Shock Valving, Spring Rates

[Shaun41178(2)]

No idea what any of that means.

I have some kybs here I can measure without speings on them. That work?

[draven]

Shaun,

I might have a line on a set of OE's just a few miles north of me to cut up and measure. Don't throw away your old OE housings in case it doesn't pan out. As far as the KYBs go, yes measure the extended length and compressed length, then the body of the strut from the bottom up to where the gland nut, or whatever they have seals the piston. Then measure the OD of the body of the strut. I think the KYBs may be too short for a press in Koni 8610 strut but with the adapter mentioned below it might be possible to use the 8611.

The Australian company Toperformance.com.au got back in touch with me and have no problem selling their weld-on koni gland nut adapter or their combination threaded sleeve and gland nut adapter. Have a few more questions for them before I buy a set or two.

[draven]

Obtain as much Velocity Force values Koni would provide over email.

Stock 88 spring rates.
205 lb/in front, 147 lb/in rear.

The Corvette 8040-1019 and GM A Body 8040-1087 are only 10mm longer but have the same stroke.

Velocity Forces @Full Soft (Rebound and compression, where available, approximately double at full hard)

Newton to lbs converstion N * .2248

Fronts
Fiero Front Shocks 8040 1027 (84-87)
5in/sec 200N static compress 900N-1800N rebound
13in/sec 300N static compress 1350N-2700N rebound

Fiero Front Shocks 8040 1092 (88) Discontinued
5in/sec 420N static compress 750N-1500N rebound
13in/sec 750N static compress 1200N-2400N rebound

Possible Front Replacements
Corvette 8040 1019
5in/sec 420 static compress 750N-1500N rebound
13in/sec 750 static compress 1300-2600N rebound

GM A body 8040 1087
5in/sec 430N static compress 780N-1560N rebound
13in/sec 900N static compress 1250N-2500N rebound

Surprisingly the 1092's are almost identical to the 1019's and 1087's. I ordered up a set of the 1092's and 1087s, as the 1087's have the same cross bar and bushing size as the 1092's.

Koni 80-2859Sport would probably also fit similarly to the Koni 30 Series setup from WestCoastFiero but perhaps with no eyelet to pin modification

Rear
Fiero Rear Struts 8741 1063 Discontinued
5in/sec 230N static compress 560N-1120N rebound
13in/sec 350N static compress 850N-1700N rebound

Possible Rear Replacements
Yellow Dual Adjustable Strut inserts 8611 XXXX
5in/sec 280N-560N Compress 750N-1500N rebound
13in/sec 400N-800N Compress 1150N-2300N rebound

Yellow Single Adjustable Strut inserts 8610 XXXX
5in/sec 600N static compress 750N-1500N rebound
13in/sec 850N static compress 1250N-2500N rebound

This is where it get's a bit tricky for a koni rear strut equivalent. As can be seen you can get close to the original Fiero Koni rear with the 8611, however, the 8611's go for about 350$+ a shock... that's a deal if you're looking for a double adjustable rear strut for autocross/hpde etc..but not so much if you're looking for a comparable strut to the 1063 at a similar price point. I'd be interested to know the force velocity's of the KYB rear struts.

The 8610's are near the same price point but the static compression numbers are probably too high for a daily driver...

So Will, it looks like the 1019 and 1087 effectively are indeed koni single adjustable "yellow's" for the fiero as you theorized some time ago on within a post on OE. And look to be suited to running 725/475 spring rate combo or even a little higher at roughly 100$ a shock. But unfortunately someone would be in for a "shock" expecting anywhere near an OE or koni 1027 ride.
Edit: duh.. I was looking up the 8040 1027 which are for the 84-87 front koni's, obtained the 8040-1092 88 front koni force velocity's and they are almost identical to the C3 Corvette koni fronts

Furthermore, Koni does make a coilover conversion for these 80.0000.1 (can run both 2.25 and 2.5" springs) unfortunately a sleeve retainer ring will have to welded onto these 8040's which koni says requires a tear down but I've found a couple of koni yellow owners who have done the same but with slow, intermittent tack welds to keep the shock body cool enough and prevent and internal damage.

[The Dark Side of Will]

Great info!

One thing to consider is that for performance the 1-3 in/sec speed range is what matters. The relatively small pistons in the twin tube Konis make high damping forces in that speed range harder to obtain.

Interesting that the '88's fronts are so much stiffer in compression than the early cars' shocks. I would expect the early cars would actually need stiffer compression damping because of their pro-dive front end geometry.

The rear struts are an interesting puzzle. The taco clamp stamping is NLA (at least from Koni? Other MFG's struts for other GM models appear unaffected?), so there's basically nothing that can interchange.
That means that relative to doing the fab work of converting a stock type strut to use a cartridge, it's not a huge amount more fab work to convert to inverted strut. Maybe that would be a good path to consider as well. Steven Snyder has looked into what Bilstein shocks for inverted struts would have the right extended/compressed lengths to work in a Fiero and has some good candidates.

Also keep in mind that with wide rear tires, the desirable rear wheel rate, even relative to the stock front wheel rate, is significantly higher than the stock rear wheel rate. I would guess that 250ppi vs the stock 170ish ppi would be good with sticky street tires and a stagger that matches the Fiero's weight distribution. Damping capabilities of replacement shocks/struts should reflect that. Maybe Koni can advise on what rates you might want to look for? (although I maybe they advised on the selection of replacements you show above). You might build a pair of 8611's, get them dialed in and then have a shop dyno them to see what the numbers actually came out to. If you have the Koni Custom Shop (Koni Kustom Shoppe?) convert Fiero PNs to double adjustable, you'll still spend around $350/corner, so the 8611 price is not out of line for the capability.

So Will, it looks like the 1019 and 1087 effectively are indeed koni single adjustable "yellow's" for the fiero as you theorized some time ago on within a post on OE.

LOL... Apparently you know my body of work better than I do at this point! I don't remember that.

Koni valving is naturally digressive, so they'll ride reasonably well, even when pretty stiff. They'll definitely be significantly stiffer than stock all around, though.

[The Dark Side of Will]

Getting started sort of copy-catting Steven's front coil overs:

[Series8217]

Gun drilling Fiero Bilstein strut top stud to add a schrader valve. Turns it into a take apart shock that takes any 36mm Bilstein valving.
There's juuuust enough room to install the schrader valve body and still fit the nut over it.

20221028_170739.jpg (2.55 MiB) Viewed 3246 times

~3" deep 1/8" dia hole. Wanted to do 1/16 but I just couldn't imagine the bit staying straight. I am not set up for real gun drilling -- no high pressure coolant feed. Just lots of pecking and brushing off the chips. Took about 45 min. Fortunately I only have to do a few.

[The Dark Side of Will]

~3" deep 1/8" dia hole. Wanted to do 1/16 but I just couldn't imagine the bit staying straight. I am not set up for real gun drilling -- no high pressure coolant feed. Just lots of pecking and brushing off the chips. Took about 45 min. Fortunately I only have to do a few.

Brush up on your G83 syntax?

[Series8217]

Disassembled one of the Fiero Bilstein rear struts today. I bought two of these from someone on Old Europe many years ago. They are no longer available new.

As a reminder this diagram shows what the entire assembly looks like. I have already removed the strut housing and the bump stop so they won't be shown in this post.


After having removed the damper from the strut housing and drilling the stud to release the gas charge, the next step to taking apart the damper was prying the bump cap out. This is the part that impacts the internal bump stop in the strut assembly.

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Underneath is the rod guide assembly. This holds the seal, guide bushing, and an extension stop.

20221029_131440-rod-guide.jpg (119.93 KiB) Viewed 3219 times

You have to compress the rod guide slightly to get the retaining clip out. It barely moves since there's another retaining clip below.

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20221029_160248-removing-clip.jpg (136.89 KiB) Viewed 3219 times

20221029_160248-removing-rod-guide.jpg (124.39 KiB) Viewed 3219 times

20221029_161148-second-clip.jpg (104.5 KiB) Viewed 3219 times

The fancy bits:

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Almost done. Need to save the oil so I can measure the volume. The correct fluid volume is very important. In this case, it was 210mL for the Fiero Bilstein strut.

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The separator piston that keeps the nitrogen out of the oil is tricky to remove. I have had success using compressed air in the fill port. Need to catch the piston and protect yourself from richochet though!

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[eHoward]

That’s great stuff. I’ll definitely be following your progress. Thanks for sharing

[pmbrunelle]

Maybe a Presta valve (for road bicycle tire) would fit better than Schrader within the confines of the mounting stud thread.

[Series8217]

Maybe a Presta valve (for road bicycle tire) would fit better than Schrader within the confines of the mounting stud thread.

I have not seen Presta valves rated to the required 500 psi and 200-300*F that the nitrogen chamber valve experiences.

The Penske IU-22S valves happen to be a perfect fit and are intended for this application.

This is the IU-22S body which takes a high pressure Schrader valve:

penske-iu-22s.PNG (24.71 KiB) Viewed 3199 times

The mounting threads and o-ring boss fit on the end of the Fiero Bilstein mounting stud.

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[Series8217]

Fill valve installed!

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Just need to decide on valving now. These struts will get 500 lb/in springs.

Has anyone experimented with atypically-low rear compression damping to reduce turn-in oversteer on a Fiero?

[Series8217]

The housings I have are in pretty rough shape. The "taco" clamp has a lot of rust. It's is a multilayered stamped steel component that is welded to the Bilstein strut tube. Lots of crevices for water to get in and not get out. The mount is actually bulging where rust has expanded between the layers!

I scanned the strut housing and used the scanned geometry to use a reference for creating a new strut mount taco clamp in CAD.

Screenshot_20221111-233420_Onshape.jpg (466 KiB) Viewed 3085 times

I designed a mount that consists of a lightly machined steel tube and some laser cut parts that will be welded together.

Screenshot_20221111-233711_Onshape.jpg (355.64 KiB) Viewed 3085 times

I'll use these parts to replace the mounts on my Fiero Bilstein housings, and to add Fiero-compatible mounts to some other Bilstein housings I have laying around.

[The Dark Side of Will]

Good that you saw the need for the top collar going around the strut tube.

I think you can ditch the "limiters" on camber adjustment. As long as the bolt is tight, the extent of the hole should be fine. That also lets you easily increase camber by slotting the hole further

[Series8217]

I think you can ditch the "limiters" on camber adjustment. As long as the bolt is tight, the extent of the hole should be fine. That also lets you easily increase camber by slotting the hole further

The tabs are for the eccentric washers on the camber bolt to push against. Makes camber adjustment much easier since the strut can't slide around while things are loose. You just turn the head to the angle that gives you the desired static camber then hold the head and tighten the nut.

GM cheaped out and used plain bolts in the adjuster slot so you may not have seen eccentric washers used unless you went out of your way to buy the AC Delco or Moog parts that make the alignment tech's life easier.

You can see the eccentric washer here with my Koni strut. The bolt head has a matching eccentric flange.

20221111_153956~2.jpg (558.41 KiB) Viewed 3071 times

The ones I have are no longer available but NAPA carries a similar bolt: https://www.napaonline.com/en/p/NCP2643609

[The Dark Side of Will]

I know how eccentric adjusters work... but I've also slotted strut bolt holes (Neon SRT-4, not a Fiero) to get more camber. That's not feasible with the bars for the eccentrics in place.

[Series8217]

I'll shift the range of adjustment so it can get a little more negative than stock. Easy enough to cut em off or leave em out if there's an issue.

[The Dark Side of Will]

Which eccentric adjusters did you use?

I had actually thought about laser cutting my own eccentric washers with larger diameter to result in larger camber adjustment... I just hadn't been thinking of using them on the Fiero strut

[Series8217]

I have been using Moog K5283. They seem to be the most readily available.

[The Dark Side of Will]

I have been using Moog K5283. They seem to be the most readily available.

Moog discontinued those? RockAuto only lists them as a wholesaler closeout... which at least makes them cheap.

https://www.rockauto.com/en/moreinfo.ph ... 2742&jsn=3

Edit: Each kit includes one concentric bolt and one eccentric bolt? Which means for two Fieros I need four kits.

Edit again: From an e-Bay photo, it looks like the eccentric at the bolt head is integral with the bolt head, so making larger washers would not work in this case. I guess I could modify the titanium bolts I was thinking of getting anyway in order to use eccentric washers on them