Muscle Car Handling Upgrades: Chassis Stiffness and Tuning

Throughout this book I’ve often referred to the balance of the car or matching your components. It’s very possible to buy a whole bunch of good-quality parts that are designed with different methodology in mind and end up with an expensive build that drives poorly, or at least doesn’t drive as good as it could. This is one reason why many folks just buy a complete package from one source. That’s certainly the easy way and sometimes it’s a good idea.

 


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If you’re thinking of buying a complete vehicle package for your car, first apply what you’ve learned here to each package—part by part—and make sure it’s going to do what you want it to do. At our shop we’ve always taken a very personalized approach with our clientele and we’re often unable to find a complete package from a single source to meet a client’s goals. Some, quite honestly, seem as if they’re assembled based on whatever the vendor has to sell rather than on what will work best for the car. As a result, in many cases, we assemble a custom package with parts from various manufacturers that best suit our client’s goals and budget.

 

Also, some suspension packages are rather application specific. In other words, they’re geared toward one specific use and may not work so well for other pursuits. A good example is a suspension package geared specifically toward actual road racing. It may provide awesome handling at the cost of a very harsh ride and a race-car-like maintenance schedule. Unless you own an enclosed car trailer, a well-worn helmet, and driving suit, this may not be the best choice for your needs.

Another package may be geared mainly toward autocross. That’s great if you plan to use the car primarily for autocross, but because it requires a very specific setup to optimize a car for such super-tight, low-speed handling the car may be a real handful on an open track and may also exhibit poor street manners. You won’t know until you do some research or you cough up the bucks and try it for yourself. Some issues can be tuned by altering alignment specs, shock settings and/or sway bar settings, etc., if that’s an option on a specific kit.

Then you run into the issue of dual-or even triple-purpose cars, basically modern hot rod multitaskers. If you enjoy cruisin’ on the street, and you enjoy occasionally taking the car to the drags and bolting the slicks on for a few quick passes, and you’d like to take it to local autocross or track day events, and you’d like to do all of those things reasonably well, then you’ve set some pretty lofty goals and you’re going to have to work to reach them. Some of these activities, such as drag racing and autocross, are very specialized so you need to review some of the systems covered here and look out for pitfalls that help in one endeavor and cause problems in another. Here is where just a little bit of knowledge and a lot of adjustability in the various suspension components can pay off big time!

Always keep the big picture in mind and work toward getting the whole car and all of its systems working together!

 

Chassis Stiffness

So far I’ve talked about all kinds of suspension components, A-arms, shocks, and so on, but I’ve left out one great big parts of the system—the chassis itself! Famous race car designer and founder of Lotus, Colin Chapman once said something to the effect of the frame being simply a bracket that holds all of the important bits together. That’s true and it’s also why the chassis or frame gets very little love. It’s not very glamorous or flashy, but without it you just have a big pile of useless parts. It’s also more critical to performance than you may think.

I talked a lot about suspension movements and how to control them but if the mounting points for the suspension are moving around and the chassis is twisting or bending then the suspension can’t do its job properly. It’s easy to think of muscle cars as beefy and strong, but more often than not their chassis are very flexible, especially in torsion, and they can be vastly improved. The result will be not just improved handling, but much more predictable handling and much more solid road feel. Ride quality usually improves significantly as well and you may rid yourself of some bothersome squeaks and rattles too.

You’re dealing with two primary methods of chassis construction. The first is “body on frame,” where the body is a totally separate structure from a ladder-type steel channel frame. The second is unibody or monococque construction, pioneered by the aforementioned Colin Chapman. Most muscle cars that use this type of construction have the front suspension mounted to beefy welded steel subframes that resemble the front of a full-framed car’s frame.

I’ve established that a rigid chassis is a very good thing, now let’s discuss how to make a relatively flexible chassis more rigid. Unibody construction is almost universal today and cars using it can be exceptionally rigid, but that wasn’t so with early Camaros, Mustangs, and such. For that matter even the later ones aren’t exactly poster children for chassis rigidity.

On cars using detachable subframes, like the Camaros, it’s the interface of the subframe and the unibody that causes most of the flexibility issues. There are four mounts holding the subframe to the unibody, each with a bushing and a single bolt. Two additional mounts hold the radiator support and hold up the front end of the fenders but add little to chassis strength. The subframe is basically can-tilevered out in front of the unibody. The factory bushings are high-compliance rubber, presumably to isolate NVH, which allows the subframe to shift in relation to the unibody. This essentially allows the car to bend and twist in the middle. If that sounds like a bad thing, you’re right. Allowing this type of movement in a high-horsepower car is an invitation to disaster.

Subframe Connectors

One of my own cars, a 455-powered 1970 Firebird, suffered so badly from chassis flex that it began to crack the roof at the B-pillar, ripped one of the captive subframe mounting nuts right through the floor, and broke the windshield. I twisted a 400 small-block-powered Pontiac Sunbird so bad that you could only close the driver’s door if the car was running and in reverse. It cracked the roof and broke the windshield too.

Both were caused by my inattention to chassis flex in conjunction with their torque-monster motors and a healthy dose of horribly abusive (read, fun!) driving. Both could have easily been avoided. I can only say, in my defense, that I was young and dumb at the time.

 

1. A step beyond regular subframe connectors, this Mustang underbody structure package from TCP adds much more torsional rigidity than conventional subframe connectors. Similar packages are also available from Chassisworks and other manufacturers for Camaros, Firebirds, and Novas. (Photo Courtesy Total Control Products)

1. A step beyond regular subframe connectors, this Mustang underbody structure package from TCP adds much more torsional rigidity than conventional subframe connectors. Similar packages are also available from Chassisworks and other manufacturers for Camaros, Firebirds, and Novas. (Photo Courtesy Total Control Products)

In both cases the solution was to use subframe connectors. These reinforcing members, generally made from square or round tubing, basically extend the sub- frame’s structure much farther into the unibody and convert the car into a pseudo full-frame format, which still also benefits from its existing unibody structure. These can be either bolt-in or weld-in units. In my opinion, if you’re going to put them in, weld them in. Bolted units always loosen up over time and are less rigid even on their best day.  On cars that use rubber subframe bushings further gains can be had by substituting polyurethane or even aluminum subframe bushings. These remove even more chassis flex and have almost no impact at all on NVH.

 

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Support Struts

Taking things a step further, consider a set of support struts or “down bars” running from the ends of the subframe to the top of the firewall. Some aftermarket sub-frames include these as part of the package, but they can be retrofitted to most other cars as well. Some bolt-in or “fab-tofit” kits are available as well. These remove the cantilevered aspect of subframe mounting and brace the subframe from the top, which typically yields a big improvement in overall chassis stiffness. On cars with loaded upper A-arms and shock/spring towers these structures can be braced in a similar way to modern strut tower brakes. For third-gen Camaros and Fox Mustangs you can use actual strut tower brakes and subframe connectors to get the same kind of results. (Specifics are covered in Chapters 8, 9, and 10.)

Full-framed cars would seem to have an advantage in chassis stiffness because their rails are much more massive than the thin sheetmetal of a unibody car. They suffer from similar problems, though, and body cracking, etc., are not unheard of in full-framed cars. Usually the ends of the frames where the suspension members mount are quite beefy but the center span of the frame is often flimsy, which permits a lot of torsional flex. A few models of muscle cars such as 1965 to 1967 Buick Gran Sports tried to address this by using full-box-section versus C-channel rails. It was an easy way of improving overall strength and rigidity that’s still a good idea today.

 

One of the very first modifications to consider on any unibody muscle car are subframe connectors. They basically tie the subframe into the unibody more completely, making it think it’s a full-frame car. (Photo Courtesy Chris Alston’s Chassisworks)

One of the very first modifications to consider on any unibody muscle car are subframe connectors. They basically tie the subframe into the unibody more completely, making it think it’s a full-frame car. (Photo Courtesy Chris Alston’s Chassisworks)

 

If you’ve got the body off the frame it’s a fairly simple task to box in the C-channel rails by welding steel plates into the open sections. You don’t need steel plate from a battleship; .095- or .120-inch mild steel is plenty. You need to relocate the fuel and brakes lines, but it’s a small price to pay for a marked improvement in chassis stiffness. The same advice about firmer body bushings having some benefits also applies. The improvement may not be as noticeable as on a sub-framed car but it’s still worth doing.

Cages

If you’re serious about chassis rigidity—and I mean really serious—then there’s one ultimate solution: Cage it. Nothing else adds as much strength, rigidity, and safety to a car as a well- built tubular steel roll cage.  Like anything else on the car, consider your goals and needs, then consider the options carefully; a cage is one of those options.

True, most of the folks reading this book don’t need a cage in their car, but they may still benefit from one. That doesn’t mean you need a funny-car-style, jungle-gym cage that you need to take yoga to get into. What may be appropriate, though, is a street friendly cage. This type of cage may not meet all NHRA or other sanctioning body requirements but it may just suit your requirements perfectly.

Again, the idea is to target problem areas then correct the problems. If the car lacks torsional rigidity a tasteful cage with unobtrusive rocker bars running parallel with the door sills or angled side bars bent for maximum seat access, both of which can tie ends of the two frames together can be a huge benefit. If done properly they’re not in the way at all. They also provide an extra degree of side impact protection to older cars that lack reinforced door beams. That may not seem like a big deal until you have a telephone pole or a van in your lap.

The side bars tie into a main hoop, which gives the car some rollover protection, and a cross bar which can be used for harness mounting and prevents the hoop from collapsing if hit from the side. On a street car this bar can be dropped to the level of the rear seat cushions and tied into the driveshaft tunnel for easier rear seat access and even more rigidity. The cage is then rounded out with diagonal bars from the top of the hoop, rear-ward to the rear frame rails. This adds a huge degree of rigidity to the portion of the frame that’s heavily loaded by the rear suspension.

 

Some muscle cars have full steel channel frames, like this example from a 1969 Chevelle. This one is from a hardtop car. Convertibles got fully boxed frames for more torsional rigidity. Boxing plates can be welded into C-channel frames to gain that same rigidity. (Photo Courtesy J. Kimber)

Some muscle cars have full steel channel frames, like this example from a 1969 Chevelle. This one is from a hardtop car. Convertibles got fully boxed frames for more torsional rigidity. Boxing plates can be welded into C-channel frames to gain that same rigidity. (Photo Courtesy J. Kimber)

 

 RideTech’s Tiger Cage shares a roughly similar format, with low side bars that don’t force the passengers to be contortionists. What sets their cage apart is how it’s all bolt-in and stainless steel. Its sticker price may seem a little high at first, but when you consider how much it costs to have a professional shop build something like this, and then include all of the labor in removing/replacing the interior for a welded-in cage, it’s pretty reasonable. Because it’s stainless steel, you don’t have to paint it; and that’s a good thing. It’s not NHRA legal (yet) but I see this as a cage for cars that would normally never get a cage because they’re true street cars. RideTech is pursuing certification for the Tiger Cage, which would be an epic accomplishment. (Photo Courtesy RideTech)

RideTech’s Tiger Cage shares a roughly similar format, with low side bars that don’t force the passengers to be contortionists. What sets their cage apart is how it’s all bolt-in and stainless steel. Its sticker price may seem a little high at first, but when you consider how much it costs to have a professional shop build something like this, and then include all of the labor in removing/replacing the interior for a welded-in cage, it’s pretty reasonable. Because it’s stainless steel, you don’t have to paint it; and that’s a good thing. It’s not NHRA legal (yet) but I see this as a cage for cars that would normally never get a cage because they’re true street cars. RideTech is pursuing certification for the Tiger Cage, which would be an epic accomplishment. (Photo Courtesy RideTech)

 

The cage SC&C built for this Monte SS is ideal for street use. The bars are tucked in close to the body, the back bars are bent to go around the windows (for a cleaner look), and the cross bar/harness bar is removable from its support cradles to keep the backseat 100-percent usable. Note also the low rocker bars for easier seat access. This cage is not NHRA legal, but this is not a drag car; it was built to be a high-performance street car and the cage was built accordingly.(Photo Courtesy Doug Lutes)

The cage SC&C built for this Monte SS is ideal for street use. The bars are tucked in close to the body, the back bars are bent to go around the windows (for a cleaner look), and the cross bar/harness bar is removable from its support cradles to keep the backseat 100-percent usable. Note also the low rocker bars for easier seat access. This cage is not NHRA legal, but this is not a drag car; it was built to be a high-performance street car and the cage was built accordingly.(Photo Courtesy Doug Lutes)

 

The rocker bars run from the frame, next to the cowl body mount, back to the main hoop. A vertical tube goes through the rocker to tie into the frame and form a rigid ladder structure, which eases daily driving.(Photo Courtesy Doug Lutes)

The rocker bars run from the frame, next to the cowl body mount, back to the main hoop. A vertical tube goes through the rocker to tie into the frame and form a rigid ladder structure, which eases daily driving.(Photo Courtesy Doug Lutes)

 

All of this can be done with very little intrusion into the cockpit. I am not a fan of headache bars on street cars. These include a front hoop or upper window bars that run next to your head. Why? Because you don’t wear a helmet on the street and banging your noggin hard on steel tubing is always bad; it can cause brain damage. If you do run a full cage, make absolutely certain that your melon cannot under any circumstances come into contact with those bars.

 

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Today there are several companies such as Chassisworks making cages that are CNC bent and tucked in nice and tight around the interior of the car. Ride-Tech has a new bolt-in cage system called the TigerCage that’s basically a simple bolt-in system. It’s also 100-percent stainless steel so you don’t have to find a painter who’s also a contortionist to paint the cage tubes. This package is not authorized by any racing organizations at this time but it’s a very clean way to add a lot of chassis strength and rigidity. It allows for easy interior access and, in spite of not being sanctioned for organized racing, should still provide a large measure of additional safety. Because it has no internal stresses from welding in place it should have better NVH characteristics than a welded cage.

A word about cages and competition: If you plan to compete in sanctioned racing events at a level that requires a cage, make sure anything you do meets their requirements. Consider that they may be at odds with what you want in a street car. Sanctioning requirements vary wildly, so don’t assume what is legal for one endeavor is legal for another. Years ago I built an open-course road race car to Silver State specs only to find out that it wouldn’t be legal for the same class at the Pony Express OCRR; it would have to run a slower class. Doh.

 

Written by Mark Savitske and Posted with Permission of CarTechBooks

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