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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101606
12/12/22 02:23 PM
12/12/22 02:23 PM
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Joined: Aug 2003
Posts: 4,682
On the parachute mount
n20mstr
master
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master
Joined: Aug 2003
Posts: 4,682
On the parachute mount
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upper hole raises the instant center. Your real problem is the short front segment of a Mopar leaf spring, and your real solution is a shock that can control the movement of the rear housing. GET A GOOD SHOCK or get what you have re valved if possible. There are a few places that will help you with a good stiff shock for the back of a leaf spring mopar. You will be surprised at just how stiff a shock it takes to control the seperation
....BAD A$$ STREET CAR.....
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Re: help me understand instant center as applies to leaf springs
[Re: n20mstr]
#3101619
12/12/22 03:19 PM
12/12/22 03:19 PM
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Joined: Oct 2015
Posts: 570
UK
rb446
mopar
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mopar
Joined: Oct 2015
Posts: 570
UK
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My mate has mono's -c-tracs in the upper hole on his RR, motor has 720ftlbs on the hit and is controlled by just caltrac 9-way shocks on 7 stiff, good DA shocks are important yes, wait till you get those mono springs onto see the difference, here's a vid of the car on a 10.35 hit, been a best 1.421 60ft.@3800lbs> https://www.youtube.com/watch?v=9tnu9cSnf2U
Last edited by rb446; 12/12/22 03:22 PM.
1969 'Cuda 446ci, best 9.96@133.9 in 1990
1971 340 'Cuda, best 11.01@122.8 in 1987
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101623
12/12/22 03:28 PM
12/12/22 03:28 PM
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Joined: Dec 2005
Posts: 11,600
Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,600
Fulton County, PA
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I am converting my cars rear suspension to a cal-trac setup.with the mono leaf springs and QA 1 double adjustable shocks.What I am replacing a set of launcher springs that i've had on the car for several years. The car is a 72 charger weighs 3500lbs and runs mid 10's @ 126 mph. with a best 60ft of 1.47. I foot brake the car ,no trans brake.
My dilemma is the front spring hanger has two mounting holes. As a starting point i am not sure which mounting position to use. Does it even make a difference?
The current set up with the launcher springs uses the upper mounting hole . One of the reasons I'm switching to the cal-tracs is the car hits the tire so hard that I'm. having trouble controlling the seperation and I'm about maxed out on my rebound adjustment with the shocks . Ultimately what I'm after is a quicker reaction time from the car and an improved 60ft time.
So what would be your recommendation or advice as to a starting point. Don't make the rear suspension less aggressive. Buy better shocks and control it. Talk to AFCO or Randy at Fastshocks. You will be flabbergasted at what good shocks will do for your car. And work on the front end. Skinny T-bars, free it all up at the control arms and strut bushings, good shocks there as well. Stock Eliminator people have been working on this stuff forever. Copy them Do all that, then start tuning.
Last edited by CMcAllister; 12/12/22 03:37 PM.
If the results don't match the theory, change the theory.
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Re: help me understand instant center as applies to leaf springs
[Re: CMcAllister]
#3101624
12/12/22 03:34 PM
12/12/22 03:34 PM
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Joined: Mar 2006
Posts: 9,847
MI, usa
dvw
master
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master
Joined: Mar 2006
Posts: 9,847
MI, usa
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Instant center location determines housing movement direction. The higher or further rearward the instant center, the more it will seperate. Housing seperation adds hit to the tire. The shock controls the speed at which the housing moves.
Doug
Last edited by dvw; 12/12/22 03:35 PM.
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Re: help me understand instant center as applies to leaf springs
[Re: dvw]
#3101626
12/12/22 03:38 PM
12/12/22 03:38 PM
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Joined: Jul 2009
Posts: 112
pa
gregcharger72
OP
member
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OP
member
Joined: Jul 2009
Posts: 112
pa
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Instant center location determines housing movement direction. The higher or further rearward the instant center, the more it will seperate. Housing seperation adds hit to the tire. The shock controls the speed at which the housing moves.
Doug This is helpful. thanks.
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101636
12/12/22 04:07 PM
12/12/22 04:07 PM
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Joined: Aug 2003
Posts: 4,682
On the parachute mount
n20mstr
master
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master
Joined: Aug 2003
Posts: 4,682
On the parachute mount
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so you are saying that the front spring mounting position does not matter in reducing or incresing the hit to the tire? Only a GOOD shock will control it? lowering the IC or lowering the front of the leaf spring might reduce the seperation, but surely not enough that a great shock isnt needed. You will find its all about controling the movement of the rear housing.
....BAD A$$ STREET CAR.....
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101637
12/12/22 04:11 PM
12/12/22 04:11 PM
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Joined: Aug 2003
Posts: 4,682
On the parachute mount
n20mstr
master
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master
Joined: Aug 2003
Posts: 4,682
On the parachute mount
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I am converting my cars rear suspension to a cal-trac setup.with the mono leaf springs and QA 1 double adjustable shocks.What I am replacing a set of launcher springs that i've had on the car for several years. The car is a 72 charger weighs 3500lbs and runs mid 10's @ 126 mph. with a best 60ft of 1.47. I foot brake the car ,no trans brake.
My dilemma is the front spring hanger has two mounting holes. As a starting point i am not sure which mounting position to use. Does it even make a difference?
The current set up with the launcher springs uses the upper mounting hole . One of the reasons I'm switching to the cal-tracs is the car hits the tire so hard that I'm having trouble controlling the seperation and I'm about maxed out on my rebound adjustment with the shocks . Ultimately what I'm after is a quicker reaction time from the car and an improved 60ft time.
So what would be your recommendation or advice as to a starting point. YES you are close to maxxed out on the rebound adjustment.....this is what im talking about. YES the caltracs are great, but they wont work on their own. Whatever suspension you use, you still need a good shock. What shocks do you have?? If they are a good, name brand, its possible they could be re valved to allow more stiffer rebound, thats control you need...
....BAD A$$ STREET CAR.....
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Re: help me understand instant center as applies to leaf springs
[Re: n20mstr]
#3101640
12/12/22 04:35 PM
12/12/22 04:35 PM
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Joined: Jul 2009
Posts: 112
pa
gregcharger72
OP
member
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OP
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Joined: Jul 2009
Posts: 112
pa
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ok that makes sense, thanks. I'm using QA1 stocker star double adj. I looked into santhuff shocks....wow are they expensive!
Does a mid 10 sec car really need a shock like santhuffs? what are other good shock choices?
Last edited by gregcharger72; 12/12/22 04:50 PM.
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101642
12/12/22 05:02 PM
12/12/22 05:02 PM
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Joined: Mar 2009
Posts: 2,464
Sydney,Australia
tex013
top fuel
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top fuel
Joined: Mar 2009
Posts: 2,464
Sydney,Australia
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ok that makes sense, thanks. I'm using QA1 stocker star double adj. I looked into santhuff shocks....wow are they expensive!
Does a mid 10 sec car really need a shock like santhuffs? what are other good shock choices? Viking make a good affordable shock .Thats what i have on the rear . Tex
New best ET 10.259@129.65 .
New best MPH 130.32
Finally fitted a solid cam,
stepped it up a bit more
3690lbs through the mufflers
New World block 3780lbs 10.278@130.80 . Wowser 10.253@130.24 footbraking from 1500rpm
Power by Tex's Automotive
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101644
12/12/22 05:15 PM
12/12/22 05:15 PM
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Joined: Jan 2003
Posts: 2,924
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,924
A shed in England
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ok that makes sense, thanks. I'm using QA1 stocker star double adj. I looked into santhuff shocks....wow are they expensive!
Does a mid 10 sec car really need a shock like santhuffs? what are other good shock choices? Get them now if you can, you won't have to buy anything else later when you run out of adjustment or struggle with the cheaper shocks unless you go to struts or a 4 link (DAMHIK) I'm only running mid 9's but they made a world of difference on mine. We went 1.41 on the rears with a 3.73 gear @ 4000 lbs + on our last pass of the season. We previously ran Menscer valved Afco's, the Santhuffs are a vastly superior piece.
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Re: help me understand instant center as applies to leaf springs
[Re: tex013]
#3101647
12/12/22 05:17 PM
12/12/22 05:17 PM
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Joined: Jan 2003
Posts: 8,028
Tulsa OK
Bad340fish
master
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master
Joined: Jan 2003
Posts: 8,028
Tulsa OK
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If your shocks are in the stock location you might try moving them so they can be more straight up. My car runs 10.40s but it hits the tire real hard and my DA vikings are maxed out. I am going to stand them up before I upgrade.
68 Barracuda Formula S 340
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Re: help me understand instant center as applies to leaf springs
[Re: Bad340fish]
#3101658
12/12/22 05:48 PM
12/12/22 05:48 PM
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Joined: Dec 2013
Posts: 4,684
Wichita
GY3
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master
Joined: Dec 2013
Posts: 4,684
Wichita
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If your shocks are in the stock location you might try moving them so they can be more straight up. My car runs 10.40s but it hits the tire real hard and my DA vikings are maxed out. I am going to stand them up before I upgrade. This worked well for us. We built an upper bracket to move the top of the shocks closer to the frame rail and get them almost vertical. Even the Calvert shocks needed/liked this and it was easy to do.
'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.
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Re: help me understand instant center as applies to leaf springs
[Re: rb446]
#3101674
12/12/22 06:34 PM
12/12/22 06:34 PM
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Joined: Jul 2009
Posts: 112
pa
gregcharger72
OP
member
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OP
member
Joined: Jul 2009
Posts: 112
pa
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My mate has mono's -c-tracs in the upper hole on his RR, motor has 720ftlbs on the hit and is controlled by just caltrac 9-way shocks on 7 stiff, good DA shocks are important yes, wait till you get those mono springs onto see the difference, here's a vid of the car on a 10.35 hit, been a best 1.421 60ft.@3800lbs> https://www.youtube.com/watch?v=9tnu9cSnf2U I just watched the video, the car looks very well controlled on the launch. That is what I'm after.
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101684
12/12/22 07:11 PM
12/12/22 07:11 PM
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Joined: Aug 2003
Posts: 43,214
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,214
Bend,OR USA
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Have you looked into switching to ladder bars with coil overs? If not I think you should  The reason I'm suggesting this is I use to race against John Calvert in NHRA stock when he was developing the Cal Tracks, he would have used ladder bars if they had been legal, I would have also  Look into a set of 36 inch long ladder bars and real good set of double adjustable coil over with 6.0 inches plus travel and go have fun getting your back and neck hurt from the G force on the leave  AKA, a 1.42 60 ft. times can hurt you if you're leaning forward on the leave, especially if you're a big guy that doesn't work out your upper body frequently   A 1.23 60 ft. time can and will make you grin a bunch  
Last edited by Cab_Burge; 12/12/22 07:12 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101685
12/12/22 07:11 PM
12/12/22 07:11 PM
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Joined: Mar 2006
Posts: 9,847
MI, usa
dvw
master
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master
Joined: Mar 2006
Posts: 9,847
MI, usa
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60 ft is also a function of power to the tire. Be it gear ratio, converter, or plain old engine power. If the chassis doesn't have excessive movement and the car hooks consistantly. The 60 ft is about what it is. Some cars need chassis seperation and pitch rotation to hook. Some don't. A lot of variables in the equation. What kind of track prep? weight distribution? A 10.50 car will generally be in the mid 1.4x 60ft range. I doubt you need Santuffs in your ET range. Are they good? Heck ya. But they're pricey. I personally run Afco's. Resonably priced. With proper valving they work well. I can't comment on Vikings as I haven't used them. Many seem to be happy with them.
Doug
Last edited by dvw; 12/12/22 07:15 PM.
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Re: help me understand instant center as applies to leaf springs
[Re: gregcharger72]
#3101759
12/12/22 10:39 PM
12/12/22 10:39 PM
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Joined: Jun 2014
Posts: 3,196
Md.
carnut68
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master
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Md.
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Do you mean body separation like this? Sorry about sideways pic.
Last edited by carnut68; 12/12/22 11:54 PM.
America First!
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