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An inside look at the Feal 441 Suspension for the B13 Sentra SE-R!

by Mike Kojima

 

The original B13 Sentra SE-R has always held a dear spot in many of our hearts. Produced from 1991 to 1994, the SE-R combined the lightweight shell of the Sentra coupe with the sparkling performance of the beloved SR20DE engine. For its time, the SE-R offered a great performance bang for the buck, and to this day, it has scores of hardcore devotees who treasure them.

The Achilles heel of the SE-R has always been its suspension. Struts with very limited travel, rear suspension that binds and front suspension that has a ton of bumpsteer in the geometry make the car difficult to get to handle really well, especially if it has been lowered. Compared to its contemporaries like the Honda Civics, handling has always been a problem with the SE-R.

The biggest problem standing in the way when trying to make the SE-R handle right is a lack of wheel travel. Lower the car 1.5" and you are close to sitting on the bump stops, especially in the front. If the car rolls over onto the bump stops in a turn, it goes into instant grinding understeer. 

New shorter struts are the answer, but the problem with the SE-R is that it was a low production volume car. Even though the car has legions of fanatical followers, their numbers are still pretty thin. So thin, that no major suspension company has ever committed to making anything good for the car. There are a few Chinese companies that make some low quality stuff, but these do not work very well. So the only choices were custom short struts that were available at one time but not anymore. The fact is there are few companies willing to make something trick for a low volume car built 25 years ago.

Martin was in the process of rebuilding the well-worn suspension and brakes of his treasured daily driver SE-R, and his existing suspension was pretty hammered. Martin's car had a homebrew set up, which for a time was the best you could build for the B13 Sentra. In the front, Koni Yellow shocks for a A32 Maxima were set into some shortened modified stock strut housings that were altered to take a threaded sleeve, allowing the use of Eibach 300 in/lb ERS race springs. In the rear, Koni red shocks were used with some custom Hyperco springs that fit the stock perch. These were made for the SE-R forum on a group buy many years ago, and they came with a 200 in/lb rate. These springs are twice as stiff as stock which helps when you don't have much travel! 

Anyway, Martin's suspension was worn out and we needed a suitable replacement. After searching for a long time, the only company we found that we were comfortable with using was Feal Suspension. Feal is owned and operated by Formula Drift pro driver Aurimas "Odi" Bakchis.  We have known and competed with Odi for years and can vouch that he is a man well acquainted with suspension technology.

 

Every set of Feal shocks are assembled and calibrated in the USA, right in Feal's SoCal office by Odi and his staff. This also provides a lot of opportunities to order your Feal Suspension with custom spring rates and valving. Odi has a lot of experience with nearly all genres of Motorsports and can make recommendations for your custom set up or build to your spec as well. 

A set of Feal Suspension starts as this knockdown kit that Feal has made for them to their spec in Asia. Now don't let that scare you, most suppliers of high-end dampers also have many or all of their internals made in Asia, as well as many Asian factories are ISO certified and can produce world-class quality parts.

Odi has gone through a great deal of effort to assure that the parts used in Feal suspension are top notch with all of his parts built with a high grade of material and tight tolerances. Odi himself has made many trips to Asia to work hand and hand with his suppliers to get the quality up to his standard. 

 

The kit contains all of the parts needed to assemble a set of Feal coilovers. The coilovers are hand assembled with special care being taken with the valve piston assembly to assure adherence to tight specs for the damping curve. 
 

A build starts with a visual inspection of all components. Then the parts to build the valve piston are pulled according to the bill of material. The washers shown lying in front of the pistons are actually the shims that make up the "Christmas Tree" of the shocks valving.  

Feal uses a deflected disc system for their valves. A deflected disc system works by stacking up layers of thin washers or shims in a closely specified way. When fluid flows through the piston's orifices, it must deflect the shim stack to flow through. The thickness and number of shims along with their diameter controls how the shim stack bends and thus how fluid flows through the pistons. 

By varying the amount, thickness, and diameter of the Christmas Tree shims, the amount of damping and the shape of the damping curve can be closely controlled. Feal tunes each shock by using the shims for the desired damping. 

 

The main body of the Feal's coilover is this tube. Most shock companies don't pay a lot of attention to the tubes' tolerances, but the tolerances are critical for consistency in damping and to keep the amount of shaft play under control. 

Feal uses seamless DOM tubing to make their tubes. DOM means drawn over mandrel, and this manufacturing process refines the metals' grain structure and makes for a stronger tube with more consistent dimensions. As a final step, Feal has their tube honed for final control of the ID, a step usually only really high-end shock manufacturers use. 

 

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Comments
czubaka
czubakalink
Wednesday, November 01, 2017 6:29 AM
Ha! I read "DU style bearing" and immediately thought, "Holy crap! They're using depleted uranium?!"
ohmfab
ohmfablink
Wednesday, November 01, 2017 1:55 PM
Mike, Thank you for the classic SE-R love! Will look into these for replacing my Hyperco Gen2 / AGX setup.

Omer

Dan DeRosia
Dan DeRosialink
Thursday, November 02, 2017 4:59 AM
Huh, that's interesting... obviously digressive in effect, but the way it's executed in piston design looks like one side is closer to what Penske would call a high flow linear piston. Which is not a bad thing at all, if anyone thinks I'm being critical - combination of linear and digressive seems to be a useful combination and that's a much less spendy way of making the piston than Penske and Ohlins do.
TnF
TnFlink
Thursday, November 02, 2017 5:02 PM
How would these compare to Fortune Auto 500 and Stance XD1 with upgraded swift springs?
TnF
TnFlink
Thursday, November 02, 2017 6:09 PM
*Stance XR1
ThisGuy
ThisGuylink
Friday, November 03, 2017 7:31 AM
With a lot of talk on having such poor shock travel was any consideration given to bump stop height when setting up the ride height/ body length? Also on the same topic, who determined the shock body length? Seeing the droop limiters in assembly photos is a little odd when trying to optimize travel(unless you are happy with what you have).
Mike Kojima
Mike Kojimalink
Saturday, November 04, 2017 7:48 PM
Sorry I was out at SEMA show. Dan DeRosia, it sorta looks like a Penske High Flow but there are differences in the port geometry. TnF, These work very well as do Fortune Auto 500's. The big advantage with Feal is that they are made to order and it is really easy to custom spec your valving and spring rates if you want that and know what you are doing enough to do so. I have not tried any of the newer Stance products so I don't know. This Guy, Feal did the initial set up of the ride height and we changed it slightly to lower the car a bit more. The droop limiters are to keep the overlap of the shock enough for strength and bearing stability more than anything else.
TnF
TnFlink
Sunday, November 05, 2017 6:29 AM
Thanks Mike, I've already talked with Feal and i am probably going with them afterall since i am looking for S13 coilovers, however they did recommend that i stay with the standard 441 instead of the road racing version which is customized even though i am running track tires (Neova's AD08R's) but i still daily the car. However i am not sure if the 8/5kg spring rate is the proper spring rate for my car. Maybe 7/5, 7/6 or 8/6 would be more suitable? (will be running 18x9.5J wheels running 245/40 tires or so depending what fits after i roll and pull oem fenders front and rear)
Mike Kojima
Mike Kojimalink
Sunday, November 05, 2017 10:37 AM
TnF, is your car for grip driving? Low or high power drifting? Your level of driving? Generally, I prefer 8/6 for an S Chassis all around. I am sure Feal will let your order that way. You will not be disappointed in how well they work.
TnF
TnFlink
Sunday, November 05, 2017 12:22 PM
Yes correct, grip driving, think of dual purpose weekend street drive/track day. Feal does let you select spring rates i just don't know which rates would be the best for me. In reality driving in hours is like 90% on the street and 10% track. However my street driving is *cough cough* hard. I rarely drift because Neova's are not the cheapest tires to replace and it's a shame to destroy them drifting, but with the current setup that is on Blistein B6 dampers/Tein springs combo (unknown rates but seem soft) and the large increase in horsepower i have issues with not enough damping on the rear making sudden front to rear weight shift lose grip in the front making the car hard to recover unless powerdrift out. I also do a fair amount of launches ("drag racing") so rear traction is important as well, and i regularly do top speed runs (although i never had an issue with this). There are specific roads however where the rear will get into its natural frequency and start bouncing (not to dangerous levels but you understand the the rears are under-damped). What was important for me was to get a damper set with digressive damping so that i can adjust the damper to streetable levels of comfort when needed, that's why i raised my budget to the mentioned coilovers pricing. KW coilovers i think would be ideal but they are really expensive for what you are getting (no top mounts/swift springs etc). From Japan all the ones i am interested are made to order as well, but it would take too long for me now since i kinda need them urgently, with the exception of DG-5's (2 weeks lead time). Finally there is also MCA suspension which generally comes with the softer spring rates i've seen standard (5/4, 6/5kg) but they seem really busy after WTAC so they are out of the question as well.
Mike Kojima
Mike Kojimalink
Monday, November 06, 2017 12:51 AM
I am meah about DG-5'S. I think Feal does a great job and 8/6 will work well all around for you. For drag racing it is really handy to have a double adjustable shock like a KW as drag requirements are unlike any other form of driving. Or have Feal do drag specific valving and switch shocks around? If Odi hasn't done this tell him to call me.
Dan DeRosia
Dan DeRosialink
Monday, November 06, 2017 8:33 AM
@Mike Definitely see differences between the Feal pistons and the Penske pistons - the edge is more like the digressive pistons, and probably other details I can't see. It's just interesting because I have a big library of shock dyno results and was wondering what Feal's pistons were looking like to have the shape they did - it explains a lot and I think that's a usefully shaped curve.

Actually... going to email them about something. I'm back in the mood to make a roadrace 1st gen RX-7 and as I just bought an engine dyno (I'm seriously not kidding) probably have too much on my plate to take up a strut development program at the same time.
TnF
TnFlink
Monday, November 06, 2017 10:38 AM
Thanks Mike again. 2-way adjustment would be nice but not necessary as i am not running at a competition to require me to have a proper solution. However thought about it and i've done some calculations and i think 7/5kg is a better match for me, which should give 1.5hz frequency at the front and 1.25hz at the rear (ball park values from data i had - which are not 100% accurate). They told me the dampers are ok with +/-2kg spring rate change so they shouldn't require custom valving as well saving me some money (either way they said i don't require the road racing version already so they must be confident on their product). The only downside is that mechanical grip at launch will suffer but maybe there is enough range on the valving to make up for it (generally not as it is generally only rebound adjustment).
Mike Kojima
Mike Kojimalink
Monday, November 06, 2017 12:05 PM
TnF, generally you want the rear to have a higher frequency than that, even higher than the front but the S13 has so much antisquat you have to kinda compromise.
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