So I know spring rate desired can be subjective, some people like a much firmer ride.
But for something like an engine swapped car, say for example the engine is 100 lbs heavier than the 2.8 was. I assume you would want 100 lbs higher rear spring rating to make up for it? But there are two springs...so maybe only 50 lb more? But then...the stock springs weren't coilovers, or adjustable height, and I don't know their pound rating...
Also I have read the 2.8 weighs 475 lbs, true?
What did / would you do?
[This message has been edited by 2.5 (edited 12-27-2017).]
"WHAT IS SPRING RATE? Spring rate refers to the amount of weight that is needed to compress a spring one inch. If the rate of the spring is linear, its rate is not affected by the load that is put on the spring. For example, say you have a 200 lb. per inch spring - it will compress 1” when a 200 lb. load is placed onto the spring. If another 200 lbs. is put onto the spring, the spring will compress another inch. At this point the load on the spring is 400 lbs. The rate of the spring, however, remains constant at 200 lbs. per inch.
Springs should typically be compressed 25-30% of the free length when supporting the weight of the vehicle. Drag race cars will normally use a lighter rate spring (about 30%) to promote weight transfer while a street car will use a firmer rate spring (about 25%).
Each car is different, so it is ideal to actually weigh the front and rear of your vehicle."
I am sure some of the roadcoarse guru's will step in but when I bought my parts to make my rear coilovers I just searched around for what others used. Hence why I went with the 300lb spring for the rear. I am sure if you hav a heavier motor you will want a heavier spring to compensate, additionally if you plan on road racing your car these spring rates are going to change as well depending what your needs are. Normal spirited street driving I would think you do not need an aggressive rate spring because it will give a harsh ride.
BTW I will be swapping in a 4.9 caddy motor and I will keep my 300lb springs, the 4.9l is not much heavier than the 2.8.
The stock spring rate IIRC is somewhere around 160 lbs on the rear, not sure of the front. I have played around with lots of rates. A 200 lb spring on the back worked great on the street for my car. But we don't have any tight turns around here so I could not feel the roll. Took it on a track and it was terrible, way too much roll. So if you live anywhere near fun roads ( I don't , flat straight and boring) I would put 350 at both ends. My suspension is not conventional but I have 450 front and 350 rear ( because of my lighter ecotec motor). The ride is actually not that bad, but I am after performance at the track.
The stock spring rate IIRC is somewhere around 160 lbs on the rear, not sure of the front. I have played around with lots of rates. A 200 lb spring on the back worked great on the street for my car. But we don't have any tight turns around here so I could not feel the roll. Took it on a track and it was terrible, way too much roll. So if you live anywhere near fun roads ( I don't , flat straight and boring) I would put 350 at both ends. My suspension is not conventional but I have 450 front and 350 rear ( because of my lighter ecotec motor). The ride is actually not that bad, but I am after performance at the track.
So factory rear springs are less than 200 lb? So if an engine was swapped in that weighed 100 lbs more, would it need only 300lb springs to support the extra weight, (if that?)
[This message has been edited by 2.5 (edited 12-28-2017).]
I did a search and I could not find a stock spring rate but 160 lbs is what I read somewhere .Maybe it is in the Ogres cave. But 300 lbs is a popular choice for a lot of engine swaps that I see.
Stock 88 spring rates are 205 lb/in in front and 147 lb/in in the rear. The 84-87 spring rates are slightly stiffer.
The motion ratio in the rear is very close to 1 whereas the front is close to 0.5.
If the rear of your fiero scales at 1600 lbs with 200 lbs unsprung weight (100 per side), the springs must support 1400 lbs. With the stock 88 rear rates, you have 294 lb/in. With 1400 lbs, the springs will compress 4 3/4", however the stock springs are pre-compressed when installed on the strut, so you will see them compress something less than 4 3/4"
Adding 100 lbs to the rear with an engine swap will only compress the stock springs about 1/3".
As far as spring rates, it is a very personal decision and is also dependent on your shock/strut design. My summer daily driver Fiero has 575/425 spring rates, konis set to full stiff, and 40 and 30 series tires.
So... if the stock rear springs are 160 lbs (ish)... I am adding 200 lbs (ish)weight to the rear, which is sort of divided by the two struts (?)... 325 lb coil over springs would be more than sufficient to keep a not overly aggressive feel?
Its a 1987 smallblock ironhead with a TPI intake, all from a Trans Am. Its technically already been in for years, I got the car with it in it. But the coilover struts that are in it look like cut off factory ones and they are kinda shot, and I cant tell what the lb rating the coils are that are in it. I could reuse them, but they seem overly firm to me. They don't seem to really move while driving and then when they do the car bounces due to worn out struts.
Its an 87 GT with a rear sway bar. Lowered approx 1 inch in back. I came across and acquired a set of excellent condition Koni that have 325 lb coilover springs on them already.
I'm really kind of curious in general, there must be a method, other than someone else in the past having run a certain lb rating, and liking it. Though if that's all I can get , the more the merrier
[This message has been edited by 2.5 (edited 01-02-2018).]
I'm really kind of curious in general, there must be a method, other than someone else in the past having run a certain lb rating, and liking it. Though if that's all I can get , the more the merrier
There is, it just requires a lot of detailed measuring of all suspension pivot points and math...
A normal family sedan has a suspension frequency in the 1.0 to 1.5 range and high performance cars will be in the 2.0 to 2.5 range.
Cool info. But yep some is over my head If we are starting with the knowledge that the stock suspension is 160 spring rate per side in the rear, and say we disregard the fact that it is slightly lowered. Taking into account the only other changes are the narrower 12 inch spring a coilover set has, and the approx 200 lbs weight added at the engine, It seems we could extrapolate a bit?
I would love to hear more peoples thoughts, and what they run with what engine, and even why. Thoughts on how much a rear sway bar takes care of "roll"?
If I were to start from scratch, this guy goes into some cool details. Though he is focusing on rock crawler trucks he hits useful concepts and data.
and another... the interesting thing is with a Fiero and coilovers, you really cant get any pre load, correct? The only load there is , is the cars weight.
Whether or not the spring will have preload will depend on a few factors. For example, if it's a light spring (low spring rate), then you may need to put some preload on it just to make the car sit at the desired ride height. The stock Fiero springs are like that. And the opposite is true for a really stiff spring. For example, the 350 lb/inch springs on my rear suspension actually have some play after the car is jacked up.
With a non-adjustable suspension, different spring rates will make the car sit at different heights. You either have to carefully select spring rates, or select a slightly undersize spring and shim it to taste. But with adjustable coilovers, you don't need to worry about that. You can select a desired spring rate, then adjust the spring perches, and you're set.
For some reason on my apple computer I can't see a lot of the videos that get posted including the ones above. So I do not know what preload he is talking about. But my interpretation of preload is how much I have to move the spring perches up to get the car to sit at the desired ride height. I have coilovers at all 4 corners that have a full eye to eye length of 14" and a compressed length of about 10". QA1 brand. With a 450lb 9" spring on the front and a 10" 350 lb spring on the back I tighten the perches so they are about an inch up from the bottom of the threads and then adjust each corner up and down from there to get the ride height I want.The springs are compressed on the shock before I put them on the car. I have a modified Arraut sport suspension on the front and my own design SLA suspension on the back, 2.2 turbo ecotec powered. No rear sway bar.
When I had a more stock like strut suspension I had 350lb 12" long springs on KYB coilovers in back and 300lb 10" springs in front and it worked well and fairly smooth ride. I had it on the track at Woodland Hills at the 25th and it worked really well. On the Tail of the Dragon it was good too but on the tight uphill switchbacks I repeatedly rubbed the front tires against the fender liners. Rears no problem.
With my current setup it is easy to change springs and I have experimented a lot with different weights. This leads to buying a lot of springs but I have found that the ones that dont work the way I want are pretty easy to sell in the Mall here on Pennocks.
[This message has been edited by wftb (edited 01-04-2018).]
With my current setup it is easy to change springs and I have experimented a lot with different weights. This leads to buying a lot of springs but I have found that the ones that dont work the way I want are pretty easy to sell in the Mall here on Pennocks.
There isn't a way to pull the rear springs without needing an alignment again is there? Except dropping the cradle?
With coilover struts, I think you can just unbolt them at the top and let them drop down. You have to take the top apart to get the spring out anyway. I use to use a sharpy and mark around the oval washers to get them back in the same place. Get the ride height the same as it was and it will not affect the allignment noticeably. With an 84 to 87 rear suspension, changes in ride height will change the toe. Align as follows: ride height, camber, toe.
I'm using a 350 lb 8" spring on mine (mainly because of the wheels I have and want to run a 245/255 Drag radial). It rides pretty decent. Better than the 30 year old stock struts that were back there.
This is my car right now with a 2.8 and on 300lbs, 12" springs. It's a little lower, but not slammed. It rides nice, but I rub all the time in it. If I hit any kind of larger bump, like a bad bridge transition or a wide dip that gets the entire car to squat or rise on the suspension it'll rub. If I take a corner too fast it'll rub on the outside as well. 20mph or so type too fast, nothing crazy. I'm going up to a 450lbs for a 3800 swap and to stop the rubbing.
[This message has been edited by mr_corean (edited 01-10-2018).]
This is my car right now with a 2.8 and on 300lbs, 12" springs. It's a little lower, but not slammed. It rides nice, but I rub all the time in it. If I hit any kind of larger bump, like a bad bridge transition or a wide dip that gets the entire car to squat or rise on the suspension it'll rub. If I take a corner too fast it'll rub on the outside as well. 20mph or so type too fast, nothing crazy. I'm going up to a 450lbs for a 3800 swap and to stop the rubbing.
Thanks. What struts are you running, and a rear sway bar?
KYB, less than a year old. No sway bar. You should get your spring rates correct before messing with sway bars because of how they affect each other. In my case I need to get mine heavy enough that I won't have the straight line issues while still keeping my fillings in my teeth. At that point I can start looking at a sway bars to clean up the corners.
I'm only running 17 inch and only lowered approx. 1.5 inch. Your tires look large. Mine currently has 400 lb springs and a rear bar. I'm surprised you need stiffer springs the 3800 weighs less than my engine, I would think a bar would help your issues. But I know what you mean about the bar tying the sides together.
[This message has been edited by 2.5 (edited 01-12-2018).]
I've got 19's in the rear, but overall diameter isn't greatly increased. With that being said I am going to a tire that will shave me another half an inch in height and add another inch in width as well. The bar won't help the straight line rubbing, just the corners. Heavier weight springs will essentially act like a weak bar so I plan on going as heavy as I can while still keeping the car enjoyable to drive. Then add a bar to that and tune bushings, diameter, ect. to meet my desires. The 300's on the car now are soft and comfortable, but the rubbing has got to go. 450's are on the work bench, but I don't think I can get an alignment done on it before the LV drive here on Saturday. So I will be rubbing on Saturday, lol.
If you are rubbing like that you may want to raise your car up to give you more suspension travel. Now if it is just the look you are going after then dont even worry about it. It does look good with that stance though.
BTW I have that same hood vent.
[This message has been edited by Spadesluck (edited 01-11-2018).]
