In 1968 the E-Type was treated to a number of evolutionary upgrades that maintained the cars standing with USA American market regulations. The series Series I½ designation is an unofficial term for these interim cars which bridged the gap between Series I and Series II cars.
Federal emissions regulations forced Jaguar to reconsider their intake system. After reviewing exhaust-air injection and fuel injection, a clever system employing a duplex manifold system and twin Zenith Stromberg carburetors was used. Only the American Series I½ cars featured Strombergs, while the European cars still used triple SU carburettors.
The most obvious change was the deletion of the front headlight covers which improved the outward vision at night and provided better access for servicing.
Later Series I½ Roadsters featured the new Series II interior with plastic rocker switches, flush choke and heater controls, a combination ignition and starter switch and recessed interior door handles. Some early Series I½ cars still had the early toggle-switch dashboard and these are sometimes refereed to as Series 1¼.
In total, Jaguar made 21 changes to the US Federal cars that distinguished it from the series 1 cars. They were first seen at the 1968 New York Motor Show and coincided with the release of the Dunlop SP Sport CB73 radial tire.
1,942 cars were made to Series I½ specification and adopted the 1E chassis number scheme that was common to all 4.2 Series I cars.
| type | Series Production Car |
| released at | 1968 New York Motor Show |
| built at | England |
| price £/td> | £1,568 |
| engine | Inline-6 |
| position | Front, Longitudinal |
| aspiration | Natural |
| ignition | Lucas Type 22D6 Distributor & Lucas HA12 Coil |
| block material | Cast Iron w/Aluminum Cylinder Head |
| valvetrain | Chain-Driven DOHC |
| fuel feed | Twin Zenith-Stromberg Carburetors , HD8 2 |
| displacement | 4235 cc / 258.44 in³ |
| bore | 92.07 mm / 3.625 in |
| stroke | 106.0 mm / 4.173 in |
| compression | 9.0:1 |
| power | 183.4 kw / 246 bhp @ 5400 rpm |
| specific output | 58.09 bhp per litre |
| bhp/weight | 220.23 bhp per tonne |
| torque | 383.7 nm / 283 ft lbs @ 4000 rpm |
| body / frame | Unitary Steel Monocoque w/Reynolds 531 Front Frame and Stamped Rear Steel Subframe |
| driven wheels | RWD w/Thornton PowrLok Limited Slip Differential |
| wheel type | 72-Spoke Knock-Off Wire Wheels |
| front tires | Dunlop SP 6.40x15R55 |
| rear tires | Dunlop SP 6.40x15R55 |
| front brakes | 11 inch Dunlop Discs w/Servo Assist |
| f brake size | 9.5 x 279.4 mm / 0.37 x 11 in |
| rear brakes | 10 inch Dunlop Discs w/Servo Assist |
| r brake size | 9.5 x 254.0 mm / 0.37 x 10 in |
| steering | Rack & Pinion |
| f suspension | Wishbones w/Torsion Bars, Hydrualic Telescopic Dampers, Anti-Roll Bar |
| r suspension | Half Shafts w/Transverse Links, Twin Coil Springs, Hydrualic Telescopic Dampers, Anti-Roll Bar |
| curb weight | 1117 kg / 2463 lbs |
| wheelbase | 2438.4 mm / 96 in |
| front track | 1270.0 mm / 50 in |
| rear track | 1270.0 mm / 50 in |
| length | 4451.3 mm / 175.25 in |
| width | 1657.3 mm / 65.25 in |
| height | 1219.2 mm / 48 in |
| transmission | Model 8 Borg Warner 4-Speed Manual |
| tran clutch | 10in Laycock-Hausserman Diaphram Clutch |
| gear ratios | 2.68:1, 1.74:1, 1.27:1, 1.00:1 |
| final drive | 3.07:1 |
| fuel capacity | 63.64 litres |
