Adjust torsion bars to launch straight

[caveman85635]

Upon searching this site trying to find the factory ride height of the front end of a '70 Roadrunner, I've pretty much come up with nothing other than one post that said "1/2 inch from the bumper"...Many posts say to set the ride height for the stance where you like it and get a FE alignment, but don't consider how the car will launch. I know the left side should be lower than the right side, but how much lower? Any info or comments regarding front end setup for launch will be greatly appreciated...
I used to have a tech sheet from Mopar about 15 years ago that gave a spec for distance between the control arms. Anybody familiar with that tech sheet or spec?

 

[Cranky]

I also set my ride height to my liking and have had them as low as 1/2" from the rubber bump stop but that is a good bit lower than factory ride height. And I like my left side with a bit of 'preload'...ie, it's higher than the right. Also, you should put your weight in the driver's seat when you make adjustments. Setting it low on the left will only make your car sit lower on the left and more so once you get in it not to mention, your preload will have the right rear tire ending up with less preload on it which is exactly opposite of what you want for drag racing. Also, the rear of the car is usually more important for straight launches but both ends are important however, if there's something wrong with the rear not being right, it will usually be more pronounced on the launch.

 

[caveman85635]

I also set my ride height to my liking and have had them as low as 1/2" from the rubber bump stop but that is a good bit lower than factory ride height. And I like my left side with a bit of 'preload'...ie, it's higher than the right. Also, you should put your weight in the driver's seat when you make adjustments. Setting it low on the left will only make your car sit lower on the left and more so once you get in it not to mention, your preload will have the right rear tire ending up with less preload on it which is exactly opposite of what you want for drag racing. Also, the rear of the car is usually more important for straight launches but both ends are important however, if there's something wrong with the rear not being right, it will usually be more pronounced on the launch.

Thanks, Cranky. I read somewhere on this site the left side should be a bit lower than the right so it will rise more and plant the tires...I don't know anymore. There seems to be conflicting information.
When I got the car, it was jacked up a mile - '70's style - and I wanted everything lowered down like today's style. Removed the shock extenders, tucked the rear tires and wheels inside the body and lowered the FE to a stance I liked by turning the adjustment bolts an equal amount. It still launched straight. Then I noticed the FE height of the car wasn't even from side to side. So, not knowing what I was doing, I made them even. That's when the rear end started kicking to the right a little at a 5 grand dump. At 3 grand it kicks left...I guess I should try leaving at 4 grand and see what happens...

 

[Cranky]

What kind of car is it and what modifications have been made to it? Are the spring bushings in good shape? If it's going one way then another at different rpm launches and you are testing in the same place (same lane at the track?), sounds to me like there might be something wrong. If things are good, it should launch the same...unless of course you're spinning the heck out of the rear tires at 5 grand vs 3 grand. What condition are all the front end parts? If you have worn parts, then that could and usually will be a factor...

 

[caveman85635]

What kind of car is it and what modifications have been made to it? Are the spring bushings in good shape? If it's going one way then another at different rpm launches and you are testing in the same place (same lane at the track?), sounds to me like there might be something wrong. If things are good, it should launch the same...unless of course you're spinning the heck out of the rear tires at 5 grand vs 3 grand. What condition are all the front end parts? If you have worn parts, then that could and usually will be a factor...

All good points you brought up, Cranky. It's a '70 Roadrunner, 425hp 383, 4-speed, 4.56 Dana 60 with a stock suspension as far as I can tell...All the front end parts are in good shape...Yes, I'm spinning the heck out of the tires. I know I need some new tires, for sure, 'cuz the ones on the rear are old and dry. Maybe I'm trying to fix a problem that isn't really a problem. When I first got the car from my cousin, his redline on the built-up 383 was 5-grand, and that's the way I drove it, too, until I spoke with some local racers and builders. Now I redline it at 6,500 rpm...

I guess what I'm looking for is a basic rule of thumb, e.g. if it kicks right, lower the left front...or raise the left front? Like I said, I'm finding conflicting information...

Maybe I just need to learn how to drive the beast.

 

[67 coronet]

the rear has much more impact on drag launches then the front.if you are spinning the tires at all in your launch you will not be able to adjust your suspention to solve any probs.get the car to hook up,then worry about any pulling durring the launch.

 

[caveman85635]

the rear has much more impact on drag launches then the front.if you are spinning the tires at all in your launch you will not be able to adjust your suspention to solve any probs.get the car to hook up,then worry about any pulling durring the launch.

Okay, I was trying to get the rear to hook up better by lowering the front end...I think new tires are going to solve a lot of the problem...Thank you!

 

[67Satty]

Here's some stuff from the Mopar Performance Chassis book (some of it is what Cranky already said):

Stance:

They say a 2-3 degree nose angle is best. They say to measure the bottom edge of the sill to the floor at the front and then the rear of the sill to the floor then compare. They say it should be 2" higher in the rear.

Getting it to going straight:

They say if you are going left the right tire is hooking better, if it is going right, the left tire is hooking better. So if you are going right and need to get the right tire to hook better, you are supposed to raise the torsion bar on the left side to put more pressure on the right rear tire. They say to raise 1/2" at a time, test, repeat until it goes straight.

I hope I translated it right. I think it's a good book to have around but then again, my car is built like something from a '70s Direct Connection catalog.

 

[b-star69]

Great stuff thanks