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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Series8217
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote: What were the numbers? How much did it vary throughout the range of motion?
I only measured a few points since it was pretty consistent.

Code: Select all

Ride Height      Damper Position
+3.15                     0                 
+1.38                     0.95             
+0.70                     1.31
  0.00                     1.67

+ ride height is droop. 0 is the lowest (most compressed) position I measured. It was roughly 2" compressed from stock ride height.
Ratios were from ~1.87 to ~1.91 across the points I measured.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

It looks like Bilstein's B46-ATAL4/ATAD4 shock (ASN Series) can be installed on an '88 Fiero front suspension using a modified crossmember top (to accomodate a t-bar for the rod end) and the lower control arm modification shown here: http://www.westcoastfiero.com/suspensio ... hocks.html

It would probably need to be run normal (body down shaft up) instead of inverted, so hopefully that's OK. I think monotubes don't care though.

I think if it were run inverted (body up, shaft down), the body might not clear the shock tower on the '88 front suspension. If it does... cool. Less unsprung weight.

The reason to use this shock is because its user-rebuildable/revalvable to accommodate various spring rates.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Bilstein strut inserts for the 1975 to 1988 VW Scirocco* front suspension are very similar in dimensions to the Fiero rear struts. A custom housing and top hat assembly could be built to put them in a Fiero.

There are 3 different Bilstein part numbers:
* 21-030338 (B4 Twintube)
* 34-001370 (B6 HD Monotube)
* 34-184530 (B8 SP Monotube)

The B6 and B8 strut inserts are ~$210 each. I have no idea what the valving is like. They almost certainly need to be revalved to accomodate track-worthy spring rates. The cost is $110 per strut to rebuild and revalve, so starting with used parts (if they can be found) may make this MUCH more economical. Worst case (new parts) is about $330 plus the cost of hats and housings, per side. These could make a quality non-adjustable rear damper for 84-88 Fieros.

I don't know if the Bilsteins can be revalved to stiffer valving than the Koni 8611s, but I've read that Bilstein tends to use the same parts in their aftermarket struts as in their motorsports application stuff, so I suspect they can be. Otherwise, there may not be a clear advantage over the Koni 8611 (which is about the same price as the Bilstein strut insert + revalve) unless the dimensions make it easier to fabricate a housing.

* - Also 1980 to 1984 Jetta, / 1980 to 1985 Rabbit / 1985 to 1993 Cabriolet
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Re: Shock Valving, Spring Rates

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The front corner weights on my car are 655 lb for the front left and 595 lb for the front right. That's with a front-mounted 23-lb battery and power steering, but no spare tire, jack, or spare tire tray, and me (140 lbs) in the driver's seat. Let's call it 625 lb average for the front corners. Unsprung weight with 12" rotors and 17x7s is ~92 lbs based on my measurements. So the unsprung mass per front corner is 535 lb.

The motion ratio for the front is 0.53 based on my own measurements and fieroguru's calculations.

535 lbs / (0.53) gives 1009 lbs of load at the spring.

I found these springs which are 3.5 inches on the upper end and 2.5 inches on the lower end: http://www.qa1.net/qa1_motorsports/drag ... rings.html

Based on the photo it looks like you could simply cut off the tapered region and get a spring with a 3.5" ID on both ends. However, it would be really short... since the full length of the spring is 8". They are designed for a Mustang with stock upper perches and an adjustable lower perch on a shock. Sound familiar?

At 700 lb/in, that spring would be compressed 1.44 inches, down to 6.5". That's ~2.5 inches of drop vs a stock spring on an '88 Fiero. Probably a bit much. However, with such a short free length compared to the stock spring, it may be possible to put a 1/2" spacer in there, especially as part of an adapter for changing the bottom spring perch from 3.5" ID to 2.5" ID.... or if you have a coilover shock with an adjustable lower sleeve with 2.5" diameter. Which is exactly what these are designed for anyway, and is what I need to do to control such rates.

700 lb/in is still slightly softer than what I want to do (my target minimum is 725), but the price probably beats custom springs and it's kind of a cool solution too.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Got lucky and found a used (return?) on the Jeg's ebay store for $50 with free shipping. That sure beats $75 shipped for a new one!

I'm going to test fit it on the upper perch on one side first just to make sure this is feasible.

EDIT: Appears it has already been done: http://www.fiero.com/forum/Archives/Arch ... 91747.html
And I had even posted in the thread and just forgot about it...
Last edited by Series8217 on Tue Jun 25, 2013 10:20 am, edited 1 time in total.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Once you get close to the rate you want, custom springs are about $250 a pair.

http://www.coilsprings.com/

They say "request a quote" but the few people I've heard from who've asked say they come back with $250/pair... that's been at least 5 years ago, though.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

This is the QA1 setup for the Mustang:

What I intend to build will be almost identical, but I will probably be using a Bilstein shock.

The QA1 shocks are $70 cheaper than the Bilsteins, and already have the right top-end mount for the '88 Fiero. They are also single-adjustable whereas the Bilsteins are non-adjustable. However, the Bilsteins are user-revalveable and rebuildable, whereas the QA1s are not.

According to the specs on the Summit Racing catalog listing for the QA1 setup, the collapsed length is 7.625 in and the extended length is 11.125 in. That's almost identical to the stock '88 Fiero stuff. It could definitely be a viable alternative to the Bilsteins if the valving (and reliability) are any good.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

I see a few clear routes at this point:

OPTION 1: OE-fitment custom spring / OE-style shock

This requires a custom spring which fits the stock upper and lower spring perches.

SHOCK OPTIONS:
* Revalved Koni Red single-adjustables (note that these were discontinued by Koni, and are not user-rebuildable) -- rebuilds are expensive ($120+)
* Bilstein AK series shocks -- direct fit available, but need to be revalved by Bilstein. Non-adjustable. Can potentially be converted to take-aparts and revalved by the end-user with standard Bilstein race parts. 46 mm models may require a modified lower control arm or bottom mount spacers.

SPRING OPTIONS:
* Any spring rates (fully custom)

PROS:
* Relatively inexpensive
* Minimal (or no) fabrication required
* Any spring rate can be selected
* Minimal shock cost ($75 each for Bilstein AK series, plus $75 each to revalve them, for $300 total)

CONS:
* Custom springs are more expensive than off-the-shelf springs (~$250+/pair for custom vs $150/pair for high end off-the-shelf springs)
* Shocks are not rebuildable or revalvable by the end user, except in an unsupported configuration (AK series converted to take-apart)
* No adjustable shock options except the discontinued Konis
* Not possible to adjust ride height / weight jacking without changing springs or adding/removing spacers
* Small non-motorsports shocks like the Konis may not be able to handle higher spring rates. The 46mm Bilsteins should work fine but require more work to fit.

TOTAL COST:
$550+

OPTION 2: QA1 Tapered Mustang Spring, Bilstein Motorsports Shock

This requires significant modification of the lower control arm.

SHOCK OPTIONS:
* Bilstein ASN series coilover shocks -- aluminum-bodied race shocks that are user-revalvable and rebuildable, with all parts available individually. Easily converted to use remote reservoirs. Can adjust gas charge pressure. ~$220 each + spring perches.
* QA1 adjustable coilover motorsports shocks for the Mustang II -- these don't have the same reputation as Bilsteins, but they are adjustable, and QA1 can revalve them and provide dyno charts. ~$180 each.

SPRING OPTIONS:
* 375 lb/in (too soft...)
* 500 lb/in (decent upgrade from the 400 lb/in lowering springs)
* 600 lb/in (getting better)
* 700 lb/in ("good enough")
* Custom (anything)

PROS:
* The shocks can handle pretty much any spring rates
* Adjustable shocks or user-revalvable shocks
* Shocks are designed for motorsports use
* Requires no modifications to the upper spring perch
* Adjustable ride height / weight jacking
* Inexpensive off-the-shelf springs ($150/pair)
* Can use custom springs if desired ($250+/pair)

CONS:
* Top mount modification may be necessary for the Bilsteins to fit, if there isn't enough thread on the end of the shaft to allow the Fiero's stock bushing-on-pin arrangement to be used. The QA1s look like they fit with minimal modification perhaps just by increasing the hole size if anything at all.
* Significant modification of lower control arm is required
* May affect wheel clearance (may need larger diameter wheels to clear the bottom shock mount)
* Very limited selection of spring rates unless custom springs are used
* Shocks are very expensive

TOTAL COST:
~$720 for 700lb/in springs, Bilstein ASN shocks (p/n B46-ATAD4), and spring seats (p/n 192190). The valving kit (p/n 192153) is an additional $300 and there are some basic tools required as well. I don't know what valving the shocks come with, if any.

A shock dyno is needed to develop valving. It's possible to make your own for $200 to $400. A commercial unit is $2000 to $8000.

I will update pricing information (valve kit, spring seats) when I find it.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Series8217 wrote:Got lucky and found a used (return?) on the Jeg's ebay store for $50 with free shipping. That sure beats $75 shipped for a new one!
Hah. The box says 8MB700 but the spring is labeled 8MB500. So they sent me the wrong spring (500lb/in...). :(
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Built a spring test rig yet? :wink:

A man with one watch always knows what time it is. A man with two is never really sure.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote:Built a spring test rig yet? :wink:
Haven't built it yet but I've been looking for parts. My current plan is to adapt a load cell and linear pot to a hydraulic spring compressor. Testing will be as simple as compressing the spring the desired amount and then releasing it. My software would compute the spring rate plot. This will make it compatible with progressive springs of any kind. It will likely resemble something like this.

I already bought a load cell and signal conditioner for my shock dyno. Next I need a velocity transducer and then all the mechanical parts. I already have a DAQ board which I can use for both the spring rate tester and shock dyno.
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Re: Shock Valving, Spring Rates

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Since I returned the wrong spring to Jegs, I no longer have an obligation to use the tapered springs. It looks like it should be relatively easy to make a non-adjustable upper spring perch adapter for 2.25" or 2.5" springs. So that's what I'll do for the top.

I ordered some Bilstein B46-ATAD4 shocks. They won't be here until the end of the month though. Still looking for a good deal the digressive valving kit. I wish somebody had an online valving calculator with dyno graphs*. I probably only need a few shim sets to get close to what I want, so it kinda sucks to buy the whole kit for $300.

* - Something like Shim ReStackor, which looks totally awesome and super cheap. I don't know enough about the Bilstein piston ("base valve") to know if this software can accurately simulate it. Once I have parts in hand I'll have a better idea.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The front shocks and coilovers on the '88 are not coaxial. The bottom of the shock is further out than the spring. I'm not sure about the upper perch. If the upper spring perch is not on axis with the upper shock mount, then fitting a 2.5" spring at the top may be tricky without the shock body hitting it at full compression. Even if the upper perch is on the same axis as the upper shock mount, the heights of the upper pivots will be significantly different so the shock will move side to side slightly within the spring. Hopefully I can still make this work. I'll have a much better idea once I get my shocks at the end of the month, and some spare LCAs (Will?) to modify. I really don't want to have to modify the crossmember...
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Re: Shock Valving, Spring Rates

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Coleman Racing had the best deal on the valve kit ($264) and Bilstein shock oil ($22, but the price shot up to $34 after I ordered; it was probably an old price).

Unfortunately they only sent me half the valving kit... just Box 2. So I'm missing half of the shims I need to complete any valving set for a shock. I haven't been able to reach them by phone or e-mail and have tried since Monday. First time I've had a problem with an order from them... I hope this isn't the new norm.

Dave Poske's performance parts had the best price on the coilover kit for the ASN shocks, so I ordered from them. They somehow missed my order for 2 weeks but shipped it the same day when I called them and asked what happened. No big deal; my shocks haven't shipped yet anyway.

Still doing my research (and working on aero and safety mods) until my shocks come in... The Shim ReStackor site has some great theory on valving and I also got a copy of The Shock Absorber Handbook.

UPDATE: Finally got a hold of Coleman Racing. The key is to dial an extension for one of the salespeople instead of selecting the "sales" option at the menu. And don't use e-mail. They're shipping Box 1 of the valving kit out to me today.
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Re: Shock Valving, Spring Rates

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Shocks got delivered today according to UPS tracking. I'll know if they're the right parts in a few hours..

If someone has spare '88 lower control arms they are willing to sell, please send me a PM. I would really like to have an extra set for the necessary modifications.
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Re: Shock Valving, Spring Rates

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The B46-ATAD4 shocks (ASN-series 4-inch travel with digressive piston) arrived, as well as the other half of the valving kit.

Bilstein didn't do anything to protect the shocks.. they just threw them in some commercial Bilstein shock boxes and tossed those boxes in a larger cardboard box. One of the shocks was jammed up and the other was halfway apart. Not too big a deal since they come in "kit" form (no oil or valving, retaining clips removed) anyway, but still kind of annoying. As I had to bang on one with a rubber mallet to get the shaft guide to pop out. Also the rod ends are different between the two shocks; one set is a little loose and the other feels tight. The material of the ball is different.

I have all the parts now except spare control arms and a nitrogen fill tool.

I ended up ordering the 8" long, 700 lb/in QA1 tapered springs. They will be easier to install than straight 2.5" springs, since I won't have to modify the upper perch or worry about the shock body hitting the top of the spring since the spring perch is separate from the shock. However, I recently realized that the spring and shock not lining up at the top means there will be a bending load on the shock... which is very much undesirable since these are shocks, not struts. Oh well. I'll probably run it that way for a few track days, then disassemble the shocks to see how they are wearing.

I also ordered a set of AK-series shocks that should bolt right up with just a small spacer at the bottom, assuming the larger bodies fit through the LCA. I'm not sure if the stock valving is any good on them for any spring rates on a Fiero, but once I'm done with my shock dyno I'll find out. If it isn't, then I'll convert them to take-aparts. The end result is a 46 mm steel housing with a shaft that works on the Fiero... for $160 a pair (for the AK-series) instead instead of $400 (for the ASN-series). It doesn't even matter if the valving is no good on the AKs since the ASN shocks don't even come with shimstacks. The disadvantage is the lack of a threaded body.
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Re: Shock Valving, Spring Rates

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I moved this thread from motorsports to tech for more exposure..
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Re: Shock Valving, Spring Rates

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AK-series shocks are here...

The 46 mm ones won't fit in the stock lower control arm, but only because the shock mounting plate has too small of an opening. It is trivial to replace this with a custom piece. There are just a few small welds to grind off, then weld the new mount on. I may do it this weekend if I can find a way to fit the QA1 tapered springs too. I think there's enough room for a spring seat adapter at the bottom. I just don't know what ride height I'll end up with.

I'm going to hold off on adapting the ASN shocks until I figure out if I can fit a 2.25" or 2.5" ID spring through the factory crossmember. I don't want to put bending loads on the shock by using the bottom of the shock as a spring mount but not also the top.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Series8217 wrote:AK-series shocks are here...

The 46 mm ones won't fit in the stock lower control arm, but only because the shock mounting plate has too small of an opening. It is trivial to replace this with a custom piece.
Looking at this again, it should fit with just some grinding of the opening in the LCA. The body of the shock may up high enough to clear the control arm, even with the required spacer (to get enough compression travel). I'll try this week.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Series8217 wrote:
Series8217 wrote:AK-series shocks are here...

The 46 mm ones won't fit in the stock lower control arm, but only because the shock mounting plate has too small of an opening. It is trivial to replace this with a custom piece.
Looking at this again, it should fit with just some grinding of the opening in the LCA. The body of the shock may up high enough to clear the control arm, even with the required spacer (to get enough compression travel). I'll try this week.
Sure enough, the Bilstein AK1195 shock fits through the '88 Fiero lower control after filing the opening a bit with a half-round file. The T-bar even fits the existing bolt holes when used with 8mm bolts. However, there isn't enough room for the original 8mm speed nuts, and there's hardly enough room to weld nuts to the control arm. In its original application (Ford Crown Victoria front suspension), the AK1195 was attached using self-tapping bolts with ~8mm diameter.
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