65 Roadster Mark 3
 
Frame Design

The Factory Five Racing Mk3 roadster frame serves as the centerpiece of the kit.  It is computer designed to be extremely strong yet maintain the beauty and elegance of early 1960’s race car frame designs.  The frame weighs 326 lbs. and is shipped as part of a pre-packaged kit chassis, ready to accept bolt-on components.  The frame is a completely welded assembly and is delivered in bare steel or with an optional gloss black powdercoating.  Most people choose to powdercoat their frames since we charge only $229 to do this.

Mk3 frames accept a wide variety of engines like the Ford 289/302, 351, 390/427, 429/460 and 4.6 SOHC and DOHC engines. The engines bolt right in without
Above: FFR Roadster frames staged for kit assembly.
 modifications.  Our customers have also used other power-train configurations such as GM and Chrysler.  Please call us and ask to speak to an engineer if you’d like to use a non-Ford engine to power your roadster.
 

The Factory Five Racing 65 Roadster Mk3 frame.
 
Vintage Looks and Modern Strength

The frame is one of the biggest reasons to buy a Factory Five.  Look at the complexity, beauty and design style of this frame and then remind yourself it is stronger and more rigid than you’ll ever need.  While it’s easier and less expensive to make a fairly strong square tube frame, we feel that a quality replica should have a period correct, 4” round tube frame.

The original style round tube frame is literally a piece of art.  The tubular ladder style frames used in early 60‘s Ferraris and original Cobras are more than just beautiful, they are representative of a period of automotive design that is legendary.   We chose to use this style of frame despite the difficulty and cost since a huge part of a quality replica is its faithfulness to the spirit of the original cars. 

Artistry is very important, but if the frame doesn’t perform, what good is it?  Vintage frames were used with the heavy, high torque, 427 FE motors of the day.  With these big motors producing 450+ hp and 500+ ft/lb. of torque, the original vintage AC Cobra frames displayed quite a bit of flexing under severe use.  We wanted the elegance of the original frame style, but we also needed to make it a lot stronger.  To accomplish this we did several things.
 
  • We added a backbone frame section and extra perimeter tubing that more than doubled torsional rigidity right off the bat.
  • We increased the thickness and quality of the steel pieces.  The 4” main rails were increased in wall thickness to use .120” wall tubing (up from .095” in the original 1960’s frames). 
  • The dash dash/cowl hoop is thicker .100” wall steel. 
  • The cockpit and footboxes have a steel cage surround structure.
  • Triangulation bracing was added to a number of locations, namely the front suspension vertical supports, dash, rear sub-frame, and trunk.
  


National Run & Gun Champion, Greg LaPoint, Mid 10's with a bone-stock FFR frame!
   
Materials
To make a better frame you need to start with better materials.  We use certified materials.  Plate steel is type A-36.  All round tubing is 1018-1020 DOM (drawn over mandrel).  Even our ¾” x ¾” perimeter tubing is cold-rolled, being one of the strongest configurations of square stock you can buy.  Higher quality steel is easier to weld, stronger, and comes in tighter tolerances.
 
Computer designed, laser-cut tooling and jigs produce better and more accurate parts.  Our welded parts are made in the USA
 

Manufacturing

The best design and materials only get you half way there.  We’ve taken several important steps to make sure that each frame is made right.  In order to control variability we built complex computer-designed frame jigs for all our chassis kits and sub-assemblies.  The CAD/CAM based jigs are built with laser-cut tooling steel and hold parts to an accuracy of .010”.  What that means to you is that all of your running gear and accessories will bolt right into place like they should.

In addition to accurate tooling, we have developed in-house manufacturing controls to help maintain quality, reproducibility and reliability.  For example, our welders all use the same MillermaticÔ 250 MIG welding machines. By keeping our equipment and settings standardized we can maintain better weld consistency.  We perform regular cross-training on manufacturing team members and our crew has established QC procedures to make sure each frame, component or assembly is done right. Before your frame goes to chassis assembly it has already passed three separate Quality Control inspections
 
We have made over 4,500 roadster frames one at a time on highly accurate tooling.  The end result of all this work is a frame that you can trust.
 
With increased wall thickness and structural upgrades, the use of better materials, and more consistent manufacturing methods, our frame is engineered to handle much higher horsepower and provides greater torsional rigidity than the original British built frames.  When you see FFR cars winning national races or lifting the tires clear off the ground, check out the “straight-as-an-arrow” frame quietly doing its job.  Today’s Mk3 frame is the third generation FFR roadster frame and has benefited from more than 10 years of refinement and development.  There is no finer replica frame period. 
 
Round Tube vs. Square Tube

There is ongoing debate about the use of round vs. square tubing in frame design.  Most of it is from people who are selling one or the other. The bottom line is that it costs more to produce an original style round tube frame because it’s more difficult to design and manufacture.  Many companies have taken the easier path of making square tube ladder style frames.  We felt our challenge was to make an original style frame stronger without losing its inherent beauty or period correctness.  Good engineering means form and function.  Once we committed to building a round tube frame we found some pleasant surprises.

  • Round tube weighs less than square tube.
  • Round tube is available in stronger steel.  There is no rectangular 1020 DOM tubing, it’s all 1010.  1020 DOM is about 30% stronger than 1010.
  • In torsion, (exactly the kind of stress that cross members are subject to) round tubing is much stronger than square tubing.  Makes sense why there are no square drive-shafts, right?
  • Under vertical bending loads, square tubing is stronger, but since the round tubing is available in higher grade steel, the advantage square stock had in vertical loads is diminished. 
  •  Round tubing helps make a lightweight ladder frame, with excellent vertical and superior torsional load resistance.
  • A well-designed round tube frame is the hallmark of professional chassis engineering.  They are complex, requiring intricate jigs, difficult to design and they are usually made from better materials.  They are also really beautiful.
 

 

In the kit car world, square tube frames are more common because they are simple to design, easy to make, and the materials cost less.  They can be made strong, but to do so means you’ll likely end up with a brutishly heavy slug of a frame.  The 1020 DOM 4” round tube that we use for our main rails and cross members costs $10.30 per foot. Similar square steel tubing (commonly used) costs $1.98 per foot. 

For a more comprehensive review of the principles involved you can read one of the best books ever written about racing materials and engineering.  The author is Caroll Smith and the book is entitled “Engineer to Win”.  You will probably feel that you got your moneys’ worth after reading just the dedication and short two-page introduction.
 
One final note: If you think we’re making too much of a deal out of just a car frame, maybe we are.  Just about any design will technically do the job.  The thing is though… The frame is the most elemental part of the car.  Unlike an engine or suspension, it’s hard to modify and upgrade later.  Not only that, the frame is a huge part of the personality, character and soul of the car.  Part of the reason you will love this car like your own child is that elegant frame… designed and built by people who see a race car chassis as functional artwork.  It will be more than just a good servant to you in your quest to build your own world class sports car.
 

With over 800 welds and hundreds of individual pieces of steel, the Mk3 frame is both engineering excellence and functional automotive art.
 
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