Project EP3 Civic Si: Installing Fortune Auto 510 Coilovers!
Over the past few installments of our EP3 project, we have been working on fixing on what is perhaps the car's major weak point, the handling. Previous Civics were known for excellent handling with 4-wheel multi-link suspension. The EP3 however, uses the suspension from a Japanese market Stream van in a really dumb case of parts bin engineering.
The van suspension did away with the excellent front multilink and replaced it with pedestrian typical, econo shit box McPherson struts. To add insult to injury, the steering geometry of the EP3 is straight out of the van with its built in bump steer.
In our previous editions of Project EP3, we laid out the base for a good chassis by upgrading the brakes, tires, bushings and sway bars and correcting some of the suspension's geometry. Now we will add some coilovers from Fortune Auto to round out our suspension mods so far. We have had excellent results with Fortune's race coilovers on our Civic race car, so we were eager to try their street/track oriented 510 single adjustable coilovers on Project EP3.
The Gen 6 improvements are a double digressive piston, which gives enhanced low-speed damping. Low-speed damping means increased damping or resistance to movement in the range of very low piston speeds. This is about 0-2.5 inches per second. This is the range that affects chassis movements like body roll, squat, and dive. As far as stuff the driver can feel, low-speed damping has the largest influence.
Low piston speed means low fluid flow, and it is difficult for shocks with conventional valving to develop a lot of hydraulic force with low flow volumes. The Gen 6 Fortune Auto 510 can develop good low-speed damping force though with its unique piston design.
This is done by making a piston with larger ports for more fluid flow and for more flow going through the adjuster valve, which is a needle valve and allows the adjuster to vary the fluid flow. This is backed up by a stack of thin washers that deflect to control the fluid flow through the ports. This is known as the “christmas tree”. The amount of damping and the tuning of the shock is adjusted by varying the thicknesses and diameters of the shims in the christmas tree.
This affects the flex characteristics of the christmas tree and thus controls the shape of the damping force curve. The Gen 6 piston has a ring around the base of the christmas tree that allows preloading of it. The preloading resists fluid flow at low volumes of flow and thus gives good low-speed damping. It is an elegant and simple approach to solving a difficult property for a shock designer to achieve.
At higher piston speeds, like when hitting an FIA curb or a pothole, the christmas tree flexes a lot, allowing a lot of fluid to blow off and giving the suspension a lot of free movement. This gives better shock absorption and a smoother ride. The blow off lets you have good platform control and a surprisingly smooth ride together!
Adjusting the KPI means that the scrub radius of the front suspension can be adjusted. Scrub radius has a big influence on both torque steer and bump steer reactions on the front wheel drive car. A lot of people ignore this and run big offsets that really make bump steer and torque steer worse.
The front struts come with 8 kg springs which we think are appropriate for a strut equipped FWD car that is to be driven hard. This is an increase from the stock 4.4 kg springs.
A cool feature of Fortune coilovers is that they use super high-quality Swift springs. Swifts are some of the best springs that we have yet to use and really resist fatigue and sacking out. Just about all other race springs we have used fatigue quite a bit after a while and will lose ride height and require continual adjustment of the preload to maintain ride height. We have never had this issue with Swift springs.
More cool features for the Gen 6 shocks are a hard anodized 7075 T-6 body which is light, strong and resists corrosion and seizing of the spring seats, stronger shafts, CNC-machined billet top caps and improved piston nuts. The Gen 6 also has dust boots and progressive microcellular urethane bump stops.
The rear springs are 10 kg. This is an increase from the stock 7.8 kg springs. If you notice that the rear springs are stiffer than the front, it is because the rear suspension of the EP3 has a pretty severe motion ratio and the actual wheel rate is somewhere around 6 kg which is relatively conservative for an FWD car. Since this is going to be a car that sees a lot of street use, conservative is better.