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flyhilandsoft
Post subject: Coilover shocks  PostPosted: Feb 11, 2015 - 04:18 AM
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Joined: May 12, 2007
Posts: 330

Just trying to get an idea on spring selection for my Countach. I am finally at the point of installing them and putting weight on the wheels. I am using custom modified rear suspension from the Corvette (C4), and a stock setup up front. I would imagine that the weight would be similar to other replicas using the BMW M70 mated to a Porsche G50. I am running two QA1 Promastar coilovers for each rear wheel. Not knowing the final weight what do you recommend so I don't end up buying more springs than I need. This has been a long time coming. Thanks for the help.

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John
Goodyear, Az
"Its a dry heat"

http://www.siennacountach.net/gallery2/album129?page=1

http://countachbuild.shutterfly.com/pictures#:albumId=2303
Password-aluminum
 
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EAMartinOffline
Post subject: Re: Coilover shocks  PostPosted: Feb 11, 2015 - 05:03 PM
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flyhilandsoft wrote:
Just trying to get an idea on spring selection for my Countach. I am finally at the point of installing them and putting weight on the wheels. I am using custom modified rear suspension from the Corvette (C4), and a stock setup up front. I would imagine that the weight would be similar to other replicas using the BMW M70 mated to a Porsche G50. I am running two QA1 Promastar coilovers for each rear wheel. Not knowing the final weight what do you recommend so I don't end up buying more springs than I need. This has been a long time coming. Thanks for the help.


It is going to depend somewhat on your suspension design. Where are your shocks attached to the suspension and at what angle are they mounted? On my design with two coil-overs per side I use 160# springs.
 
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76mxOffline
Post subject: RE: Re: Coilover shocks  PostPosted: Feb 12, 2015 - 04:58 AM
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To expand on what my bud Eric has said here, the further inboard the shock is mounted on the a-arm, the more lever arm you have and the more spring you need. Also, the more angle it is mounted at, the more spring you need to accomplish the same thing. So if it works on one car, it would be total coincidence that it would work on another. That is before you consider that the bigger the swaybar the smaller the spring rate and vice versa, which would make it even more of a coincidence. But back to your original premise of the final weight being similar, that has nothing to do with spring selection. Spring rate will determine how much weight will transfer during braking, acceleration, or cornering, but a 200lb spring will hold up a 500lb corner just as easy as a 2000lb corner.
 
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76mxOffline
Post subject: RE: Re: Coilover shocks  PostPosted: Feb 12, 2015 - 04:42 PM
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FHLS,
This is going to be your second problem. The stock Vette suspension was designed for 17" wheels and about a 28" tall tire. When you put it on a Countach, and use the stock 24" tall tire on a 15" wheel, the lower a-arm sits about 2" lower at the shock eye. Never mind the fact that this now puts the upper a-arm too level to get proper camber gain in cornering. Now unless the upper shock eye has been moved down 2" to compensate, no spring rate is going to work and probably not the shock either. I am curious about your brakes, the stock Vette stuff will not fit the Countach wheel either. I do not mean to discourage you, I would be glad to walk you through it, but it is the nature of these cars that the construction process is backwards. In a perfect world the shock and spring should have been selected and then the chassis and suspension built to accommodate that.
 
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flyhilandsoft
Post subject: RE: Re: Coilover shocks  PostPosted: Feb 13, 2015 - 04:11 AM
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Joined: May 12, 2007
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Thanks for your input. In a perfect world I probably wouldn't be asking any questions about replicas because I would have the real 400S sitting next to my Aventador, and Gulfstream G650. I believe the Corvette C4 came stock with 16" wheels. The exact same geometry was incorporated in the chassis and suspension as the stock Corvette. It will be slightly wider but exactly the same. I also realize one geometry is not one size fits all however it's better than what I could of dreamed up. The brakes and wheels fit just fine with plenty of clearance from the calipers. I checked this the same day my wheels showed up on the doorstep. Trust me....I understand what you mean when you say the construction process is backwards. I built this car from scratch with no drawing or plans. I had to build the car from the inside out in some aspects, and outside in on other aspects. I had to move the roof three times before it was correct. Basically this has been one big SWAG from the very beginning. I am not an engineer. Will it drive straight? I hope so. Will it ride fairly nice? I hope so. Will it be safe? I don't know why not. There will be no records set in this replica. I will on occasion drive the car to Sonic for burger, and fries with the wife.

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John
Goodyear, Az
"Its a dry heat"

http://www.siennacountach.net/gallery2/album129?page=1

http://countachbuild.shutterfly.com/pictures#:albumId=2303
Password-aluminum
 
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76mxOffline
Post subject: RE: Re: Coilover shocks  PostPosted: Feb 13, 2015 - 03:17 PM
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Glad it all fits. To proceed from here it is more important right now to establish the spring height (typically 8,10, or 12) before the spring rate. This will tell you what your rate range is and narrow it even further when the rates that will coil bind are eliminated. To do this, what is the travel of your shock? It will have an extended measurement and a compressed measurement. Also, at ride height, what is the distance between the lower shock eye on the a-arm and the upper shock eye on the chassis?
 
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EAMartinOffline
Post subject:   PostPosted: Feb 13, 2015 - 05:37 PM
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If I remember right the C4 is the multi link design that uses upper and lower trailing arms (like a 4-link) and lateral lower links and the axle is the upper link. Have you fabricated an upper link? What transmission and axles are you using? If your shock is mounted to the upright you have a 1 to 1 ratio for the shock rather than what you would have if it is mounted inboard on the lower arm. Can you post a photo?
 
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flyhilandsoft
Post subject:   PostPosted: Feb 14, 2015 - 12:39 AM
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I am out of town right now. I will try to upload some pictures when I get home. It is very similar to Ken Imhoffs setup. Same hubs modified almost identical. The thing I did different is I added my shock mounts directly above and slightly behind the lower control arm heim joints. Looks very similar to the OEM Countach system. I am running a Porsche G50 gearbox and shortened Corvette C4 half shafts. It is setup with two lower control arms with an upper and lower drag link. They are all adjustable with heim joints on the hub end and ballistic poly bushings on the chassis side.

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John
Goodyear, Az
"Its a dry heat"

http://www.siennacountach.net/gallery2/album129?page=1

http://countachbuild.shutterfly.com/pictures#:albumId=2303
Password-aluminum
 
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lambo1Offline
Post subject:   PostPosted: Feb 14, 2015 - 04:56 AM
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hi John , you may find this comment on spring weights and lengths helpful from Jim D
http://lamboclone.com/index.php?topic=870.new;topicseen#new

the weights Jim mentioned are the same as I was told to use for my CT by the local Countess builder.
regards
graeme
 
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flyhilandsoft
Post subject:   PostPosted: Feb 18, 2015 - 03:30 AM
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Joined: May 12, 2007
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Thanks Graeme. Good info.....I will check this out.

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John
Goodyear, Az
"Its a dry heat"

http://www.siennacountach.net/gallery2/album129?page=1

http://countachbuild.shutterfly.com/pictures#:albumId=2303
Password-aluminum
 
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