Charlie Boy's 70 Chevelle 25.2 stock front car
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The Montana Bros. P/M Monte Carlo
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North East Pro Shootout
One of the more popular chassis upgrades over the last few years is the Pro-Mod style 25.2 "back-half chassis". Addressing the growth of classes like Outlaw 10.5, "Quick 8" type racing, and NMCA/PRO class racing, the Montana Brothers have brought their wealth of Pro-Mod chassis expertise to the  world of "fast street car" drag racing.
"Charlie Boy" Micaliff - 1970 Chevelle - 25.2 chassis/stock front suspension car
Getting squared on the chassis jig
All of our chassis are constructed on a purpose-built chassis table
Step 1: Once the customer's chassis needs are finalized, the car is mounted on a chassis table. With the floor removed, the bare shell is temporarily supported by jackstands until the desired ride height is achieved. With the constraints of a stock front subframe, ground clearance and a level ride height become key concerns.
Step 2: With the ride height now adjusted for chassis and drivetrain clearance, the chassis is leveled and squared on the table. Steel posts are welded between the body of the car and the table to eliminate any movement of the car during the construction of the chassis.
Step 3: Having set the chassis centerline and ride height, chassis construction can begin. Knowing that this car is being built to SFI 25.2 certification, the chassis is built with close adherence to SFI spec. As no two cars are the same, templates are of limited value in this process. Case in point is that this customer uses an iron block motor, which will necessitate a specific motor location to optimize the center of gravity of the car. An aluminum block engine would be mounted differently, owing to the fact that it is 100lbs lighter, and that the car's chassis dynamics will react accordingly. This is where years of experience in chassis construction and tuning come into play.
Step 4: With the floor bars in place, the rest of the chassis is constructed using a tiered approach. Once the 4 link bracket location is determined we can build from there. We use 1/4" chromemoly steel plates custom built to our specs for our severe duty four link brackets. FYI, most pro mod cars use off  the shelf 3/16" moly brackets. With 2,000hp trying to move a car that may weigh as much as 3,500lbs every part of the chassis is under extreme stress. These cars can and will break "unbreakable" parts even without tire shake; so every part is designed specifically for the application. One level up from the floor, the upper 4 link brace bar is attached to the chassis floor. You can see our rear end housing trial fitted in the car to properly align the 4 link brackets.
Step 5: Now that the 4 link bars are in place, the rest of the rear chassis can be completed. Unlike previous designs, all MBRC Pro Chassis use triangulated straight bars rather than "U" / Horseshoe bars or "X" bars. The end result is a stronger, lighter chassis that is stiffer than any other design. You can see the double framerails tying to the upper 4 link bar and driveshaft loop as an integral part of the chassis in the pictures above.
Step 6: With the majority of the bars in place, we chose to jump ahead to doing some preliminary tin work on the floor and finalize our pedal placement. A double framerail car will occupy a majority of the center of the car and will necessitate a very wide driveline tunnel. As such, both the brake pedal and gas pedal were relocated 4" to the outside of the car. A trial fit by the car's owner verified the locations. A driver that is an uncomfortable seating position is at a disadvantage before they even arrive at the track. This is one of the key differences between a kit car and a professionally constructed car that is built to your specs.
Passenger side forward roof bars
Step 7: Now that all the bars are in place we go back and final weld all joints and add braces to critical welds (upper left picture  is the front of the cage as it meets the windshield/roof bars). Lifting the body off of the table 6"-8" allows for full welding penetration around the chassis where it cannot be seen (against the headliner). The next steps will be to final weld the body to the chassis, mount the rear end/wheels and tires and get the car back rolling on the shop floor.
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