Mr. Hyde's Cobra Replica
Transforming A Street Cruiser Into A Track Terror
From the February, 2009 issue of Kit Car
By Dan Reiter
Photography by Dan Reiter
Find out how we turned Dr....
Find out how we turned Dr. Jekyll, the street Mk II FFR roadster on the left, into the fire-breathing track terror we like to call Mr. Hyde.
The replica industry is based on the average person being able to build a copy of their favorite old race car. Kit Cobras, Cheetahs, GT40s, Grand Sports, and others featured in this magazine all cater to our desire to have a copy of these otherwise unobtainable cars. It's grown into a multimillion-dollar industry and made many of us very happy just to have one parked, or still in pieces, in our garages. They all make fun cars to drive and enjoy, and they draw the admiration of onlookers. It's all good. But what about those of us who do race and put these cars on the track? We'll show you what we did to a Factory Five Racing Mk II roadster to adapt it to life on the track.
In completed form and built to a standard level of street equipment, FFR roadsters are great cars and very happy on the street. They can outperform a large percentage of cars on the road. But take one directly from the street onto a racetrack and it's just the opposite, with even Miatas and Subarus lapping you. Factory Five does have the Challenge Series and specific roadsters for racing, but they differ greatly from a street car. So what's involved in making one of these cars a real track terror? The truth is a combination of many aspects of the car, all coordinated to help in a racing environment.
The X303B motor came with...
The X303B motor came with all the good stuff already installed. All we added were the intake manifold, carb, ignition, clutch, and accessories from the old motor, and it was done. Here's the motor in place, awaiting final assembly.
What we have here is a Mk II FFR that's still a street car but has had many areas modified and tweaked to help on high-speed tracks that place incredible demands on the car. We'll concentrate on the following major areas: chassis and handling, brakes, aerodynamics, safety, and driveline. With a change to street tires and untaped lights and openings, it's back to prowling the streets. Without getting too in depth into any specific modification, we'll provide an overview of what we did.
One very important point we must note is that these Cobras are famous for being unforgiving on the racetrack, and often lethal. Any racing should be done under controlled and observed supervision at a school or racetrack, and proper safety gear must be worn at all times. We have all seen videos of inexperienced drivers crashing these cars, and we all pay more insurance than most because of it. Care, caution, and always working up to the car's capabilities will result in more enjoyment and a learning experience. Let's review the main areas of attention on our subject and see how they work together to produce a stable, quick, fast, and agile dancing partner on many racetracks.
To keep the oil at optimal...
To keep the oil at optimal operating temperature, even under heavy loads, we added an oil cooler. The oil cooler is fed air from the oil cooler opening in the body.
On any vehicle destined for some serious racetrack running, a lot of attention is paid to the chassis and suspension. This Cobra is a perfect example. When the kit was ordered, using the car on-track was a given, so the three-link rear suspension, tubular front suspension, and all related upgrades were ordered and installed on the initial build. The three-link is standard equipment on competition FFR roadsters. This layout replaces the stock Fox Mustang four-link rear suspension's upper arms with an adjustable upper arm to set pinion angle and a Panhard bar to provide lateral positioning and movement control. The car also comes with coilover shocks on all four corners. The adjustable spring hats allow for precise weight balance and ride height settings. While this provides a great platform, more control was necessary, so we added a VPM front sway bar to the chassis to greatly reduce body roll during turn-in on high-load corners. Finally, to connect all this machinery to the road, a set of 17x9-inch Cobra "R" rims and Kumho V710 275/40R17 racing tires provide a direct connection and gain more grip as they heat up. Add a good frontend alignment to help with stability and a slower steering rack to take the nervousness out of the steering, and the result is a competent chassis that is very stable yet responsive.
The other huge factor in how...
The other huge factor in how the Cobra sticks to the road is tires. Here is a comparison of the 15-inch Yokohama Avids (right) we run on the street, and the 17-inch Kumho Vito-Racer A710s (left) used on the track.
Under the hood there's nothing fancy at all, just reliable midlevel horsepower. After the tired donor 5.0 finally expired with no oil pressure, we ordered a X303B crate motor with 345 hp. The roadracing oil pan and pickup were swapped over to ensure lots of oil no matter what the car is doing. Up top, the aluminum dual-plane manifold, Holley 600-cfm carb, and high-output electronic ignition, all from the old motor, keep things simple, easy to tune, and eager to respond to the gas pedal. All the connecting motor systems remain close to stock for simplicity and ease of replacement, and they all work fine. We added an oil cooler to help keep the motor's innards cool under extreme conditions when high loads are present. A good rule of thumb is to keep the horsepower conservative and reliable. With the lighter vehicle weight, the power-to-weight ratio is still on par with a supercar. In this case, a 2,250-pound vehicle weight divided by 345 hp results in about 6.5 lb-hp-very impressive numbers considering the best Detroit musclecars rarely dip below 9.
The stock dual-hump oil pan...
The stock dual-hump oil pan was replaced with a Canton roadracing pan from Breeze Automotive. This pan holds seven quarts of oil and has a baffled pickup area to keep oil covering the pickup.
Now that the Cobra is plenty fast and handles like a Formula car, it needs to stop-not once, but repeatedly, braking hard many times every lap from all speeds, without fade, boiling fluid, or any fuss. This is probably the most critical system, and one where proper parts selection delivers optimal results. There are countless aftermarket brake systems available boasting multipiston calipers, bling-sized rotors, and even full race setups. Most of these will provide amazing results on the track, but will require large rims and reduced brake performance on the street, not to mention a sizeable investment. (Remember, this Cobra sees a lot of street use.) In addition, on the street, 15-inch GT40-style rims keep the authentic look, so the brakes have to fit inside.
After much research, we chose a system with Ford components, upgraded pads, and flexible lines. Up front, the rotors and calipers come from a Lincoln Mk VII with a larger 73mm piston. In addition to more clamping force, it bolts onto the stock FOX Mustang spindles, and a wide variety of brake pads are available. The main reason we used this system is because it provided the best available braking combo that would fit inside the 15-inch GT40 rims. If we were running 17-inch rims, then something much more exotic would reside there. Out back, the rear disc calipers and rotors come from a mid-'90s Mustang GT, complete with an integral parking brake that bolts onto the 8.8-inch axle with a simple adapter kit. All the runner brake lines were replaced with high-performance flexible lines, so no ballooning (line swelling) can occur.
Pictured is the driver-side...
Pictured is the driver-side VPM sway bar. You can adjust the bar's end links and the position the end link is connected to the bar to increase stiffness. We immediately felt this addition; it had a profound positive effect in the handling department.
As for brake pads, this is probably the most critical component in the brake system. With many manufacturers and the numerous types of pads available, this topic tends to be confusing. Pads are available with the full range of compounds, starting at street-only that tolerate little heat up to full-race materials that need to be warmed up, then grip like crazy. After talking to many racers and asking advice on racing forums, we picked the Hawk HP-Plus pads, which are a track-level pad, but not quite the soft, race-only pad. On the track, they do need a lap or two to warm up to be totally effective. On the street, they take a lot of pedal effort to stop, squeak a lot, and get the rims very dusty. The only other alternative is to keep two sets of pads and swap for the given use, but this will kill the rotors. Lastly, make sure the master cylinder has a correctly sized bore that matches the piston surface area. In our case, a unit from a '94 Mustang SVT with a 15/16-inch bore was perfect. While a proportioning valve is installed in the feed to the rear brakes, it is currently run wide open, as the balance is good.
Now that we can go fast and...
Now that we can go fast and keep our bodies safe, it's time to stop our slithering missiles at the end of a fast section of track. While it is not necessary to buy 20-inch brake rotors and 12-piston monoblock calipers, a well-thought-out and properly sized and matched brake system is critical.
Happily, combined with the roadster's lighter weight, this system works incredibly well. Whether slowing down from a high-speed straight or a quick jab in between corners, the brakes have yet to falter. We also added cooling hoses blowing cool air from the openings on the front of the body, which blow into the rotor hats and onto the calipers to help get rid of heat. When we stepped up to the slicks, the brakes worked incredibly well, but we had brake fluid boiling problems. Providing cooling air resolved that, and the ducts add to the race car look!
The last area we covered was driver safety and skill. A racing-style seat is used to keep the driver in one place, combined with a full five-point harness to secure the driver. The last thing a driver wants is to have to brace him or herself in addition to wrestling the car. A proper helmet, gloves, and shoes all protect the driver and actually make driving the car easier. Probably the single best investment is attending as many racing schools as possible. Here is where you can learn proper car control, how to drive corners, and braking. High-performance driving on the track is totally unlike driving on the street, and the best way to learn is by getting as much seat time as possible.
The most common aerodynamic...
The most common aerodynamic facet of Cobras is their lack of any aerodynamic qualities at all. As quoted, these cars have the wind-cheating qualities of a brick.
With the Cobra equipped in this manner, it made a great track car on slower tracks, was just amazing in the corners with its handling, brakes, and quick acceleration out, but is a very nervous car on the straights at speed. As everyone knows, Cobras have the aerodynamics of a brick, and a big brick at that. Back in the '60s, Shelby American remedied this problem by designing and producing six Daytona coupes for racing. More effective aerodynamics for the roadster opened up an area where we could experiment. An aluminum front spoiler had been previously purchased and run with good results, but we felt there was more that could be done to help the car. We removed the wind wings and visors to eliminate the turbulence and drag, with just the windshield to catch the air. Serious Cobra racers eliminate the windshield entirely, so we figured there was more we could do. We spent a lot of time on racing forums on the Internet, reading and asking questions about aerodynamic principles and what could be done to help our brick in the wind.
The first order of business...
The first order of business was to get the air out from under the car. We had already mounted the FFR front spoiler used on their competition cars, but we wanted to extend it. A plastic wicker was added that extended the spoiler lower lip by 1.5 inches. It just barely scrapes the track under the most extreme braking.
We finally divided our attack into two areas. First, we wanted to push as much air over the car instead of letting the air get under and in the car. We created an extension of the front spoiler out of clear Lexan, which extended the spoiler by 1 1/2 inches. We determined this by trial and error, so this Lexan wicker only scraped during extreme braking. On the street, it gets clobbered. We also put ducts in the brake and oil cooler openings on the Cobra body. This helped to restrict air getting in and provided cooling to the two vital areas. The grille is a giant air intake, and we were curious about blocking that. Other racers found that roughly a third of the opening can be blocked off without affecting cooling, so again, we used clear Lexan.
Next, we wanted to reduce underhood air pressure by minimizing air entering the engine compartment and helping it vent out quickly. We cut rearward-facing NACA ducts into the hood to act as air extractors. We blocked off the hood scoop so no air could get underhood directly. We also added a strip of aluminum at the front by the hood hinge to further restrict any air getting underhood. Yes, the car still has the famous Cobra silhouette, but it now has some unique features!
The transformed car returned to Watkins Glen this summer to see how it would perform. It is very hard to pinpoint which modification worked the most, but the result was a Cobra absolutely glued to the racetrack, rock steady at 130 mph, a slot car in the corners, and just a happy, noisy, eager track companion. As the driver, I spent all my time working up to the car's potential, and I left a lot of potential still to be found. The car is truly amazing-fast, agile, yet comfortable to drive. From this point forward, time will be spent tuning the car's aerodynamics and experimenting with ride height, brake pads, tire pressures, and other facets of the car. It's not quite your typical street Cobra, yet it still passes inspection every year. It's also uncommon to see Cobras on the track, so the car does get attention.
Brake pads are where the real...
Brake pads are where the real braking action happens. Street pads are designed to work well when cold and provide miles of clean, trouble-free use. Racing pads are just the opposite. They only work well when heated up, create a ton of dust on the wheels, and only last a few races or a season.
The front brake openings were...
The front brake openings were also filled with Earl's inserts, and hoses were attached to the three-inch necks and then aimed directly at the front brake rotors and calipers.
One of the more unique ways...
One of the more unique ways we tried to reduce air getting into the engine compartment was to block off part of the huge opening called the grille. A few racers noted they had blocked off roughly a third of the grille with no overheating issues, and they felt this helped keep air out from underneath.
Another unique item on this...
Another unique item on this car are the NACA ducts cut and molded into the hood to act as hot-air extractors. We took the idea from the '69-70 Shelby Mustangs. One per side was cut into the hood and mounted as rearward and to the outside edge as possible.
Up top is the hood scoop....
Up top is the hood scoop. If you are not running a sealed Ram Air, the scoop is more detrimental than good. Many racers reported that blocking it off helped reduce underhood pressures, so we used some black plastic and Gaffer's tape to block that off.
Here's a photo from a recent...
Here's a photo from a recent racing school at Watkins Glen. On the track, the car was rock steady, stuck great, and was fast. The author spent most of the first day slowly getting up to speed, feeling how the car handled and braked and felt on the track.