355 ssuspension rebuild - DIY attempt

The following thread should have the data you're looking for:

http://www.ferrarichat.com/forum/showthread.php?t=259974

 

Thanks, but that data is what I already have to support my claim that the dynamic spring rate is roughly 425 lbs/inch.

In Mitch's thread (see link), 4071 Newtons (912 pounds) moves the front spring 54.5mm (2.15 inches) from static to full bump. That comes out to a spring rate of 424 lbs/inch. The 180 lbs/inch cited earlier by someone else is what I get when I compare the applied load required to move the spring from it's free height to it's static installed length.

Has anyone else cranked out the math or tested the factory front springs on a spring rate tester? As a couple of people already know, it has been 18 years since I was the coil spring and damper business, so I have really forgotten a lot of equations.

 

Oh jesus christ Ed, are you the same Mazda Miata SSC Ed Zabinski that I used to see at Southern Pacific Regional and National races in the early 1990's?!!

 

Never mind, you are! I am sending you a PM to say hi. This may jog your memory: Richard Jonec and I were running RX-7s in Southern Pacific Division in 1993, and I also ran in the Golden Gate Region that same season. At Sears Point, I spun my car and lost a couple of positions, so I was able to tuck behind Rich and bump draft him for the rest of the race. He passed Bill Brecht or Tom Brecht due to the bump drafting and as a result, I got black flagged for a 1 lap stop-and-go. You were on the pit wall laughing your ass off! Good times man!

 

LOL, I forgot all about that!! Thanks for the PM...that seems like a thousand years ago now!!

 

Glad you got it off, sorry it was Friday night man!

 

We may be slow but we are watching...

 

What tires do you plan on running - or are you undecided?

 

Glad to hear it's easy as I will be taking mine off soon for a rebuild and new H&R springs.

 

Dont replace the bearings... They can be re-greased. I did mine. The grease was all dried up... I cleaned them out and re-packed them and they are good to go.
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Also have a pic of when I did my bushings. I ended up buying a mini-lath and some delrin and made up all my bushings for the front and rear control arms...
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Hi J, thanks for updating this thread. I'm very interested in your upgrades because there is very little information available for track day setups on these cars. After Rob gives you the spring rate information and the shock dyno graphs (hopefully he'll provide those), can you also post what his recommendations are for the ride height too? This is a critical piece of info and ties back to what spring rates he suggests as a starting point. I am curious as to his choice of front ride height, spring rate, and bump stop selection.

There are some pretty good guys following this thread too. I know Mitch has always been generous with providing others with the suspension math, and Apex97 (Ed) was the 2008 SCCA National Champion in the T1 Class driving a Ferrari 360.

Good luck on the project and we are tuned in for more updates!

-Greg

 

Did you ever get zero'd in on what Spring rates you were going to try? I had some additional thoughts about this topic so in the interest of clarity here is what I am thinking.
As drivers, engineers are our best friends and worst enemies. As you see here there is a lot of discussion about motion ratios and effective spring rates. To have an intelligent discussion between driver and engineer you must stay apples to apples, and keep the discussion about either "measured" spring rate OR "effective" spring rate.
I always discuss this using "measured" spring rate because it doesn't require any math!
You will be hearing higher numbers like 1800 lb/in and 2200 lb/in using the measured rate.
I am at a slight disadvantage here because most of my experience with racing Ferraris has been the 360/430 chassis and I dont know what the measured rates are for the 355 street car and challenge cars are, but I think my advice here may still get you thinking correctly about this.
Here is what I am getting at: Just because "real" race cars seem to be stiff and low, does not mean that will be faster with your tires and skill level. There is a relationship between the amount of available grip from the tire and the best spring rate choice. In general the more grip available, the stiffer spring you can get away with. There is also a relationship between the driver and how the spring rate "feels".
In general, stiffer springs will change the how quickly the car breaks away at the limit and will approach that limit with less communication to the driver.
Since you say that you are going to run "street tires" rather than slicks you can take a look at any spring between the stock rates and the "stiff" Challenge option as a reasonable range. In my experience with the 360 on Hoosier A6 tires, we found that the "soft" challenge option was the perfect compromise. My guess is that it will be the same with the 355. But keeping in mind that you are on tires with even less grip than the track only Hoosier and you intend to do at least some driving on the street, perhaps a little softer than that would be even better. I would also recommend not going super low with this car for the same reasons. I would also start with the stiff challenge front bar and the soft rear bar and adjust balance from there using the rear ride height to change rake. From level adjust Higher= less understeer/lower=more rear grip.
I am sure the 355 experts here will shoot holes in this, but most of my experience with Ferraris is the 360 and 430 so forgive me if the 355 needs something different.
And my final thought is that race cars should be set up for DRIVERS, not for tracks or engineers! Make the driver confident and he will put his foot down and go faster!

 

That is an interesting thought. What brand lathe? Is it for metal or wood? The whole job cannot be more expensive than buying all the bushings and it sounds like fun to learn a new skill.