cad plating to resist rust. Once again raiding Nissans corporate parts bin, some calipers from a Maxima SE were procured. They were a direct bolt in replacement for the stock 200SX calipers with even the lines and parking brake cable lining up perfectly. The Maxima calipers had a slightly bigger piston that brought the front brake bias to an acceptable 82 percent. The Maxima calipers also have bigger brake pads for more swept area. Since the rear brakes on a FWD car are lightly stressed, we will be using stock rear brake pads for now. If we are to go to high-speed open track events we will be switching to SMC carbon kevlar pads.
Cosmetically the much bigger Maxima rotors fill our 17-inch wheels better; the tiny stock rotors looked ridiculous. Now people don't think our wheels are really 17's because the brakes look normal in those huge wheels!
Brake proportioning is now correct; the front wheels lock just before the rears. We were planning to install an adjustable proportioning valve but after test driving Project SE-R, it does not seem necessary now.
SMC also supplied us with Motul 600 brake fluid to replace the Motul 5.1 that we were previously running. Motul 5.1 is a high performance OEM type fluid especially formulated for ABS brakes and longer service intervals. Motul 600 slightly sacrifices longer service intervals for maximum boiling resistance. As Project SE-R does not have ABS, we thought we would give the racing 600 a try. Motul 600 does not boil until it reaches a mind blowing 600 degrees or about twice that of regular brake fluid. We have been totally impressed with Motul's performance. In our experience during SCCA and IMSA sedan racing, it was standard procedure to bleed the brakes as many as six times in a race weekend to maintain a firm pedal. When we switched to Motul, our bleeding frequency dropped to maybe six times for an entire season! This was with Motul's older formula of fluid. Motul 5.1 and 600 promises to exceed that significantly. The Motul 600 gave a slightly firmer pedal feel which seemed to get firmer and better as the brakes got hotter.
Project SE-R stops like a dream, the brakes feeling incredibly powerful. With front brakes bigger than that of the much more heavy 300ZX and rear brakes from the much larger Maxima, we should never lack stopping power.
Ground Control Springs
The 200SX is a pretty tall car. Not only does it have a lot of ground clearance, but a high roofline as well. This gives the car a high center of gravity and a lot of body roll under cornering. In our search for the ultimate in handling prowess, and to control some of this unwanted body roll, we needed to lower the ride height of Project SE-R more. With the spring rates available from the regular add-on performance spring kit, this task was not possible to do correctly. Unfortunately, Nissan's suspension design uses short, low travel struts. Since the suspension has such short travel, a high spring rate is needed to prevent bottoming under high cornering loads. The available spring rates of street type springs were too light to prevent bottoming under severe cornering if they were to be modified for a lower ride height, a phenomenon that we knew should be avoided at all costs. At a local autocross, it was observed that even with all the modifications that we had done, there was still a significant amount of body roll present. To accomplish our goal, we needed spring rates other than what was available from the bolt on market.
For help, we turned to Jay Morris at Ground Control in Sacramento, CA. Ground Control specializes in the development of racing suspension systems for sedan-based SCCA and other competition. If you race SCCA IT, AS or production class you probably run Ground Control's stuff. The Ground Control crew whipped up a set of their adjustable ride height coil over spring systems for our GAB shocks.
Ground Control's coil over conversions feature Eibach springs specially wound to Ground Control specs. These race-style Eibachs (or ERS for Eibach Race Springs) are the same ones used by many F-1, Indy and NASCAR teams. All Eibach springs are made of high quality, chrome-silicon spring steel. Chrome-silicon steel features much better fatigue resistance than conventional spring steel. The base chrome silicon stock is cold wound by a computer-controlled spring forming machine. This ensures accurate forming and a consistent spring rate with less than two percent variation from set to set. After winding, the coils are heat-treated to restore their temper and pre-set to reduce settling after installation. Finally, the springs are shot-peened to stress relieve them and to improve fatigue resistance. Most importantly, the race Eibach springs are available in many different spring rates so that you can custom tune your suspension to your preferences.
To run the 2.5-inch diameter ERS springs, threaded collars are slipped over the shock body on top of the stock spring seat. The collars are held in place by the stock spring seat and isolated from the shock body by rubber rings to prevent rattling. Special internally threaded spring seats are spun over the threaded collars and another small diameter spring seat replaces the upper spring perch. These parts are machined from lightweight but tough 7075 T-6 aluminum that is anodized red to prevent galling and corrosion, and because it looks cool.
The adjustable collars permit easy and rapid adjustment of ride height to suit your personal preference or driving conditions. Adjustable collars also allow for the setting of corner weights which can be tuned to optimize the chassis for a particular type of corner during racing or for consistent understeer/oversteer balance in right- or left-hand turns. Adjusting corner weights is a racing trick where the static weight is taken from each wheel by using a special set of scales. The amount of weight on each corner of the car is one of the factors determining the amount of slip angle that each tire will run under cornering loads. If you are turning right and want to have more understeer you can jack up the left front to add more corner weight. The left front tire will run a greater slip angle and you will have more understeer. You can also equalize the cross weight percentages so the car will be balanced from side to side. The complete scope of these adjustments is beyond mere mention and will need to be covered in more detail in a future issue.
It is also important not to set the ride height too low -- even though it looks cool -- to avoid bottoming the suspension during spirited cornering. As explained in our first article, when a car bottoms in a turn, the spring rate for that corner of the car will instantly become infinity (or at least really close). This causes massive slip angles at the corner where the car is bottomed. If the front bottoms the result will be massive understeer. If the rear bottoms wild oversteer will result. Excessive lowering can even cause damage to the shock absorber valving. If we were to enter the vehicle in a car show, we might consider dropping it to the weeds but it would have to go back up for the drive home!
As a nice extra touch, Ground Control whipped up a trick upper spring seat for Project SE-R. The special seat has a Torrington thrust roller bearing to reduce the stress on the spherical bearing in our Stillen camber plates. Now, the Torrington bearing supports the weight of the car taking the load off of the support bearing of the camber plate. This also reduces steering friction, which makes a noticeable improvement in road feel.
Jay recommended that we initially run a 300 lb/in front spring with a 200 lb/in rear spring, amounting to over twice the stiffness of the stock springs. Reminding Jay that we wanted a reasonable street ride, Jay said, "trust me it won't be so bad!" We set the ride height of Project SE-R slightly lower in the front and about the same in the rear as before, giving the car an Integra Type-R-like stance. When driving the new spring combination we were pleasantly surprised. The ride really wasn't so bad. The car was much better on larger bumps and the stiffer springs prevented bottoming on most reasonably sized obstacles. On small bumps like tar strips and botts-dots the ride was slightly worse, with the little bumps feeling harsher. The added rebound energy of the stiffer springs made the car feel a little floaty at high speeds. We cured this by going up a click on the adjusters on the GAB shocks. Now we have the adjusters on 2-3 on the front shock instead of 1 and 2-4 on the rear, instead of one. This speaks highly of the adjustment flexibility of GAB shocks in accommodating such a wide variation of spring rates. There is still plenty of adjustment range in them so if we decide to go to even heavier springs, we can.
When installing the springs, we decided that we needed to take the pre-load out of the anti-roll bar. When someone is sitting in the driver's seat of the car it tilts slightly toward the driver's side. Because of variance in production, sometimes one side of the anti-roll bar is slightly higher than the other side. These issues can contribute to more weight being transferred to one side or another of the car during cornering resulting in a car that handles differently in left or right turns.
To take the pre-load off of the anti-roll bar we first added the equivalent weight of the driver to the driver's seat. Then we loosened the end links of the anti-roll bar. This should be done with the car on the ground. If you jack up the car to loosen the links, be sure to roll the car a few feet in each direction to let the suspension settle. Once the tension was off of the bar, we noted that the driver's side end-link had a one-inch gap between the bar and the bushings when the passenger's side had none. We then stacked one-inch of fender washers on the drivers side end-link between the bushings and the cup washers until it had equal gap and tension to the passenger's side. Taking the pre-load off the anti-roll bar had an observable effect. Whereas previously the car used to understeer less on left turns than right turns, now the difference is noticeably less. In addition, the anti-roll bar has less friction in the bushings now that the static load is reduced, so the ride is a little better. Eliminating pre-load is one of those neat little extras that doesn't cost very much but can produce a distinctive ride. Later, when we adjust the corner weights of Project SE-R we will have to check the anti-roll bar pre-load again.
The difference in handling after the installation of the ground control spring kit was amazing. The ground control springs are the biggest single influence on the handling of Project SE-R out of everything done so far. Lean in corners is practically eliminated, as is dive under braking and squat under nitrous application. It is now possible to induce oversteer by tapping the brakes or drastically lifting the throttle; this helps rotate the car -- a useful maneuver in race and slalom situations. Response in transient maneuvers is much improved. Project SE-R now feels almost like a well set-up rear wheel drive car. Later when we adjust the corner weights and alignment, we are expecting even bigger gains. Our current suspension set up would work well for all-out racing with a few adjustments -- that it is fairly comfortable on the street is icing on the cake.
Reprinted with Permission