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  #1  
Old 08-09-2002, 09:52 PM
moparguru71 moparguru71 is offline
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Default wheelbase

what is the shortest wheel base offerd by mopar? is 108 and which bodies have it?
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Old 08-12-2002, 09:33 PM
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cant anyone on here help wanting to find mopar with wheelbase as short as posible 104 would be best
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Old 08-12-2002, 09:58 PM
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Well, the fact is that Chrysler never made a rear wheel drive car with less than a 108" wheel base. The A-body Demon, Duster, Dart Sport, and 2 door F body Aspen and Volare all have 108" wheelbase.
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Old 08-13-2002, 01:49 AM
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What about two door 68 or 69 valiants, I think it was like 106, but Ive been wrong before.
Long cars are the way to go I think, short cars are too squirley
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Old 08-13-2002, 02:29 PM
340duster1 340duster1 is offline
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A 2dr Valiant 67 and up has a longer wheelbase than a duster Iit is the same as a dart). I believe it is 110" or 111". Might check a 66 and earlier dart of valiant
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Old 08-14-2002, 12:36 AM
moparguru71 moparguru71 is offline
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thanks guys does anyone know the wheelbase of 64,65,66barracuda?
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Old 08-14-2002, 01:08 AM
340duster1 340duster1 is offline
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106"

See http://www.completelycudas.com/index.asp:)
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  #8  
Old 08-20-2002, 07:26 PM
340king 340king is offline
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Question Shorter is Better?

I think that Cageman brings up an interesting point and I also think it needs some explanation. The first thing I want to point out is that wheelbase does affect terminal speed in cornering. It has to do with polar moment of inerita(the resistance to turning about a vertical axis through the roof of the car), wheelbase leverage on that center axis and weight distribution.

First, we need to look at polar moment of inerita. This is the thing that makes the car hard to pivot in the turn or maybe a better way to look at it is this is the resistance to turning caused by the momentum of the car's mass. It comes from Newton's laws of physics. Objects in motion tend to stay in motion unless acted upon by an external force. In the case of our racecars, the external force is the lateral force the tires apply to the chassis when the wheel is turned. This force varies with slip angle, tire construction, track friction, load force and air pressure. There are alot of variables involved in generating the lateral or side force. Oh, I forgot chassis geometry too. Longer wheel base cars tend to have greater polar moments of inertia due to the weights of the suspension components. The polar moment of inertia is based on the radius of gyration, the distance from the centroid to the mass. In the case of inertia it is calculated using the square of the distance. This can be offset somewhat if the weight of the car is well below the required minimum, allowing selective ballast placement.

Leverage on the polar axis does have an effect on the relative cornering ability. Longer wheel base cars tend to react slower than shorter wheelbase cars. The longer wheelbase cars can be easier to drive and keep in a straight line. The leverage advantage is linear, however and does not make up for the increase in polar moment of inertia that usually accompanies the longer wheelbase. This is due to the radius of gyration thing we just talked about and it being raised to the power of two.

Weight distribution can work for or against you in a longer wheelbase car. The longer wheelbase allows for a greater degree of adjustability due to the distance bewteen the rear axle and the center of gravity. Large radius corners help to reduce the difference wheelbase makes in cornering. This is because the rate of rotation around the centroidal axis is slower. This requires less of the total tire traction to be used up creating side bite just to overcome the additional inertia of the longer wheelbase car. Typically, shorter wheelbase cars are lighter, allowing more ballast to be placed.

Basically, what I am saying is there are two forces involved in turning the car. One is the centripetal acceleration that must be dealt with to keep the car in a corner of constant radius. Then there is the force required to actually turn the car about its centroidal axis, represented by its polar moment of inertia. Is an of this making sense? Cars of equal weight will require the same centripetal acceleration regardless of wheelbase, but the same cannot be said for polar moment of inertia. This is where the difference is.

In theory, shorter wheelbase cars are better from the standpoint of physics. So can you race a longer wheelbase car and still be competitive? Yes! You just have to be better than the competition.
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Old 08-21-2002, 12:32 AM
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When I race against metric GM,s I notice that a slight contact with each other and they spin out, now with my car they hit me and they spin or loose control and my car keeps going without notice, unless they flat out take you out, then your out of luck short or long. I have driven a legend or two and they are real sensitive to gas and steering due to there short wheelbase and lightness, now maybe that will make you a better driver in the long run if you can get enough practice in that car but I like my long car, it is intimidating to other drivers.
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  #10  
Old 08-22-2002, 04:30 PM
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My info shows the '61-62 Dodge Lancer 170, 770, the '64 Valiant Barracuda, and '65-'66 Barracuda, Barracuda Formula S as 106.5" W.B. cars. Aspens are listed at 108.5, 108.7, and 112.7, shorter ones are 2-drs. Those early A bodies, by the way, had very small engine compartments.
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  #11  
Old 08-23-2002, 10:55 PM
moparguru71 moparguru71 is offline
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thanks again guys and 340king you obviously know your stuff but i got to be honest,most everything you said was over my head could you possible over simplifie for this dumb mechanic,,, well i read it again and it made more sense to me boy you must really lay awake at nite with all that in your head i hopefully am not offending you i just wish i could have stay awake in geometry class
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  #12  
Old 08-28-2002, 06:32 PM
340king 340king is offline
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Lightbulb Calculus Class

Well, I did my staying awake late at night working on things like calculus, Machine Design and other related engineering type stuff. It is I that owe you and anyone else that felt this was over their head an apology. I never intend to write over anybodies head. I do however, try to get everyone to think about things that maybe they haven't considered. There is always another way to skin a cat!

More or less, what I was trying to say in the previous post is that longer wheel base cars enjoy the advantage of a longer lever arm due to the increased distance from the wheels to the center of the car. This leverage, however, is not sufficient to overcome the disadvantages due to the location of the associated weight of the chassis components, i.e. the rear axle. The reason for this is that the force the weight generates goes up by the square of the distance, whereas the leverage only goes up by the distance.

An example might be good. If you have a mass M located say 30" from the centroidal axis, then it would be represented by 900M or 900 times the mass, while the leverage is 30. Now lets move the rearend 2" farther back. The formula is 32 squared times M or 1024M while the leverage is 32. This is nearly a 14% increase in the mass force while the leverage shows only a 7% increase. In other words, when we increase wheelbase, the math says that the force created by the mass moving rearward increases faster than the leverage effect of the increase. I was just wanting everyone to look at the thing from a purist or mathematical viewpoint.

So how does this work in the real world. Honda built a motorcycle that had the fuel tank and other heavy items as close to the ground as possible to create a better handling bike back in the late 80's. What they found out was that the bike handled very poorly. This puzzled them for a while, until they realized the the bike must pivot around an axis that parallels the ground. By placing the weight as low as possible, they were in effect increasing the distance of the mass from this rotational axis. This led to slower reaction during rotational movements, like the one they use at the corkscrew on Laguna Seca. They determined that the closer the center of gravity and the center of rotation were, the better the bike handled. This is the same thing we are talking about here, mass centralization.

Now, before anybody flames me for implying that the pendulum effect is the only consideration, hear me out. It is an effect as real as any other. But like all aother things in racing, you need to look at what the overall picture looks like. If you have a car that has great weight proportionality and needs ballast, where is the best place to put it? The answer is what Honda found out, as close to the center of gravity as possible. Adding weight to areas farther from the COG increases the effect they have, but there is a very real tradeoff for placing it a long way from the COG. The same thing is true for side to side weight, but the distances are shorter and the effect is much smaller. Think about the Honda example. A four hundred fifty pound bike and very small distances and yet there was a measureable effect.

I liked what was said about trimming the front end of the vehicle. Every pound of front weight you remove is worth more like two pounds. One pound for the rear weight it would have taken to offset it and another for the total loss associated with it.
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Old 08-28-2002, 07:23 PM
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Just for info.....guys the original Kit Cars were 108 and 112 on the same chassis. Spring locations for both. Dual shock mounts etc. Ran one for years on pavement and dirt. Used both wheelbases depending on track. Always preferred the 112 setup. 108 felt twitchy on dirt and would not produce equivilent side bite. Lots of help from Mopar.....still got the plans, patches on the uniform, and about 100, 000 miles on the experience tab and about a $100,000 drain on the bank account. Would'nt trade it for anything. Now, if the uniform would just fit.
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  #14  
Old 08-28-2002, 10:57 PM
moparguru71 moparguru71 is offline
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thanks 340king i really hope that i didnt offend after i read your post and made i reply i read it again and it made more since but we finally found a setup that worked real well on our car not sure if it will be good enough for dry but last week we had a better car that the bowtie brigade did on a tacky track so really think we may have something for dryjust let me throw some numbers at ya and tell me what you think109 wb duster gm metric stub 3500 pounds 52.8left52.4 cross 61%rear1.25stagger3/8inch rear steer on left shorter wheel base on that side tell me what you think of those numbers and what you would change
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  #15  
Old 08-29-2002, 11:08 AM
jelsr jelsr is offline
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Gotcha,
I'm with you on the WB. My brother likes the 108"
setup but I prefer the 112". It is just more stable. Really got a kick out of your remark on the firesuit fit. Seems the sand is beginning to shift in my hourglass figure also!
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  #16  
Old 08-30-2002, 06:01 PM
340king 340king is offline
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Question Setup Advise

Moparguru71, it is hard to provide much useful advise across the internet. There are general ideas that those of us that participate on the board can express, but in the end each setup must be tailored to the track, the class, the drivers taste and current track conditions. I can't even begin to tell you if your setup would work for your tracks dry slick conditions. I wish I could, don't get me wrong.

There is only one thing that stands out as being a little out of the ordinary to me. That is the shorter wheelbase on the left or driver's side. To me this should loosen the car slightly throughout the corner and may hinder forward bite under some circumstances. Typically, rear steer is employed as a dynamic component used on multiple link rear suspensions. Again without a much greater knowledge of the track, rules etc. it would be almost impossible to render a worthwhile opinion, sorry.
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Old 08-30-2002, 08:32 PM
jelsr jelsr is offline
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I have to agree with 340 King on the rear setup. It will be looser that way compared to stock and would be a detriment when dry slick. The standard rear setup on a Mopar has the front leaf spring mount below the axle centerline. This causes the differential to turn into the corner and induces push which is a more desireable condition and is easy to compensate for. Your setup will have the differential turned out in the corner and will induce oversteer or loose. But I was wrong once, years ago. Then again, I could be mistaken.
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  #18  
Old 08-31-2002, 08:19 AM
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Jelsr.....email me a gotcha@acnet.net. I have a lot of 86 D50 parts you can have. Stripped one out for my new 10.5 tire class car (drag racing). Will run 505 Big Block. Currently 360. Let me know via E-mail.
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Old 08-31-2002, 10:02 AM
jelsr jelsr is offline
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Gotcha,
Consider it did!
Jim
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