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MECHANICAL: The HC weighed in at an average of 4% more than the equivalent HB model and therefore an increase in engine power was required to maintain the same performance, this was only partially successful. At launch in September 1970 Vauxhall claimed that an increase in engine capacity was rejected due to the high tooling costs, in fact the 1256cc engine was all ready for production but Vauxhall simply did not have the finance to make the changes, and it would be over a year before it finally did get introduced.

On the Basic & Deluxe versions the standard 1159cc engine carried over from the HB produced 50bhp (net) @ 5300rpm compared to 47bhp @ 5200rpm, a 6% increase. With the “90” engine, optional on Deluxe & standard on SL models, power went from 59.5bhp (net) @ 5300rpm to 61bhp @ 5200 rpm, only a 2.2% increase. The increases in output were obtained by simply enlarging the inlet valve diameter by 7%, from 1.32ins to 1.36ins on both and the standard unit was fitted with the “90” exhaust manifold. The optional 1600 OHC engine, available on SL models only, was de-rated in the last of the HB Vivas by fitting a lower lift camshaft in an effort to try and improve the uncompetitive fuel consumption but in the HC the benefit was negated by the increase in weight so the performance & fuel consumption was worse than the models they replaced. The 1600 produced 70bhp @ 5100rpm and 83.5lb.ft of torque @ 2200rpm, the flat torque curve did mean that the 1600 could pull away in top from a walking pace – possibly its only advantage over the “90” engine. The OHC engine also featured improved oil sealing, which had always been a weak point.

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The transmission options were carried straight over from the HB, 4 speed manual as standard with the larger Victor gearbox fitted to the 1600, but the GM Strasbourg 3 speed was now optional only with the “90” or 1600 models, the rear axle ratio was standardised across the range at 4.125:1 to compensate for the larger 13ins wheels, a 3.9:1 was an option in certain export markets. In an effort to improve refinement Vauxhall engineers cured the HB’s vibration problem due to a lack of concentricity and face run out in the flange to which the rear UJ was bolted, this was solved by a shortened & strengthened pinion shaft and a longer length propshaft. A slightly larger 6.5ins diameter clutch was fitted to the 1159cc models while the 1600 retained the 8ins as before.

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SUSPENSION & BRAKES: An area of concern during the HC’s development was to greatly improve the ride quality which was an area of consistent criticism of the HB and was largely down to the rear axle’s tendency to hop and bounce on uneven surfaces and compounded by the interior seat design. This was improved with revised damper settings with a stiffening of the rebound pressure and a completely new design of seating with a new type of springing and padding. New more resistant rubber bushings on the frontsuspension arms also improved road noise.

The HC was also the first Vauxhall to feature negative offset geometry steering which meant some control was retained in the event of a front tyre blow out.The braking system followed advances by other GM divisions and featured a split hydraulic system so that if a leak developed it would not result in a total loss of braking. Standard & Deluxe models used 8ins diameter drum brakes front & rear, servo assisted 8.5ins diameter front disc brakes were optional and standard on SL, “90” & 1600 models.

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BODY STRUCTURE & SAFETY: Although the HC gave the impression of being much larger than the HB in fact it was only 1ins longer and 1.7ins wider, this impression of size was emphasized by a much larger glass area than before greater side curvature. Despite the small increase in size the interior benefitted from 2.5ins extra front legroom, 2.5ins extra rear shoulder room & 2ins extra in the front along with a 16% increase in luggage capacity. The body was also made from thicker grade steel, as much as 28% thicker than some competitors, and was necessary for increased crash worthiness with specific crumple zones front & rear. The body’s torsional stiffness was also 20% better than the HB - which was already pretty good. Safety features built in included dual circuit brakes, collapsible steering column with safety steering wheel, standard front seat belts with strengthened anchorages along with fixing points included for fitting rear seat belts (standard fitment in Canada), breakaway interior rear view mirror, padded sun visors, collapsible front seat backs and no protruding interior objects that could cause personal harm in an accident which included a safety designed top windscreen header that helped to minimise head injury. Completely new anti-burst door locks were developed in conjunction with AC Delco which gave a 100% increase in longitudinal burst strength & a 50% increase in transverse burst strength and were required to meet Canadian regulations.

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HEATING & VENTILATION: The Viva HB used facia mounted air vents which relied on pressure pushing through the door seals for extraction, the HC featured larger “eyeball” style vents at each end of the dashboard and proper ventilation extraction through the louvres in the lower edge below the rear window or above on Estate models. In addition an air blending heater unit was fitted as standard on all models which gave far better temperature control than a water valve system and was combined with a quieter running 2 speed blower fan.These changes meant that more effective door seals could be fitted thereby reducing wind noise which was also aided by the deletion of front window quarter windows.

LAUNCH: The public & motoring press reaction was a mixed bag, it was seen as an effective re-body and mechanical upgrade of the HB rather than a completely new car. Nearly all the major components were carried over with only mild changes. The body exterior design was quite well received and incorporated a wrap around rear light design that had first been shown on the XVR design exercise from 1966. The interior was far less satisfactory and was not up to matching the competition at the time. The dashboard had obviously been designed to make LHD conversion as cheap as possible and the extensive foam moulding was specifically designed for the Canadian market where Pontiac dealers sold all versions of the car as the Firenza. The motoring press criticised the lack of power from the standard engine and also the subjective lack of performance from the 1600 which should have been much better. Also there was no replacement for the HB Viva GT, Vauxhall knew the Firenza was coming but didn’t realise what a flop that would be. There were also complaints about the lack of standard equipment even compared to home grown competition let alone Japanese imports which were really starting to make inroads into the UK market. Despite this initial sales were quite good, Vauxhall made great play of the Millbrook connection which was a little tenuous as most of the major development work was done at Chaul End before Millbrook became operational. The launch slogan – “The car we beat around to beat any car around” – sounded punchy but in reality the early HC reliability was highly unsatisfactory, particularly in Canada which is dealt with in the Firenza section of the site

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