73/74 RR Torsion Bar Question and Opinions

[RR Fan Dan]

I’ve been working with Matt at Firm Feel to upgrade the suspension on my 74 RR. We are discussing the front torsion bar and he initially recommended a 1.06” replacement bar. I told him I wasn’t racing and I asked him if that would make the ride hard and bumpy. And also asked him what the stock diameter bar was. He said the stock bar was maybe 0.92” and maybe the 1.00” would suit me better. I am looking for opinions and suggestions as what to go with? Is my stock bar 0.92” and will another 0.08” (1.00” bar) make a difference, or should I jump to the 1.06” bar for a 0.14” increase? Or should I keep it stock? The upper control arms are being replaced with Firm Feel, the lower control arms are stock but will have reinforced bars added. A 1-1/8”Firm Feel sway bar kit is also being added.

 

[WileE]

What is a torsion bar ? It is a spring. Springs have "spring rates" meaning a measure of its "stiffness". Higher a spring rate, the stiffer. The larger the torsion bar diameter, the stiffer. It's really a matter of personal preference dependent on your intended use. If you're seeking a firmer ride, perhaps a slightly stiffer spring with a quality shock absorber would be suitable ?

 

[DeltaV]

and torsional stiffness is to the 4th power of the diameter.

 

[DeltaV]

Post in thread 'BB torsion bar part numbers please?' BB torsion bar part numbers please?


Look at the other replies in that thread too. For example:

Post in thread 'BB torsion bar part numbers please?' BB torsion bar part numbers please?

 

[DeltaV]

1 1/4” inch front sway bar kit hand fabricated by firm feel.

A 1-1/8”Firm Feel sway bar kit is also being added.

A typo somewhere? Which diameter front sway bar are you going to use?

Did you tell Matt you ordered a 1" rear sway bar from Addco?

What does Matt recommend for front and back sway bar diameters?

 

[DeltaV]

Does your '74 have large rubber "donut" isolators between the K member and body? If so, they probably need replacing if you can find replacements. My '79 has them, but I don't know when Chrysler introduced them to B bodies.

 

[pnora]

Does your '74 have large rubber "donut" isolators between the K member and body? If so, they probably need replacing if you can find replacements. My '79 has them, but I don't know when Chrysler introduced them to B bodies.

They started is 73 as I recall.

 

[pnora]

Post in thread 'BB torsion bar part numbers please?' BB torsion bar part numbers please?


Look at the other replies in that thread too. For example:

Post in thread 'BB torsion bar part numbers please?' BB torsion bar part numbers please?

 

[RR Fan Dan]

A typo somewhere? Which diameter front sway bar are you going to use?

1 1/8”

Did you tell Matt you ordered a 1" rear sway bar

Yes

Matt recommended the 1” for a softer ride but didn’t know exactly what diameter the stock bar was. He thought it was maybe 0.92”. 1.00” minus 0.92” = 0.08” difference. That doesn’t seem like much of a difference. And if you look at the chart above, I’m guessing since it was originally a RR 318 car it’s more than likely a 0.94” stock bar. So that makes the difference between a 1.0” bar and a 0.94” bar 0.06”. That small amount of difference seems to me that there will not be a noticeable effect. For the $600 cost of the torsion bar, I would like to notice a difference, so now I’m contemplating the 1.06” bar that Matt initially suggested. I just don’t want a really hard stiff ride where I feel every bump in the road. Does anyone here have experience with larger torsion bars, and if so what did you go with, and what is your impression with what difference it made in the ride and handling of your car?

 

[DeltaV]

and torsional stiffness is to the 4th power of the diameter.

That doesn’t seem like much of a difference.

See my comment above. Ergo, it does make a difference...it will be noticeable.

That small amount of difference seems to me that there will not be a noticeable effect

See my comment above. Ergo, it does make a difference...it will be noticeable.

Look up torsional spring stiffness and notice the J (or I) term with d to the 4th power. You can algebraically compare the effect of going to a different diameter.

Or, take Matt's advice.

I’m guessing since it was originally a RR 318 car

I believe I and others were under the impression your car is a factory 440 car.

***
Just a comparison, the torsion bars on my B-body '79 300 heavy duty suspension have a diameter of 0.98"; and the same 43.6" length as your car. Ergo, my car has the same torsion bar dimensions as a '74 RR with the 440. Furthermore, checking my documentation, mine are the same part numbers as the '74 RR 440.

My 360-4V engine is lighter than your 440-4V. I would go with the 1.06" diameter torsion bar for your car since our B-body cars are similar (not similar in appearance).

 

[RR Fan Dan]

I believe I and others were under the impression your car is a factory 440 car.

No it was originally a 318 manual on the floor 3 speed RR. It was changed to a 440 manual 4 speed. I wish it was a factory 440. That would make it a rare 74 GTX.

 

[RR Fan Dan]

What’s ergo?

 

[DeltaV]

What’s ergo?

Shorter version of therefore.

 

[RR Fan Dan]

Shorter version of therefore.

Okay now your post makes sense to me. So you think the 1.06” is the smart choice? I was doing the the math comparing to the size of the sway bar I’m getting and the sway bar is bigger (1.125”), so maybe 1.06” would be fine. It’s the middle pick on their site too.