John Shiels

Recieved the spring and 876 was written on the spring so I take it that was what it actually tested at. Now when I put it in and run the car I am wondering if I need to replace the rear also with a heavier one. Will testing on the street give me a indication of how it will handle? I will be running the April 8th with Viper Club of NJ and want to be ready guess I need a warmup session or can the street tale the tales with tires that are not hot? Thanks :steering: :seeya


[Modified by John Shiels, 12:10 PM 1/30/2003]

Jim 47

John, your stock Z51 front spring has a 525 spring rate, so you have increased the front spring stiffness by 67 percent. I would think that this increase in roll stiffness at the front will cause the car to understeer in turns, and unless the rear roll stiffness get stiffened up also, the car is NOT going to corner very well. What do the experts at Vette Brake have to say about your question?

I don't think you can get any idea of how your car with a 876 pound spring is going to handle at Pocono by driving it anywhere on the street. Unless you find a way to increase the rear roll stiffness, I think your car is going to Push Push Push :(

ghoffman

Yes, yes, yes! Get a rear to balance this!

BTW, don't forget to up your damping rates by a similar amount, damping is porportional to spring rate.

jmX

Why do I see so many people getting just the front spring from vettebrakes? Surely this isnt a good thing in any situation, is it what they are recommending?!

John Shiels

Gary I guess I have to change the shocks? The spring is flat as a pancake, is the stock one that flat when out? Someone said just try the front figured I could always get the rear as this is the winter. What am I pulling to remove it? Can I slide it out or the A-arms need to be removed? I could tell better if I was looking at it. Thanks. I'll need teeth guards with this :D on a rough road.
Vette Brakes said 700 lb. rear as I remember. Jim what is the rear Z 51 rate.


[Modified by John Shiels, 8:01 PM 1/16/2003]


[Modified by John Shiels, 8:03 PM 1/16/2003]

Jim 47

John, the stock rear Z51 spring rate is 633. To remove the front spring, you should have a "transverse springcompressor tool" (J33432-A), but if you don't you will have to remove the bottom A arms and disconnect the ball joints, and you'll have to do a lot of jacking/ supporting the lower A arms with jack stands, to remove the ball joints and slowly remove the spring tension. This is generally a PITA. If you can get a spring compressor tool then you only have to remove one A arm and ball joint, and don't have to mess with the jacking /supporting crap.

Your replacement spring should be the same shape as the original stock spring at no load, but because of it's higher spring rate the car will sit higher, and therefore will have to be adjusted with the front spring adjuster bolt, and if there is not enough travel available to get the height desired, then you'll have to reduce the height of the rubber cushion bushing. This can be done prior to the new spring installation, since the spring adjuster bolt is attached to the end of the spring. Also, record the cam settings on the lower A arms so the allignment will be the same after the spring change. Also measure the ride height of your car before the spring change, so you can return it to the same height after the installation with the spring adjuster bolts. This is NOT an easy project, but possible to do by yourself if you take your time. :thumbs:

John Shiels

Jim thanks for the infomation! If the stock rear Z51 spring is 633 ad the new Vette Brake spring is 700 it's not that much difference? Maybe I should try it with the stock rear spring, no? The 900 lb. spring was tested at 876 so I
could end up with new spring with only 25 more lb. which hardly seems worth it. I was ready to order the rear but may hold off till I get the front in and try it. Jim where did you get the spec's on the spring and what is the front Z51 thanks :thumbs: What you doing on yours? How did the duct idea pan out?

I just read this post and saw all the words jammed together and with letters missing :eek:


[Modified by John Shiels, 9:31 PM 1/27/2003]

LTC Z06

Jim do you know the spring rates for Z06s too?

Jim 47

John, I've been collecting data on the C5 ever since I got it in Oct'99, and I'm not sure where the spring data came from. One thing's for sure, the data is only as good as the source, and since I can't vouch for it's authentisity at this point, you may be wise to seek another source in the event the data I have is incorrect. I do not have any data on front spring rates for the Z06, but an artical about the Z06 by Hib Halverson back on 8/17/2000 said that the rear Z06 spring was 10 percent higher spring rate than the 2000 Z51 spring. If the Z51 rear spring is 633, the Z06 rear spring should be in the 700 range. Maybe the 700 pound spring that Vette Brakes sells is a Z06 rear. The artical didn't mention any change in the front spring from the Z51 suspension to the Z06 suspension, so I think that the Z06 front spring is the same as the front 2000 Z51 spring. Someone with a Z06 could confirm this by looking at the bottom of the front spring. If the paper sticker on the spring has the letters "AY" , then the Z06 spring is the same as the 2000 Z51 spring.

You could beef up the roll siffness in the rear with a stiffer stabilizer bar and/or with shocks with increased low velocity damping (like the Z06 rear shocks) and/or very hard stabilizer bar bushings to compensate for the increase in roll stiffness in the front.

I drove my car today for the first time in about 7 weeks. Many small changes and improvements, but I did stiffen up the rear by very slightly reducing the lever arm on the rear stabilizer bar (I was getting tired of the inherent understeer). If this proves inadequate, I will replace the rear stabilizer bar bushings with the hard poly bushings which will also add stiffness in the rear. Both these things are reversable if I find I've stiffened the rear up too much. I've got plenty of air going to the front brakes (4 sources for each wheel) so I should be able to out brake most all the "stock" rotor/calaper guys and maybe even some of the moded front brake guys. Still only 2 air sources for each rear wheel. I couldn't find a practical way to use the 2.5" NACA ducts I have, but I'll keep looking. :cool:

John Shiels

I have the poly bushings throughout and the T-1 bars maybe the shocks should be revalved? Doubt I can get the feel on the street but I might as well try. I'll give Hib a yell for the spring rates if he desn't know he will have a source. What four air sources in the front Jim did you use the scoops?

LTC Z06

Thanks Jim, I'll look for that AY if my stickers are still there.

Jim 47

CPT Z06, let us know if the "AY" letters are there. Or maybe another Z06 guy could take a look at the bottom of his front spring and give us all a report.

John, You'd have to see this to believe it. It's real crowded with black flexable hozes behind each front wheel. I don't have a camera, so I try to describe the 4 sources in a later post. Right now I've got to get out of here. I'm singing in Princeton this afternoon. :cool:

VBP

We feel for auto-x the stock rear springs are sufficient unless you are running huge slicks. The front upgrade is to prevent nose-dive under hard braking and help the body-roll. Our springs are manufactured totally different from GM and start with a lower arch. We can achieve higher rate's and keep the car around stock ride-height or lower because they are adjustable. The spring-rates listed on your front will actually ride a little better than the stock Z-51 and perform better. You won't have any problem with the car pushing pending your alignment, shocks and driving style.


[Modified by VBP, 10:22 PM 1/27/2003]


[Modified by VBP, 10:31 PM 1/27/2003]

John Shiels

So I guess I'll give it a shot with just the front replaced? The car has Bilstein Sports and T-1 bars and a tad more camber than ZO6 but will increase it for next season. I am running 275/315/17 kuhmos but may go bigger. Kerry Hitt told me to talk to Paul L. @ VB who is this I am speaking with? Thanks for your help. I was going to get the shock revalved any suggestions? What are the rates for the stock Z51 springs. I know there was a thread previously but don't remember a definitive answer. Thanks!


Jim 47 I se the rates you stated are 633 rear and 525 front is that correct? I would think the front to be more no :confused:


[Modified by John Shiels, 9:41 PM 1/27/2003]


[Modified by John Shiels, 9:44 PM 1/27/2003]

VBP

My name is Brian and I do technical advise on the phones and all the Corvette Forum monitoring. The Bilstein sports are good for auto-x but if you want to do any high speed you can revalve them or for the price of revalving we use the Koni adjustable. It depends if your particular class will allow adjustable shocks. I thought the stock rear rate's changed a little between manual and auto tranny? My chart dosen't specify Z-51 but I will do some research to find the original Z-51 rate's. My chart shows 525.31lb. for front and 633.80lb. for MAN and 645.22lb. for AUTO on the rear on an FE-3.


[Modified by VBP, 2:48 PM 1/29/2003]

John Shiels

Brian thanks for the response which Koni's are they exactly and price I guess I can see on line? I just do track events so the only rule is try to stay ahead :D Revalving is 55 ea I doubt the shocks aere that. I still am very interested in the Konis
Brian I just looked and they are 500 which is what I expected. What is the adjustment procedure? Can they be tweaked on the car or remove to adjust them? I run track event which can get a bit speedy at times. I hope to approach 170 at Pococno this season. It went 163 last year on my second session of the year + passenger. I now have more power too. Thanks.

Jim47 looks like your info was spot on! :D


[Modified by John Shiels, 11:13 AM 1/29/2003]

VBP

You can view the Koni's we have on our web-site. Click on "Shop Online", then go to "Shop Now", then go to page #30 at the top of the page. They are a single-adjustable Koni which is rebound adjustable only. The compression is already set from the factory and we've had good results with these in auto-x and Road-race applications. I like the adjustability factor for setting the car up for different tracks and fine tuning your vehicle for different drivers if applicable. They are a straight bolt-on in place of the stock shocks. The shocks are more than I thought the revalving would be but you still won't be able to adjust the Bilstein even with the new valving. I thought the revalving would be like $75 with the shipping and handling. The single adjustable Koni's are still cheaper than a dual-adjustable or the Penske's. We thought about using a Bilstein which was revalved for our Xtreme shock on the C-5 but we liked the adjustability factor on the Koni's.

VBP

You can view the Koni's we have on our web-site. Click on "Shop Online", then go to "Shop Now", then go to page #30 at the top of the page. They are a single-adjustable Koni which is rebound adjustable only. The compression is already set from the factory and we've had good results with these in auto-x and Road-race applications. I like the adjustability factor for setting the car up for different tracks and fine tuning your vehicle for different drivers if applicable. They are a straight bolt-on in place of the stock shocks. The shocks are more than I thought the revalving would be but you still won't be able to adjust the Bilstein even with the new valving. I thought the revalving would be like $95 each with the shipping and handling both ways. The single adjustable Koni's are still cheaper than a dual-adjustable or the Penske's. We thought about using a Bilstein which was revalved for our Xtreme shock on the C-5 but we liked the adjustability factor on the Koni's.

John Shiels

I see now they are 249 ea are they adjustable on the car or do they have to be removed? Thanks :seeya

jmX

VBP, does KONI offer a shorter single adjustible shock for lowered C5's? Can't they just cut down the shock body?