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Big end stablity
#893707
01/01/11 06:13 PM
01/01/11 06:13 PM
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Joined: Mar 2008
Posts: 553
Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 553
Kentucky
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I am upgrading my power over the winter and am shooting for 10.0's. I currently run a MT ET Drag 28/10.5 on an 8" rim and run them at 11.5 lbs. I currently get a little movement on the big end at 125mph. I have always thought the movement was due to the lower pressure trying to get the tire to lay down. Will a 10" rim enable me to increase the tire pressure and possible become more stable or do I need to consider a different tire (i.e. stiffer sidewall/QTP/MT Street radial)or both?
I am in the debate of whether or not to mini-tub to get more tire under the car (75 Duster) but I am thinking I may be just as well off to do a stiffer sidewall tire on a 8" or 10" rim. The good thing with the radials is that you can get more tread width for the section width, the bad is that it adds nearly 12lb a tire.
'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Big end stablity
[Re: clovis]
#893708
01/01/11 09:11 PM
01/01/11 09:11 PM
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Joined: Aug 2003
Posts: 43,180
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,180
Bend,OR USA
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I have ran my Duster with MT ET Streets, 12.50x30x15 on both ten and twelve inch rims, no noticeable differences except for a little more pressure on the 12 inch rims, probally a pound and ahalf or two pounds  I adjust the pressure by looking the sixty foot and reaction times after each change I do run the same size ET Street Radials also on the better tracks, I do not notice any movement with either set but I'm getting old and some things don't bother me anymore  My duster weighs 3450 lbs with me in it, ladder bars and coil over rear suspension with a diagonal link for locating the rear end  It runs mid to high tens at 128+ MPH I started drag racing a long time ago when we where using 7 inch wide slicks on a 5 inch wide wheel,. I ran high 12.s in a 4200 lb car at 107 mph, it would wiggle around real bad during the intire run  One of the old timers told me to keep the front wheels straight, make very minor steering adjustmenst to keep it in the center of the track and don't try to over correct it during the run, keep it straight and the rear wheels will have to follow the fronts  Hard to do the first time but it worked, same thing on the other end, keep the front wheels pointed straight(very minor corrections only ) and let the back end squirm all it wants
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Big end stablity
[Re: MR_P_BODY]
#893711
01/02/11 01:10 AM
01/02/11 01:10 AM
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Joined: Mar 2008
Posts: 553
Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 553
Kentucky
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The car weighs 3300 with me in it. At 15 lbs the car will not hook, it actually seems very sensitve to tire pressure. I am running a caltrac setup (bottom hole with two flats of preload)with the ranchos (set at 6).
The car has never 60ft well, but I have always though it was more of converter issue than suspension. I am going to bring the rear of the car down as when I dropped the front to get my 5" of travel, it really has a nose down stance.
Here is a picture at launch.
'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Big end stablity
[Re: clovis]
#893712
01/02/11 01:12 AM
01/02/11 01:12 AM
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Joined: Mar 2008
Posts: 553
Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 553
Kentucky
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Here is one before launch
'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Big end stablity
[Re: rowin4]
#893714
01/02/11 01:44 AM
01/02/11 01:44 AM
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Joined: Mar 2008
Posts: 553
Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 553
Kentucky
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After I dropped the front we put it on an alignment rack and got it dead nuts on. I had actually just gone through and overhauled the entire front end, so I feel pretty good about the front end being in good shape.
Funny thing is I know i am on a good pass (ET wise) when I feel it start to move after the 1/8 mile. Its not bad I can just feel it moving, I just don't want it to get worse at 132.
'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Big end stablity
[Re: MR_P_BODY]
#893716
01/02/11 02:42 AM
01/02/11 02:42 AM
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Joined: Mar 2008
Posts: 553
Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 553
Kentucky
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I did try to slow down my separation and put the shocks at 9, but I did not change the air pressure. At 9, just after launch it would unload the tire and spin  .
'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Big end stablity
[Re: MR_P_BODY]
#893718
01/02/11 08:37 AM
01/02/11 08:37 AM
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Joined: Mar 2008
Posts: 553
Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 553
Kentucky
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At the same time we dropped the front, we also put on some calvert 90/10. When we had the shocks off for the change, the front appeared to move freely. Even after the installation of the shocks the front seems to move without any hesitation.
'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Big end stablity
[Re: clovis]
#893719
01/02/11 10:00 AM
01/02/11 10:00 AM
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Joined: Jan 2003
Posts: 5,894
Florida
Locomotion
master
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master
Joined: Jan 2003
Posts: 5,894
Florida
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Quote:
The car weighs 3300 with me in it. At 15 lbs the car will not hook, it actually seems very sensitve to tire pressure. I am running a caltrac setup (bottom hole with two flats of preload)with the ranchos (set at 6).
The car has never 60ft well, but I have always though it was more of converter issue than suspension. I am going to bring the rear of the car down as when I dropped the front to get my 5" of travel, it really has a nose down stance.
Here is a picture at launch.
Are you footbraking?
A car will be extra sensitive to carb tuning if footbraking.
Accellerator pump cam and squirter tuning can affect how hard it hits and how well it stays planted. Getting too lean or rich and/or too short or too long of squirt duration in the first 60'-100' can keep it from "planting" or can unload it after the initial hit.
Another variable can be the track. There are some who don't maintain it as well as they can, especially in the summer and on test-&-tune days where anybody and everybody, including lots of treaded street cars, are mixed up. But if most other similar cars are hooking, it is in your car.
I don't think it would affect top end stability too much, but do alignments with you, or an equal amount of your weight, in the seat.
Last edited by Locomotion; 01/02/11 10:05 AM.
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Re: Big end stablity
[Re: Locomotion]
#893720
01/02/11 11:32 AM
01/02/11 11:32 AM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Change your idler arm to a new Moog one. Problem solved. Bump up your rear tire pressure to 12.5lbs. Front Tires to 37-38psi
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Re: Big end stablity
#893721
01/02/11 12:03 PM
01/02/11 12:03 PM
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Joined: Jan 2003
Posts: 9,999
Frostbitefalls MN (Rocky&Bullw...
gregsdart
master
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master
Joined: Jan 2003
Posts: 9,999
Frostbitefalls MN (Rocky&Bullw...
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Do you have plenty of front travel and very light T bars in it? Shocks very loose? That is a good place to start retuning. Making sure your carb is set up properly is very important,so that should come first. Then you can move to the back.
I run a 15.1 x 33.6 tire with 10 psi. Compared to your car, that is very high. So I think if you start by making sure the front is loose as a goose, tune the carb, then start playing with the back end till it works, you will have a great base to start working with the front end. Then you will be able to judge how much you can do with travel limiters ,torsion bar rates, and shock settings to keep the front down down track.
I don't see any wheelie bars, which are great for providing info on what the rear axle is doing on launch.
If you can video the back of the car and watch that rear axle frame by frame, you will learn a lot. You may need to add something to the rear that will stick out the back of the axle so you can better see what is happening.
A video camera doesn't take enough frames per second to catch the speed of the rear axle properly. Things happen so fast 33 frames per second isn't enough. But by taking multiple videos and studying them several times, you will see what is really happening. Good luck with it!
Last edited by gregsdart; 01/02/11 12:17 PM.
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Re: Big end stablity
[Re: MRMOPAR622]
#893724
01/02/11 04:38 PM
01/02/11 04:38 PM
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Joined: Mar 2008
Posts: 553
Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 553
Kentucky
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To answer the questions.
-Footbrake
-It has 6 cylinder torsion bars with the Calvert 90/10's, so the front is about as loose as I know how to make it.
-You may get an idea of rear height from the picture but it rides on 6 cylinder springs with the caltracs, and everything is in the stock location.
So what has been the experience of anyone going from to a wider rim and/or from a slick to drag radial?
'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Big end stablity
[Re: clovis]
#893725
01/02/11 05:19 PM
01/02/11 05:19 PM
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Joined: Jan 2003
Posts: 5,894
Florida
Locomotion
master
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master
Joined: Jan 2003
Posts: 5,894
Florida
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Quote:
So what has been the experience of anyone going from to a wider rim and/or from a slick to drag radial?
Don't know about drag radials, but in IHRA and NHRA Stock, where we are limited to a 9" slick, most people run a 10" rim, if it will fit. Depending on the car and tire, pressures can be anywhere from 14 lbs to 24. But I have heard of some being higher. As mentioned before, the wider rim allows more air, which stiffens and prolongs the life of the sidewall and helps maintain a fuller contact patch. Radial slicks are faster and usually need more air pressure. But they are more sensitive to track conditions.
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Re: Big end stablity
[Re: Locomotion]
#893726
01/02/11 05:24 PM
01/02/11 05:24 PM
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Joined: Jan 2003
Posts: 19,363
Las Vegas
Al_Alguire
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 19,363
Las Vegas
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IMO go to a wider wheel, IMO an 8" wheel is to narrow for the 10.5 tire. Get the front end alignment checked at ride hieght. Also from that launch picture I think I would want to stiffen the extension on the rear shocks if you can. Would like to see some launch video..
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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