Guide: Iso IR300 & IR340
Background
Renzo Rivolta was an industrialist from Milan who made his first fortune manufacturing refrigeration units. Isothermos was established in 1939 and Rivolta soon expanded to home appliances.
After World War 2, Rivolta began to produce motorcycles; by 1950, Iso was the third largest manufacturer of two-wheeled vehicles in Italy (behind Vespa and Lambretta).
In 1952, Rivolta moved into the automotive market with his Isetta micro car which he subsequently licensed to BMW.
Having successfully produced a range of affordable vehicles for several years (and with the micro car market in decline), Rivolta decided to enter the lucrative arena for high end sports cars.
His first model would be a luxurious Coupe with a high powered engine, handsome styling and excellent build quality.
However, rather than follow Ferrari and Maserati, Rivolta took the route of Jensen, Bristol and Facel Vega; an off-the-shelf power unit would be sourced from America and most of the other mechanical components would come from established suppliers.
The large, inexpensive and powerful engine would be dropped into a custom chassis and clothed in a sophisticated body penned by one of the top Italian studios. Such an approach would enable Rivolta to sell his car for around 25% less than a comparable Ferrari and 10% less than the equivalent Maserati.
In late 1961, Rivolta enlisted ex-Ferrari designer, Giotto Bizzarrini, to begin work.
Bertone were commissioned to style the exterior and interior.
A new company, Iso Rivolta, was established in early 1962. That summer, a prototype of the new Iso IR300 was shown to select members of the Italian press. The car was given a public launch at the Turin Motor Show which opened on October 31st.
Production began in April 1963. It was hoped over 1500 examples would be sold every year.
The new model would be joined by a smaller and sportier Coupe in 1965 (the A3/L Grifo) and a GT racing car (the A3/C) as Rivolta ambitiously planned to establish his auto maker as a serious rival to the European aristocracy.
Chassis
For this first Iso, Giotto Bizzarrini designed a platform chassis built up from pressed sheet steel stiffened with a massive central backbone and boxed side members. A wheelbase of 2700mm ensured the cockpit would offer sufficient space for a generous 2+2 seating layout.
The front suspension layout comprised unequal length double wishbones. At the rear, Bizzarrini employed a De Dion axle with twin trailing arms and a transverse Watt’s linkage. Coil sprung hydraulic shocks were fitted all round along with a front anti-roll bar.
The brake system ran off a hydraulic single circuit. Servo-assisted Dunlop discs of 11.75-inches were fitted up front while those at the rear were 11.25-inches and mounted inboard.
Centre-lock Borrani wire wheels measured 15 x 6.4-inches and were originally shod with Pirelli Cinturato tyres.
A 100-litre fuel tank was installed underneath the spare wheel in the boot floor.
Engine / Gearbox
To power his new car, Renzo Rivolta approached General Motors and secured a supply of L75 motors as fitted to the recently introduced Chevrolet Corvette C3.
These all-iron, small block 90° V8s employed pushrod-operated overhead valves (two per cylinder) and wet-sump lubrication. Displacement was 5350cc thanks to a bore and stoke of 101.6mm and 82.55mm respectively.
Once landed in Italy, the engines were modified with an enlarged ribbed light aluminium-alloy oil sump, a small diameter oil radiator and a bigger water radiator.
A standard Carter AFB double barrel carburettor was retained.
By the time production started, Iso offered their blueprinted Chevrolet motor in two states of tune.
The IR300 had a compression ratio of 10.5:1. Peak output was 295bhp at 5000rpm and 360lb-ft at 3200rpm.
The optional IR340 featured a different camshaft and valve arrangement, mechanical instead of quieter hydraulic tappets and a higher 11.25:1 compression ratio. In this configuration, peak output was 335bhp at 6000rpm and 343lb-ft at 4000rpm.
Transmission was through an all-synchromesh Borg Warner T-10 four-speed manual gearbox, a single-plate clutch and Salisbury differential.
Bodywork
Instead of Pininfarina, Touring or Vignale, the new Iso was equipped with a body and interior designed by Bertone. The project was executed by a young Giorgetto Giugiaro who created a handsome exterior and equally stylish cockpit.
At the front of the car, single headlights were mounted either side of a wide primary intake that housed a natural alloy grille. Inverted eyebrows above the headlights gave the car a distinctive appearance and wrapped around to the front fenders where they swept back to a bank of engine cooling vents behind the front wheel. The underside of the vents formed a swage line that travelled all the way to the back of the car.
More vents were added behind the rear wheels and on the C pillars. The hood was accessorised with an artistically crafted cooling intake.
Wraparound front and rear screens were installed and the door windows featured an opening quarterlight.
Full width bumpers were fitted at either end and chrome-plated sills strips broke up the otherwise slab-sided design.
At the back, a deep rear apron partially shrouded the single exhausts on each side.
The all-steel body was welded to the chassis. Iso went to the trouble of producing expensive press-tool dies for the IR models but volumes never justified the investment in presses to go with them. As a result, the dies were kept at factory and periodically sent out to be fitted to a sub-contracted press in the local area where a batch of body panels was produced.
Interior
The Iso’s well-insulated cockpit was equipped to as high a specification as any of its esteemed European rivals.
Connolly leather was used to cover the seats, door panels, knee roll and sidewalls. The dash top was black vinyl.
A wood-rimmed steering wheel had three natural alloy ventilated spokes. Well-cushioned seats were designed for long distance comfort.
As per the front and rear centre consoles, the dash was given a teak veneer fascia.
Instrumentation comprised a large speedometer and rev counter with a small oil pressure gauge in between. A fuel gauge was positioned on the outer side of the dash and four additional read outs were located towards the centre. Stacked two by two, they included an ammeter, water temperature gauge, oil temperature gauge and clock.
Housed on the knee roll was a bank of flick switches. Underneath were the controls for the ventilation system.
Electric windows and a lockable glovebox were standard.
The long wheelbase meant there was space for four adults. Visibility and build quality were both excellent.
Options
In addition to a choice of interior and exterior colours, Iso offered a three-speed automatic transmission, fabric upholstery, air-conditioning, fog lights, a Salisbury Powr-Lok limited-slip differential, Armstrong Selectaride dampers with four-way electric adjustment, a choice of three final drive ratios and a radio.
Weight / Performance
Both IR300 and IR340 variants weighed in at 1549kg.
The IR300 had a top speed of 135mph and a 0-62mph time of 6.8 seconds.
The IR340 could hit 142mph and sprint from 0-62mph in 6.5 seconds.
Production Changes
During the course of production, Iso enlarged the rear brake discs to a 12-inch diameter.
Later, the expensive wire wheels became an option as alloy rims with chrome hubcaps were phased in. Like the wires, the cast alloy rims were manufactured by Borrani.
Iso also went on to offer the option of a five-speed manual gearbox or two-speed automatic.
A few cars were reputedly equipped with 365bhp engines at the request of their owners.
Death of Renzo Rivolta
Unfortunately, on August 19th 1966, Renzo Rivolta unexpectedly died of a heart attack. He was 57 years old.
The company was taken over by his 25-year old son, Piero, who had graduated from university with a doctorate in mechanical engineering.
End of Production
Despite ambitious sales targets for the new Iso, IR production never came close to the anticipated figures.
By the time the model was discontinued in 1970, a mere 797 had been completed.
Of these, 630 were to IR300 specification and 167 were the more powerful IR340 variants.
The model was succeeded by the Lele which remained in production until Iso’s closure in 1974.
Text copyright: Supercar Nostalgia
Photo copyright: Iso
