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MK4 Roadster - Design

Better than it ever was

There can be no greater testimony to a legacy than to continue it. The Factory Five Racing Mk4 Roadster is designed to accurately reproduce the looks of the legendary cars of the 60’s, keeping its essence intact, while using modern technology, parts, and materials to improve performance, reliability, and comfort.

The combination of vintage design and style with modern technology and engineering results in a vehicle kit that delivers period correct styling without compromising daily driver dependability, comfort, and performance. Technology delivers better quality AND more affordability.

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    Frame / Chassis


    A Great Car Starts with a Great Chassis.

    A chassis is the foundation of the house. Today’s fourth-generation Mk4 Roadster frame has benefited from years of refinement and development. It is both lightweight (376 lbs.) and strong.

    We use high-quality, precision-cut plate steel with 1010 and 1020 DOM tubing. The Mk4 frame stands head and shoulders above the original 1965 legend thanks to better tools, better materials, and modern technology. Our welded parts are made in the USA with American labor.


    • The Mk4 chassis features a beautiful round tube front X-member, which helps make for an authentic and strong chassis.
    • Plate steel is laser-cut from high-quality A-36 steel stock.
    • The 4” round tube main rails are made from higher quality steel and are thicker than the original frames: 0.120” wall DOM (drawn over mandrel) tubing, up from .095” in the original 1960s frames.
    • Engine, transmission, and suspension mounts are ready to accept bolt-on components.
    • Hood, doors and trunk are all hinged to the structural frame, not the fiberglass body.  Many fiberglass bucket replicas have a flimsy dash hoop bolted to the floor.
    • The dash/cowl hoop is 0.10” thick wall steel, welded to the frame as part of the cockpit surround cage.
    • The driver-side roll bar is higher and stronger than the original, with passenger-side mounts on every frame so you can add a passenger roll bar anytime.
    • Front and rear energy absorbing crumple zones help protect driver and passenger.
    • Welded steel side impact bars, door steel, footbox, and cockpit dash hoop surrounds help make the Mk4 frame far safer than original cars.
    • The cockpit and footbox areas feature a steel cage surround structure taken directly from our NASA racing series.
    • Triangulation bracing has been added to the front suspension, vertical supports, dash, rear sub-frame, and trunk.
    • We added a backbone section to the original ladder design and extra perimeter tubing that more than doubles torsional rigidity of the Mk4 frame over the original.

    Since 1995, the Factory Five Roadster frame has become known for its strength and ability to protect its occupants. With over 800 welds and hundreds of individual pieces of steel, the Mk4 frame is both engineering excellence and functional automotive art. The frame is a completely welded assembly and requires no welding or cutting.

    When you see Factory Five cars winning national races or lifting the tires clear off the ground, check out the “straight-as-an-arrow” frame quietly doing its job. There is no finer replica frame. Period.

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    Chassis Assembly


    Authentic Design, Race-Proven Engineering

    You want to compare kits? Start with the frame. The artistry, strength, and complexity of the Factory Five Mk4 frame is reason enough to stop looking right here. The beauty of our design is accentuated by the fact that it is stronger and more rigid than you’ll realistically need.

    We use an authentic 4” round tube design. We feel strongly that a quality replica should have a period correct, 4” round tube frame, just like the original legend. The tubular ladder-style frames used in the original 1960s AC cars are more than beautiful, they are representative of a period of automotive design that is legendary. We chose to use this style of frame despite the manufacturing difficulty and cost, since a huge part of a quality replica is its faithfulness to the spirit of the
    original cars.

    While originality is very important, if the frame doesn’t perform, what good is it? We kept the design style, but used CAD technology, better materials, and more consistent manufacturing methods to make it more than twice as strong.

    Since 1995, the Factory Five Roadster frame has become known for its strength and ability to protect its occupants. With over 800 welds and hundreds of individual pieces of steel, the Mk4 frame is both engineering excellence and functional automotive art. The frame is a completely welded assembly and requires no welding or cutting.

    When you see Factory Five cars winning national races or lifting the tires clear off the ground, check out the “straight-as-an-arrow” frame quietly doing its job.  There is no finer replica frame. Period.

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    The Sub-Frame


    “This Ain’t No Kit Car.” – Mustang & Fords Magazine

    A traditional kit car may use a fiberglass tub and body bolted to a cheap platform frame, but you won’t find modern streetcars or racecars built that way. Even vintage 1960s cars like the original ACs, Ferraris and GT-40s used proven racecar construction methods of tubular frames and riveted/bonded aluminum panels.

    The aluminum chassis panels found in our Mk4 combines this traditional quality with the latest CAD/CAM technologies and superior construction methods. The entire cockpit, trunk and engine bay of the Factory Five Mk4 is precision laser-cut 6061-T6 aluminum, without any fiberglass structural items. Underneath these aluminum panels, a matrix of steel tubing provides support surfaces for a close, tight-fitting installation.

    Why 6061-T6 aluminum? Conventional 4000-series aluminum is easier to bend and form, but not as strong in tension. We invested in learning how to correctly form the 6061-T6 to get the benefit of increased strength for the same weight.

    The strong foundation of our world-class frame combined with our aluminum chassis panels bonded and riveted to it represents just one of the major design and functional differences between the Mk4 and almost every other replica sold today.

    The strong foundation of our world-class frame combined with our aluminum chassis panels bonded and riveted to perimeter frame tubing represents just one of the major design and functional differences between the Mk4 and almost every other replica sold today.

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    Composite Body


    Period Correct Shape, Made Right Period.

    The body shape of the Factory Five Mk4 is extremely accurate benefitting from, and a direct descendant of, two original cars, CSX 3042 and the late Dick Smith’s famous #198, CSX 3035.

    The composite body is a one-piece, hand-laid vinylester part that is engineered to complement the strong steel and aluminum chassis, which provides structural support. The hood, doors and trunk have molded liners and come complete with hinges and pre-drilled mounting holes. The body shell is laminated to a thickness of 3/16” all around, with a .015” red gel coat outer finish.

    The composite body is shipped pre-assembled to the frame. The parts are unfinished (requiring bodywork).
    Panels are CNC router trimmed.

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    Body Assembly


    The Best Composite Body and Panels in the Industry

    Let’s talk about fiberglass and what we’ve learned in more than ten years making composite parts. Since 1995, we’ve built and shipped more than 8,000 body shells, over 30,000 body panels, and designed and built over 150 complex molds and tools.

    The way we use fiberglass in making replica bodies is completely different than most kit car companies, and not at all like the classic kit car of fiberglass plopped on top of a flat ladder frame.

    The average weight of a fiberglass replica body (just about every single kit out there) can exceed 700 lbs.! The reason for all this weight is the fiberglass is commonly used as a major part of the structure and interior.

    By using fiberglass for the exterior body shell and panels only, we removed the stress and significantly reduced the weight while maintaining rigidity with the underlying matrix of ¾” steel tubing and aluminum panels (the right material for the job). The result is a body that weighs in under 200 lbs., yet is strong and rigid. Also, the FFR body shell is much more resistant to stress cracking due to its non-stressed mounting design and correct gel coat thickness (heavy gel coat can lead to “spider cracks” since there is no strengthening fibers).

    Is our car lighter because of a thinner body shell? No. The body laminate schedule is a common thickness (3/16” nom.) for hand-laid composite body shells. The weight savings comes from the use of aluminum instead of fiberglass in the cockpit, footbox, trunk and wheel well areas.

    The body specifications are quite simple. Our body incorporates approximately 110 sq. ft. of surface area and weighs about 190 lbs. total. Our aluminum chassis panels weigh in at bout 75 pounds total. Kit cars using fiberglass tubs (cockpit) and/or wheel wells and trunk/engine bay liners have about 100 sq. ft. of additional fiberglass. This would account for an increase in overall weight of about 200 pounds (providing the lamination was the same), but more commonly adds about 350 lbs. to the vehicle weight since the cockpit is usually thicker as it’s being used for structure. To make matters a bit worse, companies that use “chopper gun” fiberglass have a hard time controlling laminate thickness and can end up with even heavier parts!

    From our very first molds in 1995, we have learned a great deal about the tools that molded parts need to be made right. The quality of the part you get comes down to three simple things… 1) The quality of the raw material (resins/cloth), 2) The quality of the tooling (molds, trimming equipment, etc), and 3) The skill of the people who actually lay-up, cure, and trim the parts.

    To control our quality, we design, build and own all of our own tooling. We use an Eastman M9000 CNC cloth cutting machine to ensure consistency of all composite fabrics and patterns. Our 10 man molding department uses only hand-laid processes for every single part, and molded parts are trimmed on our RPT Technologies robotic trimming machine.

    Our molding technologies have grown tremendously over the years. Today we put as much QC work into our fiberglass parts as we do our steel frames. You’ll notice that the parts carry control numbers that correspond to the date of manufacture, mold number, and molding department member who made the part.

    You can count on us to deliver a part that is engineered to be the correct strength and fits right. The FFR Mk4 body shells are shipped assembled to the frame. The parts are unfinished (taken right out of the mold and require bodywork). Recently we changed our process from molded edges on panels to a high speed router trimming method. This eliminated air voids on tight radius areas and enabled us to make the parts match the openings better (the panels are actually made too big, enabling you to make really tight gaps on all hoods, doors and trunks).

    Bottom line is that the parts we make are strong, designed to fit, and made right each time so that you can build the car of your dreams.

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    Suspension & Brakes


    The artistry and strength of the Factory Five Roadster chassis would be a waste without an equally well-designed suspension and proper braking. Computer simulations and hundreds of hours on the track under the most extreme conditions have helped our engineers design world-class suspensions and brakes that deliver great car control.

    Front Suspension Base Kit
    • Fully independent front suspension with unequal length upper and lower A-arms
    • High-end KONI mono-tube adjustable coil-over rod-end shocks
    • Uses donor Mustang front lower arms, spindles, and brakes

    Front Suspension Complete Kit
    • The Factory Five Racing Mk4 complete kit includes the entire front suspension assembly and Ford brakes.
    • Includes Ford GT brakes with 11” rotors, twin piston calipers, and stainless steel brake lines, fittings, and fasteners
    • Includes brand-new spindles and tubular control arms

    The Mk4 Roadster Kit is delivered ready to accept bolt-on rear suspension components in one of three rear suspension configurations:

    1. Four-Link Rear Suspension
    Our standard 4-link is a great performance street car suspension. It comes with custom anti-squat geometry and is ready to accept Ford Mustang 8.8” solid axle donor rear suspension parts.

    2. Three-Link Rear Suspension
    The upgraded 3-link rear suspension is standard in Mk4 complete kits and all FFR Challenge Series cars. It includes the frame brackets, panhard rod, control arms, KONI mono-tube rod end coil-over shocks (matched to the fronts) and springs. Recognized as a proven and worthy upgrade to the standard Mustang 4-link, this suspension eliminates any bind and provides an amazingly predictable ride at the track or on the street.

    3. Independent Rear Suspension
    Our Independent Rear Suspension (IRS) option is designed for those looking for the most comfort, authenticity, and performance. The IRS can be added to either the base or the complete kit. It includes a welded-in cage, upper and lower tubular control arms, high-end KONI mono-tube rod-end coil-over shocks (matched to the fronts), and custom assembled axles and CV joints.  The IRS option for the Mk4 kit requires the 8.8” center section, rear spindles, and brakes from a 2015 or later Ford Mustang.

    The base Mk4 Roadster kit uses the rear-end and brakes from a 1987-2004 Mustang donor car. The Mk4 Roadster complete kit comes with brand-new front brakes including S/N 95 style spindles and Ford GT 11” front rotors with twin piston PBR aluminum calipers. We offer a range of optional Halibrand replica wheels that are affordably priced and in the correct sizes/backspaces to work with our cars.

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    Running Gear


    Put a Ford in a Ford.

    It’s important when taking on this project to decide on an engine and transmission configuration that will deliver the power you need and that is within your budget. You can use the full spectrum of Ford engines in either our base kit or complete kit package.

    The Mk4 base kit is configured to use the entire engine/transmission/rear-end out of the Mustang donor car (5.0 or 4.6 liter V-8, T-5, T-45, TKO, T-56, or 3650 transmission, and Ford 8.8” rear end). The kit is
    designed so that these parts literally bolt right in. You can use almost any Ford engine in the Factory Five Mk4. Select from:

    • 289/302
    • 351W and derivatives
    • 390/427 FE
    • 429/460/514 crate engines
    • 4.6L SOHC & DOHC Modular V8
    • 5.0L Coyote Modular V8

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    Climb into the Past. Rocket into the Future.

    The connection between man, machine, and road is experienced behind the wheel. We’ve strived to capture the essence of the vintage car interior while improving on cockpit space, ergonomics, sound/heat control and safety features. Inside you’ll find the largest cockpit possible for the car’s authentic exterior dimensions. The Mk4 has good legroom and excellent front/rear visibility.

    Mk4 kits include a complete interior:

    • Original British style bucket seats in black with tubular steel frames (not inexpensive fiberglass buckets); optional leather seats are also available in black
    • Padded dash cover, aluminum dash, toggles and indicator lights
    • Complete carpet set
    • Emergency brake handle boot, shifter handle boot/ring, shifter and shifter knob
    • Authentic door latches, door hinges and leather check straps
    • All trim and gauges (or gauge conversion kit)
    • 5-point Simpson racing H-harnesses for both driver and passenger
    • Authentic wood/aluminum steering wheel with aluminum boss and center section
    • Rolled edge along the entire cockpit
    • We offer either modern or vintage-style electronic gauges, both made to match well with Ford electronics.

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    Authentic Parts.

    People will look long and hard at the outside of your creation, so the exterior and trim of the car is as important as what is under the hood. We provide authentic British and vintage-style parts that hold up well to close scrutiny.

    Mk4 kits include complete exterior and trim:
    • Authentic chrome-on-brass windscreen
    • Vintage-style headlight assembly with DOT-compliant lighting
    • Authentic style winged amber turn signals with improved DOT-compliant specifications
    • Authentic style red dual tail/brake-lights, with DOT-compliant specs
    • Original style polished stainless license plate light with DOT-compliant specifications
    • Original chrome “bullet style” racing mirror and classic pedestal mount rear view mirror
    • Authentic three-lock set (identically keyed) with L-shaped handles for hood and a T-shaped handle for the trunk
    • Dual aluminum side louvers
    • Beautifully crafted steel side pipes with integral mufflers (polished stainless steel is an available option)
    • Original front and rear quick-jack bumpers with fasteners standard
    • Authentic Aston LeMans flip-type gas cap with integral pressure cap and flared neck for fuel line hose
    • High-quality trunk, door and hood hinges (hood hinge standard on the complete kit; available as an option on the base kit)
    • Three-point, 0.120” wall DOM steel competition roll bar, powdercoated black; mounts directly to the frame with included stainless steel fasteners

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    When Projects Become Projectiles

    With a power-to-weight ratio that can be as low as 3.5 pounds per horsepower, the Mk4 Roadster is a match for any sports car made today. 0-to-60 acceleration times in the three second range, and 10-second 1⁄4 mile passes are not uncommon. Factory Five customer Steve Berg has run his own FFR Roadster down the drag strip at an amazing 9.13 seconds at 154 MPH! With a well-built, modestly powered Factory Five, you will simply own any stoplight.

    When it comes to road holding, our cars fare equally well. FFR cars have routinely run in the 1.00 to 1.05 range in skid pad tests on street tires. That means your FFR turns as fast as it falls through the air! On a track or a twisty section of road you will hold a line that others in lesser cars (like a Porsche 911, 0.91G) will not be able to hold. These numbers are borne out in the real world by the staggering number of autocross and road racing wins FFR customers have racked up over the years.

    “The Factory Five Roadster was the quickest horse in this derby – 3.6 seconds to 60 MPH, 9.0 seconds to 100 MPH, and 12.3 seconds @ 113 MPH in the quarter!” – Larry Webster, Technical Editor, Car & Driver Magazine

    Performance Numbers, Car & Driver Magazine
    The vehicle tested was powered by a modest 325 HP small block Ford 302 engine with an 8.8″ Ford rear end with 3.55 gears and Factory Five 3-link suspension.

    0-60 in 3.6 seconds
    0-100 in 9.0 seconds
    1/4 mile in 12.3 seconds @ 113 MPH
    70-0 braking in 181 feet
    Skid pad lat G – 1.00
    Curb weight – 2,162 lbs.
    Price as tested – $32,109

    Front suspension type – Independent double arm
    Rear suspension type – Solid Rear Axle 4-link, 3-link with panhard bar, or IRS
    Shock-springs – Koni coil-over with ride height adjustability
    Steering – Manual or power assisted rack and pinion
    Brakes – Vented 11/11.65 disc f/r
    Wheels – Vintage or modern 15”, 17”, or 18” diameter
    Tires – Common sizes are 245 series front/315 series rear

    Weight – 2,250 lbs.
    Weight distribution – F/R 46.9/53.1 (percent)
    Wheelbase – 90 inches
    Overall length – 158 inches
    Front track – 58.5 inches
    Rear track – 58.5 inches
    Overall height – 48.0 inches
    Overall width – 70.5 inches
    Ground clearance – 4.5 inches
    Fuel capacity – 15 gallons

    Layout – Front/mid engine RWD Roadster
    Frame – Twin tube space frame with integral backbone
    Roll cage – 3 point, structurally mounted 2 inch DOM Tubing
    Sub-structure – Aluminum paneling riveted and bonded to frame
    Restraint system – 5 point Simpson Harness

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    Our Safety Record Is No Accident.

    The legends of the 60s were built not only from racing victories, but from
    tragedies as well. Back then, many basic safety features were either not used or not available. Today’s Factory Fives are stronger, faster, and safer than the original cars.

    In the world of hot rods, customs, and kits, we stand miles above the crowd. As the only replica company that has a dedicated racing series, we speak from a unique

    We have a company that is single-minded in our
    passion for racing and performance, so safety is our daily religion. You can trust our products because the chassis that you build as a hot rod project is the same one that our team trusts with their lives on the track. Safety is a combination of good engineering, correct materials, and careful construction.

    • Low vehicle center of gravity and balanced 45-55% weight distribution
    • Energy absorbing tubular steel frame and aluminum chassis panels (not fiberglass)
    • Front and rear energy-absorbing crumple zones
    • SCCA-derived footbox steel tubing protection and cockpit steel surround structure
    • Side impact bars and beefy plate steel door hinges
    • Frame mounted doors
    • Externally mounted and shielded fuel tank with fuel pump impact shut-off switch (from the Mustang donor)
    • Collapsible steering column
    • Driveshaft safety bars
    • 3-point, 1.5” OD, .120” wall, mandrel bent, frame-mounted driver’s roll bar (optional passenger
    roll bar available)
    • 5-point Simpson brand, racing H-harness for both driver and passenger
    • Vintage components that are individually FMVSS compliant (i.e. lighting, carpets, seating material,
    safety glass, etc.)
    • Manufacturing controls that maintain high degree of consistency in welding and fabrication
    • Acceleration, turning and stopping abilities above almost any current production vehicle abilities above almost any current production vehicle