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Project Phoenix SE-R...Getting A Grip On Things - 1991 Nissan Sentra SE-R

May 1, 2003 SHARE
0305_turp_02_z+1991_nissan_sentra_ser+rear Photo 1/1   |   Project Phoenix SE-R...Getting A Grip On Things - 1991 Nissan Sentra SE-R

In our last three segments of Project SE-R, we focused on developing power out of our SR20DE powerplant, lots of power. Our car is fast, real fast-fast to the point where the blown, wonkey suspension the car came with is woefully inadequate to the point of being dangerous.

Our Nissan came complete with worn, blown-out shocks, mushed out and cracking bushings, worn and rattley ball joints and saggy lowering springs of unknown origin.

The car looked nice and low, but it was settled on the bumpstops, making the ride mushy and soft, yet still bouncy and jarring, and the car would bottom out with the slightest provocation. When power was applied, our tremendous torque would cause the suspensions geometry to change, resulting in severe torque steer.

Project Phoenix SE-R was a handful to drive under these conditions. We wanted a no-compromise suspension system with maximum grip and stability first and ride coming a distant second. We also wanted the suspension to be fully adjustable for damping, ride height, roll stiffness and alignment; in short we wanted something close to a racecar's suspension.

We borrowed a lot of suspension technology from a NASA SE-R Cup road racer. In fact, our suspension is nearly identical to what these fast road racers run on the track. With the exception of slightly softer spring and damping rates, the Phoenix's suspension is identical to the winning NASA car's.

ShocksAfter perusing and rejecting offerings from manufacturers of street-type shock absorbers, we decided since Project Phoenix SE-R is more powerful and faster than many racing cars, we would need real racing shocks.

We turned to Ground Control's awesome state-of-the-art Advance Design racing shock absorber for help. We selected Ground Control because of several reasons; the other brands of racing shocks we checked out were pure racing universal types originally intended for real purpose-built racecars. This made adapting them to the SE-R's production based street car suspension a difficult and expensive task, which would require lots of machining, welding or both.

The Ground Control shocks have a modular design that makes them easily adaptable for both racecars and modified production sedans. In fact, GC already offers shocks for most popular offerings such as the Nissan Z cars, Hondas, Acuras and the Supra. Different types of end mounts and shock shafts can easily be screwed onto either end of the shock body to adapt the shock to most types of car. Ground Control also makes fabricated, ultra-strong strut bodies for the AD shock so they can be adapted to cars using a McPherson strut-type suspension. This is what we used to adapt the shocks to the SE-R. If Ground Control doesn't currently make an application for your car, it probably can on a custom basis.

The shock body itself is designed to be easily lathe cut to the correct length for any application. Ground Control makes Spherical Bearing, Polyurethane Bushing and Clevis ends for the shocks to make them easily adaptable to just about any sort of car.

In the relatively short time that they have been in production, Ground Control shocks have amassed quite a few victories. Many SCCA road racing and solo championships have been won on these shocks that have been produced for less than three years! This is an impressive accomplishment for this new design and a tribute to the design's basic soundness.

The SE-R's stock suspension has one major disadvantage-the stock struts don't have much wheel travel and the car can't be lowered more than an inch without the car bottoming excessively.

The car's travel is so short that it can bottom under cornering load alone with sticky tires. This can make cornering unpredictable with the front or rear of the car suddenly breaking away if the suspension bottoms under load. The Ground Control shocks are 1.5 inches shorter than stock so the car can be easily lowered up to 2.5 inches while still maintaining a useful amount of wheel travel. This lowers the center of gravity of the tall, boxy SE-R, further helping cornering.

When the wheel travel is maintained, you can go up in spring rate considerably while not giving up ride quality.

The other main reason we selected the Ground Control shocks is they feature digressive valving. Digressive valving is a revolutionary way of valving shocks that is entirely different than in previous shock designs. A digressive shock has stiff progressive damping at low shaft speeds, typically shaft speeds of less than 3 inches per second. This helps control body motions, such as rolling, squating, and diving, just like a typical stiff racing shock absorber.

At shaft speeds higher than this in the 3-to-10-inch-per-second velocity range, the damping force stays more or less constant, despite the rapid change in shaft velocity. This helps maintain a supple suspension response to bumps and irregularities in the pavement. This suppleness helps the car maintain traction by reducing hop in bumpy turns and gives a good ride, even at high damping rates needed for body motion control

Digressive valving is the opposite of how shocks have been traditionally valved. Usually, shocks have more damping force at higher shaft velocities than lower. This curve can be shaped and regulated to a degree by adding different valving stages. Valving stages are hydraulic fluid bypasses with check valves of differing rates and flow volumes that blow-off hydraulic fluid inside the shock at different set shaft velocities for better bump response. Even with these tricks, a conventional shock's damping curve is different than a digressive shock's curve.

Conventional shocks tend to have more damping when the shaft velocity is higher, despite multi-stage valving. Digressive shocks were first used successfully in rally and off-road racing and have only recently made their way into the on-road racing area.

The GC shocks have a general valving layout and a single tube construction much like a conventional DeCarbon-type shock such as Bilstein. A single tube shock has the advantage of better cooling and the ability to run a larger piston. A larger piston displaces more oil. Greater oil flow through the valves gives better damping control.

The piston is attached to the shock shaft and uses a flexible Swedish steel stack of thin, precision ground, shaped washers to control fluid flow. The washers cover the bleed orifices drilled into the piston for compression and rebound fluid flow.

There is a washer stack on both sides of the piston to control fluid flow going either way, in compression or rebound. The washer stacks act like one-way check valves for the fluid. As the incompressible fluid passing through the orifices in the piston hits the washers as the piston moves, they flex and bend out of the way to allow the fluid to pass.

The stack of the washers is kind of like a leaf spring, with the profile of the stack and the thickness and diameter of the washers controlling how the washer stack flexes. This controlled flex regulates how fluid passes through the orifices in the piston. That is one of the main ways Ground Control can precisely control the shape of the damping curve.

Another ingenious trick that Ground Control uses to control the shape of the damping curve is to use shock pistons with varying concaveness in the surface that the washer stack seats against that allows the washer stack to be set with differing preloads.

The shape of the damping curve can be precisely tailored with great flexabilty by changing the diameter, thickness and contour of the washer valve stack, the size of the orifices drilled into the piston and the amount of concaveness of the pistons sealing surfaces.

The Ground Control shock can be adjusted for both compression and rebound damping by a slotted shaft running up the shock's main shaft, which controls the size of the shocks major bleed orifice. In a very easy-to-reach, convenient way, the shock can be adjusted at the very top of the shaft by turning the two stacked knobs at the very top end of the shaft; a red knob adjusts for rebound and a blue knob controls compression. This beats the typical, hard-to-reach adjusters used by most racing shocks.

To help prevent bubble-forming cavitation, to increase the Redline synthetic hydraulic fluid's boiling point and to give room for the shock shafts displacement under compression, a floating piston separates the oil from a chamber full of high-pressure nitrogen, filled to about 200 psi.

Separating the oil from the gas allows for the valves to flow only fluid, which improves damping action. In conventional shocks, the oil is mixed with enough air to allow for the shock shaft's displacement. Sometimes bubbles pass through the valves, creating dead, undamped spots within the damping curve.

Since conventional shocks aren't pressurized, it's easy for the fluid to have localized boiling inside the shock under rapid shaft motion due to cavitation. Also, since the shocks don't have more than ambient pressure, it is possible for the fluid to boil itself under extreme use.

The nitrogen pressure can be easily adjusted through a schrieder valve at the bottom of the shock. Sometimes this can be a useful tool to increase the suspension's preload without changing the spring rate and/or ride height, or the gas pressure may need to be increased to prevent foaming and boiling under severe conditions.

The shocks feature high-overlap Teflon bushings to reduce static seal friction-or sticksion, as engineers call it-and to also ensure a long service life. Low-tension Teflon oil seals with built-in scrapers also ensure long, leak and sticksion service intervals.

The shock's body is machined from lightweight 6061 aircraft aluminum, then hard anodized inside and out for corrosion and wear resistance. To prevent a harsh, chassis-unsettling jolt when bottoming out, the shocks have a trick microcellular urethane bumpstop. This soft material is shaped to provide a controlled progressive stop to the end of the wheels travel.

MCU bumpstops have made a huge difference on some of our other project cars and we think it's great that Ground Control has provided them as standard equipment. Ground Control shocks were twice as light as the stock shocks were. This can go a long way in reducing unsprung weight.

The shock's body is threaded externally to accept Eibach ERS racing 2.5-inch coil-over main and tender springs. The spring hats and adjusting collar hardware are machined from 7075 aluminum and hard anodized for wear and corrosion resistance. The Ground Control Advance Design shocks are designed to be simple to rebuild and maintain. With a few tools, you can even revalve, rebuild and repair the shocks at home. If not, you can simply send them back to Ground Control for a quick rebuild.

SpringsSince we are SE-Rious about eliminating lean and understeer in the corners, we used stiff Eibach ERS 450 in/lb front racing springs with a 350 in/lb ERS rear spring. These rates are only slightly softer than what is run in a NASA SE-R Cup racecar.

Even though these springs are more than three times the stiffness of the stock springs, as we have found in the past, stiff spring rates are essential for keeping lowered cars off the bump stops for consistent handling. Even though the ride is quite firm, it is still more comfortable than our bouncing, overly lowered old suspension.

Ground Control Camber/Caster PlatesWanting to do more adjustments and lower the car a little more without losing wheel travel, we installed some Ground Control Camber plates. These plates can lower a '91 to '94 Sentra or NX2000 or a '95 to '99 200SX-Sentra by about 0.5 inches with no reduction of wheel travel.

They also are adjustable in caster as well as camber. We have found running close to three degrees of positive caster helpful in getting our cars to turn in better. With positive caster, the camber tends to go more negative as the wheel is turned, which is exactly what you want. The wheel actually leans into the turn as the wheel is turned, giving you negative camber on the outside wheel, plus the camber goes toward positive on the inside wheel, just the way you want it.

The Ground Control plates are unique in that they mount on top of the shock tower. This top mounting moves the whole strut assembly upwards, lowering the car without reducing the strut's travel like adjusting the shock lower will.

Because of this top mounting, the Ground Control camber plates won't work with all strut tower braces. They worked with our Eibach strut tower brace. Shigspeed also sells an adaptor so the Ground Control plates will work with Stillen billet strut tower braces.

Another good feature of the Ground Control camber plate is it has a roller-type Torrington thrust bearing to support the vehicle's weight, taking a lot of stress off of the spherical bearing that supports the shock shaft. This feature makes the spherical bearing last several times longer than on a typical camber plate with a single spherical bearing. Usually the spherical bearing is a fast-wearing item on most camber plates.

Finally, the Ground Control plate has a conical seating surface for the upper spring seat. This allows the seat to locate itself while the steering wheel is turned and not bind or cock sidewise. This feature makes the plate quieter than other brands. Most camber plates rattle and clunk as the wheels are turned, especially when doing things like slow-speed, tight turns. The Ground Control plates are quieter than most others we've tried. Overall, we think these camber plates are the best on the market.

The world's best chassis man, Darren Nishimura of West End Alignment, set Project SE-R's camber at 2 degrees negative, caster at 3 degrees positive and toe at 1/8-inch toe out. Darren set the ride height 2.5 inches lower in the front of the car and 2 inches lower than stock in the rear.

This slight rake helps reduce aerodynamic drag and lift. We corner-balanced the car with 180 pounds in the driver's seat. This is not the best set-up for long tire life, but should work well on the road course and still be fairly reasonable for street tire wear.

If we have to do any changes from this baseline at the track, we use a digital Smart Camber camber caster gauge from True Choice and toe plates from Longacre Racing. For drag racing, we can quickly reset our camber to negative 0.25 degree and zero toe for a better launch using these tools in the pits.

If your car is set up to have a lot of suspension adjustability like ours is, then these tools can save you a lot of money and allow you to adjust your suspension to its fullest potential.

Shock MountsTo bolt the shocks in place with a minimum amount of soft rubber which can cause a small amount of undamped travel, we obtained some Shigspeed Pillow ball upper shock mounts for the rear shocks.

The Shigspeed upper shock mounts feature an all-aluminum construction, mounting the shock shaft by means of a single spherical bearing instead of a big, squishy biscuit of soft rubber. This makes every bit of suspension motion go through the damper instead of having undamped travel due to flexing of the upper mount. On some cars, this flex can be as much as 1 inch up and down-not good, considering this is uncontrolled wheel motion.

Energy Suspension BushingsBecause our power has increased tremendously as we added the turbo system with more and more boost in our series, we had been noticing more and more deflection in our front suspension under power.

On the dynojet we noticed that our wheels would flex forward about 1.5 inches under load. While speed shifting, observers told us our wheels seemed to jump forward about three inches!

Even though our JWT motor mounts had eliminated about 40 percent of our previously terrible wheel hop, we still had some minor vibration through the wheels while doing burnouts. Our wheels were still hopping a little.

When accelerating hard out of tight turns, our torquey engine was beginning to make the car torque steer. We figured much of this torque steer was caused by toe-change induced by the flexing of the lower control arm bushings.

Energy replaced our lower control arm, steering rack, rear links, and shift isolator rod with its own proprietary hard polyurethane.

The polyurethane was much harder than the gushy stock rubber bits. The lower control arm bushings were the most critical; the deflection of the soft, gushy rubber was the main reason for the wheels' up-and- down hopping and fore-and-aft motion. The monkey motion was also contributing to torque steer. The stock bushings are so soft, we recommend the Energy replacements for just about any performance application.

We also changed our ball joints, tie rod ends, steering rack boots and axles using Moog ball joint and Genuine Nissan for the other parts. Before we installed our bushings into our links and lower control arms with a hydraulic press, we had everything powdercoated gloss black to give the underneath of the car a fresh new look.

The Energy bushings are a direct press-in replacement for the stock Nissan bushings. The bushings made a big difference. Not only did they reduce wheel hop but they eliminated the wheel fore-and-aft movement.

Torque steer out of turns decreased about 50 percent and straight-line torque steer was eliminated. Shifting feel was also improved slightly. The car had a more direct steering feel with less mushyness.

Surprisingly, the car rode better as well. We theorize it's because the urethane bushings have less stickshion than the stock rubber bushings so the suspension can respond better to small bumps. There was more vibration through the steering wheels and more road noise in the cabin, but this wasn't an issue; it was barely worse than stock and much better than full race metal bushings.

The Energy bushings are a good bang-for-the-buck modification, especially with the car making healthy power.

Anti-Sway BarsWhat suspension build up would be complete without a set of performance anti-sway bars? The anti-sway bar's, or sway bar or anti-roll bar as it's also known, main job is to reduce body roll under cornering. This keeps the tire's tread flatter on the road so they can produce more grip. By limiting the amount of roll, sway bars can also make your car a lot more responsive to steering input because they allow the car to change directions before it starts to lean.

Sway bars also can be used to help balance car handling by reducing under- or oversteer. They do this by altering the amount of weight distribution under roll. By reducing roll on one end of a car more than another with a larger sway bar, the amount of weight transfer to the outside tire on that end of the car is increased. This causes a bigger slip angle of the tire on that corner of the car, therefore making that corner of the car slide out sooner.

A car that understeers (front end slides out first in hard cornering) can be balanced by a stiffer rear sway bar. A car that oversteers (rear end slides out first) can benefit from a stiffer front bar. Most cars are designed to understeer by the factory because it's safest for inexperienced drivers.

We will be shooting for neutral steer. Neutral steer is when both the front and rear tires slide equally under hard cornering. Neutral steer provides the best cornering power because both front and rear tires are used to their fullest potential

The sway bars for Project SE-R were supplied by Progress. The Progress front sway bar is a stout 1-3/16-inches in diameter, up from the stock bar's 1-inch diameter. It uses polyurethane for the mounting bushings, which is much harder and more durable than the stock rubber bushings.

Harder bushings allow the sway bar to be more effective by transferring the roll forces directly to the sway bar instead of compressing the soft rubber first. The rear sway bar is 13/16-inch instead of the stock part's meager 9/16-inch diameter, and bolts to a reinforced bracket attached to the car's spindle instead of the stock part's flimsy, failure-prone shock body mount.

The Progress bars feature three-way adjustability for both the front and rear bars, which makes them the hot tip for racing or ultra-high performance street cars. This allows tuning of the understeer/oversteer balance by placing the sway bars' end links in one of three holes. The hole closest to the end of the bar is the stiffest position and the hole farthest from the end is the softest.

To increase understeer, stiffen the front bar and soften the rear. To increase oversteer, soften the front bar and stiffen the rear.

Unlike many aftermarket swaybars, the Progress units are designed to be at the proper angles on both stock height and lowered cars. Most sway bars are designed for a car at stock ride height and bind or contact parts of the car's suspension on a lowered car. This causes a stiff ride and even unpredictable handling as contact can increase wheel rate drastically.

The Progress sway bars also feature spherical bearings on the end links instead of the usual rubber or urethane bushings. The spherical bearings get rid of all sticksion and bind inherent with bushings and actually improves the ride. The bearings also have no give so every bit of the car's body movement gets instantly transferred to the sway bars.

Strut Tower BracesChassis flex is a no-no for high-performance cars. Chassis flex makes for a rougher ride, allows squeaks and rattles to develop, causes the suspension geometry to shift under load and negates some of the ability of changing sway bars and springs to tune the handling balance.

The old B13 was designed in an era where chassis stiffness was not such a design priority as it is today. The B13 is a flexi flyer, which makes suspension tuning more difficult and reduces overall handling precision. Our foam injection that we used previously helped considerably, but our chassis still needed more help.

Short of a tube frame, a carbon tub or a not-so-practical- for-street, eight-point roll cage, strut tower bars are the most cost-effective way to stiffen your ride's chassis.

Strut tower bars stiffen the chassis by tying the shock towers together, keeping the suspension geometry from changing under load. The trick, elliptical, aircraft-aluminum-tubed front strut tower bar on Project SE-R was made by Eibach.

This bar is fairly rigid and is compatible on top of the shock tower-mounted Ground Control camber/caster plate. Since no one makes a rear strut tower bar for the '91 to '94 SE-R, we made our own out of a piece of 0.060 wall thickness 4130 chrome-moly with a one-off bracket we bent out of some sheet steel.

We bolted our home-grown special to holes drilled in the rear shock tower with some stainless-steel Allen bolts. The stress bars tightened up the Project SE-R's body noticeably. The difference in turn-in and cornering stability was actually noticeable

Our project now has incredible handling to go with our huge influx of power. Many racecars don't have this sort of chassis sophistication and adjustability. We can honestly say Project SE-R is perhaps the best-handling FWD car we have ever experienced. With much better handling, our car feels more balanced and integrated, with the fun-to-drive factor going up three-fold. With our suspension's great amount of adjustability, we can optimize our set-up for everything from drag racing to autocross to even road racing.

Stay tuned, next month we bring our tiny, fading, weak and worn brake system in line with the performance goals of the rest of the car. Our once abandoned, rotting econobox is quickly forming into one mean exotic eater sleeper.

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Sources

Energy Suspension
San Clemente, 92673
888-913-6374
http://www.energysuspension.com
Jim Wolf Technology
El Cajon, CA 92020
619-442-0680
http://www.jimwolftechnology.com
Nissan Motorsports
Gardena, CA 90248
310-532-3111
http://www.nissanusa.com
AEM
Hawthorne, CA 90250
800-992-3000
http://www.aempower.com
Mackin Industries
Santa Fe Springs, CA 90670
562-946-6820
http://www.mackinindustries.com
Xenon
Anaheim, CA 92806
714-632-1709
www.teamxenon.com
MagnaFlow
Rancho Santa Margarita, CA 92688
800-824-8664
www.magnaflow.com
The Progress Group
Anaheim, CA 92806
714-575-1193
progressauto
Motivational Engineering
310.639.7320
http://www.motivational.net
Hose Techniques
www.hosetechniques.com
Eibach
Corona, CA 92879
800-507-2338
http://www.eibach.com
Speedway Muffler
(951) 371-6454

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