Front spring eye height setting.

[68 gt man]

Ok so here's what I have been rolling around in my head. Maybe racers can help me. I'm going to make a trip to the dragstrip with my 68 Dart this summer. Street tires just to see what it does. It's got the US. Car tools spring relocation setup on it. That has 3 front spring eye holes. I've got 296/50/15s on it and they clear fine on any of the settings. The middle one is stock ride height which is where it is now. Do you guys see an advantage for me to move it one way or the other before my trip to the track? I've tried the top and middle which is stock ride height on the county road. Couldn't tell any difference there as it just blows them off anything past 1/3 throttle and doesn't get much weight transfer. Oh also guesses for tire pressure? Thanks in advance for opinions.

 

[MOPARMAGA]

I don't know what to tell u about the heights But...thats an f'n nice dart !

 

[68 gt man]

I don't know what to tell u about the heights But...thats an f'n nice dart !

Thanks man it's only taken 20 years. I swear there was always something keeping me from getting it done. Ended up trading a fox body mustang I picked up dirt cheap to a body guy for him to put quarter skins and trunk floor/ dropoffs in it and the mini tubs. My welding isn't what it used to be and when that was done I was motivated just looking at it. But I did everything else. Built drive train interior and paint. This is what it looked like when I got it. Didn't even have a K frame!

 

[MOPARMAGA]

Thanks man it's only taken 20 years. I swear there was always something keeping me from getting it done. Ended up trading a fox body mustang I picked up dirt cheap to a body guy for him to put quarter skins and trunk floor/ dropoffs in it and the mini tubs. My welding isn't what it used to be and when that was done I was motivated just looking at it. But I did everything else. Built drive train interior and paint. This is what it looked like when I got it. Didn't even have a K frame!

View attachment 1715729658

WOW, f'n nice is an understatement then.
Great work !

 

[furrystump]

On a leaf spring car, the instant center is the front spring eye. Draw a line from the contact patch of the rear tire through the IC/spring eye up through the center of gravity. If this is true your car will have zero % of rise. A bodies leaf spring cars never have that. Without scales and trig formula you won’t know where the center of gravity is, but if you draw a line parallel to ground trough the cam and draw a line through the center of the converter might be close to the center of gravity. A bodies have a high % of rise. They hit the tire HARD. Lowering the front spring eye hits the tire softer. Less body separation, less bouncing of the tire. Slo-mo video helps a ton!!

 

[flyfish]

With street tires, I don't think it matters....they won't stick regardless, unless your engine is near stock (then it still won't matter). Just my 2 cents. If you like the stance the way it is set I would leave it alone.

Edit: Tire pressure, don't go too low (again because they are street tires). My drag radials like 18psi....I would guess a standard radial would probably not be good under 20-25psi.

 

[furrystump]

Tire pressure. Spin the tire and check the pattern. Dark on the edges go up 2 lbs, light on the edges, go down 2 lbs. once you get even color across you are ready for the track. Then fine tune the pressures.It gets you in the ballpark

 

[68 gt man]

On a leaf spring car, the instant center is the front spring eye. Draw a line from the contact patch of the rear tire through the IC/spring eye up through the center of gravity. If this is true your car will have zero % of rise. A bodies leaf spring cars never have that. Without scales and trig formula you won’t know where the center of gravity is, but if you draw a line parallel to ground trough the cam and draw a line through the center of the converter might be close to the center of gravity. A bodies have a high % of rise. They hit the tire HARD. Lowering the front spring eye hits the tire softer. Less body separation, less bouncing of the tire. Slo-mo video helps a ton!!

First off thanks. Ok on center of gravity I don't have scales but have been thinking about weighing my car at the feed store anyway. If I weigh just the front then the whole thing I should be able to get close with measuring to give me a front to rear weight center. But as far as the up and down I'm still thinking. I understand what you said with the cam parallel line but i didn't quite follow you on the line through the converter part. Do you mean vertical through it intercecting the cam line? One more thing on rear tire contact patch. Use center of it right?

 

[68 gt man]

With street tires, I don't think it matters....they won't stick regardless, unless your engine is near stock (then it still won't matter). Just my 2 cents. If you like the stance the way it is set I would leave it alone.

Edit: Tire pressure, don't go too low (again because they are street tires). My drag radials like 18psi....I would guess a standard radial would probably not be good under 20-25psi.

It's definitely not stock. I was guessing but planned to try 22 psi

 

[68 gt man]

Tire pressure. Spin the tire and check the pattern. Dark on the edges go up 2 lbs, light on the edges, go down 2 lbs. once you get even color across you are ready for the track. Then fine tune the pressures.It gets you in the ballpark

Thanks now that you said that I remember hearing that and it makes sense!

 

[furrystump]

The formula for it you can look up, the process is weigh the front, weigh the back. Both at race weight. Driver in the car. Then you install something, a block of wood. Replace the front shock with a fixed rod. Something that keeps the front ride height the same. Then you lift the rear of the car and weigh the front again. You can get away with lifting the rear a somewhat smaller amount, but accuracy suffers a bit. The formula will explain how high and how you use the lift amount. I haven’t done it, but watched it done on a second gen Camaro. A bit nerve racking on lifting the rear that high and they had a fork lift. So you could go it with that style of scale. Put the front tires in exactly the same spot on the scale. I never felt the need, leaf spring car, I know the front spring eye needs to go down. They all do basically. Super tall rear tire and a very light nose. Maybe not, but probably. Very important info for a four link guy.

 

[33IMP]

I was gonna post essentially exactly what furrystump said in#5, he is dead on. The only thing....i agree with flyfish too, with street tires it wont matter.
Wanna go fast at the track? Invest in some race only tires and wheels. Lots of used wheels, and lots of used slicks out there too.

 

[furrystump]

Much easier to go bigger tire and it will almost drive itself. I have only ever raced on a 6” repo poly glass red line tire. During drag week they made you run a “race” tire. I swapped over to a M&H musclecar DOT. tire. I could hammer that as hard as I could, it was very weird for me. My point is there is nothing special in my car to run a 1.70 60” on the repo redline. 5000 stall converter....yeah that won’t work with a small tire. A reasonable converter sure. Load the converter a bit so it doesn’t flash to high. Roll into it and Bob’s your uncle, you are putting down all that motor will do with almost stock cast iron heads.