The Story

This Arntz 427 Cobra replica is one of only sixteen Type 4 models ever produced, representing Steve Arntz's final and most advanced design. It was purchased in 2013 from Jason Smith of Avila Beach, California, a former employee of Ron Butler, who is one of the foremost authorities on Arntz and Butler Cobras. Jason purchased it in 2007 from the original owner who purchased it directly from Steve Arntz in 1999. The Type 4 distinguished itself from earlier Arntz models with a completely redesigned body featuring structural reinforcements in the body and doors, and an engine positioned farther back in the chassis for optimal weight distribution. At the time of purchase, only two unfinished Type 4 models were believed to exist, making this likely the last unassembled example of its kind. If you have any knowledge of this, please leave a comment with details.

The Arntz Cobra story begins with Steve Arntz, an engineer who built Shelby Cobra replicas from 1974 through 1980. Arntz's engineering approach was methodical and performance-focused: he moved the engine 6-8 inches rearward to achieve near 50/50 weight distribution, designed a heavy-duty rectangular tube steel frame with outriggers, and created a robustly constructed multi-layered fiberglass body. The Type 4, introduced late in Arntz's production run, represented the pinnacle of his work with only sixteen ever made, and just five known to exist today. When Arntz closed shop in 1980, he sold his molds and tooling to Ron Butler, who refined the Type 3 design into what became the acclaimed Butler Cobra. Butler Racing produced 104 vehicles between 1980 and 1994, continuing the tradition of meticulous craftsmanship that Carroll Shelby himself recognized when he said of Butler, "Ron Butler is one of the few Old World craftsmen left." The Arntz Type 4, however, remained a distinct and separate design.

The owner acquired this Type 4 with ambitious plans for a high-performance street and track machine. He immediately began sourcing premium components and became active on the Club Cobra forum, documenting his progress and seeking advice from the tight-knit Arntz/Butler community. Work progressed until 2020, when other projects took priority, including a Cigarette boat restoration. Following the owner's passing, his son is now offering this Type 4 to the community that will ultimately finish it and get it back on the road as his dad intended. The path is clear and will allow the next owner to finish it to their exact specifications, representing a significant opportunity to own and complete one of the most exclusive Cobra replicas ever created. Included with the sale are the original Arntz spec sheets, pricing, customer letters, brochures, engineering plans, and magazines. Something not found in any other Arntz Cobra sale listing are a poster of the dash wiring diagram and photo sheets of the original research vehicle, racing action, and a rare look at the Edelbrock dyno facility. Leave a comment if you know what motor that is!

The Cobra has never been titled and a serial number was not located on the body or frame from the topside, but the buyer may be able to find one with the car on a lift if it exists. There is a reserve that will need to be met in order for it to sell.

What You Get

Drivetrain/Chassis:
The powerplant is a custom built small block Ford 427ci stroker making a reported 592 horsepower and 561 lb-ft of torque. This was gathered from the owner’s Club Cobra posts. Other engine specs from the forum are a forged rotating assembly, 11:1 compression ratio, CNC-ported AFR 225 aluminum heads (2.08/1.60), a Holley XP Ultra 950 carburetor, and stepped headers with 1 3/4” primary tubes, stepped to 1 7/8", then 2”. The valve covers have "FPS" embossed in the middle of the Cobra logo, but we were unable to verify who this engine builder is, so please comment if you know. The carburetor was not dialed in completely on the dyno, so this engine could easily hit the 600 HP mark. Upon physical inspection and removal of the valve covers, aluminum roller rockers and stud girdles top off the heads. The heads are stud mounted with ARP hardware. The Edelbrock Victor Jr. intake has been ported to match the larger intake ports. The water pump is an electric unit from Meziere Enterprises. The distributor is of unknown brand, but appears to be a billet Duraspark type. High capacity Canton road race oil pan handles the lube. It is unknown if the block is an aftermarket 4 bolt main or not.

The 5-speed manual transmission is a Tremec TKO 500 with 26 spline input shaft and 31 spline output. The ratios are 1st: 3.27, 2nd: 1.98, 3rd: 1.34, 4th: 1.00, 5th: .68, Rev: 3.00. It is connected to the engine with a Quick Time steel bellhousing. The owner posted on the forum that he was undecided on single or dual disc clutch, so that is unconfirmed, but the McLeod instruction manual pictured shows a single disc. The Jaguar rear differential is fitted with 3:31 gears and posi traction. It was sent to Kurt at Hamilton Industries to re-work it, adding Wilwood Dynalite calipers and vented discs.

The Cobra has 4 wheel independent suspension thanks to the Jaguar rear end and modified MGB front suspension with Ron Butler upgrades. A selection of shocks and coilovers are included to finish the suspension. The wheels are 15” Trigo Knocks-offs with NOS Mickey Thompson S/R radials purchased from the Club Cobra forum with an asking price of $1,200.

New parts included are a Moroso Oil accumulator with solenoid operator valve, Barry Grant electric fuel pump and filter, MSD HVC-L box with rev limiter chips and coil, Hi-Torque mini starter, Canton remote oil filter, Setrab oil cooler, Canton oil cooler thermostat, radiator, SPAL 16” electric fan, fan shroud, Tilton master reservoir for brakes and clutch, a Fuel Safe fuel cell, billet plug wire separators, and Wilwood calipers and parking brake kit. Current retail value for these parts is approximately $5,000.

Interior:
The interior soft items included are grey bucket seats and door panels. A full host of Smiths gauges are ready to install, including speedometer, tachometer, oil pressure, oil temp, amps, water, fuel level, fuel pressure, and a clock. New and out of date (2009) 4-point seatbelts are included. Multiple styles of Interior door handles are included. An original style hard top is included and appears to be very similar to the original Cobra hard tops. The fiberglass transmission tunnel cover is included. A wood Nardi steering wheel and mounting adapter are included.

Body/Frame:
The thick fiberglass body is in excellent condition, surviving very well over the past 45 years. The doors close with incredible confidence and you can feel the weight of the additional bars inside of them. They line up and close so well that no adjustment appears necessary. Each body door has a steel guard rail constructed of 2x4-inch ⅛-inch-wall mild steel tubing connected to hinges that have been pressure-formed in a huge press. All of the holes for lights and other fittings are present. The body is bonded to the frame and appears solid with no visible issues. With a frame that was designed to be more than twice as strong as the original Cobra, rear fender-wells that allow for 50 percent wider tires, and a motor set back in the frame, this Cobra is ready to handle big power.

New parts included are the original windshield, Lucas PL-700 headlights/buckets, brake and turn signal lights, Yellow Lucas Fogranger fog lamps (used, purchased from Greece - expensive!), door opening handles, and the fuel filler neck gas cap.

What You Need

Drivetrain/Chassis:
The engine was built in late 2013, so the proper precautions should be taken for an engine that only has dyno time and then sat for 12 years. The MSD ignition system is ready to install. Fuel and oil systems will need custom lines made to finish installation. The headers should be removed and ceramic coated. The hydraulic line for the clutch throwout bearing and throttle linkage need to be installed. The crankcase breather system can be designed to taste with the existing AN fittings on the valve covers or swap for the covers of your choice. The engine compartment and front sections of the frame need finishing and painting prior to the oil cooler, radiator, and electric fan being installed. The trunk needs finishing with the installation of the battery, fuel cell, and plumbing the fuel lines along with electrical connections for fuel gauge. The Cobra needs a full wiring harness installed. There is one included of unknown condition and looks to have been removed by the owner.

The front brake calipers have yet to be installed, along with brake lines for the front and rear, and the brake fluid reservoir. The suspension is mostly in place except for the driver’s side rear coilover and both front shocks. All suspension and brakes need to be inspected, verified for fit, and torqued to spec. It appears that the steering rods are included with new U-joints to connect to the installed steering rack. The tires are new according to the forum post, but are out dated now, so they should be replaced.

Interior:
The dash panel was not located but may turn up upon final extraction. All of the gauges are included and are ready for install and wiring. All interior soft parts including carpet, seats, and door panels are yet to be installed. Use the existing seats and door panels or swap for your own. 4-point racing harness seat belts are included and not installed. The door opening pull mechanisms need sorting prior to the installation of the opening handles. A new emergency brake is provided and requires installation.

Body/Frame:
The original glass windshield is still in the box and ready for installation. At least one of the winglet glass pieces is included, and the other may surface when pulling everything out of the garage. The body does not appear to need anything major except for paint prep and some extremely minor fiberglass touch-ups. All lights and body mounted items require installation. One item that the owner had not sourced yet was the roll bar, which he wanted the correct Arntz style with the angled bar on the inboard side. The correct mounting holes are present. The other decision that had not been made was the hood scoop, for which there are two different styles included. The trunk lid mounting brackets and lid need installation. The top, which appears to be a replica of an original unit, is in good condition and only needs cosmetic attention.

The frame only needs beautification. The owner inquired on the Club Cobra forum about removing the body from the frame, but since it is bonded together and the bonds appeared in good condition, he decided not to separate the body to powdercoat the frame.