BZX and NNL

Lots of discussions equal amount of confusion.

So I understand these are the second and third stiffest springs, respectively, that GM had on third gens.

I’m not able to find exact spring rates for those springs. I even went to gm parts and nada.

I see people say 550/107 was the stiffest GM offered on WS6 Firebird and FE2 Camaro. I also see people say 701 and 204 or something like that.

I also found that people say year to year the spring rate may have changed from time to time.


I have an 87 350 t roof. Please any clarification hugely appreciated. Thanks 🙏

 

What are you really asking?

Technically the codes go up a few more letters. They're in the catalog, but pretty sure the spring rates aren't.

GM chose different springs based on a computer generated algorithm. Out here in the world, you replace like for like or play fast and loose.

Most people arent going to worry about the rates or codes, they just slap in some universal Moog garbage for an El Camino, or a set of Eibachs and call it a day.

Edit - To elaborate, the codes are in the book in a chart. But they're only listed as higher/lower rates. Generally speaking a later letter is a higher spring rate, but not always. Fronts go up to BZZ in some years, BZY in others.. NNM is the highest rear, but there's an NNN that's a lower rate. Then there are CDB fronts. Different codes were used with different years and options. But without the actual spring rate, what does it matter? So as you can probably gather, it's not the most clear cut subject.

 

This will give you a feel for OEM spring rates. Likely not complete but good enough for government work.

https://www.thirdgen.org/forums/susp...ring-info.html

 

appreciate that I did locate that earlier my best guess would be 598 to 748 in the front but those were federal rates and not sure they were factory specs.

ive also found in my research that the 748 (5662) spring could actually be a 648 and a misprint at 748 lbs so I take the Moog/federal specs with a bit of skepticism for that reason also which is why I came to a conclusion that the oem springs would be in the 550-700lb range for the fronts but it’s just a best guess.

i can’t see a company like eibach saying their pro kit at 714/177 would improve handling if irocs came with 748lbs in the front stock. Also 748 front spring with a 107 rear spring factory sounds like a crazy odd combo to me. Not convinced on those numbers either. 550/107 makes more sense. Even a 648/107 doesn’t make a lot of sense to me. But that’s my dilemma I’m just guessing at the rates.

I think it maybe a futile effort to keep perusing this info, seems impossible to confirm exact specs and all I’m trying to do is find an aftermarket spring that will ride close to stock on stock shocks without going lower than 1” or so.

I guess hotchkis is the default winner then at 600/140 it seems to have the closest rates to factory and I want to make sure the stock shock valving can handle the new spring. It currently has intrax lowering springs in it, 2 to 2.5” drop rides like crap cause the oem shocks and with a heavy front end, ac, smog, heater, iron block TPI etc... it really weighs the front end down and sits too low for me.

 

There's no solid correlation between Moog numbers and stock. Partially because GM is less than forthcoming with stock numbers. The places that we look for accurate information are geared toward making sure the right part gets in the right car on the assembly line and when it's serviced by the dealership. GM used broadcast codes for that, they didn't need the Oompa-Loompas getting confused over spring rates. Moogs springs are not exactly application specific. You can pull them up on Rock Auto and list applications they were used in, and see that much. Or look at all the threads over the years where people installed Moog springs and now they are going to Monster Jam next SUNDAY! SUNDAY! SUNDAY! to take on the Legendary BIG FOOOT!!!.

Now I'm going to get lost into personal theories, the legend of Loch Ness and more, so proceed at your own peril. Most aftermarket companies aren't worried too much about replicating the factory ride height, feel, handling, etc. Moog wants to sell you a spring, not necessarily the spring that fits like a crystal slipper. Eibach is selling lowering springs with a touch of performance, they care about image, and maybe performance, but they may just believe a thirdgen doesn't need a spring rate as aggressive as GM used for the best compromise of ride and comfort, and performance.

The OE springs are stiff. So stiff they really require a high end damper to control the spring and keep it from jarring occupants. An argument could be made that GM went too stiff. Start modifying a car and the car no longer matches the specs GM entered into the computer to get the 'right' springs. So in the case of weight reduction, or increases, the OE spring isn't even going to be right anymore. Not to the degree GM was going. Knowing that GM often didn't even use the same springs on both sides in front, they were being extremely specific on the assembly line. You can look at the service charts in the GM parts catalog and see that for about ten OE springs, GM only had about 4 service part numbers, with several overlapping. So does that mean that it's really not that specific, or that GM didn't want to inventory a gazillion springs that most people would never replace? In the same vein, GM designed the suspension as a system. The stock springs were intended to work with stock struts and shocks. Where are you going to find true replacements for the stock dampers in 2020? GM hasn't made exact application specific shocks/struts for these cars for decades. Everything is one size fits all. Which by extension means that you're not going to replicate stock exactly anyway, unless you've got a time machine.

So where does that leave us... If you give any thought to it at all beyond "cool, I'll take the red ones", you're doing more than most people. If you trust anyone's opinion or info on the subject, you're probably missing something or likely putting garbage into the equation. Personally, I'd say run a 30 year old spring and accept that it may have settled slightly, and use a high end damper like Konis, and you'll probably be satisfied. Or buy springs from Eibach or Hotchkis (same thing last I checked) and run a quality damper, and you'll probably be satisfied. Or if you're a Moog fanboy, get some Moog springs, cut them two or three times, blame the stock springs for sagging instead of Moog for selling you the same springs they sell someone with a 1979 El Camino, toss on some KYBs, and you'll probably be too dumb to know any better, thus you'll probably be satisfied. There, I think I've probably offended everyone thoroughly, so I return you to your regularly scheduled forum topics, already in progress.

 

I love this response bc it’s the truth! Lol Could not agree more.

I bought my car with only 13k miles on it. It still has 13k miles on it. Aside from the the intrax lowering springs on it now that were installed by someone at around 9k miles and the 17” iroc reps he also installed, there’s no other aftermarket part on the car. Not even floor mats. I don’t want to replace the shocks for this reason and I don’t want to install the stock springs since it looks like based on measurements, there’s little no sag at all.

I do not like 4x4 look as you said that’s why I figured a 1” drop spring would be ideal and and why the spring rate was important to me.

Based on what I’ve been learning, the feedback I’ve been getting and what my gut says, I’m going with Hotchkis. I like the BMR springs too just a touch stiffer at 620/160 but I fear they may sit too low at an advertised 1.25-1.5” drop vs 1” of the hotchkis. The BMR are almost $100 cheaper too but sometimes saving $100 isn’t worth the compromise so something I’ve accepted and moving forward with. Plus I’d rather have a stock looking black spring or gray at most. Red or purple or yellow all these rainbow colours are just not for me.

 

I once had Hotchkis springs in my car for a couple weeks and it rode rougher than heck and the car was a basket case under throttle with fishtailing galore. Put the Ground Control weight jacks back in and it rode smoother and straightened up under throttle. Go figure.

 

what were the gc spring rates and what shocks did you pair the hitchkis with? They seem to have the closest spring rates to stock at 600/140 so that’s not I wanted to hear for sure. Did you have any other suspension mods like sway bars or poly bushings etc...any non stock components?

 

My weight jack spring rates are 800 front and I think I had 150 rear with Koni shocks front and rear. Now I have Viking double adjustable shocks in the back with 180 rear Eibach springs. My entire rear suspension is spherical joint.

Yes, I have large sway bars.

 

Getting ready to start revamping my 100k mile 89 RS. Just wanted to double check that this comment was focused on the cheapest KYBs and see what the consensus on the KYB AGX shocks and struts was.

I'm looking for reasonable performace on my stock RS coils for a nice street driver and not break the bank. I was planning on trying to find some IROC sway bars and run poly bushings and tubular panhard and LCAs.

It's not going to be a big power car or raced. Mainly a beach cruiser for the wife and I.