Take one part SL90, one part Victor 2000 and add a dash of Cresta. The Viva GT was a strange concoction of various parts sourced from the then current Vauxhall lineup. Obviously the body and interior came courtesy of the HB Viva, while the Victor 2000 was used to source the 1975cc single ohc engine, along with the final drive and brakes.
To add good measure, the Cresta's close ratio gearbox was used to ensure the new Viva GT was worthy of wearing the GT badge.
The car did retain the Viva suspension set-up, however the engineers fitted a front anti-roll bar as standard.
Fitting the larger 2 liter engine was a relatively painless affair, as when the HB Viva was originally designed back in 1964 the designers had allowed enough room for the brand new Victor engine then still on the drawing board. Canting the engine to a 45° angle was all that was needed to ensure it would fit comfortably under the bonnet.
A large engine in a small car was not without compromise however, and the exhaust manifold and downpipe were a snug fit, while the radiator had to be re-located to the front of the cross-pressing. A new sump was also needed to ensure it would clear the suspension cross-member, a cast alloy pan being chosen, partly to augment the engine beam stiffness.
In standard form the Victor engine produced 88bhp @ 5500 rpm, which would have by itself made the car very spirited, but the engineers went one further, tuning the engine to ensure it delivered performance to match the blacked out bonnet.
Internally there were no changes, with the original camshaft, compression ratio and porting retained, but externally the single Zenith 361V downdraft carburetor was replaced with twin Zenith-Stromberg 150CD constant-vacuum units mated to a more efficient manifold.
The new manifold featured ports blending to 1 and 4, and 2 and 3 for maximum efficiency, then exiting through twin tail pipes. These somewhat minor changes were enough to bump the 88bhp up to 112bhp @ 5600 rpm, with maximum torque at 117 lb. ft. @ 3400 rpm (instead of the standard 109 lb. ft. @ 3000 rpm.)
When you compare that to the standard 1159cc Viva's 47 bhp, the 90 variant with 60 bhp and Brabham tuned 90 at 69 bhp
you begin to realise just how powerful the new GT actually was. There was only one small problem, the Ford Escort Twin-Cam still having the wood on the Viva, it producing 109 bhp.
To ensure there would always be spirited performance on hand, the engineers selected the close-ratio Cresta gearbox.
There were no fitting problems with the Victor engine, as the gear clusters were interchangeable within almost identical gearbox casings. This in turn transferred power via the Vauxhall Victor 2000 differential with a 3.9:1 final ratio, although the axle tube was new. Despite the low ratio's of the gears the car could still top 100 mph, although it was not ideally suited as an autobahn flyer.
Making It Handle
The engineers fitted the Viva GT with an anti-roll bar which added to the understeer already caused by the heavier front end, but it kept the roll in check. There was also an unavoidable minor modification required at the rear, where the upper radius arms were shortened slightly because of the bulkier victor based rear axle. In fact the Viva and Victor front suspension geometries were identical, the Viva GT being fitted with the stronger Victor wishbone arms and supports, plus bigger ball-joints for a longer life.
The Victor 2000 front disc brakes bolted straight on to the strengthened front upright, and the victor 9.0 x 1.75in. drum brakes were fitted to the rear. The total swept braking area was 287 sq. in., identical to that of the Victor, but an amazing 44% up on the disc braked Viva's. Even Victor wheels were fitted, these being 13 in. in diameter with a 4.5 in. wide rim, these being shod with radial ply tires.
The Viva GT Cosmetic Touches
Almost as important as making a car go fast is making a car look fast. Thankfully the designers did a pretty reasonable job of it. An entirely new fascia panel was created, along with a handsome centre console and up-market door trims. While the seats remained similar to that of the donor car, additional floor mounting points were created so that the driver could better find their perfect driving position. Even the steering wheel was made over, having padded leather trim.
The instruments were much better than the SL90's, the long strip speedo being replaced with a twin circular dials, one for the speedo and one for the tacho. Another 4 gauges were included, two each side of the centre instruments, for fuel, ammeter, oil pressure and water temperature. The centre console stretched from the fascia panel to the gearbox tunnel, it having provision for a radio along with a (very rare) oil temperature gauge and clock.
Outside the panels remained the same, but there were a raft of minor cosmetic changes that made all the difference. Most obvious was the blacked-out bonnet and grille. There were new colors too, which featured a double coach line following the waist line. The bonnet had two small air-vents situated above the engine, the designers claiming they helped with engine cooling in stop-start traffic conditions. Naturally there were GT badges to help you identify the go-fast Viva, these being located on the grille, back and rear guards.
On The Road
The considerable changes to the suspension were to avoid nay-sayers claiming the Viva GT could go quickly in a straight line - but little else. Unfortunately however the added weight over the front wheels was noticeable when cornering, the additional power at the rear wheels not being sufficient to counter this. Explore the limits of the car and you would quickly learn that, when pushed, the front end had a will of its own.
That was a shame, as the rest of the car was particularly well sorted. Straight line stability was, as expected, excellent. The GT had a better ride than the lesser Viva's, and the car had little body roll. But you would always be tested if you wanted to explore the upper limits of the cars handling during cornering - and that was undoubtedly the cars Achilles heel.