torsion bar recomendations

[flyinlow]

Gearing up for front end work the winter.

73 SE . 318 car with 446 now.  frame tied, 15" wheels ,BFG tires, street cruiser. 4ooo miles annually.

rear : new Mopar xhd springs, shackle bushings and KYB gas adjusts ,addco 7/8 swaybar, '71 8 3/4 axle ,no isolators

Happy with rear suspension

front : will be replacing ball joints, control arm bushings, offset uca bushings,strut rod bushing kit, all Moog, addco 1 1/8 sway bar allready  installed. kyb twin tubes installed ( too soft)

front has original .920 bars was considering Firmfeel replacements.  recomendations?

[Nacho-RT74]

1" will be enough... will be better upgrade with thicker sway bar and AT LEAST KYB GR2 shocks.

I fit 1.06" and got plenty happy, but BB. I think still 1" was to be enough too.

[HPP]

What's your driving plans?

[flyinlow]

Weekend cruiser. 4000 miles a year . 1000 mile trip once a year. Drag strip once a year with street tires.

The rear suspension is fine. Bigger front and adding the rear bar has improved the handling alot .

Want the front to feel
as firm as the back. Not harsh and no squeeks.

[HPP]

I'd say 1.0 or 1.06. These are firm without being harsh. They are the police/HD sizes, so they are tolerable for extended trips, but will step up the rate a good 25% or more. A once a year trip to the 1320 isn't going to be concern for major weight transdfer, plus the added rate actually makes the car more predictable and consistent for bracket racing.

[Back N Black]

i have .96 in my car and it rides like a tank! 

[flyinlow]

i have .96 in my car and it rides like a tank! 

.96 Mopar or firmfeel?   2nd gen bars are shorter, so I would think for a given diameter, that a' 68 would ride stiffer than a '74.

[HPP]

Ride can be somewhat subjective and I have heard of people complain that the .92 Hemi bars were too rough a ride.  So it is all a personal call. To me, a .96 bar is the minimum you would want on a 66-71 small block B body. Something to keep in mind is that increases in t-bar rates, or any spring for that matter, requires more control from the shock as well. A matched rate shock will make a HUGE difference in the way the ride is controlled and transmitted to the driver. For example, the XV front suspensions are typically using 1.12 to 1.16 bars in their B body kits, but the high end shocks they supply are able to smooth everything out to reduce the perceived harshness.

Like flynlow says, length is also a factor in the bars resistance to twisting. The 1.0 bar rate is highest in A bodies at 195#, then 66-71 B bodies at 175#, and then 73-80 B bodies at 160#, and finally C bodies at 142#. I've enver measured the bars in my Suburban, but they are plenty long and plenty large in diameter. Much bigger than anything I've seen under a mopar and it rides pretty nicely.

[FJMG]

I'm with Nacho on this, bump up the front bar first and match the shocks. You have increased the roll resistance of the front by a much smaller margin than you have on the rear (many of these cars were optioned with just under an inch in the front). Nascar used huge springs to support the downforce at 200 mph high banks. Road racing does not require as much spring rate but DOES require substantial roll resistance (larger anti-roll bars). Try to pick the brains of your local road-racing club.

[Rolling_Thunder]

I have .96" bars on my 68 and with my ass on the fender (300lbs at the time) the front would go down about 1/4"     -  they seem to be plenty stiff...     

[HPP]

Lets do a little comparative analysis. I think most would agree that a BMW M3 is a pretty good handling car. In general, a good handling M3 will run spring rates around 425-500#. Not all of that rate is applied directly to the tire because coil springs cannot mount directly to the control arm's pivot point like a torsion bar can. Once you multiple that spring rate by the motion ratio, the M3 has an effective wheel rate of 195-230#. Comparing wheel rates is how you take dis-similar suspension systems and compare their actual application of force to the road. So in the mopar torsion bar suspension for 73-79 B bodies, a 1.0 bar is 160#, 1.06 is 208#, and 1.12 is 248#. So, closest resembling rate to a BMW M3 is 1.06.  That same M3 also weighs in around 3400 pounds, give or take a few. By contrast, the 74 Charger is close to what, 4000? So that similar wheel rate is now supporting 600# more, which is going to soften its feel to the driver You also already have XHD springs and a rear sway bar, so you have added enough wheel rate at the rear to have a car that will oversteer at the limits of traction. To bring this back in to line, you need to step up the front rate a corresponding amount. I stick by a 1.0 or 1.06 t-bar, I'd suggest 1.06 to go with the 1.125 sway bar you already have.

[flyinlow]

1.06 sounds good to me.

Will kyb gas adjusts be enough dampening ?