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New Look at Fiberglass:  

 

Q&A
By the staff at Unlimited Products 
2025 Unlimited Fiberglass. All rights reserved.

This content is the intellectual property of Unlimited Products and may not be reproduced without written permission.

 

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What are fiberglass body parts for drag racing?

Fiberglass body parts are lightweight, high-strength components designed to replace heavier steel panels on drag race cars. Common parts include hoods, doors, fenders, and front ends. These components reduce overall vehicle weight, improving acceleration and track performance. Ideal for custom builds and performance upgrades, fiberglass parts are also easier to modify than metal. With nearly five decades of experience, we offer over 3,000 fiberglass parts trusted by racers across the country.
 

Benefits of fiberglass vs carbon fiber for drag racing.
 

Fiberglass offers an ideal balance of strength, durability, and affordability, making it the top choice for most drag racers. While carbon fiber is lighter and stiffer, it’s also far more expensive and less impact-resistant. Fiberglass is easier to repair and perfect for larger panels like hoods and doors. We provide fiberglass parts trusted by racers nationwide for performance and value.

 

How to install fiberglass body parts on a drag car

Installing fiberglass parts on a drag car starts with proper test-fitting. Trim as needed, then mark and drill mounting points carefully. Use lightweight fasteners like Dzus buttons or brackets for easy removal and access. Reinforce stress areas with backing plates to prevent cracking. Avoid overtightening to maintain panel integrity. With 49 years of experience and over 3,000 parts, we’re proud to support racers with quality components and expert installation guidance.

Installing fiberglass panels requires a few common tools and some race-specific hardware. You’ll need:

• Body saw or cutoff wheel – for trimming and shaping panels

• Drill and bits – to pre-drill mounting holes

• Rivet gun or Dzus fastener tool – for quick-release hardware

• Cleco pins – to hold panels temporarily during fitting

• Measuring tape and marker – for precise alignment

• Sanding block or grinder – to smooth edges and adjust fit
   

Optional: backing plates, panel adhesive, or epoxy for reinforcement.

How do you align fiberglass panels for a
proper fit?
Start by loosely mounting the panel with temporary fasteners like Clecos or clamps. Check the fit against neighboring panels, door gaps, and chassis lines. Make small adjustments by trimming edges with a sander or body saw. Use shims or adjustable brackets if needed. Always fit the full set of panels before final drilling to ensure proper alignment across the entire body. Take your time—precise alignment ensures a clean look and optimal performance.

What type of fasteners work best for fiberglass drag parts?
Dzus fasteners are the top choice for fiberglass drag racing parts—they’re lightweight, secure, and allow quick panel removal at the track. For permanent mounts, aluminum rivets or stainless bolts with backing washers work well. Always avoid overtightening, as fiberglass can crack under pressure. For larger panels like doors or front ends, use a mix of hinge mounts and quick-release latches. Proper fasteners ensure both safety and ease of maintenance between rounds.

Do fiberglass parts require special trimming or cutting?
Yes—fiberglass parts often require trimming for a perfect fit. Most panels are made slightly oversized to allow custom alignment to each vehicle. Use a body saw, cutoff wheel, or sanding disc to trim edges carefully. Always wear protective gear, as fiberglass dust can irritate skin and lungs. Mark your cuts precisely and test-fit often. With proper trimming, fiberglass parts will align cleanly and perform reliably under the stress of drag racing.

Can fiberglass panels be painted like metal?

Yes, fiberglass panels can be painted just like metal—but they require proper prep. Begin by sanding the surface to remove any mold release or gloss, then apply a fiberglass-compatible primer. Use flexible automotive paint systems to allow for panel flex without cracking. A quality topcoat and clear finish will provide a durable, professional look. With the right prep and products, fiberglass panels can match or even outshine factory metal finishes.

 

How do you reinforce fiberglass to prevent stress cracks?

To prevent stress cracks, reinforce mounting points and high-stress areas with aluminum or steel backing plates. Use body washers under bolts and Dzus fasteners to spread the load. In areas prone to flexing, consider adding extra layers of fiberglass mat or cloth on the backside. Avoid overtightening hardware, and always support large panels with brackets or substructures. Proper reinforcement ensures long-term durability, especially under the rigors of high-speed drag racing.

Can I use my original glass windows and roll up window mechanism in fiberglass or carbon doors?

Not a good idea. Our doors have an upper flange to mount lexan windows.. This upper flange would have to be cut out. The steel mechanism needs to mounted to the inner panel, ok, but the entire structure adds too much weight and the door will sag at the hinge. Extra reinforcement from the hinges area back to the latch would be required. It can work, but needs re-engineering..

Should I mount fiberglass parts directly to the chassis or use a substructure?

For most drag cars, it’s best to use a lightweight substructure or mounting framework instead of attaching fiberglass panels directly to the chassis. A substructure allows better alignment, flex control, and easier panel removal. Direct mounting can lead to stress cracks from chassis flex and vibration. Using aluminum tubing, brackets, or composite supports helps distribute load evenly and protects the panel from damage—especially important for one-piece front ends and large panels.

What’s the best way to install a one-piece front end?
The best way to install a one-piece front end is with a tilt or lift-off system. Use lightweight tubing to build a hinge or support frame at the firewall. Secure the nose with Dzus fasteners or quick-release pins at the rocker panels and radiator support. Always reinforce mounting points and allow clearance for engine access. A properly installed one-piece front end saves weight, simplifies maintenance, and adds a clean, professional look.

How do you install Dzus fasteners correctly?
To install Dzus fasteners, first align your fiberglass panel and mark the mounting points. Drill matching holes through the panel and support tab. Install the spring clip on the backside tab using rivets or screws. Then, insert the Dzus button through the panel and twist to lock. Ensure the spring is properly tensioned—tight enough to hold the panel firmly but easy to release. Dzus fasteners offer a clean, race-ready look with quick removal.

Do fiberglass parts need special care after installation?
Yes—fiberglass parts require some care to stay race-ready. Inspect fasteners regularly and avoid overtightening, which can cause cracks. Wash with mild soap and water; avoid harsh chemicals that can damage gelcoat or paint. Store the vehicle indoors or use a cover to protect against UV exposure, which can fade finishes over time. With proper care, fiberglass body panels will stay lightweight, strong, and great-looking through many race seasons.

What’s the difference in mounting fiberglass vs. carbon fiber panels?
Mounting fiberglass and carbon fiber panels is similar, but carbon fiber requires more care. Fiberglass is more forgiving and can flex slightly, making it easier to trim and fit. Carbon fiber is stiffer and more brittle—drill slowly to avoid cracking, and use larger washers to distribute pressure. Both materials benefit from Dzus fasteners or brackets, but carbon fiber panels should be handled gently and mounted with precision to avoid delamination or damage.

Is bonding or bolting better for certain panels?

Both methods have their place. Bolting (or using Dzus fasteners) is best for panels that need to be removed frequently, like hoods, doors, and front ends. Bonding with adhesives is ideal for smaller, non-removable parts or where a seamless look is desired. Bonded panels offer cleaner aesthetics and fewer stress points but are harder to remove. Many race cars use a combination—bolting for access, bonding for strength and stability.

How do you maintain alignment under high-speed racing stress?

To keep fiberglass panels aligned at high speeds, use reinforced mounting points with backing plates and secure fasteners like Dzus buttons or locking bolts. Add support brackets to prevent flexing or shifting under wind pressure. Ensure all mounting holes are snug, not oversized, and check alignment regularly. Proper panel gaps and symmetrical fitting reduce drag and prevent flutter. Consistent inspection between runs helps catch early signs of stress or loosening.

What safety considerations should I follow when installing lightweight body panels?

Safety starts with secure mounting—use locking fasteners or Dzus buttons to prevent panels from detaching at high speed. Reinforce all critical areas to avoid cracking or failure under load. Ensure no panels interfere with steering, brakes, or fuel lines. Always wear protective gear (gloves, mask, goggles) when cutting or sanding fiberglass. After installation, perform a full systems check to confirm that visibility, access, and mechanical safety are not compromised.

Can fiberglass panels improve my ET (elapsed time) at the track?

Yes—fiberglass panels can significantly reduce your car’s weight, which improves acceleration and overall ET. Lighter body parts like hoods, doors, and front ends reduce strain on the drivetrain and allow the engine to work more efficiently. Every 100 pounds saved can equal up to a tenth of a second in ET. For racers aiming to go quicker without engine mods, switching to fiberglass is one of the most cost-effective upgrades.

More Reasons Fiberglass Improves ET

1. Reduces Overall Vehicle Weight
   Less weight equals quicker acceleration and shorter 60-foot times—crucial in drag racing.

2. Better Weight Transfer
   Lightweight panels help shift weight to the rear tires during launch, improving traction and reducing wheel hop.

3. Less Rolling Resistance
   A lighter car puts less load on the tires and suspension, allowing for faster movement off the line.

4. Increases Power-to-Weight Ratio
   Fiberglass doesn’t add power, but by dropping weight, it effectively boosts your power-to-weight ratio—translating to faster ETs.

5. Improves Braking & Handling
   Quicker deceleration and improved balance allow for more aggressive shutdown and better control at high speeds.

6. Simplifies Access & Maintenance
   Lightweight parts like lift-off front ends or hoods make between-round maintenance faster, giving teams more time to fine-tune performance.

7. Custom Fit for Aerodynamics
   Fiberglass can be molded for sleeker shapes, improving airflow and reducing drag, especially at higher speeds.

More info on Fiberglass Doors:

In most cases, you cannot directly use your original glass windows and roll-up window mechanisms in aftermarket fiberglass or carbon fiber doors, especially those designed for racing or weight reduction. There are significant compatibility and structural issues to consider.

Key Points:

• Racing-Style Fiberglass/Carbon Doors:
  Most aftermarket fiberglass and carbon fiber doors, particularly those intended for racing, are not compatible with factory roll-up window mechanisms. Manufacturers like Unlimited Products, explicitly state their doors are "not compatible with factory roll-up window mechanisms" and require the use of fixed polycarbonate (Lexan) windows instead. The windows do not roll up and down in these applications6.

• Why the Incompatibility?

  • These lightweight doors often lack the internal structure and mounting points needed to support the weight and operation of glass windows and the associated regulator hardware.

  • The doors are designed for minimal weight, so they omit reinforcement and mounting provisions for window mechanisms6.

• Possible Workarounds:

  • Some custom or high-end fiberglass/carbon doors (especially for street cars) may be built to accept factory hardware, but this is rare and usually requires special ordering or significant modification.

  • Enthusiasts sometimes use formed Lexan windows and attempt to adapt factory seals and guides, but this typically results in fixed or slider-style windows, not full roll-up operation38.

  • In some cases, you can try to custom-fit Lexan into the original window frames and use stops to hold them in place, but this is not the same as having fully functional roll-up glass windows8.

• Street vs. Race Applications:

  • For street use, retaining roll-up glass windows is possible only if the aftermarket door is specifically designed for it, which is uncommon.

  • For racing, fixed polycarbonate windows are the norm for safety, weight, and simplicity.

Conclusion:
Unless your fiberglass or carbon fiber doors are specifically engineered to accommodate factory glass and window regulators, you will not be able to reuse your original glass windows and roll-up mechanisms. Most aftermarket lightweight doors require fixed polycarbonate windows and do not support roll-up functionality638. Always verify with the door manufacturer before purchasing if you need to retain full window operation.