Torsion Bar Upgrade for '65 Barracuda Formula S

mvh said
I put in .890s as an upgrade to the .870s in my 67. This incremental change is probably only worth doing if you already have the front end apart for a refresh. However, it is a good upgrade that helps control dive and does not result in an overly stiff ride.

It is really the sway bar that contributes to cornering performance — you don't need super-stiff springs for handling. On real-world curvy roads, which are generally secondary roads in rural areas that are not always well-maintained, extremely stiff springs will rattle your teeth out and reduce the amount of contact patch as the tires leave the road surface.

I just finished (well, almost finished — DNF'ed with a blown head gasket) a 850-mile vintage car tour on secondary and tertiary roads in Northern California. I have done this rally in one or the other of my Barracudas several times (not this occasion). The slant six convertible with the softest factory springs plus sway bar was just as capable as my tweaked Commando fastback for this kind of activity, although I wouldn't take it to track day at Willow Springs. Meanwhile, the replica Ford GT40 was crawling in low gear half the time (although as soon as the road surface smoothed out he was out of sight).

I did just install Bilstein shocks on the fastback and that seems to be an improvement over the KYBs, but I haven't had it on a rally yet.

Respectfully, I disagree with pretty much all of this.

Sway bars are only a single, and secondary, component for improving handling. Yes, there are very experienced drivers/racers that have some differing opinions on wheel rate tuning with springs vs sway bars. But ultimately, with a good set of tires there is not a commercially available sway bar big enough to increase your wheel rate enough to compensate for .87” or .89” bars. You’d have to make your own NASCAR style splined sway bars to get large enough in diameter to get where you need to be.

As for rattling your teeth out on tertiary roads in Northern California, no sir. That’s what good shocks are for. Between my ‘72 Challenger with 1.12” torsion bars (270 lb/in wheel rate) and my Duster with 1.12” torsion bars (300 lb/in wheel rate) I’ve logged well over 100k street miles, the vast majority of which are on secondary and tertiary roads in Northern California. The Duster has 1.12” torsion bars AND Hellwig sway bars.

Maintaining suspension travel is one of the biggest considerations for going to larger torsion bars. Go too high in wheel rate and your wheels no longer track the ground. Go to low in wheel rate and you bottom out your suspension all the time, which ALSO results in your wheels not maintaining traction because you have 0 suspension at that point.

With 1.12” bars on my Duster, and maintaining the factory ~5.5” of total suspension travel, I still bottom out my suspension on occasion (mostly on little back roads!). Which means, smaller bars would bottom even more, resulting in worse handling.

Bob Jasinski said
I really appreciate the torsion bar feedback. To add perspective, (I'm in a reflective mood so skip to the bottom if easily bored) allow me to share a little bit of history of this car and how I came to own it. In April 2002, I found it sitting in an industrial park in Newark California, with "For Sale $2000" written across the windshield. I saw the tach in the dash and the FS badges. I took pictures of it and the fender tag, went home and did some research. I determined it was a real Formula S, and called the phone # on the windshield. He bought the car from the original San Jose owner, cut one side of the inner fender for a planned header installation and a built 340. His wife got pregnant and the car had to go. He included a full Legendary interior kit, front/back seats and full carpet, and extra parts. I offered him $1500 and he had to deliver it to my house, he agreed.

I enjoy rare cars, I own a 300G convert as an example, this FS was rare. Up to this point, I had owned 17 Plymouths, from a '48 to a '75. Deluxes, Furys, Sport Furys, Belvederes, Satellites, sedans, convertibles, wagons, 2 dr hardtops, never an A body, never even driven an A body, to this day. So, my goal for the car was a restoration, not a "build project". Didn't care to drop in a 340, hey, its already a factory performance car right? Well, I sent for a copy of Tom Condran's (then) recent book "Performance Handling for Classic Mopars". It really inspired me to give thought to minor upgrades that would "enhance" the handing experience of an already well handling car, albeit one that came new with skinny bias ply tires, but hey, they had blue streaks, so there's that right?

Well, that was 20 years ago, and the body and paint is now finished, only waiting for the headliner to be installed at the shop (my avatar will change soon I promise) . The original engine is rebuilt, .040" over, domed pistons, etc. It's mounted on the K frame and will be installed from below (I have a lift). The factory sway bar is going back in, and I'm ordering a new set of rear springs from Espo. I've followed Condran's advice and installed Moog offset bushings in the UCAs, and have a KH disc brake setup ready to go in. I'm going to 15" radials with new rallyes. This car will be driven to shows and weekend getaways in the wine country and coastal hiways, twisty roads, that sort of thing. I actually have a set of new KYBs, but if they don't work out they're easy to change. Does it make sense to put the original torsion bars back in? I think not.

72nuNblu says "I'd go 1.03", MVH says he likes his .89". So far, no one is telling me to stay with the original .87" bars. I'm going to call PST and discuss it with them. I'm leaning toward the 1.03" at this point. The KYBs can change but the factory sway bar stays.

You can look at my response above, but again, I’ve been running 1.12” bars in my Duster for years driving mountain and coastal roads in Northern California. I run Hotchkis shocks and Hellwig sway bars. If I do anything, I’d go UP to 1.18 torsion bars.

Now, my Duster has 275/35/18’s on the front and 295/40/18’s on the back with 200 tread wear tires, so with less traction and loading you’d want less wheel rate. But when I was running 225/60/15’s and 1” torsion bars on my Duster the ride was still quite soft and the body roll was still quite substantial- more than my current Hellwig bars could tame.

I do set my cars up pretty aggressively, but I also drive some pretty sketchy back roads. And I’ve never been bounced off the road because the suspension in my Duster or Challenger was too stiff. I have gotten out of shape because I bottomed out my suspension though.

All that said, I think 1.03” bars would do you just fine, and would significantly improve the handling on your car especially paired with a decent set of shocks (RCD Bilstein, Hotchkis Fox’s, RideTech, etc).

Another great resource for you is @BergmanAutoCraft , he will have much better knowledge and advice than PST.