What poundage springs?

[Iain]

It would appear that my springs for the front shocks (that came with my kit) are wrong!

I've kind of worked out what the size should be physically but I've also changed my engine from what I originally intended to run.

So, my question is, what kind of poundage springs should I be looking at for a Ford 302 engine (standard heads, crank etc.) with a 4 speed Toploader.

It's a Jaguar chassis by the way...

Cheers...

[Miket]

Iain

I have 450lbs on the front with a Chevy 350, I find it a little to stiff, If I every did it again I would possibly drop down to 400lbs.

[wilf]

Iain - the spring rate is dictated not so much by the overall weight of the car etc., but more by the geometry of the suspension - distance from suspension pivot to wheel centre vs distance from pivot to damper mounting point etc. It is a leverage thing.

Thus it is very difficult to check that what works for one kit would work for another. Maybe only another Viper owner could help. (unless there is a generic configuration to the suspension).

Are yours too strong or too weak?

[Iain]

Wilf,

It's not exactly a matter of what's wrong with them... more like what's right with them.

I didn't realise (many years ago when I got them) that since they were such a ba***rd to fit that they were actually far too long for the shock so even with the shock wound right down, they are still compressed. I am assuming that even if they were the correct length then they would be too strong as they were originally for the Jag V12 engine.

To fill you in completely, all the shocks and springs were ordered with the kit from Ken "Knobhead" Cook. The front shocks look the right length but the springs are too long for them. The rear shocks themselves look too long as the car sits like a 4x4 even with the springs wound right down (but that's another problem to sort when I get the car back).

I've e-mailed Bob Busbridge at Cobretti for his advice but I am still waiting a reply.

Cheers...

[chesterak]

Iain,
In the early days of building my Viper (now owned by HowardB) I spoke with a guy by the name of Nigel at Avo (tel: 01604 708101). He advised 375Lb springs 83/4" long for the front to match the dampers supply by Cook. He was knowlegable and helpful.(No, not Cook!)
As for the rear...I cut out the top mountings completely and moved them inboard to lower the back end by about 3". I would have done this anyway as the original build quality was garbage. As the rear geometry has now changed, the impression I had from "bouncing" the car (I know, not a proper engineering method), the spring rates as supplied looked ok as it seemed to have a reasonable adjustment range (soft to very hard). For more upright suspension mounting, the corresponding spring rate should be lower. Trial and error I'm afraid to get ride height/spring rate correct.
Hope this helps....

[Iain]

Originally Posted by chesterak

He advised 375Lb springs 83/4" long for the front to match the dampers supply by Cook.

Hi Stan,

I measured what I considered to be an uncompressed length with the help of Martin (Tinka) and as I recall, I thought I needed 8 inch uncompressed and 5.5 inches maximum compression. Not exactly what you got advised...

Now I'm really unsure...

Cheers...

[tony c]

As Stan said, it is trial and error to get them right. At least your springs are too long so why dont you cut them down to whatever size you think best suits the car as far as ride height is concerned (bit by bit rather than reduce them too far) then once they are at the correct height if you think they should be softer or firmer you can use them as a pattern and have new ones made up to the correct length and poundage. Of course you might strike lucky and find that after chopping them down the firmness is ok although reducing the length does increase the poundage which from the sound of it is too high anyway. The important thing is to arrive at a starting point ie. the correct length.

Tony

[russell_ram]

' it is trial and error to get them right'

No it's not, it's science. Given the factors that Wilf discusses in his answer and a few more, and knowing what bounce frequency you should be aiming at you can calculate everything you need to fully specify the spring you require. Then you 'tune' around a given starting point.

'reducing the length does increase the poundage'

No it doesn't - a rate in Lbs per inch is a rate in Lbs per inch of compression of the spring. It is independant of the free length of the spring. We do not generally using rising or variable rate road springs or get anywhere near coil bound in our applications. The rate of a 'cut down' spring is EXACTLY the same as it was before you cut it.

A goolgle on road spring design will turn you up a spread sheet that will design you springs for you - failing that a trip to the local library will get you the appropriate text book.

Russ

[chesterak]

Originally Posted by russell_ram

' it is trial and error to get them right'

No it's not, it's science. Given the factors that Wilf discusses in his answer and a few more, and knowing what bounce frequency you should be aiming at you can calculate everything you need to fully specify the spring you require. Then you 'tune' around a given starting point.

'reducing the length does increase the poundage'

No it doesn't - a rate in Lbs per inch is a rate in Lbs per inch of compression of the spring. It is independant of the free length of the spring. We do not generally using rising or variable rate road springs or get anywhere near coil bound in our applications. The rate of a 'cut down' spring is EXACTLY the same as it was before you cut it.

A goolgle on road spring design will turn you up a spread sheet that will design you springs for you - failing that a trip to the local library will get you the appropriate text book.
Russ

Failing that....jack the car to the ride height front and rear(approx as its adjustable via the spring platform), measure the distance between top and bottom mounting points and call AVO (or, possibly, other suppliers). They will be able to select a damper/spring combination for you to give a good starting point. I suggest AVO as they had dealings with Cook and have chassis weight data. They have no axe to grind (he tried to get the receptionist sacked!!) and I'm sure will help.

[hfbradley01]

Originally Posted by chesterak

Failing that....jack the car to the ride height front and rear(approx as its adjustable via the spring platform), measure the distance between top and bottom mounting points and call AVO (or, possibly, other suppliers). They will be able to select a damper/spring combination for you to give a good starting point. I suggest AVO as they had dealings with Cook and have chassis weight data. They have no axe to grind (he tried to get the receptionist sacked!!) and I'm sure will help.

Stan

Am I glad you sorted the suspension out before I bought it from you.

Cheers