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FHA spring question

Old 12-06-2018, 12:00 AM
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jefnvk
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Default FHA spring question

I was looking at my springs tonite, and I noticed that my front is marked FHA, which various tables around here indicate is a 93.1 spring rate. It is supposed to be an RPO FE1, is a 1992, I was not expecting to see that. I was examining this because I was interested in possibly taking it up to the Z51 specs springs, and this is what I was going to buy anyhow. I was told it was stock in this regard, and it definitely has the stock shocks, were these actually built with FHA up front? It is also marked with 1-5 under FHA, is this some sort of date code, or is there any other way to tell if this is a replacement?

The rear is the expected NYR 39.9, I just find it odd the front would be swapped and not the rear.
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Old 12-06-2018, 11:16 AM
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Originally Posted by jefnvk View Post
I was looking at my springs tonite, and I noticed that my front is marked FHA, which various tables around here indicate is a 93.1 spring rate. It is supposed to be an RPO FE1, is a 1992, I was not expecting to see that. I was examining this because I was interested in possibly taking it up to the Z51 specs springs, and this is what I was going to buy anyhow. I was told it was stock in this regard, and it definitely has the stock shocks, were these actually built with FHA up front? It is also marked with 1-5 under FHA, is this some sort of date code, or is there any other way to tell if this is a replacement?

The rear is the expected NYR 39.9, I just find it odd the front would be swapped and not the rear.
When I swapped springs in my car (to softer) I discovered that I had a front spring that wasn't used on any 94's or any verts according to the parts fiche.

Like you, I found it odd that a DPO would change the front and not the rear. Maybe just careless documentation by GM.
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Old 12-06-2018, 02:47 PM
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Kevova
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Original front spring failed and the FHA was available. PO didn't like how car cornered. It's hard to say. FHA is rated the same as the Z07 although not the same code. The Z07 / Z51 rear spring NYU would complement the FHA
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Old 12-06-2018, 03:23 PM
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I don't believe the FHA is an unusual find in most any year C4. In the past I've had FHA removed from a '91 and also an FHA removed from a '93. These were known to be from a '91 and a '93. There's very different fabrication used on the ends of the spring. If you check closely there's I believe an 1 1/4 X 1 1/4 pedestal on the control arm end of your spring. Through '91 there was only a molded pad on the control arm end. If you search eBay for FHA spring you'll find snapshots and images of both fabrications. Way to much is 'assumed' using these suspension charts etc on the Internet!!

Date codes on the later with 1 1/4 X 1 1/4 pedestal I believe is on the top side of the spring.

This eBay offering has an image with the dated information on the top side.

https://www.ebay.com/itm/88-96-Corve...Cwqs:rk:2:pf:0

Notice that regardless the fabrication everyone sells fronts as '88 through '96. That just 'ain't so' - Fit yes but very different!!!

**** The actual production code is in a block of the 'BUILD SHEET' Give the NCM some of your $$$

Last edited by WVZR-1; 12-06-2018 at 03:31 PM.
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Old 12-06-2018, 03:44 PM
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Hib Halverson made a chart listing the different spring codes FHA was the base front spring for a coupe 88-91 FSS base 92-95 FSK 92-95 Z07.
NYR base rear spring 86-93
Although unlikely early 92 assembled with in correct front spring.
The spring pad on the FSS is just a square attached to the center of the tip verses a large full tip pad.
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Old 12-06-2018, 03:45 PM
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Cool, well I guess that saves me a couple hundred bucks and saves me some work on something I wanted to do anyhow! I plan on getting the NYU to match, and the beefier bars.

Originally Posted by WVZR-1 View Post
**** The actual production code is in a block of the 'BUILD SHEET' Give the NCM some of your $$$
I've only had the thing a week, give me some time!
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Old 12-06-2018, 08:51 PM
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Originally Posted by WVZR-1 View Post
Notice that regardless the fabrication everyone sells fronts as '88 through '96. That just 'ain't so' - Fit yes but very different!!!
Hmm, guess some other things came through between me opening the page and actually hitting reply earlier. Does that mean that later FHAs aren't really that high of spring rate, that they are, or that no one has any clue? And perhaps more importantly, is there a way to positively ID one of the 90ish spring rate springs on eBay? I'd hate to replace what I have with the same thing, or worse, replace it with something softer. Or maybe I just replace the shocks now and with the plan of dealing with new-new known springs after I run it a while.
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Old 12-06-2018, 09:20 PM
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Originally Posted by jefnvk View Post
Hmm, guess some other things came through between me opening the page and actually hitting reply earlier. Does that mean that later FHAs aren't really that high of spring rate, that they are, or that no one has any clue? And perhaps more importantly, is there a way to positively ID one of the 90ish spring rate springs on eBay? I'd hate to replace what I have with the same thing, or worse, replace it with something softer. Or maybe I just replace the shocks now and with the plan of dealing with new-new known springs after I run it a while.
You maybe answered your own question!!!

You said "I've only had the thing a week"
What makes you 'think' you need a thing? If you don't understand the effort required in spring replacement (on the front) and have a very good reason to actually 'NEED' - I believe you drive it and enjoy!!!
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Old 12-06-2018, 09:31 PM
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Originally Posted by jefnvk View Post
I was examining this because I was interested in possibly taking it up to the Z51 specs springs, and this is what I was going to buy anyhow...The rear is the expected NYR 39.9, I just find it odd the front would be swapped and not the rear.
As noted, you have the base spring that would have come in your car (FE3). In 1991 there was no Z51 according to the Halverson chart, but the Z07 for 1991 had the same spring rates as the previous year's Z51, and these are commonly known as the "Challenge" springs. The front spring for this is coded FHB, and it's 115.5N/mm. The rear spring is NYU with a rate of 57.2N/mm. So you could find these springs and do your upgrade, which would get you to the 1991 Z07 spec (or 1990 Z51 spec). Swap to the solid 30mm front swaybar and 26mm rear and your suspension is then full Z07.
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Old 12-06-2018, 10:19 PM
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Originally Posted by WVZR-1 View Post
You maybe answered your own question!!!

You said "I've only had the thing a week"
What makes you 'think' you need a thing? If you don't understand the effort required in spring replacement (on the front) and have a very good reason to actually 'NEED' - I believe you drive it and enjoy!!!
That is precisely the path I'd normally take, to be honest I'd prefer if I really had a time to trial it with these. However, I bought it for AutoX, and the shocks absolutely need done (its sitting on the originals with 170k miles, and really needs brakes and every other wear item done) before the Spring. Being keen to shocks and springs working together, before I decide which direction to go with shocks, I was trying to figure out what was the best solution with springs.

Basically, I don't want shocks to be something I have to repurchase if I get halfway through the year and decide to bump up spring stiffness. Plus, ripping it apart and putting it back how I want it is the only fun I can have with it til April, it is much easier to work when it is already up on stands and ripped apart, and in the Spring I'd rather be driving it

Last edited by jefnvk; 12-06-2018 at 10:32 PM.
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Old 12-06-2018, 11:21 PM
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Originally Posted by jefnvk View Post
That is precisely the path I'd normally take, to be honest I'd prefer if I really had a time to trial it with these. However, I bought it for AutoX, and the shocks absolutely need done (its sitting on the originals with 170k miles, and really needs brakes and every other wear item done) before the Spring. Being keen to shocks and springs working together, before I decide which direction to go with shocks, I was trying to figure out what was the best solution with springs.

Basically, I don't want shocks to be something I have to repurchase if I get halfway through the year and decide to bump up spring stiffness. Plus, ripping it apart and putting it back how I want it is the only fun I can have with it til April, it is much easier to work when it is already up on stands and ripped apart, and in the Spring I'd rather be driving it
Your reasoning is sound. That said, you have two options for really good shocks that have adjustable rebound: Koni Sport and Ridetech HQ. Either of these would work with your current stock springs, and you can increase their stiffness if you replace the springs later. I'd try the Ridetechs if I were in your shoes. Depending on what class you want to run, you might want to try to find even stiffer-than-Z51 VBP springs on the used market (VBP is out of business, sadly)...or wait a year or so and see if Van Steel starts making them (as they are rumored to be planning to do).
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Old 12-07-2018, 12:23 AM
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It will serve as a nice Friday to work and fall color run type cruiser as well, I don't want to take it quite to full race suspension. Shooting for ST class, still haven't quite decided between Koni adjustable shocks and shipping the OEMs off to Bilstein with the springs they'll be used with and telling them to valve them in a street performance/AutoX manner. I'll look into those Ridetechs too, haven't heard much about them.

Never realized the build sheets were more detailed than the RPO label, maybe I should pick one of those up sooner rather than later!
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Old 12-07-2018, 01:04 AM
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Originally Posted by jefnvk View Post
It will serve as a nice Friday to work and fall color run type cruiser as well, I don't want to take it quite to full race suspension. Shooting for ST class, still haven't quite decided between Koni adjustable shocks and shipping the OEMs off to Bilstein with the springs they'll be used with and telling them to valve them in a street performance/AutoX manner. I'll look into those Ridetechs too, haven't heard much about them.
I hear you on the dual-use thing. I will say that even with my spring rates, if I have the Konis on all four corners on a medium-ish setting, the ride is suprising decent. Shocks generally have a bigger effect on perceived ride comfort than springs, and my experience with Bilsteins has generally been that they ride fairly harsh. I suppose they have a higher proportion of compression damping, but I'm not sure. The Ridetech shocks are made from Fox monotube internals, so they are high-quality shocks at a good price (slightly cheaper than Konis, but the Konis are less desirable twin-tube designs) and effectively a lifetime warranty.
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Old 12-07-2018, 12:02 PM
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Default FHA Spring

FHA 476 Spring 88 to 91 coup spring rate 93.1 lbs
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