Front coil over shock set up help:Update

I swapped my front shocks last winter from a set of single adjustable extension steel Koni coil overs to a set of Afco double adjustable aluminum coil overs with 350 Lb. rated springs. They didn't come with instruction on how to set the preload up on the coil over springs so I ended up setting them with no preload at all due them raising the front of the car up one inch with no preload on those springs The car has ran a new best 60 Ft. times that way this year with a 1.24 compared to a best of 1.27 ever with the Koni on it
I'm in the middle of changing the springs to a set of 300 lb. rated Afco coil over springs and I am wondering if any of you drag racers have played with different amount of preload on the col overs or not on the front coil overs and if so what your thoughts are on doing this
All comments welcomed

I would put the 300 springs in the same as the 350s, raise evenly if the car sits to low in front. What shock settings did you have on the front when it went 1.24?

If my old memory is any good, I think you want the spring to be compressed about 35% at rest. Also, depending on how much travel you want I like to have about 1-1.5" of the shaft showing.

Mike

Preload?

Spring rate on front coilover/a arm suspension is determined by the location and geometry of all of the components. Typically, the lightest spring that will hold the front end at desired ride height/correct shock C-C is used. Similar to using 6 cylinder torsion bars on stock Mopar front ends. Separation is then controlled with the shock and/or travel limiters.

Adjusting front springs to different heights is sometimes used in conjunction with doing the same with the rears to adjust rear corner weights and have the car set level.

For example, winding the right rear spring up a bit will put some weight on that corner but also make that corner set high. Winding the left front up a touch will add a bit more weight to the right rear and level the car.

No preload on the springs, stiffest setting on extension and in the middle on compression.
I'm hoping to get the ride height back down to where it was before switching from the Koni to the Afoc by switching to the 300 lb. springs now instead of the 350 lb. rated ones
I'm going to call Afco tomorrow and ask them why they don't cover setting the coil over preload in their instructions, I had Strange coil overs on the rear of my old Duster and their instructions called for setting them up so it had 2/3 travel up and 1/3 travel down at static ride height ready to race.
I'll post what Afco says about this on here later this week after putting the car back together with their advice results

Spring just holds the car up. I think you're spring is too heavy imo.
Get a 300 spring and put a little preload in it. I think you dont want that spring to deflect during acceleration and braking.

If the car hooks with little or no travel the lighter spring wont help. If it needs travel in order to hook the lighter spring with preload to maintain ride height will help the car pitch rotate. The lightest spring compressed the furthest without going into coil bind will help pitch rotation the most. Since it's working with the shock setting you listed, it wont need much front end travel.
Doug

Yes. played with it a ton on my Duster....But you need notes from your ride height how it was previously setup. I measure the bottom lip on my fenders in the same spot every time. I have a mark on all four...So when I change spring weights, I set the ride height the same. That might mean there is no preload in the springs to a bunch of preload in the springs, I shoot for the same ride height. To get the front to weight transfer, I found having a bit of rake angle front to rear works best. As far as preloads go, well that gets interesting. The more preload, the more stored energy in the spring, and it will tend to lift the front higher on the hit. But it also has to hold the car up. So going to a lighter spring to improve weight transfer & 60ft is the right direction for you, until it goes up too high or won't hold the car up....Then going to a stiffer spring will hold it down some.

Then there is all the valving to tinker with. Eventually you find a spot that you like. I am at a 1.29 now, and just amazed how the car sticks it.

Shouldn't be a problem, but make sure the springs can't coilbind. Also if you have no bump stops you will want foam bump stops on the shock shafts to cushion the stop. Afco only sells a cup that is 1/2 inch hole size ( slide bumpstop onto shock shaft, then cup. You will have to drill hole in cup to 5/8. My shocks are currently getting rebuilt. Didn't have those bump stops and blew out one shock. Bummer, they only held up for 21 years😁

Front coilovers get set up with 3/8 - 1/2" of shaft showing, or less, if we're using the short front a arm type shock. Spring rate shouldn't be affected by different shocks unless the mounting location was changed.

Is this a stock type front end? Tube chassis? Backhalf Super Stock type deal? How long are the shocks and springs?

I talked to the Afco rep that sold me the shocks last year, he says to set the preload so I have 1 1/2 inch travel both ways at static ride height, these shocks have 3.0 inch of travel so he is saying set them up in the middle of the travel.
These shocks have a thick rubber bumper on the shafts to prevent topping or bottoming out the shocks
My setting them with no preload has made those bumpers get hit hard enough to make some rubber get worn enough to allow some small pieces to come off of it when I took it apart to change the coil springs
I'm going to put one full turn of preload on the shocks on the bench and installed them and let the car down off of the jacks stands so it is being supported by the coil overs again and see what I have for travel and ride height
More to come.
I'm going to attach 3 pictures of my Afco front coil overs, one with the spring off to show the rubber bumper on the shaft, one with the coil installed with no preload and the last one with one full turn of preload on the bottom height adjuster to remove any free play on the spring to the adjuster.
I need to finish the other side before going any further on the adjustments, I'll put one full turn on it and then let car down and see what the ride height looks like and go from there

When I say at rest, I mean when the car weight is compressing the shock.

Mike

I completed changing the front coil over springs today, the car is now compressing the 300 lb. spring right at 1.0 inch at rest without me in the car and no fuel in the 7.5 gallon front mounted fuel cell with one full turn preload on these new springs. I'm going to leave there for now and check it again in the spring before I take it out racing with the fuel cell full and my weight in the driver seat
The Afco rep said to adjust the preload to get the shock in the middle of the travel, which is 3.0 inch without the rubber bumper installed, 2.5 inch travel with the bumper in place.

Sounds like you need to go down to 250 springs? Better to be able to slow front end rate of rise with the shocks than to have it sprung too stiffly. With a 1.24 60 ft i assume you are running almost 9.0?

What I was told was with the shock at recommended ride height the correct spring should be compressed 3/4" to 1". That means the spring platform should have 3/4" to 1" preload on the free shock then when the weight of the car is on the shocks they should compress to the recommended ride height of the shock. Obviously you can run a lighter spring with more preload for better pitch rotation but a heavy spring gets too close to being loose on the shock. The spring platform really should not be used to correct ride height.

The spring platform really has nothing to do with it. What matters is that the shock travel is in the correct location when at static load. Thsi may or may not be dead center. Depends on what the car needs. After setting shock travel, height can be set by moving the shock mounting location up/down. If you cant get the ride height correct by moving the mount , you need to modify the mounts or change the spring rate. If the spring is soft, that platform gets cranked up to set the the shock travel. As long as the spring wont go into coil bind during compression, you're good. A stiff spring needs to stay in contact with the platform at full rebound. Beyond that it's all about how much stored energy you need. Stiff is less, soft is more. As long as the shock can control the speed of the suspension movement, the softest usually works the best.
Doug

The quickest ET has been has been 8.866 and 8.862 last year at Woodburn in late July, it ran 8.866 ET at 148.33 MPH on the first pass shifting the Powerglide at 7000 RPM, I moved the shift RPM up to 7300 RPM and it ran 8.862 at 150.77 MPH
I haven't focus on getting the fastest and quickest ET out of the car yet due to other things occurring like me getting old and not driving it well

Cab.. your gonna need to look at getting a driver.. I prefer young females.. they seem to have
faster reflexes.. I found a guy that drove for me but he ended up having a heart attack like I did
and he quit