We ran my friends Valiant Coupe today with some mixed results. It was the first time out since mini tubbing the car, and unfortuantely the car went 2 tenths slower than the previous outing. The 60ft times (1.65-1.69)were also the same, although a little more consistant. Previously, the car went a best of 11.47@117mph, this time around 11.65@117mph.
The rear was originally factory leafs, clamped, with a pinion snubber, and a 26/8.5-15" M/T slick. Revalved (90/10)factory shocks in the front. 4.11:1 gears in the rear.
Changes made were relocating the springs into the rails, fitted sliders in the rear, Rancho Shocks 9 Way, Caltracs and 29/11-15" Hoosier slicks. The front shocks have been sent back twice, and after this meeting, will be sent back again, they don't seem to be correct.
There are a couple of things that still need attantion, for one, the Brake bias seems to be off, as it struggled to hold the car in the water box, so I feel half the traction problems were due to too short a burnout.
I made many different changes to the Caltrac settings and Shock settings with very little , or no change in 60ft times. I started out with the shocks set at 5, top front hole on the Caltracs, with a 1/4 turn of preload. Tyre pressure was 15psi. The rear would basically just rise, higher than the front out of the hole, the front would then drop after the 60ft mark, and the rear would eventually settle down a little after. I tried the shocks at 1 and 9 with no real difference in launch , or 60ft.
I then dropped the tyre pressure down to 12 then to 10psi, which seemed to help, the rear would not raise as much, but it just didn't seem to be working.
After tearing my hair out a little, I changed the Caltracs to the lower front hole, and adjusted them so there was Zero preload. This setting didn't effect the 60ft times, but the car seemed a little better out of the hole. I tried it at this setting with a little less tyre pressure, with no real change. We called it a day after the oil pressure started to drop.
I was hoping that someone could shed some light on what changes to the pre load effectively do.
What does adding preload actually do?
An air gap on the front bar would effectively hit the tyres harder?
I am a little rusty on what changing a rear suspensions instant center does , I cannot remember if lowering the IC hits the tyres harder or softer. Running the bar in the lower hole lower & or lengthens the IC?
I am going to try lowering the rear a couple of inches, and getting some decent front shocks in before going out again.
If anyone has any suggestions, I am open to any suggestions or advice.
Many Thanks
AL....
Caltrac Help?
Moderator: Team
I don't have any experience with Mopars, but with Chevy's the front a-arm bushings can really stiffen the front travel up a bunch. Freeing up the movement of the front suspension is important so the shocks and springs can do their job. With the spring out (or torsion bar disconnected?) and the suspension together otherwise, it should freely move up and down with no resistance. If it is stiff or hard to move then you need to find out whats causing it and free it up. The best front shock in the world won't make up for this.
Also, I haven't seen where the cal-tracs are all everyone claims either. No better than a good traction bar in the cars I've seen make the switch. Lots of hype and one guy says its worth 2 tenths and everybody follows.
Rick
Also, I haven't seen where the cal-tracs are all everyone claims either. No better than a good traction bar in the cars I've seen make the switch. Lots of hype and one guy says its worth 2 tenths and everybody follows.
Rick
The car now transfers the weight on launch, but it doesn't seem to hold it there. We have had problems with the front shocks before, they have been sent back a few times already because they were far too easy to compress. I have a couple of idea up my sleeve, which I will try out next time.
Rick , you couldn't be anymore on the money regarding Caltracs, so many people carry on like they are the miracle cure for Leaf spring cars. I knew I would have to take abit of time to dial them in, so far they have been no better than the factory rear springs with the front segments clamped, and a pinion snubber.
Thanks
AL....
Rick , you couldn't be anymore on the money regarding Caltracs, so many people carry on like they are the miracle cure for Leaf spring cars. I knew I would have to take abit of time to dial them in, so far they have been no better than the factory rear springs with the front segments clamped, and a pinion snubber.
Thanks
AL....
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BillyShope
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The Caltracs and the pinion snubber are doing essentially the same thing, but the Caltracs does have a bit of an advantage in that you're allowed to bias the loading and, in this way, cancel a portion of the driveshaft torque's tendency to unload the right rear. The idea is to have the right side bumper make contact well before the left. Unfortunately, you're dealing with very large forces and very small deflections, which makes the adjustment quite sensitive.
Whether the rear of the car squats or rises affects the manner in which the weight transfer loads the tires, but it does not affect the magnitude of the weight transfer. When the rear rises, the rear tires receive additional loading as the rear is being accelerated upwards. This might sound good, but, as the saying puts it, what goes up must come down. As the rear reaches its highest point, it decelerates, unloading the tires. In other words, it's like hitting a speed bump in the parking lot: You get bounced around a bit, but the net effect doesn't amount to much. Same with squat, of course, but it's a little more deceptive. You see that rear end dropping and you think: Wow! I must realling be "hitting" those tires! But, think about it. If you were lying under the car and pulling down on the rear, you'd pull your back up off the ground, wouldn't you? Well, that's what's happening to your tire loadings as the car accelerates downward. Yeah, the loadings increase as the rear bounces, but, again, it's like hitting a speed bump in the parking lot.
The weight transfer is determined by the acceleration and CG location. Period. Don't be hoodwinked by anyone's claims otherwise.
You didn't mention atmospheric conditions during this last outing. Were they the same as before? That can make a very significant difference.
When you do finally get the Caltracs sorted out, there's a little trick you can pull with a Mopar. Run the lightest (lowest spring rate) torsion bar you can find at the left front and the heaviest at the right front. The torsion bars offer adjustability similar to that of coilovers, so you can adjust and get the rear loading back to where it was. (Borrow some wheel scales from your circle track buddy to make sure.) Why the different bars? Well, visualize the extreme and you'll quickly understand. Suppose the right front had no suspension. As the front lifted during launch, the right front would immediately come with it. Since the sum of the right front and right rear tire loadings must always be equal (otherwise, the car would be rolling over), that means the weight transfer is being directed to the right rear, thus acting to cancel the effect of driveshaft torque.
Note that I'm NOT talking about any kind of preload. While you've got your buddy's wheel scales, you might want to also add some preload. You do this by cranking up the left front, of course. The wheel scales will tell you just how much you've cranked in.
Good luck.
Whether the rear of the car squats or rises affects the manner in which the weight transfer loads the tires, but it does not affect the magnitude of the weight transfer. When the rear rises, the rear tires receive additional loading as the rear is being accelerated upwards. This might sound good, but, as the saying puts it, what goes up must come down. As the rear reaches its highest point, it decelerates, unloading the tires. In other words, it's like hitting a speed bump in the parking lot: You get bounced around a bit, but the net effect doesn't amount to much. Same with squat, of course, but it's a little more deceptive. You see that rear end dropping and you think: Wow! I must realling be "hitting" those tires! But, think about it. If you were lying under the car and pulling down on the rear, you'd pull your back up off the ground, wouldn't you? Well, that's what's happening to your tire loadings as the car accelerates downward. Yeah, the loadings increase as the rear bounces, but, again, it's like hitting a speed bump in the parking lot.
The weight transfer is determined by the acceleration and CG location. Period. Don't be hoodwinked by anyone's claims otherwise.
You didn't mention atmospheric conditions during this last outing. Were they the same as before? That can make a very significant difference.
When you do finally get the Caltracs sorted out, there's a little trick you can pull with a Mopar. Run the lightest (lowest spring rate) torsion bar you can find at the left front and the heaviest at the right front. The torsion bars offer adjustability similar to that of coilovers, so you can adjust and get the rear loading back to where it was. (Borrow some wheel scales from your circle track buddy to make sure.) Why the different bars? Well, visualize the extreme and you'll quickly understand. Suppose the right front had no suspension. As the front lifted during launch, the right front would immediately come with it. Since the sum of the right front and right rear tire loadings must always be equal (otherwise, the car would be rolling over), that means the weight transfer is being directed to the right rear, thus acting to cancel the effect of driveshaft torque.
Note that I'm NOT talking about any kind of preload. While you've got your buddy's wheel scales, you might want to also add some preload. You do this by cranking up the left front, of course. The wheel scales will tell you just how much you've cranked in.
Good luck.
Another thing to consider, and this might sound strange, is tire speed. It could be that with the cal-tracs the car hooks too good. This can cause the motor to bog or labor and not accelerate as quickly. I have had lower hp cars that even though they were spinning the tires a little, would et better because the motor was allowed to accerate quicker, until the car,tires and everything else caught up to it. This was of course past the starting line when your not trying to put something in motion, but help something already in motion accelerate. Even with high power cars, prostock etc, tire speed is critical. Just a thought.
shawn[/i]
shawn[/i]
caltrac help
i have 3 recommendations for you...1: buy the CD interview with John Calvert...2: buy the CD interview/"doorslammer"package from Dave Morgan...3: call Calvert racing and speak to Matt, Travis, or John. Great bunch of guys, and completely knowledgable on their fine products! what ive learned so far goes like this: the upper mounting holes "hit" harder than the lower holes, moving the instant center fore and aft by working with the leafspring much like a 4 link setup. "preload" works opposite to what you'd think, in that more turns of the bar softens it's action. this is especially useful in keeping the car straight during wheelstand, and it moves alot of weight on a set of scales. finally...shock absorbers affect the amount of time the tire "sees" the launch "hit". a softer setting allows more intense chassis reaction and quicker unloading, where a firmer setting slows down the "hit" over a longer period of time, planting the tire "longer". also, the settings only affect compression on the ranchos, extention is fixed.my 60ft dropped from 1.93s to 1.58 from the bars and shocks...and the first night out, it lifted the front end 6 inches and rotated the rims 90 degrees inside the tires, necessitating rimscrews! plenty of traction in my book.after that, i found that the shocks were being fully extended on launch, causing an unloading tirespin. they helped me figure this out, and it should 60 much quicker now after a swap to longer shocks which they sent for free. havent been back to the track since the swap, but its already run a traction limited 11.36@118 on DOT tires, pumpgas, and mufflers. not too bad for a street driven BOSS302 in a 3300lb mustang. give them a call, they'll be glad to help! hope that helps Duke