Project EP3 Civic Si: Installing Fortune Auto 510 Coilovers!

by Mike Kojima


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.

To read more about Project EP3 check here!

The Fortune Auto 510 coilovers are a high-quality coilover set. They are single adjustable with the adjustment primarily affecting the rebound stroke of the damper. They are of monotube construction and have the ride height independently adjustable from the shock stroke. We got their just released, Generation 6 dampers for our car with all of the latest bells and whistles. 

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! 


The Fortune Auto 510 front struts come with pillow ball bearing camber plates. The lower mounting ears that bolt to the knuckle is also slotted for adjustment. This allows the user to have a lot of flexibility in adjusting the camber and the king pin inclination angle or KPI. 

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. 


The Fortune Auto 510 rear shocks have a really short body which, like the front struts, is independently adjustable for ride height and spring preload.  

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.


There is so little space for the rear shock in the EP3 that the shaft has to be offset via this odd extended upper mount that lets the shaft extend into the rear hatch area. 

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. 


Page 1 of 4 Next Page
Bookmark and Share
Monday, June 05, 2017 2:58 AM
I am debating on whether or not to increase the spring preload on my FWD vehicle. The thinking is that preloading the rear springs on FWD vehicles can enhance straight-line traction and acceleration. Because the springs won't react to a load above a certain preset amount, then the front axles is basically forced to the ground. The preloaded spring is essentially infinitely stiff until the preload is removed. However, other things, such as the tire, the damper internal rebound limiter, etc., still allow some compliance, so the total system is not infinitely stiff, but the increase would be significant enough to provide a 'anti-squat' force.

I have ruled against adding much preload to the front axle because I like my front to be fairly soft, and compliant. I believe in predictable front, with a some 'flickability' in the rear, as the fastest way to get around a corner.

Let me know what you guys think, I noticed that the Fortune Auto 510 has independently adjustable ride height and preload, so it is certainly something to think about for your car.

I'm thinking the preload would also provide a certain level of roll stiffness, I hope I'm not incorrect in thinking this, but it makes sense to me. What do you guys think?
Mike Kojima
Mike Kojimalink
Monday, June 05, 2017 8:48 AM
I am very much against a lot of preload in suspension. Preload does not affect the spring rate but increases the initial amount of force needed to move the suspension. That is the opposite of what you want to do.
Monday, June 05, 2017 1:23 PM
8k/10k spring rates is gonna be a pretty understeery setup. I had 10k/14k on my RSX (same suspension) and it still understeered a bit, even with a pretty aggressive alignment
Mike Kojima
Mike Kojimalink
Monday, June 05, 2017 1:26 PM
probably not, the rear bar is 5x stiffer than stock
Monday, June 05, 2017 1:34 PM
I was on stock sway bars, I guess that should help.

you guys should have FA send you a locking lower collar like the one in the pics below. I had the standard one like you guys have and it would always come loose, a week or 2 of regular street driving. Even with blue loctite, the perch itself stayed locked on the threaded shock body, but the lower part with the steering arm would come loose. Since getting the locking collar with the bolt through it, I haven't touched it in over a year and its still tight (my sisters car now). In my opinion, this should be standard for all DC and EP coilovers.


or my rsx forum post:
Mike Kojima
Mike Kojimalink
Monday, June 05, 2017 1:49 PM
Good idea, I am worried about that happening with ours.
Monday, June 05, 2017 2:14 PM
That's a reasonable conclusion but lacking a solid argument.

For one, I did not say 'alot of preload' but, rather preload at all. The reason why I belabor this point is because every stock suspension I have ever worked on (many different cars, by now) and the OEM spring was always preloaded, and very significantly I might add.

Now, I'm a Mechanical Engineer, so I know, I absolutely know with 100% certainty that OEM's don't do things without reason. Either they do it to cut costs, in increase performance.

I'm talking about adding 'at most' a couple hundred lbs of preload to the rear suspension only. Personally, I already know I'm going to do it, and I've heard some very good results from race engineers at the highest levels of motorsport. There is a REASON why some manufacturers actually ship coilovers with a set preload and ask that you not adjust it if ride height is independently adjustable. Not to mention the fact that all OEM vehicles with strut suspension have a significant amount of spring preload (otherwise you would never have to use a spring compressor).

Once more on preload:

Pre-loading does not change roll resistant rates (rate from the springs and anti-roll bars). It changes the degree of jacking, and therefore the 'anti-roll' "stiffness" contribution of that effect.

For those who are unfamiliar with jacking effects, think of it as being the same thing as anti-dive, except lateral, not longitudinal - ie - a self-stiffening of the suspension in reaction to the lateral loads being fed thru the a-arms.

When finding that amount of preload that works for your car, you are actually looking for the amount of force left on the spring ( and weight left on the tire) for the particular lateral g level at which the push becomes noticable. It is at lateral loads above that level that you are changing the effect of jacking by actually reducing it a bit.

When the shock tops out, the ACTUAL roll center shifts to (nearly) the center of the inside tire contact patch - for any further roll, the car now pivots about that point. The only way it can pivot is to lower itself, and it is in that lowering that the jacking is reduced.
Mike Kojima
Mike Kojimalink
Monday, June 05, 2017 2:35 PM
Well I am a Race Engineer at pretty high levels of Motosports and the is more than one way to skin a cat, but I do not heavily preload on anything I do. The most preload I run is within the range of the tender spring for the same reasons you describe, to help return the tire faster on the lightly loaded side of the car but I never intentionally run the preload up or use it as a tuning tool. I disagree that preload controls jacking, jacking is a function of the moment between the centrus of mass distribution, roll center and the location of the lateral instant center of the suspension. Roll center migration has nothing to do with spring rate, preload or topping out of the suspension other than its effect on the overall moment. It has everything to do with the location of the suspension pivot points and lengths of the arms.
Monday, June 05, 2017 2:59 PM
Mike, what are your thoughts on using a little bit of preload (~1/2") to get a bit more droop travel with really heavy springs. Like 12k on the front of an NC Miata for example if someone is too cheap to fork out for helper springs... :D
Mike Kojima
Mike Kojimalink
Monday, June 05, 2017 3:02 PM
That is perfectly fine.
Monday, June 05, 2017 3:18 PM
sweet! now I have the approval of a race suspension engineer! I'll win all the internet arguments :D
Wednesday, June 07, 2017 4:38 AM
" I disagree that preload controls jacking, jacking is a function of the moment between the centrus of mass distribution, roll center and the location of the lateral instant center of the suspension."

I'm going to start by saying this statement is wrong, but I'm going to limit this discussion to Mac Struts, because that is what the EP3 Civic has and the current suspension on my 'racecar'.

Let's start with a solid definition of 'jacking'.

"Jacking forces are the sum of the vertical force components experienced by the suspension links. The resultant force acts to lift the sprung mass if the roll centre is above ground, or compress it it is below ground."

Now, using that definition for jacking, then the degree to which preload affects Mac Struts is pretty simple. By introducing a spring force to the suspension which acts to counteract compression. This means that preload is DIRECTLY proportional to the amount of jacking that occurs in Mac Strut suspension.

"The key to understanding this is that the initial 400lb compressed the spring the 1st inch, and the spring is pushing back with an equal 400lb force. Now, if you clamp the damper body in a vise and push on the extended shaft, it initially will not move because it is held fully extended by the 400lb spring force. As you add force (say 125lb) to the damper shaft, you reduce the tension on the damper shaft by 125lb, but as long as that force is less than the 400-lb preload, nothing will move, because the net force (now 275lb) on the damper shaft is still holding it fully extended. As soon as you get to 400lb, the damper shaft the extra force will be 400-400=0lb, and the damper shaft will start to move and the spring will be operating as if no preload existed.

Now, I will go out of my way to say I was a suspension engineer that was part of a World Championship winning race team. By, I'm just bragging now. ;)
Mike Kojima
Mike Kojimalink
Wednesday, June 07, 2017 10:27 AM
Your definition of jacking is different than mine. You include every upward force is that correct? That is not jacking as how I consider it, I don't think most suspension engineers do either but now that you pointed out to me, it is an additional force component to consider and is probably the solution to an odd thing I have been seeing in the data on one of my customer cars. I am gonna run some numbers and see!

Oh yeah I do some OEM work as a consultant on some well-known and well-regarded cars I am just under NDA so I can't talk about it. What racing program do you work on?
Boxed Fox
Boxed Foxlink
Wednesday, June 07, 2017 6:58 PM
An engineer from Modulo (basically a Honda engineer) explained to me that OEM replacement springs are preloaded because they need to achieve a compromise between spring rate, total length, ride height, rate linearity, and noise reduction.

Basically they need to achieve a specified ride frequency for the ride height in the spec, and with the spring steel that they have available to them that often results in them having to either use a thin gauge spring wire with a lot of coils or put a bunch of dead coils at the top or bottom. Thin wires aren't great for longevity and dead coils waste material (and they're noisy if you space them wrong). Preload gives them a means to keep dead coils and noise to a minimum while having a relatively small impact to ride height at the rates they work with.

All of the calculations are done by cool propriety software (that the guy wouldn't show me) and the designers choose the shape they like the most out of the workable result set.
Boxed Fox
Boxed Foxlink
Wednesday, June 07, 2017 8:08 PM
Back to the original question. I don't think you actually want the effect of an "infinitely stiffly" preloaded spring if you're looking for better traction. Preloading the wheels to achieve this effect causes the rear end to skip when you lift a wheel while going over kerbs or go through a tight corner (if your car lifts the inside rear like many FWD racecars do). From what I understand, race teams go to great lengths and cost to avoid this behavior.

Like Mike said, preload does not increase the roll stiffness of the car. It's just a static force acting on the car that only looks makes it seem like you increased the roll stiffness when a wheel lifts off the ground or when the car is at rest. For the same reason it's very different from anti-squat or anti-dive. The effects look very similar on paper when the car is at rest but as soon as you get the tiniest amount of travel it's effectively not there.

What preload does give you is a way to use the spring through the range where it's most consistent. If you've ever fully stroked a coil spring through a spring tester, you'll notice that they are very stiff when they're barely compressed, increase linearly in rate for a few inches (where the spring is meant to be used) then becomes extremely stiff again before it blocks. That middle section where the spring is relatively linear in rate is surprisingly small, usually only a few inches in your average coilover spring. By playing with the preload, you can maximize the amount of time that the spring spends in that usable range where the spring is relatively linear in rate.

As you can imagine though, this is a massive pain in the ass and the spring manufacturers know it. One of the reasons that Swift uses such a weird alloy is that it maximizes this usable range. Hyperco winds their springs in a special way so that the springs aren't as stiff when they are at free length. Both solutions minimize the need to play with preload to get the springs to work "as advertised." It's the main reason Hyperco gets so much business in Japan and why Swift Springs are so desirable in circle track cars here in the US.

Back in the days when I was getting to grips with the nuances of car suspension, I experimented with preload a fair bit and played with it a bit on some suspension modeling software. The conclusion I came to that it was probably more of an annoyance than a useful tuning tool and that I should look elsewhere to get the behavior that I wanted out of the car. Nowadays I just install helper springs or just let the main springs clatter around, depending on what the car is used for.

All that said, I'm also curious. What race team did you work for?
Boxed Fox
Boxed Foxlink
Wednesday, June 07, 2017 8:16 PM
One last thing - If you do play with preload on any coilover that uses Swift springs, make sure that the coils will not touch at full compression. That HS5.TW alloy is amazing stuff but it does not tolerate blocking/coil binding at all. Swift themselves say that if you let one of their springs coil bind, it will lose its shape and it will basically be junk.

And yes, I've accidentally done this myself. That a painful $250 mistake.
Mike Kojima
Mike Kojimalink
Wednesday, June 07, 2017 11:56 PM
I think many short length wire springs get messed up if you go into block, Swift designs are higher stress than many but the steel quality seems to be better. Cars don't seem to have settling issues with Swift or Hyperco.
Thursday, June 08, 2017 1:33 PM
I've had 2 car's now with Swift coilover springs (RSX and Miata) and both have settled. Friend of mine has a C7 Vette with Hyperco coilover springs and that settled as well.

That being said, I don't think its that its that big of an issue... install your coilovers with height just eyeballed in, driver around for a week and then dial in your hieghts or corner weight your car then.
Boxed Fox
Boxed Foxlink
Thursday, June 08, 2017 2:01 PM
Well pretty much all metal coil springs settle. It's just that good springs tend to lose less free length over time and they do it consistently. I've taken Eibach coilover springs off of cars after a few thousand street miles and seen a 1/2 inch free length difference between the left and right sides.

In comparison, the Swift main springs on my ITS car have been on there for three seasons and they measured within a few millimeters of each other this past winter. If I put them in a spring tester I'm willing to wager that they'll still be within two percent of each other through the middle 40mm (where it's a steady increase in rate) even though I've been doing all sorts of kerb hopping and unintentional off-roading with them.
Thursday, June 08, 2017 4:16 PM
oh I see, I did think of it from that point of view
Wednesday, June 14, 2017 4:47 PM
So, I did actually go ahead and do this 'rear preload' modification on the rear suspension of my VW Jetta (torsion bar). I can definitely say, that it DEFINITELY IMPROVED the ride and handling of the vehicle.

Full Disclosure, (for posterity) adding preload was NOT the only modification performed. I'm sorry, but I'm not a lab, and when you have the car apart you tend to do all the work at once. So, no apples-to-apples comparison.

First, I added approx. 40mm of preload to an H&R Progressively Wound lowering spring. At this time, I also added upgraded to a FK shock with firmer valving and optimized for lowered vehicles (it was about a 50mm inch shorter shock body, as well).

Second, I lowered the rear ride height approx. 30mm.

So, I will admit. In the process of increasing the rear preload, my damper stiffness was increased (compression/rebound), and the rear ride height was lowered. Obviously, I can not, in good faith, say that the all the handling benefits came directly from the preload.

Ok, that said. Conclusions?

The rear roll stiffness is absolutely increased. It feels like there is a nice big rear swaybar on the rear now. Also, there is significantly less squat and brake dive. As far as I can tell, there has been NO detriment to the ride quality of the vehicle (although, the rear feels marginally stiffer, I actually like it that way).

For such a simple modification, try it on your vehicle to see if it improves your ride and handling (if you have dampers that allow it). Because it's just about the easiest modification to do, and undo, if you don't like it.

Hope this helps add a little bit to the 'Panoply of Suspension Geek Wisdom.'

Thanks for reading, if you made it this far!
Mike Kojima
Mike Kojimalink
Wednesday, June 14, 2017 4:50 PM
By torsion bar, you mean twist beam?
Wednesday, June 14, 2017 5:12 PM
Yeah, I believe VW refers to it as a 'torsion beam', IIRC.

Dang, I typed out a good response to you, but it deleted it. I will sum it up again.

"Oh yeah I do some OEM work as a consultant on some well-known and well-regarded cars I am just under NDA so I can't talk about it. What racing program do you work on? "

I'm in a similar place right now. All I can really say is that I work with a electric vehicle company called 'Arcimoto' on their suspension.

My 'championship winning' days were at the University. When I joined the team, we hadn't even placed in the Formula SAE ranks before. And, we soon won the US series, and the World Championship after that. It means a lot to me, because our Professor didn't really lead the team, it was student lead.


Also, I never learned much about suspension in Engineering college. Of course, they teach you the basics. But you have to read all the books, which eventually, I did (of course, before college I started with SCC , and Mr. Kojima's book). I can say that John Dixon's books gave me the equations and knowledge to actually make some good simulations in Matlab that really helped me understand suspension loading. Personally, without his books I would know a fraction of what I know. So I really, have to attribute my knowledge to him. It is not coincident that we had success shortly after I read these books (especially the shock absorber handbook):


Wednesday, June 14, 2017 5:26 PM
"Back to the original question. I don't think you actually want the effect of an "infinitely stiffly" preloaded spring if you're looking for better traction. Preloading the wheels to achieve this effect causes the rear end to skip when you lift a wheel while going over kerbs or go through a tight corner (if your car lifts the inside rear like many FWD racecars do). From what I understand, race teams go to great lengths and cost to avoid this behavior."

This is why I kept the modification to the REAR of my FWD vehicle. I personally, do not think the preload will help as much with the wheels that provide tractive power. My thinking is that preload is just an additional 'tuning' mechanism by which you can fine tune your handling. It is not a cure all to bad handling.

I would really like for other people to try this out, and report back, if possible. For one, consensus builds support for further development.

I've been studying suspension for well over 10 years now, and I'm still figuring out new things all the time. And that's with fairly static designs that haven't changed in many, many years.

I believe suspension is one of the more complicated parts of vehicles, that I believe is commonly ignored, but effects just about every aspect of performance, ride and handling...meaning, you may love or hate the car, depending on the suspension.
Mike Kojima
Mike Kojimalink
Wednesday, June 14, 2017 6:14 PM
I like just enough preload to keep the inside wheels planted on the ground when the loads are light but not so much that it overpowers the damper. I also like putting the spring in the sweet linear spot of its rate curve. I don't like what some Japanese suspension guys do like running tons of preload with no droop travel. I think that loses a lot of traction and makes the car behave in a snappy manner.
Friday, June 16, 2017 10:25 AM
I wish they'd make these for my G37.
Friday, January 12, 2018 3:08 PM
fortune auto doesnt have these listed on their site, also the springs look to be the standard spring option not the swift, i would like to change what i have currently for a coilover from progress to these but they dont have ep3 or dc5 available. i already have the rsx-s swapped engine and 6 speed and 5 lug wheels done, could use an other set of coilovers did you have them specd with rsx fronts and ep3 rear lowers due to the diffrence in the lower bushings, i am on my 2nd set of coilovers first were h&r that i was a huge fan of for 5 years then progress but the front strut has play and its not as good of a ride of the h&r with bilstein struts, but i had to modify the rear lowers by grinding down the bushing on the bottom of the strut
Mike Kojima
Mike Kojimalink
Friday, January 12, 2018 3:49 PM
You might want to try contacting Terry at Fortune.
Tuesday, March 27, 2018 7:17 AM
What would you recommend for someone who wants to keep a near stock ride height? Would you still recommend the fortune 510s with the longer shock mount, or an a-spec kit? If keeping a near stock ride height would the Hardrace tie rod ends and roll center correcting ball joints be needed?
Post Comment Login or register to post a comment.

MotoIQ Proudly Presents Our Partners:

© 2018 MotoIQ.com