Club Cobra Keith Craft Racing  

Go Back   Club Cobra > Manufacturers, Engine Builders, tools, and parts. > Antique & Collectibles

Keith Craft Racing
Nevada Classics
Main Menu
Module Jump:
Nevada Classics
Nevada Classics
Keith Craft Racing
MMG Superformance
Advertise at CC
Banner Ad Rates
Keith Craft Racing
MMG Superformance
MMG Superformance
March 2024
S M T W T F S
          1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31            
  #1 (permalink)  
Old 07-12-2012, 06:30 PM
CC Member
Visit my Photo Gallery

 
Join Date: Sep 2009
Cobra Make, Engine: A&C Cobra, 521 CU BBF, Holley ProJection, T56 Magnum, 3.5:1 TruTrac 9-inch
Posts: 275
Not Ranked     
Default suspension tuning

Hi folks,

I have a thread going in the "Tech talk" forum, but since this is somewhat A&C specific, i wanted to post it here.

I started doing some autocross and HPDE/track days with my Cobra.
I found it to be a little scary in that it had

1) excessive body roll at autocross. meaning the front wheel well lips would actually hit the tires. also it was quite bouncy from front to back, tilting up on the gas, and down on the brakes.

2) on the track, the steering was way to sensitive. i have power steering on it. when you went over a bump or a wobble in the track, the car would be tossed a bit. as the car was being tossed about, that would cause your arm to move, tweak the steering a bit, and increase the tossing of the car.

3) body roll issues as well on the track.

From what A&C said, I was running 450 pound springs in the front and 250 pound springs in the back. The shocks were aldan and mcaren(?) with alden adjustable in the front.

So, i bought a few suspension books and such.
In the process of reading these, I came across two terrific websites

The first
The Strawberry Hill Cobra 427 S/C

read the "suspension project" pages

The second
Purchasing Spreadsheets

This is the winner! this guy takes most of the key suspension data contained in the books and boils it down to a 15-20 page PDF and an excel spreadsheet. You make all of the measurements/etc/etc as directed in the spreadsheet and you can re-tune the suspension of the car!

The critical areas are
1) motion ratio
2) unsprung weight
3) wheel rate ratio between front and rear

motion ratio is bascially the leverage that the spring/shocks exert on the wheel when accounting for the fact that the wheel and springs are on a lever. The lever is the control arm and since it is fixed at a point, the actual spring rates are dependent on the distances between the rotation point of the control arm and the distance to the tire and the spring.

unsprung weight is basically how much your wheel weighs, brakes, steering knuckle etc. basically anything that is not 'above' the springs or held up by the springs.

wheel rate refers basically to how much energy each wheel exerts back into the suspension in a corner.

at any rate.....

i ran through all of these calculations, measurements,etc and i came up with

1) 650 QA1 pound springs on the front
2) 300 QA1 pound springs on the back
3) single adjustable QA1 shocks on all four wheels

My power steering setup is a little different.
I am using an electro-hyraulic pump from a volvo s60 and its connected into a thunderbird rack.
I added a cutoff switch to disable the pump, so I can run a powerless rack on the track.

After all of these changes, I then took the cobra back to watkins glen for 2 days of track time.

WHAT A DIFFERENCE!
Very little body roll and lean in the turns
Alot of the vibrations are gone, the camera from the track almost takes a steady picture now
Shutting down the power steering pump helped immensely with the steering stability of the cobra as well. Perhaps a manual steering on these cars is really the way to go.

So in short, if you want to possibly improve your suspension or tune it for something specific, check out the links above.

I'm still new a track days and making more upgrades. I just ordered a new set of AVON tires for the cobra and will be going back to Watkins at the end of this month to try them out along with a few other updates.

I did manage to get my best time of 2:45 lap though. Previously, I was running 3:10 with the Cobra, which is a little slow :O

the 'fast' guys are running 2:15-2:25 on the track. I am hoping I can get to 2:30-2:35 soon.

Here is the 2:45 run I did.
watkins 071012 2 45 lap - YouTube

slow baby steps
__________________
Driving fast keeps you young. Just ask Einstein....
Reply With Quote
  #2 (permalink)  
Old 07-12-2012, 06:40 PM
CC Member
Visit my Photo Gallery

 
Join Date: Sep 2009
Cobra Make, Engine: A&C Cobra, 521 CU BBF, Holley ProJection, T56 Magnum, 3.5:1 TruTrac 9-inch
Posts: 275
Not Ranked     
Default

and one other thing i did.

I bought a set of longacre digital scales and put each wheel on an independent digital scale. I then was able to 'corner balance' the cobra


cobra-070712-balance by sspano01, on Flickr

who says a big-block cobra is too front end heavy?!
__________________
Driving fast keeps you young. Just ask Einstein....
Reply With Quote
  #3 (permalink)  
Old 07-18-2012, 10:33 AM
CC Member
Visit my Photo Gallery

 
Join Date: Sep 2009
Cobra Make, Engine: A&C Cobra, 521 CU BBF, Holley ProJection, T56 Magnum, 3.5:1 TruTrac 9-inch
Posts: 275
Not Ranked     
Default

more details: here are the exact part numbers from JEGS that I ordered

300 pound rear springs #122-12-300
QA1 promastar rear shocks #122-DS501
650 pound front springs #122-9-650
QA1 promastar front shocks #122-DS401
4 pieces of top-stud conversion #122-SS110SDM

I used the lower rubber/roller bearing portions of the original A&C kits for both front and rear shocks. I used these original A&C parts in the QA1 shocks so that everything would fit in the front and rear lower suspension mounts. You could use the QA1 rubber/roller mounts, but you would need to add some spacers
__________________
Driving fast keeps you young. Just ask Einstein....
Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 05:13 AM.


Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
The representations expressed are the representations and opinions of the clubcobra.com forum members and do not necessarily reflect the opinions and viewpoints of the site owners, moderators, Shelby American, any other replica manufacturer, Ford Motor Company. This website has been planned and developed by clubcobra.com and its forum members and should not be construed as being endorsed by Ford Motor Company, or Shelby American or any other manufacturer unless expressly noted by that entity. "Cobra" and the Cobra logo are registered trademarks for Ford Motor Co., Inc. clubcobra.com forum members agree not to post any copyrighted material unless the copyrighted material is owned by you. Although we do not and cannot review the messages posted and are not responsible for the content of any of these messages, we reserve the right to delete any message for any reason whatsoever. You remain solely responsible for the content of your messages, and you agree to indemnify and hold us harmless with respect to any claim based upon transmission of your message(s). Thank you for visiting clubcobra.com. For full policy documentation refer to the following link: CC Policy
Links monetized by VigLink