MKII Slabside from
Superformance is proud to announce the availability of our newest model the Superformance MKII Slab Side – designed to emulate the great Cobra 289 street cars from that nostalgic golden era of racing in the 1960s. Unlike most competitors, the Superformance MKII Slab Side is built on the successful Tojeiro-styled round tube chassis and features an authentic transverse leaf spring suspension to give owners an exceptionally authentic driving experience. Through our exclusive agreement with Carroll Shelby, the MKII Slab Side is the latest licensed Shelby product in the Superformance lineup.
The Chassis is the original John Tojero designed 3” tubular rail ladder with cross-member. This chassis is reproduced using drawings obtained from AC cars and also implements the necessary changes to utilize rack and pinion steering . The 3” tubes are tig and mig welded to guarantee a safer and stronger chassis. This is much stronger than the arc and gas welded originals. Pain staking efforts were made to reproduce the chassis as close to original as possible while incorporating a few modern improvements. Building the cars with a meticulous eye on authenticity took time, but in the end, we feel that effort pays off in a superior driving experience for our customers.
To compliment an original chassis you need to follow the same rules when it comes to the suspension. It had to be period correct, or as close to it as possible. While the original used a transverse leaf spring style suspension, that arrangement requires different length springs to change camber settings. Because of that, the decision was made to go with heim joints, just like some of the original competition cars used. In fact, two options are offered here – The first being rose joints and the second being adjustable rod ends with poly bushings for a slightly less harsh ride.
Another change with regards to safety was to add an additional pick-up point to the chassis to increase the shear strength of the bolt passing through the lower control arm rose joint or poly-bushed rod end. The original springs were made of thinner steel than that available today. In an effort to keep compression rate the same, this car comes with one blade less and “free camber” was changed to keep the ride heights equal from front to rear. This insistence on authenticity means that owners of a Superformance MKII roadster will have virtually the same driving experience as the original.
The Superformance MKII roadster bodywork replicates the later of the 289`s which incorporated modifications to fender flares that will accommodate the slightly wider tires fitted onto chrome wire wheels. One of the improvements made by Hi tech was that the footwells were tweaked so that the taller North Americans can now sit comfortably.There are pedals made for short, medium and long legs. Side fender airvents are also fitted.
Again, attention to small details like the replication of the glove box knob and the correct use of gauges make this car stand out from the others. A Side screen pocket is fitted behind the seats on the rear bulkhead and door map pockets are also incorporated in the doors. Lush carpeting finishes off the cabin for a comfortable feel on the road.
An Original would have probably been a 289 with a B.W T10. Today, the recommendation would be a 289/302 based engine with a more modern Tremec T5 or similar transmission.
History and Origins
The Shelby Cobras were based on an aging, but light and strong, British roadster, the AC Ace. AC cars were at this stage trying to source different engines with the Buick/Rover V8 being one of them. Initially, the 260 cubic inch small block Ford was adopted and after 75 cars an upgraded 289 was fitted. Some significant body changes took place with this modification. Front fender louvered side air vents were fitted and the nose altered to allow more air in.
The chassis was also tweaked by Alan Turner at the AC cars factory. Heavier gauge tubing with extra cross bracing was used and because the rear brakes had been moved from inboard to outboard, the differential area could be modified and strengthened as well. The first 126 frames used the same front suspension tower as the Ace but when the change to rack and pinion steering took place, a different type of front shock tower was used. This allowed for further strengthening.
The change from worm and sector to rack and pinion transformed the handling of these cars. At the same time the bottom control arm pick up points were able to be repositioned. Originally the 3" tubing was all arc welded whilst the body framework, consisting of ¾" and 1" steel tubing, was gas welded. 1 ½" tubing was used to strengthen the scuttle area. Today we use state of the art technology that has vastly improved on these methods, although hopefully none of the charm has been lost.
The John Tojeiro designed 3” tubular rail and cross member ladder style chassis, with front and rear suspension towers welded to it, started off life under a Cliff Davis 2-liter special in 1953. The little red Ferrari 166 barchetta look-a-like body placed on top of this chassis proved to be a formidable force in the local club racing events... so much so that AC cars decided to buy the design when it was offered to them.
The first Aces used a Weller-designed ohc engine and then later the more efficient Bristol BMW based 2.0-liter unit. When Bristol stopped producing these in 1961, AC tried various other options including the 2.6-liter Ford Zephyr engine tuned by Ken Rudd. This motor was fitted for a short while and because of the extra weight and horsepower, strengthening of the chassis and slight body changes were done. The nose and hood line were changed, (lowered) improving aerodynamics. From these changes the Ace 2.6 evolved.
It was at about this point that AC's owner, Charles Hurlock, was approached by Carroll Shelby to use a Ford V8 in the Ace chassis. The result was the AC Cobra in 1962. Production of the Ace ended that same year, but the AC – and later Shelby – Cobra went on to win Le Mans and become the fastest "production" car in the world. It also become one of the most recognizable and admired sports cars of all time.