DragStuff

Good times.... I run a 6.50 index from April to October every Friday night....
Your numbers are in line with what I run on the bracket....

What RPM did you leave at?

I left at 3200 rpms on the footbrake and shifted at 6700. That shift was about half track. Motor spins easily to 7000. I feel like I should be shifting sooner. When I crossed the traps it was just starting to breathe good. I crossed the traps somewhere between 5700 and 6000. It was my first pass in almost 4 years so it was all I could do to force myself to look.

Howdy Guys,
Someone asked about spring rates in leaf springs. This is a tricky issue because the rate changes as the spring moves. A big part of this change has to do with a jacking effect that occurs at the rear shackle. As it rotates forward, it stiffens the spring and the reverse happens when to rotates rearward. The oval guys have neat little slider boxes that can be welded to the frame rail. They replace the shackle design and help to keep the spring rate more constant.
As far as what your rate is, it will take some work, but you can find the rate yourself.
Measure the distance from the axle CL to the lower edge of your wheel well opening while the car is at ride height (with you in the car.) This identifies the position of the spring at ride height. Also measure the distance from the CL to the top of the spring pad where it mounts to the housing. Now you will know how far the spring pad is from the wheel well opening. Then raise the car and remove the housing, wheels and tires. Place a floor jack under the spring, with a wheel scale sitting on the jack so you can measure the pressure on the floor jack as you jack the spring back into the car. With every inch of travel, write down the weight on the scale. As you approach the ride height distance, pay very close attention to the wheel scale readings. The rate that you have will be found as the spring bows to its ride height position. Along the way, notice how much the rate changes as you load the spring. To find out what rate you need, use a common spring rate formula for coil springs, but use your leverage ratio as 1:1..
Concerning shocks, the Afco big gun units will do you a good job, but I’s also suggest you research some on digressive valving versus the more popular linear valving. This design reacts quickly and you’ll need that quickness to help control your spring. Double ditto if you run a radial.
I hope this helps.
Dave

Dang look who the cat drug in ?

Wassup Dave?

Howdy John,
As expected, you must have been parked at your computer. I left the track in North Dakota and moved to New Jersey, simply because there are so many race cars here. I'm now associated with Fonse Performance which is a father/son machine shop. They have an engine dyno and chassis dyno. I've been doing setup work and crewing on their 8.5 Index car. I've been writing quite a bit for Pro Media also... keeping busy. Otherwise, all is well.
Dave

Well it's good to hear from ya Dave sounds like some things might be going better for you now.

What should the rake be? For example if I'm running a 30" tall rear radial slick what size front runner should I use? Or does it matter. Right now I have a 24" on and I'm redlighting.

Pro Tree or Sportsman?

Sportsman 500 full tree bottombulber. Trans is a powerglide with a pro tree brake but I'm footbraking leaving between 3200 and 3500 5500 stall convertor.

Dave Morgan wrote: Concerning shocks, the Afco big gun units will do you a good job, but I’s also suggest you research some on digressive valving versus the more popular linear valving. This design reacts quickly and you’ll need that quickness to help control your spring. Double ditto if you run a radial.
I hope this helps.
Dave

Who makes the degressive valved shocks? Do they act softer down track to help on a bumpy track?

Afco, Varishock and Penske have digressive valving available, but you need to call the factory direct.
Dave

Dave Morgan wrote:Afco, Varishock and Penske have digressive valving available, but you need to call the factory direct.
Dave

Thanks Dave.

I'd like to find something that will handle the power early in the run but let the car go over bumps without breaking loose. I think that's what happened to me when I got into the wall this summer. The compression is full stiff on my double adjustable QA1s to keep the tire planted but there's a pretty good bump where that track transitions from concrete to asphalt.

luv454 wrote:Sportsman 500 full tree bottombulber. Trans is a powerglide with a pro tree brake but I'm footbraking leaving between 3200 and 3500 5500 stall convertor.

A taller front tire will slow the reaction time down some.