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Avanti GT

March 16, 2016

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Avanti GT

March 16, 2016

 

For anyone not familiar with the Avanti nameplate, it makes for an interesting history lesson.  The Avanti was originally produced by the Studebaker Corporation in 1962 and 1963 and was designed as “America’s only 4 passenger performance car”.  With an inspiring European design with many trend setting mechanical and safety features, it should have been enormously successful.  Unfortunately, that was not the case.

The Avanti’s fiberglass body was produced by the same company that supplied the 1963 Corvette body to General Motors and not surprisingly, GM was a higher priority than the much smaller Studebaker Corporation.  Studebaker was forced to produce their own bodies but with many delays to address quality issues and get production up to speed, showrooms were left empty with backorders and eventually, many cancelled orders.

 

The Automotive Division of The Studebaker Corporation was in financial trouble.  All production in South Bend ceased on December 31, 1963 but shortly after the factory closed its doors two Studebaker dealers, Leon Newman and Nathan Altman purchased the rights to the Avanti name and design, as well as all of the tooling required to resume production.  To differentiate from the original car, it was rebranded as the Avanti II and remained in production by Newman and Altman until 1982 and by various other owners until 2007.   

 

The Avanti Corporation found a new owner in 1982 in Steve Blake, a young real estate developer who had tried to purchase the company for several years.  Prior to purchasing Avanti, Blake hired Herb Adams to develop a high performance prototype.  Adams was a former General Motors engineer and was famous for developing the Z28 Camaro for the Trans Am series.  With the change in focus from luxury performance to a true high performance sports car, the pair decided that competing in the IMSA-sanctioned 24 Hours of Daytona race would be the fastest and most impactful way to change Avanti’s brand image. 

 

Blake and Adams did compete in the 24 Hours of Daytona, but in a re-bodied, tube chassis Trans Am car instead of their Avanti prototype.  After Daytona, the prototype was completed with a modified Avanti body and many C4 Corvette components.  It raced in the Escort, Showroom Stock series successfully in late 1983 and 1984.  

 

 

 

 During Blake’s tenure at Avanti, the Grand Touring Coupe was introduced as well as a convertible, and a 4 door sedan.  For 1986, Blake hoped to boost sales by introducing a 2 passenger Avanti GT to replace the 4 passenger coupe.  However, quality concerns and financial problems began to plague the company.  On June 28th, 1985 Blake filed for bankruptcy. 

 

Intrigued by Blake’s plans to introduce a 2 passenger, high performance Avanti and after discovering the detailed plans in the book “More than they Promised ----- THE STUDEBAKER STORY”, my father decided to build a tribute to the Blake Avanti GT that was designed, but never built.

 

In April 2015, a 1973 Avanti II that was in very poor condition was purchased and became the donor body for what will become the Gibson Avanti GT.  While “More than they Promised`` provided a general outline on key components of the GT prototype, it offered few details.  The 1983 Escort Avanti GT prototype provided a good insight to many mechanical aspects, but with its lowered stance, the full length body seemed even longer than it really was.  The two tone paint and modern bumper treatment added more bulk and exaggerated the impression of length.

 In 1963, an Avanti 2 passenger concept car was developed and many detailed photos can be found both in print and online.  With eight inches removed from the cabin, its design contributed to the concept of a two passenger concept but keeping close to its original height did not provide the correct stance for a high performance grand touring car. 

 

Combining design elements from both cars while paying careful attention to proportion and stance would ultimately provide the blueprint to the Gibson Avanti GT.  A plan to borrow from Blake’s plan for a 48” roof height, use of fender flares and a more modern bumper treatment while retaining the core 1963 styling elements slowly began to take shape.

 

With a plan now established, the 1973 Avanti II donor was driven into the garage and onto the hoist to begin the disassembly process.  After all the electrical and mechanical points were disconnected, the body was lifted off the chassis.  The complete chassis and drivetrain was sold and rolled back out of the garage and onto an awaiting trailer. 

 

The body was lowered onto a dolly and moved to the other side of the garage for removal the entire interior and doors. Knowing major surgery was about to begin, a grid of internal structural 1`square tubing was built to maintain door opening dimensions, and alignment of front and rear sections of the body in both a vertical and horizontal plane.  By incorporating 1.25” square tubing over the 1”square tubing, dimensions could be maintained while having the ability to move (telescope) the rear section of the body forward once a section was removed.

 

With the internal structure complete, cut lines were marked on the body, 8`` out of the roof and middle of the fender above the wheel opening, and 4`out of rear quarter window, as well as 4`` behind the rear quarter window.   Up front, the front wheel was moved forward 3`` to cut down on the front overhang to promote a 50-50 weight distribution and provide space for the steering rack in front of the engine.

The body and dolly were then moved outside for the scary and messy part of the project and after the first cut, there was no turning back!  First the rear seat floor section was removed and some extra support was provided under the tire carrier portion of the trunk.  The section of the rear fender was cut out, followed by removal of the rear quarter window.

 Alternate sections of 4” X 8” of the roof were then removed in a staggered pattern, so as to create a finger joint.  The next task was to cut along the top of the fender following the horizontal body line, continuing inside detaching the fender well from the outer body.

 

 

The rear section of the body was then pushed forward, closing the 8” gap.  The pieces removed from the fender and roof were then fitted to the inside, treated to fiberglass mat and resin, and pop riveted in place until the fiberglass cured.  During this process roof alignment was obtained by cutting almost 1” out of the “B” door post.  

Once the roof and fenders were reinforced and fiber-glassed back together the wheel openings had to be defined and cut out.   Small cuts were made to open up the areas and then wheels with tires of the size to be used were positioned in front at anticipated ride height.  The front was moved forward an additional 1” to cut down the front overhang to improve proportionsAfter reviewing many options, a set of 1.5” fiberglass fender flares for a 1967 Mustang were purchased and the area around the wheel wells prepped for installation.  However major modifications to the fender flares were required to tighten up the curvature and accommodate the ride height.  Initial fitment resulted in an “added on look”, so additional reshaping and fiberglassing was required to get the desired contour.  

 Once body had been shortened, the desired stance established, and the fender flares installed, the wheelbase and track finalized, work on the chassis could begin.  Since all the floors and transmission tunnel had been removed, along with the “hog troughs”, it was necessary to reinforce the rocker panel area to accommodate the safe transfer of the body on and off the body dolly, the hoist, and trial fitting of the chassis.  This was done by attaching a .25” aluminum 2” X 3” angle iron to the vertical portion of the “hog Trough” that remained in the rocker.  This would also provide means to channel and attach the body to the chassis.

 

While pleased with the overall proportions and lowered stance, it resulted in the rear section looking heavy, as it seemed to be too close to the ground. Eliminating the spring shackle covers and the bumps where the bumpers attached helped to clean up the look.  Raising up the license plate up closer to the trunk opening also provided the space for exhaust outlets in the centre of the car. 

The 3” removed from sides will be reinstalled inside the fender so that the lower curvature is re-established to stiffen this area.  This is work in progress, and these pictures do not reflect the final product which will incorporate modified and painted C3 Corvette split bumpers that will frame the exhaust outlets.

 

To add to the GT theme, heat extraction vents in both the hood and upper fenders were planned.  After many hours researching various OEM and aftermarket options and several made mock ups were made from cardboard and chrome tape.  Many were too large, while others with their chrome finish commanded immediate attention, detracting from the desired smooth and subtle look of modifications beyond the radical lowering and shortening of the body. So, we decided to resort to a low budget, old school approach by cutting slots for vents.  This proved very effective thirty years ago on the c2 corvette race car.

 

Once the Avanti GT is painted a stainless steel screen will be installed inside the fender and under the Hood.Here is the highly modified body shell in its current state sitting on 4” X 4”, shimmed to ride height, with some wheels in position to simulate the proportions and stance of the Avanti GT when finished. At this point all the remaining red paint needs to be stripped, and any cracks repaired.  The backside of all body modifications need to be reinforced and smoothed out.  Hopefully it will go to the body shop by early December for full coats of primer, block sanding to flatten all panels, adjust gaps, and paintinG.

 

More than they Promised indicated that the 1986 Avanti GT would use a chassis very similar to the one in the 1983 - 84 Escort Avanti GT.   It specified a backbone, step down style chassis with both front and rear independent wishbone suspension and four wheel disk brakes, with rack and pinion steering.   Given the era and the close connection to GM by both Adams and Blake, one could anticipate that many of these components would be C4 Corvette, including the aluminum differential, although the rear (wishbone) upper and lower A frames would have to be custom built.

 

The plans would be updated slightly for our Avanti GT tribute, as the majority of the suspension and driveline components were sourced from a 2007 C6 Corvette.  Leaving out the torque tube and converting a C5 rear differential to an open driveshaft would allow the use of a 2010 6L80E six speed automatic transmission in the conventional position, attached to the rear of the engine.       

To understand the design detains of the Herb Adams chassis, an old copy his book’  “Chassis Engineering” was pulled off the shelf, as it has a whole chapter devoted to the backbone chassis.

 

The unique feature of the backbone chassis is that the transmission and driveshaft tunnel become the primary structural componenent supplying a high level of torsional rigidity, linking the front and rear suspension components.

 

The step down feature refers to the floor being located at the bottom of the frame, providing a lower seating position, and thus a lower center of gravity  to promote good handling.   With a good understanding of how the Avanti GT chassis should be designed following the Herb Adams concept, we needed to understand how to incorporate the C6 Corvette suspension components.

 

The first priority was to identify all the drivetrain dimensions, stock C6 suspension pick up points, then modify them to accommodate a slightly narrower track width.  

 

As a GT touring car, it was important to come close to the handling potential of the modern Corvette, and it was very important to have a comfortable ride for long distance travel.  Once complete, plans  for the Avanti GT include several long road trips, such as participating in Hot Rod's Power Tour.  This would require the suspension to have greater travel than a Corvette, requiring some of the suspension pick up points to be relocated.  We had to ensure negative camber gain was managed with greater suspension travel in a manner that did not result in a significant change in toe in or out.

 

All of the key measurements were collected, including the dimensions of the modified body to establish the wheelbase, front and rear track width.  Then, several sketches were made in an attempt to better understand how to connect everything together.  The plan was to build 1.5" X 1.5" 0.125 tubing modules for front and rear chassis, connected to 1.5" X 3" 0.125 perimeter frame to support the passenger compartment. 

 

With the Chassis layout designed and sketched out with dimensions, it was time to test the modified suspension pick up points to be sure they would perform as required.  All the critical data was entered into Performance Trends “Suspension Analyzer“ computer program that was instrumental in redesigning the geometry of our late model stock car, as well as the 66 Studebaker track car.  By using the different heights available for the inner pivot points of the upper A Frames, we were able find the best position, that gave us the desired negative camber gain, with minimal toe change.

Before actual fabrication could start, a “frame table” had to be built out of heavy wall 2" X 4"s heavy wall tubing so that all the components could be assembled in a square and level manner.  The table was built with 12” legs with leveling adjusters and removable wheels, so that it can be used as a dolly for the chassis or body.  The 16” height was chosen to work with our 12” high alignment and scale racks, so that with minor shimming, construction will be at ride height, with the wheels sitting on the scale racks.

 

First, a simple rectangle was made from 1.5” X 3.0” X .125 mild steel tubing, 57” wide to fit up into the rocker panel area, and 60” long, the size of the modified central passenger area of the body.   This was squared and tack welded to the frame table.  The rear cross member was marked and drilled for the area where the driveshaft will pass through but not cut out.  Similarly the front cross member ran the full width, and the area for the transmission will be cut out later.

Next, the front module was laid out, positioning the lower C6 A frames exactly as they are on the Corvette, except with a slightly narrower track.  The 1/4” thick attachment brackets welded to the 1.5” X 1.5” X.125”square tubing are spaced about .5” wider than they are on the Corvette to provide the opportunity to provide an additional means to adjust castor, or fine tune the wheelbase from side to side, by inserting large aluminum spacer washers to either end. 

The Howe upper A frames are mounted to their shafts with bearings at each end. The shafts are bolted to 5/8” plates with machined slots, in which various slugs with different offset holes are captured between the shaft and mounting plate.  This mounting plate is positioned to provide the same degree of anti dive as the Corvette, 10 degrees of positive caster, and 1 degree negative of static camber, and a centered roll center about 3” above ground. Use of slugs with different offsets provide the ability to raise or lower the inner pivot points of the upper A frames to adjust the rate of negative camber gain or to move the roll centre.  The use of shims on the A frame attachment bolts, provide adjustability for static caster and camber. C6 Corvette Uprights and spindles connect to the lower and upper A frames.  

 

 

 

 

 

 

 

 

 

 

 

Initially, C6 – Z06 rotors and calipers will be used, which will readily accept many high performance aftermarket systems later if we decide to upgrade.  Coil Over springs and double-adjustable Viking shocks will provide the ability to easily tune ride quality, handling and ride height. The universal mounts for the steering rack are intentionally placed low so that the intermediate brackets required to mount either the initial C4 or anticipated custom built steering rack can be spaced for optimal bump steer.

 

The C5 Z06 – 3.42 Differential, has been converted for use with a conventional open driveshaft using an adapter from Chassis Concepts.  Laser cut 1/4" plates attach to the front and rear of the differential and are welded to cross members to attach to the rear subframe with rubber mounts from Howe Racing.

Frame work for the rear C5 differential and suspension was fabricated in a similar manner to the front, duplicating the C6 Corvette suspension pick up points but with a slightly narrower track width.  Attachment of the rear upper A frames to the chassis is by way of a removable bracket.  No height adjustment is provided, but once the Avanti GT is complete, a different bracket can be substituted to lower the roll centre or increase the rate of camber gain if deemed an improvement through testing. 

The structural backbone consisting of the transmission and driveshaft tunnel was fabricated with the two lower rails made of 1” X 3” X .125” rectangular tube that established shape and size of the tunnel.  The two upper tubes are made of 1” X 1” X .125” square tube, and established the height of the drive shaft tunnel at the rear, increasing in height in the transmission area.  The shape mirrors the bottom tubes, but is narrower, so that the sides taper in at the top. While the top is flat above the driveshaft, the additional height of the transmission and bell housing area required a domed top framed with the 1” X square tubing.  The upper and lower tubing are joined with 1’ X 1” square tubing, and stiffening bridging is provided by .750” X .750” X .125” square tubing.

External 16 gauge steel sheeting, welded to all the framing components ensures that the backbone structure is extremely rigid.   The top above the driveshaft and console area is removable, as further fabrication will be required to mount the console, shifter, and possibly the emergency brake in this area.   Torsional strength is provided by three cross members, one welded in at the rear, a mid bolt in transmission mount, and an engine plate at the front of the transmission.

It was now time to weld all the modules together to create the chassis.  Additional 11 gauge plating extends the central backbone into both the front and rear modules, flaring out to connect to the left and right frame  sections.  The sheeting was plug welded to additional diagonal bracing to improve torsional strength

Then it was time to test fit the LS2 engine and 6L80 E transmission.

Unfortunately, despite measuring and checking numerous times, the huge transmission could not be raised high enough to provide the desired ground clearance for it’s oil pan, which is about 2” lower than the engine oil pan.  The contact area just behind the bell housing had a rib which was touching the cross framing of the transmission tunnel. Trimming both gained some clearance but not enough.  Moving the engine forward 1”allowed both the engine and transmission to be raise an additional 1” to provide adequate ground clearance.

 

Everything was then disassembled, to prepare for painting. The inside of the transmission tunnel was reconfigured, and the motor mounts were redone using the stock C6 Corvette mounts, swapped side to side.  At the same time, the frame was modified to allow the stock Corvette air conditioner compressor to fit in the stock position, so that the serpentine drive belt could remain in the stock position, tight to the block on the harmonic balancer.  Mounts for the mid engine plate also had to be relocated.   At this stage the cockpit floors were added, as well as numerous brackets and mounts for such things as the bumpers, battery, gas tank and trunk floor.  The C6 Corvette sway bar mounts were also slightly re-positioned.

Prepping the chassis for paint was done while the body shell was at the body shop for painting.  It included rolling the chassis over to inspect, and redo any suspicious or missing welds, dress all welds smooth to the surrounding metal where possible, and fill others with spot putty and then prime paint.

 

Visible areas of the frame are painted 2006 Mustang Tungsten Gray (leftover paint from the ’66 Commander) with a semi gloss clear coat.  The underside of the floors and wheel wells will be painted with black bed liner.  

With a fresh coat of paint on the chassis, it was finally time to start the re-assembly process while the body received some additional attention in the paint booth.  

 Soon, the paint was complete and the body was back at the shop, ready to be lowered onto the chassis.

 

Additional metal reinforcement was added, connecting the door hinge boxes, lower dash support, and firewall to the chassis, in both the engine bay and welded to the lower chassis rails at the front of the door, and by welding the original Avanti roll bar to the chassis at the back of the door.   At this point the Avanti GT became virtually a unibody structure.

 

To accommodate the recessed firewall and make room for the Vintage Air system, a spacer was made to move the dash and seating position back 4.5”.   

The Vintage Air controls will be installed in the original radio dash recess and a new Kenwood Audio and Navigation system will be located at the front of the modified original console, where the air conditioning outlets were formerly located.

Since upholstery in the window areas must be installed before the glass, the remaining suspension was temporarily installed to create a “roller”, so that the Avanti GT could be transferred to Route 66 Upholstery.   A 1963 Turquoise and Elk “faux leather” upholstery theme was adopted for the interior, utilizing Procar Rally seats and AAC Tuxedo Turquoise and Black carpeting. 

 

 

With minor changes, the original Avanti shifter and air controls were retained to continue the theme.  The dash now has two large round Dakota Digital analogue gages connected to the ODB2 outlet of the ECM for the LS2 engine and transmission computers. In addition to greatly simplifying dash wiring, the Dakota Digital system provides multiple inputs of modern secondary information, as well as electronic safety start controls and a manual tapshift with a digital gear position indicator for the 6L80e transmission.

 

Upon return to my shop (unfortunately many weeks later than planned), a new windshield was installed, along with the original rear window, door glass, and the shortened (4.0”), and still functional, rear quarter windows; all with their respective newly polished stainless. 

 At this point, a Speartech wiring harness and modified ECM were installed to control the LS2 Corvette engine.  This was merged with a Painless wiring harness and fuse block to control all lighting and other electrical systems. Extensive use of relays minimized electrical loads on switches and wiring within the passenger compartment. The overhead switch console remains functional

 

With the wiring almost complete, attention was next focused on plumbing lines for the brakes, fuel and cooling lines for the engine and transmission. All suspension components were refinished, and permanently installed. Once the driveshaft and rear axles were shortened to the correct length, and installed, the C6 Corvette brake rotors and calipers were also re-installed

Progress slowed during the summer months; partly due to very hot weather, and partly due to other automotive "distractions" that tend to fill up the calendar during the all-to-short summer months.

With the cooler fall weather, a flurry of activity resumed, addressing the many remaining details, which included installing the flush mount front bumper and the rear modified C3 Corvette split bumpers which frame the four outlet center exhaust tips.

 

We were hoping that car could be finished by mid November, to allow a debut display of the Avanti GT at the Muscle Car and Corvette Nationals Show in Chicago.    However, the ECM was not communicating correctly with the transmission control module and the result was that the car refused to move.  Both the ECM and TCM were removed (not easy), shipped to Indianapolis for reprogramming, returned and re-installed, all within the first week of November. 

 

Just before leaving for Chicago, a custom stainless MagnaFlow exhaust system, complete with “high flow bullet cats” was fabricated installed by the Harrington Built rod shop.

The Budnik built “Remington” SKO custom 18” wheels were further customized with gold accents in the brushed areas, for a subtle “magnesium style tint”.

 

Yes, we made it to Chicago, with the first significant drive of the Avanti from the trailer to our display site adjacent to the Avanti Timeline display, which had been superbly coordinated by Ed George and friends .

The Avanti GT was well received in a show where the stars are the rarest of factory original Muscle Cars which are revered as well as numerous period correct modified race cars.  

 

Over the winter there are still a few details to complete, and others to be improved upon.  No doubt, road testing will expose a few flaws to repair and like any custom vehicle, it will never truly be finished.  In any case, we are looking forward to some long distance cruising this summer and a Paxton R2 upgrade sounds like a great project for next winter!

 

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