Project Grandma: Safe and Stiff – Building Grandma’s 25.5 Chassis Engineering Roll Cage

Old Grandma just ‘aint what she used to be, and what she used to be wasn’t much. So when we set out the plan to put a monster 555ci big block under the hood of our 1978 Malibu with big 295/65 Mickey Thompson Drag Radials, we knew that a roll cage and mini tubs were in order.

We turned to Chassis Engineering.

They stepped up with their chromoly cage and mini tub kit. We found a well-known local fabricator, Mike Ryan, to do the work. The following article is our story documenting the Chassis Engineering roll cage, mini tubs, and safety equipment for our Project.

While a 10-point cage is the perfect fit for a hot street car you might have seen at the local track, we expect to see Grandma running in the mid-eight second range on the quarter mile. Those times are enough to call for a full 25.5-spec roll cage. Additionally, NHRA rules call for any car running faster than 150 mph in the quarter mile to have a parachute. We got some help from Simpson with that.

You can follow along with our entire build below, or you can watch our installation video. Your call!

Mr. Mike Ryan

While we have some skill in welding roll cages and building cars, we felt that it would be smart to recruit an experienced drag racing fabricator for the build. After asking around, we found Mike Ryan of Ryan Fabrication. Mike has built and worked on almost every type of race car during his years as a fabricator – everything from door cars to 10.5 cars to dirt track sprint cars.

And the best part? He signed up to help not only build the roll cage and install a few other chassis components, but also to see the build all the way through to the car hitting the track.

Chassis Engineering provided us with their 10-point pre-bent roll cage, mini tub kit, and parachute mount kit. They literally make anything you need for building a 12-second bracket car or a 6-second Pro Stock car, and everything between. They also offer numerous options for many of the kits and components, ensuring that they’ll have what you need for the car that you’re building.

Chassis Engineering’s Curt Perry helped us choose the correct parts for our build and explained all of the different options we had.

Mini Tubs

We started out with the Chassis Engineering Mini Tub kit, so we wouldn’t have to work around all of the bars or worry about clearance if we installed the roll cage first. Our kit came complete with everything but a welder and the cut off wheel needed to install it.

We began by removing some of the stock sheet metal. Mike cut out the sheet metal between the rear trunk hangers and the wheel tubs. He used a combination of a cut off wheel, sawzall, and the ever popular Cornwell Tool’s Plasma Cutter to remove the 30-year-old metal. First up was the plasma cutter: Mike used the high amp cutter to rough-cut the fender wells out before picking up the cut off wheel for the precise finial cuts.

Gotta Love that plasma cutter!

Next, we removed the floor behind the area where the stock rear seat had been mounted. This would make it easier to install the mini tubs and run the necessary bars for our 25.5 cage. Mike found an easy to mark surface, approximately eight inches up from the floorboard, and a perfect cut-ready marked seam just below the rear speaker deck to make his incisions.

Cutting this section of sheet metal out of the way opened up the top of the frame rails so we could notch them without interference. There is a seam in the sheet metal slightly higher than the area where we ended up cutting the floor, but cutting along that seam would not have given us the full working area that we needed in order to cut the frame rails and add some support bars later.

Once the floor was removed, the reliable sawzall was used to remove the stock upper spring perch that’s attached to the frame rails and the rear cradle where the upper control arms mount. We will be using a set of QA1 double adjustable coilover shocks and are going to fabricate the mounts for them, so this part was no longer needed on the car.

The spring perches were the last component standing in our way before notching the frame rails to make room for our 295/65/15 Mickey Thompson Drag Radials. We marked where the center of the axle tube would run under the frame rail. Then we measured out from there to mark where we would need to make our initial cuts to create enough room for the tires.

It was back to the sawzall again as Mike cut and removed the face of the frame rail, in hopes of reusing it to create a finished OEM looking frame rail after the notching was complete.

From there, Mike removed more of the center of the frame rail and welded the ‘cap’ he had cut out initially. However, once we performed a test fit of the tire in the frame rail, we found that we had not removed enough metal. The tire was rubbing on the inside of the fender well as well as the frame rail.

There wasn’t much clearance for the tire.

After we cut the cap off that we had just welded on, we removed more metal to make room for the tires. Unfortunately, once we had removed enough metal, there wasn’t much left to support the rear of the car. In order to fix this issue, Mike bent a piece of tubing, cut it in half, and welded it to the inside of the frame rails where we had removed most of the support.

Welded in completely. Notice how the bar goes through the upper control arm cradle and is welded there for strength.

Much better fitment now.

Finally, to add even more strength to the area, we decided to box the ends where we had made our initial cuts. This would give us the support we needed and provide a cleaner look. Mike traced the necessary shape onto a flat sheet of metal before cutting it out and welding it in.

Here is the completed cap with melted body bushing. Nothing smells better.

We decided to be a little more creative in the front. Mike traced out another shape on some sheet metal and bent it using a beefy sheet metal brake to create a piece that he welded onto the frame. This gives us a clean look and the triangulated gusset shape gives us much needed support.

This is a crucial point that cannot be stressed enough: If you plan to do this yourself, you can’t just remove metal and not add support back in, unless you’re making a lowrider that drags the bumper on the ground. We are after mid-to-high 8-second passes on the quarter mile, and the thought of doing so in a shower of sparks is not appealing.

Chassis Engineering offers four different kinds of wheel tubs that will work with virtually any size tire. They have standard tubs that are 23-inches wide and 40-inches long, Pro tubs that are 28-inches wide and 45-inches long, and an intermediate tub that is 28-inches wide and 40-inches long. The smallest Sportsman wheel tubs are available either in .040-inch aluminum or .024-inch steel.

Since we were doing a mini tub and not a full back half, we chose the smallest steel tub that Chassis manufactures. We also knew that the tub’s width would need to be trimmed down as we didn’t want to use our entire trunk, and the stock narrowed frame rails would limit us. Our wheel wells were shipped unassembled, and like all Chassis Engineering wheel tubs, incorporate a “Pittsburgh” seam that allows for easy assembly.

Mike used an angle grinder to clean up the cut lines created when he removed the stock wheel. That left a nice surface for him to take measurements from, in order to determine how much he would have to cut the tubs. Because metal is expensive and difficult to test fit in the car, Mike built a cardboard mock up of the mini tubs to get the perfect fit before transferring the design to the finial metal components.

Although it is difficult to see their logo, Chassis Engineering also supplied the cardboard for the mock.

To make building the tubs a little easier, Mike brought a tub-jig down from his shop that he’d made out of wood. He had to modify it slightly to make it work for this job because of the tire size that we chose for our project. This jig made it easy to crimp the ‘Pittsburgh’ seam of the tub to hold the two pieces of metal together. While we can’t give you a price on what it would cost to make one of these yourself, we can tell you that Mike recommends using something similar – it makes the job much easier.

Although Chassis Engineering doesn’t require it, Mike went ahead and riveted the end of the kit together before crimping down the edge. That way, there is no way for the two parts to slip or slide apart, which would change how it fits into the car during test fitting or installation. After that, he used a hammer and pounded down the Pittsburgh seam to secure the tub together.

As mentioned previously, the Chassis Engineering wheel tubs are capable of fitting up to a 32-inch tall tire that is at least 14-15 inches wide. Obviously we won’t need that much room with our tire size, so he simply cut down the blank tub to the size needed to fit into the car. Not wanting to have to go back and add metal in later, he cut them out a little big and trimmed them to a perfect fit before, repeating the same process for the passenger side tub.

Mike used the TIG welder to finish off the mini tub install. While you would ordinarily weld the tub into the inner fender as well, our car will be retaining her ’70s appliance-white paint job, so we didn’t want to risk bubbling its unique surface. We’ll just fill in the gap with some seam sealer later when we weld the rest of the floor back in.

To supplement not having the support of being attached to the body, Mike added a few little gussets in the middle of the tub to keep it from deflecting. They’re pretty sweet. This will give them more than enough support.

It is important to seal up as much as possible. That keeps smoke from the burnouts from getting inside the car.

That wraps up the mini tub install. The Chassis Engineering kit provided us with high quality components that made adding mini tubs to Grandma as easy as pie. The kit also saved us the long grueling task of having to fabricate them from scratch, which would have taken at least twice as long.

25.5 Spec Roll Cage

With the mini tubs installed, work could now begin on the roll cage. We wanted to overbuild our cage, so we went with a 25.5 spec cage that will allow our car to run 7.50s in the quarter mile.

A 25.5 spec cage might look like a monster to build, and one look at the SFI drawings of what the cage looks like is enough to scare off even the seasoned cage builder. We decided to divide the build into three parts: frame support & general prep, 10-point cage foundation, and converting to 25.5 spec.

Building a roll cage is not for the amateur welder. The strength of the welds during this part of the build could be the difference between the driver walking away from a nasty crash and taking a ride to the ER. If you don’t know what you are doing, find someone like Mike Ryan who does. Besides, if the welds and overall design look like garbage, the guys at the tech shed won’t pass the car anyway. Have it done the right way.

Frame Support

Many of the small details that we are building into the car are required either by rule regulations or for SFI certification. This next part falls under those categories.

Mike Ryan used some flat metal to box the frame rails the entire length of the car. The G-Body was built with a parameter frame with open C-channels running down the sides. This is a fine frame for driving the kids to school and going to Tuesday night bingo, but we needed our frame to be able to take the force of our 555 ci Edelbrock big block out on the strip. The plan was set to box the frame. First we needed to lift the body off of the frame to gain access to the inner frame rails to do some welding.

Using our Cornwell plasma cutter, Mike cut out two long strips of metal the same size as the frame rails and clamped them onto the frame. From there, he laid down a nice bead of metal to secure the new metal to the frame rails.

Next, Mike needed to remove the spare tire well to make room for a rear cross bar that will be the support for not only the rear portion of the cage, but also the parachute. Using a sawzall, we cut the spare tire well out and welded in a flat piece of metal to cover the hole.

Finally, Mike could begin work on the roll cage. We chose to construct our cage from an assortment of Chrome Molly tubing, with the sizing of the tube varying depending on which part of the cage it made up. SFI has outlined what size tubing needs to be used where in their 25.5 SFI handbook. This handbook can be purchased directly from the SFI Foundation for around $35. It’s well worth the small investment to make sure that you build the cage correctly.

We chose Chrome Molly tubing over Mild Steel for a few reasons. It’s stronger than Mild Steel, an important quality in a system designed to protect a driver. We also chose it for its weight. Chrome Molly weighs almost half as much as Mild Steel, and with the amount of bars going into our car, the weight savings is well over 300 lbs.

Starting under the car, the first bar that Mike installed was a cross bar just in front of the rear suspension cradle. This would help support the other assembly of bars that he added later. Mike attached this bar to two plates on either side of the inner frame rail that he had welded in for support. One important note: Mike used his TIG welding skills for the entire roll cage, as SFI specifies that all Chrome Molly cages must be TIG welded for strength. From there, the same plate treatment was given to two bars that run parallel to the frame rails, starting just behind where the engine will mount, and attaching to the cross bar seen in the photos below. To comply with SFI specs we used 1 5/8 inch tubing for everything under the car.

Inner frame rail bars.

Next, we wanted to add some strength to our rear suspension. Mike added two more bars that would link the rear suspension cradle to the cross bar mentioned above. By doing so, he created a nice triangulated support system that directs the force applied on the frame evenly throughout, and not just at one or two points.

Remember, lower control arms push while upper control arms pull. Mike is designing this chassis so that the lower control arm force is directed squarely into the frame of the vehicle, and not into the flex in the stock attachment points.

Before moving topside, Mike added another cross bar under the trunk area in the back of our Malibu. This bar not only adds some support to the rear of the car between the frame rails, but also will serve as the down point for the rear bars to come down from the main hoop. Of course, we’ll also use this to mount our fuel cells, battery mounts, parachute, etc..

10-Point Cage Install

Next, Mike unpacked the Chassis Engineering 10-Point Roll Cage. This kit consists of all the bars needed to construct a 10-point cage, including the pre-bent main hoop and halo bar. As with the mini tubs, this saves us the hassle of having to bend our own hoop and halo bar, saving us a lot of time and getting us out on the track more quickly.

Mike started things off by cutting four holes in the floor of Project Grandma. These are the points where the front down bars and the main hoop will pass through the floor. Mike cut these holes not only large enough for the tubing to fit through, but wide enough so that when the bar was being installed he would be able to have enough room to stick his welding rod in there as well, for that perfect weld.

The old saying measure twice and cut once can’t be said enough. With that in mind, Mike broke out the Cornwell tape measure and jotted down all of the measurements he needed before cutting into the metal included in the kit.

Once he was happy with the fitment of the main hoop in the car, Mike decided to get ahead of the game a little. You see, he finds it easier to attach some of the necessary bars needed for the funny car cage portion of the 25.5 spec cage to the main hoop prior to welding it into the car. This way, he has plenty of room to lay down a nice TIG welded bead on the cage without interference from anything else.

Using 1½ inch tubing, Mike constructed the inner rear helmet bar and part of the inner shoulder bar outlined in the 25.5 spec handbook.

Before welding in the main hoop, Mike fabricated some really slick looking pieces that cover the hole needed to weld the hoop in. Using a hole saw, he cut out a hole for the tubing to fit through and crafted the originally flat piece of metal to fit the contours of the floor. Nice work Mike!

With the main hoop in, the next pieces to be installed were the two rear down bars that run from the top of the main hoop down to the rear trunk cross bar that Mike welded under the trunk.

He started by cutting two slots in the rear deck to give the bars plenty of clearance to run into the trunk area. Next, he cut two holes in the trunk directly above the rear cross bar for the rear kicker bars to link to. From there, he grabbed some more tubing from the Chassis Engineering box and measured, bent, and cut them to the shape of his liking before welding the two bars in.

Again, we tried to seal everything up as best as we could.

Here is another angle of the rear of the car, the Chassis Engineering mini-tubs, main hoop, and rear down bars. As mentioned previously, you can see the main hoop and the start of the funny car cage installed in the car on the right. Notice how the cross bar is mounted lower than you would normally see in a 10-point cage.

From there, Mike moved to the halo bar. This was another easy install, as the only thing that Mike had to do to fit the Chassis Engineering piece in place was cut it down to size and notch the bar so it fit flush against the main hoop and weld it in.

However, before he could finish welding it in place, he needed to add the windshield bars to determine the halo bar’s final resting place. Using the pre-bent bars included in the Chassis Engineering kit, all Mike had to do was measure the length and cut the bar down to size before notching it to fit flush with the halo bar and welding it in.

Finally, we added two more gusset bars running from the cross bar on the main hoop down to the front side of the rear suspension cradle. These bars will help support the pulling force that will be created by the upper control arms. We ran these bars directly behind where they mount.

Converting To 25.5 Spec

After he finished the 10-point foundation, Mike took on the task of adding the Chrome Molly tubing that makes up the funny car cage, and the other bars necessary to pass tech for 25.5 spec. These bars are custom fitted to the driver and the seat that will be mounted into the car. Each bar in this section is hand bent and fish-mouthed to fit precisely to the cage. Mike had to approach this task with patience. Trying to take too much metal off of a bar or overbending a bar would mean starting all over.

The first bar that Mike bent (using 1½ inch tubing) was the forward funny car cage bar – otherwise know as the outer bar. Following the guidelines in the 25.5 spec handbook, he came up with a design that would work best for our application. From there, he used the same size tubing to fabricate the inner shoulder bar. Next, he grabbed a stick of ¾ inch tubing for the helmet guard bars and bent it in the same fashion as the inner shoulder bar. These bars prevent the driver’s head from moving outside of the funny car cage in the event of a crash. When he was happy with the fitment, Mike TIG welded everything in place.

Next, we had to install the door bars. To make it easy to get in and out of the car, we went with the x-bar design. Mike tied in the bars that complete the funny car cage, as well as the main hoop. Just remember, the more places your roll cage bars meet, the more ways the force will be spread out on impact.

Now in the homestretch, Mike got to work adding in the dash bar. This is the bar that runs between the two down bars running from the halo bar to the frame rails.

Then it was on to the front of the car, where Mike was working on the front cage extensions that would run to the front of the G-Body’s front frame rails. These bars tie in to the rest of the cage right next to the dash bar behind the firewall. This would strengthen the front of the car substantially.

That wraps up the 25.5 spec cage conversion on Project Grandma. Now the old gal has a little more strength in her back – and everywhere else for that matter. As we continue to build out our G-Body Malibu, we are still thinking of adding in a few more bars in places we feel necessary – such as X-bars underneath the floor to prevent a car from slamming through the floor, should Grandma end up on her side going down the track.

Parachute Mount & Handle

We already plan on stopping Grandma using a set of Aerospace Components Brakes on both the front and the rear. While those brakes will provide us with tons of stopping power, NHRA rules require that all cars running faster than 150 mph in the quarter mile also use a parachute.

While our Malibu came well equipped for 1978, a parachute mount was not on the option list. Once again, we turned to Chassis Engineering. They provided one of their Parachute Mount Kits that came with both the parachute mount and all the tubing needed to mount it in the car.

Mike started out by cutting a 1 5/8-inch hole in our ‘pristine’ bumper. Then Mike notched one of the bars so that it would fit flush on the rear cross bar under the trunk.

Drilling the hole in the bumper.

Additional bars were then added to the provide more support. These bars were also included in the Chassis Engineering kit. Mike added a bar on the outside that supports the parachute itself, and added the latch securing the parachute onto the car just below, on the first bar that was installed.

Check out the photos below:

Nice and strong.

In order to open our parachute, we used Chassis Engineering’s Parachute Release Cable kit. The kit includes everything needed to open the parachute, including a high quality 18 foot Teflon lined cable and all of the necessary hardware (including the handle) needed to operate the system.

Mike started off by mounting the handle inside of the car. When mounting the handle, you should pick a spot that is comfortable and can be easily accessed by the driver. We chose to mount the handle just off to the right of the driver’s seat. Depending on how you mount the handle, the system can be operated using a pushing or a pulling motion. We liked the pushing style more, so that’s the way we mounted it.

With all of the safety equipment now on Grandma, she is more than able to provide the proper protection should the unthinkable happen. The 25.5 spec cage certifies our car to run 7.50’s in the quarter mile and the parachute on the back lets us do it going faster than 150 mph.

With the chassis now squared away thanks to Chassis Engineering, we are ready to move forward and are one step closer to completing Project Grandma. Now that we can fit our 295/65 Mickey Thompson Drag Radials under the fenders in the rear, the next step will be getting the Currie rear end and Pat Musi / Edelbrock engine in, along with the TCI transmission.

To see pictures of the entire installation from start to finish click here.

Hardcore Chevys in your Inbox.

Build your own custom newsletter with the content you love from Chevy Hardcore, directly to your inbox, absolutely FREE!

Free WordPress Themes

We will safeguard your e-mail and only send content you request.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine


We'll send you the most interesting Chevy Hardcore articles, news, car features, and videos every week.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine


We will safeguard your e-mail and only send content you request.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine


Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

Hot Rods & Muscle Cars
Drag Racing
Engine Tech

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • streetmusclemag Hot Rods & Muscle Cars
  • dragzine Drag Racing
  • enginelabs Engine Tech

Chevy Hardcore - The #1 Performance Bowtie Online Magazine


Thank you for your subscription.

Thank you for your subscription.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

Thank you for your subscription.

Thank you for your subscription.