Vortex91

I'm in the process of redoing my suspension and one of the things I'm confused about is the front springs.
My car is a 91 RS with a 305 TBI, when I go to Summit and search for springs I see they list MOG-5610 with a rate of 454 lb/in, looking at Z28 springs the stock number is different and searching the posts here it appears that the rate would be somewhere around 700lb/in.

I'm looking for stock height and I'm trying to figure out what would be best go with 454 or the 700 ones? My bushings are ES polyurethane and as mentioned above the engine is 305. I do have a 350 that I would like to put in eventually but that's down the road.
The sway bars are stock and from what I've read so far if the sway bar is "soft" the spring rate should be higher and the other way around if they are bigger/harder.

What do you guys think, should I go with the 454 or the 700?

My car is not a daily driver and I like to "have some fun" with it when I drive it, having said that, I don't want the springs to make the car so "stiff" that I end up with a headache because of them every time I drive it.

Also, should I buy the rubber mounts for the springs and struts and shocks? The millage is just over 127000 Km.

Thanks

D.

safemode

iTrader: (1)

Poly bushings and hard springs == firm ride. Poly bushings for the most part transfer vibrations more than their rubber counterparts, no matter what spring is used or the sway bar. Since you have the poly on there, you could go with the softer springs and get a bigger sway bar to counteract the leaning when taking turns. That'll give you a softer ride without making it feel like a boat. You also have to match your struts to your springs too, if you care about ride quality.

it really is up to how bad the roads are around you. If potholes and such are rare, then go with the firmer ride. It's not like riding on rails, like a lowered car would feel. If your roads are a hodgepodge of patched crap, then you may be better off with the softer ride, without cracked subframes. Girlfriends usually dont prefer the firm suspension, i've found, on such roads.

Vortex91

Haha, no girlfriend here, I've got a wife.

The roads are OK in general, plus the car is not my daily driver.
Initially I was concerned that the two rates (RS vs Z28) were model specific due to engine size (305 vs 350) and like I mentioned, I'm planning on putting in a 350 hopefully next year.

The struts I have are KYB Gas-a-just.

I guess it's easier to swap the sway bar than having to replace the springs.

I'm not sure if anyone can describe how firm of a ride it would be if I went with the higher rate springs but getting a "feel" for it would help me a lot to decide which one to use.
Safemode, your description is good but maybe someone else can pitch in and let me know what they prefer based on their own experience from using various spring rates.

Thanks for your reply Safemode.

D.

customblackbird

iTrader: (15)

stock replacement will give u a better stock ride. the z28 springs will be alot stiffer and the ride will be alot harsher but u will be able to dip into the curves better and faster with less body roll.

with the z28 springs AKA moog5662s are a 700lb rate and u will feel most of the bumps in the road. a better bet for u if u want improved performance but not as harsh as the 5662s u could go with moog5660 they are about 600-650rate, will be stiffer than urs but u wont feel as many bumps in the road compared to the 454lb rate. 454lbin is a pretty soft spring. u want comfort then stick with the stockers if u want better id go with the 5660 or 5662(being the max). dont go for the 5664s unless u want super stiff like me, course i cut 3/4 off for a 1.5" drop and 875lb spring rate.

the weight diff between the 305 and 350 is basically nothing. they are the same size block/heads(besides chamber size etc). biggest diff is that 305s came with manual vs 350s only came with auto trannys (weight difference)

also KYB doesnt make gas-a-justs STRUTS for our cars, only the rear shocks. u have either KYB GR2s or AGXs(adjustable). gas-a-justs only for rear shocks... i kno bc i have them.

Vortex91

Custom, you are right they are GR2, I bought them last year with the Gas-a-just shocks and they are still in my basement with the ES bushings and Moog boll joints.
Once I decide which springs to use I will overhaule the suspension.
I think I'll go with the 5660s you suggested. I just checked them on Summit's site and they are actually $30 cheaper than the 5610 (bonus). One question though, they list them as pickup or SUV, are you sure the 5660s are conpatible with our cars? Is there a place where I can check?

What are your thoughts on the rubber mounts for shocks/struts and rubber ring (I forget wat is called) used for the spring? Should I replace them as well?

Thanks for your reply.

D.

customblackbird

iTrader: (15)

here is a great site for looking at the moog springs. the part number is 5660, also look and u see the 5662 and 5664 front springs. they show everything about it. now the 5660 rate is between the 598lb/in rate in this website but they are also thought to be 639lbin rates... either way they arent as stiff as the moog 5662 with a 704lbin rate. and still stiffer than your stockers.

http://bbb-carb.com/moog_Coil_Springs.htm

the 5660s are compatable. they have the correct free hieght/and load height as well as the right ends. one square end and one tangendal end. it lists all the moog springs. the firebird.camaro springs are the fronts(5660,5662,5664) i dont bother with any of the others. the rears are the 5665s. dont mind the 5662/5664 spring rates... they are backwards. the 5664 has a thicker wire DIA so it has the higher 748lbin spring rate. this was a problem for a while since someone messed up those 2 rates.

the moog 5660s will fit our cars. and summit isnt the cheapest. i got my moog 5664s for 54$ with free shipping. summit wants 59$ plus the 10-12$ handling fee. i got mine from amazon.

umm the rubber rings are usually fine. unless yours doesnt have one or its really beat up i would just leave them. u have to attach them correctly to the front springs. i use electrical tape to hold them on. alot of ppl ditch the sstock rubber mounts and rap 3/4" heater hose around them and it does the same thing... its just easier to do. the rears arent the same. they have a thick rubber mount that has metal in it. alot of ppl take this out and wrap heater hose around the rears and just the deleting of the stock mount nets about 1/2" drop in ride height in the rear.

also the KYB GR2struts/gas-a-justs shocks dont have poly ends on them. the front struts dont have any bushings and the rears are all rubber.

Vortex91

Hi Custom, THANK YOU very much for your reply. That's exactly what I was looking for.

I'll have to shop around and see where I can get the best deal.
When it comes to shipping to Canada nobody offers free shipping so I'll have to keep that in mind, plus the government will charge 13% tax and the shipping company will charge brokerage free.

Most likely it will be cheaper to buy from the States anyway but I have to do my homework.

Thanks again for your help.

D.