Shock Valving, Spring Rates

Real tech discussion on design, fabrication, testing, development of custom or adapted parts for Pontiac Fieros. Not questions about the power a CAI will give.

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fieroguru
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Re: Shock Valving, Spring Rates

Post by fieroguru »

bse53 wrote:
Are your readouts, calculations or did you physically measure the suspension?

Brian
I had Zac88GT on Old Europe run them for me based on the dimensions from Blooze's initial drawings, but modified for the lower stance.
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Re: Shock Valving, Spring Rates

Post by bse53 »

Received the Koni 30-5436. 5" stroke, 4 compression, 3-6 rebound. At first I wasn't sure they could be adapted, but if I can find a machine shop that can thread the rod deeper, I can turn it into a pin style. The threads are 14mm x 1.5 pitch.
Koni lists the compression at 45 lb @ 2 in/sec, which is close to the 30 lb @ 1 in/sec calculated on the Grant's Dynamic Calculator.
Rebound lists 285 lb - 330 lb - 385 lb - 490 lb/ 10 in/sec. I think these are in the ballpark, though on the lower end.
Anyone have an opinion whether these rates are in the ball park?

The shock is listed at 10.75" minimum and with the 1" bump rubber, I need about 12.5" by extending the upper shock mount 1.5".

I'm running 600 lb springs right now and have a set of 700 lbs that turned out to be too long. I may cut them down and try them, since that only raised the wheel rate to approx. 200 lbs.
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Re: Shock Valving, Spring Rates

Post by bse53 »

Since the idea of the Koni rod threads being lengthened isn't possible, the next option was to create an extension.
Like this:
Image

the threads on the Koni's are 14mm x 1.5, so I'll weld a bolt onto a nut. this is a 7/16" bolt, but I think a 3/8" will work fine, since their shouldn't be any side loads. Just need to figure out how to keep the bolt parallel to the nut.
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Series8217
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Re: Shock Valving, Spring Rates

Post by Series8217 »

I got back to thinking about Bilstein struts again this morning.

In order to reassemble the Bilstein strut damper without special equipment, a high pressure schrader valve needs to be installed so the gas chamber can be pressurized after filling the damper body with oil and installing the rod guide/seal. With a shock this normally isn't a problem, because the bottom of the shock body (where the gas chamber is) is out of the way of the spring, and well, pretty out of the way of anything, making it a great place for the schrader valve.

That doesn't work on a Bilstein strut, because the bottom of the shock body is actually the upper end of the strut "shaft", so putting the valve in the same places causes it to interfere with the coilover spring. Move it further up, and it interferes with the spring perch / upper mount plate.

I mentioned this in my previous post, but the "cool" way to do it is to gun drill the mounting stud to put the fitting on the end, or weld in an inset cup with a schrader valve like shown here:
Image

It's only possible to put the fitting on the end of the mounting stud if the stud has a large enough diameter to accommodate the threads for the screw-in high-pressure schrader valve, shown below.

Image

If the strut is to be removable from the mount plate without having to dump and refill the gas, the mounting stud nut will also have to fit over the installed schrader valve. I'm not too concerned about this -- I can always make the bottom mounting flange clamp on if I need make spring changes possible without dumping the gas.. but refilling the gas isn't really that big of a deal anyway.

If the the stud cannot accommodate the female threads for the screw-in schrader valve, there is still another option. This option does prevent the upper strut plate from being serviced without the fill fitting being removed, but it packages better than the axial schrader valve.

Shown below is the AST 5300 strut for E82/E90 BMWs. The fittings you see are two 90-degree banjo-style fittings. The first one slips over the strut stud and is retained with a circlip, and the second one is retained to the first also with a circlip. They appear to be designed to swivel, as they are retained with C-clips and not nuts or bolts.

Image

This is the top of an AST remote reservoir strut for an Evo:
Image

On the AST strut for the Evo, you can see the strut stud has been gun-drilled and then plug-welded... I think. I'm not sure what's holding the fitting directly to the shaft here. Perhaps a clip is missing? It's also possible that the weld we see is holding the top ring on and fixing the fitting in place. That would make servicing the camber plates quite a challenge on this assembly though, since it wouldn't be possible to remove the nut that holds the strut stud into the camber plate center bearing. The second fitting is clearly held on by another circlip.

I started looking around for these swivel-style banjo fittings and I can't find anything from the common industrial suppliers and racer supply companies. I don't think the bore on a typical banjo fitting is necessarily smooth enough to take o-ring seals (with the o-ring grooves machined into the strut stud), so these are probably application specific. Does anyone recognize these fittings?
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

If you fill the gas at the bottom, will it work its way to the top as the strut operates?

If so, put a port in the very bottom of the strut and come off with a 90 degree Shraeder valve to avoid the CV joint.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote:If you fill the gas at the bottom, will it work its way to the top as the strut operates?

If so, put a port in the very bottom of the strut and come off with a 90 degree Shraeder valve to avoid the CV joint.
No, the bottom of the strut housing is exposed to the atmosphere. It is not part of the damping hardware.

One of the prime advantages of the monotube damper is that the gas is completely separated from the oil fill to prevent foaming. The only place gas can be filled into the damper is into the gas chamber. If it "works its way" into any other part of the damper, then the gas separator piston seal is broken.

This is what a Bilstein monotube shock looks like:
Image

This is what a Bilstein monotube strut looks like:
Image

Make more sense now?
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Snazzy way to do it.

Looks pretty tough unless you can work in a fitting for a schraeder valve off center and maybe at a 90 degree angle around the base of the top stud.

Or make a new top stud and weld it in...
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Re: Shock Valving, Spring Rates

Post by Series8217 »

On the Fiero Bilsteins, the mounting stud has M14x2.0 threads, which have a minor diameter of ~11.2mm. I can drill through to the gas chamber, but I can't fit the 1/8" NPT threads that are on the Bilstein schrader valves (p/n 191001). Those threads would leave a wall thickness of 0.5mm on the stud. The M14x2.0 nut also wouldn't fit over the hex on the Bilstein schrader valve. I could fit 1/16" NPT threads on the stud, but I haven't been able to find a high-pressure 1/16" NPT schrader valve. Still looking.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Do you have a set?

Remove the original mounting stud and weld a 16mm or larger mounting stud to the housing?
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote:Do you have a set?

Remove the original mounting stud and weld a 16mm or larger mounting stud to the housing?
Yeah I have a set. I can do that; but it means having to design and fabricate new strut mounts too.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Series8217 wrote:
The Dark Side of Will wrote:Do you have a set?

Remove the original mounting stud and weld a 16mm or larger mounting stud to the housing?
Yeah I have a set. I can do that; but it means having to design and fabricate new strut mounts too.
Need to ditch the rubber in the stock strut top mounts anyway...
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Hmmm... I came back to this thread today to find the valving specs for the Bilsteins I assembled and they're not here. Has anyone seen that post?
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Found my sheet. This is for the front of an '88 Fiero with 700 lb/in springs.

Code: Select all

Valving: 300-160D (Digressive)

With the nut facing up, here's the stack up. All shims have 8mm ID. The rebound stack comes first:

Nut
(Rebound Stack)
21.5 x 3.0
15.5 x 0.50
36 x 0.60
B46-742A1 (2 notch, 0.15mm thick, 0.9 mm^2 bypass area)
28 x 0.10
(/Rebound Stack)
B46-699A (Digressive piston)
(Compression Stack)
28 x 0.30
B46-743A1 (4 notch, 0.15mm thick, 1.8mm^2 bypass area )
36 x 0.50
18 x 0.50
18 x 0.50
B46-22 (32.0 x 2.5)*
(/Compression Stack)
Piston rod

* - Bilstein calls for a 21 x 3.0 in their valving guide but my valving shim kit only had a 21.5 x 3.0
** - Bilstein lists the B46-22 as 32.5 x 2.5 but I measured it from my shim kit at 32.0
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Re: Shock Valving, Spring Rates

Post by Series8217 »

It seems I've misinterpreted the numbers in the Bilstein valving manual.

In the motorsports catalog, the valvings are listed as pounds-force @ 10 in/sec. However, other references (such as http://corner-carvers.com/forums/showpo ... ostcount=2) say that the valvings in the manual are in 10s of newtons @ 0.52 m/sec (20.5 in/sec).. so a valving number of 300/120 would be 3000N @ 0.53 m/sec on rebound and 1200N @ 0.52 m/sec on compression.

If that's true, my 300/160D valving is a little more than I'd like --- I actually want something more like 220/90 according to Dennis Grant's dynamics calculator.

However, the higher valving rate I am using might be making up for the fact that the calculator doesn't consider the affect of the motion ratio on the damper speed...
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Re: Shock Valving, Spring Rates

Post by mender »

Have been racing my '87 Fiero GT in Chump for the last three years and using a set of Herb Adams sway bars with cut-down stock springs. Recently the rules have been changing and the spring options have opened up, so I'm wondering if anyone has a track-sorted spring/shock combo that works with the Herb Adams bars, or alternately one that uses a different or no rear bar that they like.

Present set-up:
Front: AK 4040 front shocks with 260#/in front springs with the 1" HA bar and heim ends, poly control arm bushings, relocated lower control arms for anti-dive, '01 TA ps rack.
Rear: KYB rear struts with 300#/in coilovers, 1.25" HA bar, monoball control arm bearings, relocated pivot points for more anti-squat and better camber curve, relocated and shortened toe links to correct bumpsteer.
Car weighs 2500# with full fuel , 43/57 weight split and has an LX9 with the stock 282. Tire sizes are 225/45/17 and 275/40/17, brakes are 12'' front and 11.75" rear with C4 calipers.

Car presently handles nicely, can control the car with the pedals, nose stays off the ground, camber curves are decent front and rear. As expected with the soft springs and shocks, it moves a fair bit but isn't skittish, handles curbs well. I had 200# front springs which was my preference as the car turned in nicely and was balanced under throttle but I found that my other drivers were a bit afraid of the car and their laptimes suffered as a result (2-3 seconds slower than mine). Changing to the heavier front springs for more understeer narrowed the gap by speeding them up but slowing me and another driver down slightly; all part of team racing. I like the car to be neutral/settled under throttle and drive the car hard off the corners. On very tight low speed corners (40-50 mph/2nd gear) I can induce a bit of inside tire slippage if I'm aggressive but overall it grips well out of the corners. I typically wear my rear tires at about 2:1 to the fronts.

I'm looking at going to another series with a more open rulebook plus it's time for a major overhaul. I have the front and rear '88 suspensions here as well but don't think I have much to gain over my present modified suspension and unless I can be convinced otherwise will be staying with the early suspension. Power will be going up to around 280-290 whp and I'll be adding a front splitter and rear wing, probably about the same downforce levels as Series8217 is likely at. Will be trimming more weight out as well as I find it. The HA rear bar weighs about 35# by itself so that could go if needed but like the flat cornering and balance of the HA bars. I have a set of Koni reds that I can use; the fronts are fairly new but the rear struts need rebuilding, so I'm thinking that it might be rebuild/revalve time in accordance to whatever spring package ends up on the car.

I'll either continue developing my present package (BB/SS) or move to a stiffer spring set-up and develop that. Thoughts/experiences? Links to established/proven set-ups?
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Re: Shock Valving, Spring Rates

Post by mender »

So have been reading the Autocross to Win site and will try out the numbers generated on the Dynamic Calculator. Has anyone adapted Mustang front struts to the rear?
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Re: Shock Valving, Spring Rates

Post by Series8217 »

mender wrote:Has anyone adapted Mustang front struts to the rear?
Not yet.

I purchased some for R&D a couple years ago. It doesn't look like they would be difficult to adapt. You need to add a spring perch and new mounting ears to the housing, and make a new strut top mount. The hole in the Fiero upper strut mount is too tall.

They also might need to be shortened, but that depends on your setup (ride height and travel).

If you intend to revalve them yourself, the top stud is big enough that you could gundrill it into the nitrogen chamber and add a Schrader valve to refill the gas. Otherwise, you can send them to Bilstein to be revalved and then you won't have to worry about the gas charge.

I'm hoping to get around to this project next summer.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Why use Mustang struts?

ETA: by that I mean it sounds like it would be as much work to adapt Mustang struts as it would be to build strut housings in order to use a shelf Bilstein shock.
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Re: Shock Valving, Spring Rates

Post by mender »

Thanks for the replies.

Class rules might allow the Mustang struts but not a dedicated motorsports or owner rebuildable struts. The two factory struts that look close are the Mustang struts and the 3d Gen F-body struts but I'm open to suggestions for other adaptable OE strut options.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote:Why use Mustang struts?

ETA: by that I mean it sounds like it would be as much work to adapt Mustang struts as it would be to build strut housings in order to use a shelf Bilstein shock.
Much easier to adapt the Mustang struts! Adapting Mustang struts requires welding on new ears, adding a stop for a coilover spring sleeve, and new upper strut mounts (larger hole). Making new strut housings requires all of the above plus sourcing material, boring and honing the housing, fabricating and welding in the end plate, and assembling bearings and seals into the housing.
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