Rover 3500 V8

A new kind of Roving

Although the Rover 2000 was designed from the outset as a four-cylinder car of around 2-litres, the possibility of increasing both power and refinement by the use of a large unit with more cylinders was contemplated from a fairly early stage in the development period. At one time, six cylinders were envisaged, but when development work began on the light-alloy V8 now used in the Rover 3.5 litre, this became a natural choice. With the design of the 2000 so new throughout, however, resources were concentrated in the first place in getting the basic, four-cylinder car into production. The result, as everyone knows, was the most successful car produced by Rover to date and further consideration of a bigger-engined version was inevitably shelved until production of the normal 2000 (and the subsequent TC and Automatic versions) could be matched to demand.

Now the time has come for the 3 1/2-litre V8 engine to be wedded to the basic 2000 conception and the result is the new Three Thousand Five. This car, it should be stressed, is in addition to the Rover 2000 which is likely to continue as Roverīs best seller, with a production figure currently running at around 800 per week. The new model will appeal mainly to buyers who want the now well-known handling and handiness of the Rover 2000, plus the extra refinement and performance given by the light-alloy V8 engine. Just what this means in terms of performance will be found in the road test report. Here, to put the story in perspective, it is necessary only to say that a maximum speed of 117 mph was recorded together with a 0-50 mph acceleration figure of 7 seconds and a touring fuel consumption of 21.3 mpg.

Mating the V8 engine to the 2000 was not the simple exercise it might appear. Most of us have had experience of cars in which the alternative-engine plan was not an unqualified success simply because the car was designed for one unit in the first place, and little was done to tune its characteristics to suit the new one. This certainly does not apply to the Rover Three Thousand Five, although the initial instructions to the engineering department were to "make minimum alterations". The ideas of Rover engineers on acceptable standards meant that "minimum" was interpreted very freely and a great deal of development work was, in fact, carried out to achieve results which would satisfy them.

To the engine itself very little has had to be done and almost all of it for installation convenience. To be specific, the exhaust manifold now has a centre outlet instead of a rear down pipe in order to clear the modified 2000 hull, the external oil filter has been reangled to clear the front cross-member; the air cleaner is now of round instead of oval section, the power steering pump with its belt drive has been omitted as power assistance is not required, and the alternator now has a finger quant for safety - a feature which has also been adopted on the Rover 3.5-litre.

In all other respects, the very successful 90-degree V8 engine is unchanged. Notable features include cylinder blocks and crankcase formed in a single light-alloy sand casting, into which dry cylinder liners are pressed; die-cast light-alloy cylinder heads with inclined in-line valves operated by push by push rods and rockers from a single central camshaft; self-adjusting hydraulic tappets and rockers of light-alloy with sintered iron inserts for the push and sockets and steel inserts in the valve stem pads; wedge-shaped combustion chambers; and pistons with shallow depressions in their crowns to give both a beneficial effect on the quench area and a ready means of varying the compression ratio to suit particular markets.

How the V8 engine was installed in the hull is a minor development story in itself. As the unit would not "drop in" as it stood, the obvious course was to extend the nose of the car. This was tried but had three disadvantages: overall length was increased, new wing and bonnet pressings would have been needed, and there was too much forward weight. Next, two cars were built on a "cut-and-shut" basis, existing structures being cut about and welded up to accept the new engine with a minimum of alteration. These two cars were proved useful for development work but despite the obvious advantage of a "mini-mod" policy, much more was thought necessary.

Finally, a very careful rearrangement enabled the engine to be installed with no increase in overall car length, no undue front axle weight (the V8 engine weighs the same as the "four" within a few pounds) and without any need for new bonnet or front-wing pressings. This arrangement involved moving the battery to the boot (where it is neatly recessed into the floor in a light but very strong box of expanded, high-denaty polyethylene), moving the front cross member forward (but not so much that the grille would have been pushed beyond the bonnet nose) and tilting the engine back 3 degrees 54 minute to enable the starter to clear the propeller shaft tunnel. The effect of the engine tilt on the action of the universals is greatly reduced by correctly phasing the universals and suitably aligning the final drive assembly so that minor variations in prop-shaft speed are largely cancelled out.

Although the bonnet pressing is unchanged, its stiffeners have had to be modified to avoid fouling the front cross member, the headlamp apertures have had to be placed nearer the ends of the extruded grille, and various detail modifications made to inner wing pressings, engine mountings and so on.

In addition, considerable work had to be done on the cooling system. Obviously, greater heat dissipation was needed and a desired radiator area of about 360 was obtained by installing a cross-flow radiator of 20 in. wide and 18 in. deep. Because this extends well below bumper level, a stout protection channel is bolted below it to prevent accidental damage. The radiator incorporates oil-cooling tubes in its side "header tank" for the Borg Warner automatic transmission, and its location is such that there is room for a condenser in front of it when this is required for air conditioning.

Although the radiator capacity was considered adequate, troubles were experienced with the engine getting too hot and the car heater not hot enough. This apparently contradictory state was eventually traced to the fact that the low position of the filler cap made it impossible to bleed the system completely. Although the circulation was vigorous enough to clear the air pocket, the result was to aerate the water with small bubbles and introduce problems of heat transference. One the trouble had been located, it was easily cured by connecting a bleed pipe from the inlet manifold water jacket (where the air accumulated to the filler cap side of the radiator tank, thus enabling the offending air to be expelled by running the engine up to normal temperature with the filler cap removed.

Air locks in the fuel system are not uncommon with big engines under small bonnets and this has been forestalled by a spill-return system. A bleed hole at the second carburetter is connected back to the tank reserve outlet so that cool fuel from the enlarged (15-gallon) tank is always circulating when the engine is running.

The only other engine modification is a redesigned exhaust system employing double-skin pipes for noise suppression wherever possible. The two pipes from the manifolds meet behind the engine and a single pipe then leads to a modified forward silencer, beyond which the system is identical with that of the 2000 except for the tail pipe where an increase of only 1/8 in. (to 1.7/8in. o.d.) has been found to give a power increase of slightly over 1 bhp.

In unit with the engine is a Borg Warner Type 35 automatic transmission with D1 and D2 positions, as on the big Rover, except that the maximum shift speed from intermediate to top has been lowered from a nominal 4.600 rpm to 4.200 rpm, while clutch pressures have been modified to improve shift quality. The internal gearbox ratios are unchanged but, as one would expect, the final drive ratio has been raised compared with the 2000 to take advantage of the much higher power (47% over the TC) and torque. The change is from 3.54:1 to 3.08:1.

A four-pin differential is used to cope with the added loading and advantage has been taken of the need for a new and larger final drive casing to reposition the filler more accessibly. The mountings of the differential casing are of the same design, but stiffer material is used for the flexible bushes because there is no need to cater for the secondary out-of-balance forces present with a four-cylinder engine.

Although the general layout and principles of the final drive/rear suspension assembly follow the 2000 design and the drive shafts, hubs, de Dion tube, Panhard rod and rear differential carrier are interchangeable, there are considerable differences in the remainder of the system. One of the most important is the use of a new front cross member. On the 2000, a short cross member carrying the nose of the differential case extension is bolted to the propeller shaft tunnel. On the new design, the cross member is considerably extended so that it picks up on rubber mountings on the body sills which are less susceptible to noise transmissions. In addition, the forward ends of the bottom suspension links are now flexibly mounted on the cross member instead of on the body. The new arrangement considerably reduces both road and transmission noise.

Other changes with the same end in view include larger rear bushes for the top links of the Watt linkage; there are styrene butadiene rubber which gives slightly more damping than natural rubber. The result is to increase compliance at the top link, and the bottom link bushes are correspondingly stiffened to restore the status quo.

Spring rates have been increased from 230 lb./in. to 265 lb./in. and new telescopic dampers of 1.3/8 in. bore are used in place of the 1 in. size. They also have improved rubber and polyurethane mountings top and bottom. At the front, the bottom links have been modified to clear the engine and the suspension has also been stiffened slightly - with spring rates up from 150 lb./in. to 170 lb./in. at the spring - and the leak settings on the dampers adjusted to give more control. With a view to improving directional stability, castor has been increased from 3/4 degree to 1 1/2 degree (plus or minus 1/2 degree).

These changes would normally have stiffened the steering slightly and accordingly a minor change has been made in the steering ratio. With the new Burman recirculating ball unit used, the ratio in the straight-ahead position is now 21.5:1 compared with 20.3:1 - and more on full lock.

As one would expect, the added performance has brought some brake changes in its train and the diameter of the front Girling discs have been increased from 10.312 in. to 10.82 in. At the rear, the disc diameter is the same, but it is worth noting that (as on the 2000 now) the inboard brakes are of the Girling swinging caliper type with integral handbrake. Increased servo assistance is provided by a Lockhead unit of 8-in. effective diameter in place of the 7-in. type, giving a boost ratio of 4:1.

Much development work went into the choice of wheels and tyres, including many miles of high speed tests on Italian autostrada. Investigations were concentrated on 175 and 185 normal sizes and 190 low-profile tyres. Eventually, the 185 section was chosen as providing an ample safety margin, although one tyre manufacturer would have been quite happy for the smaller section to be used. An additional factor taken into consideration, was that when the car comes to be exported - it is a home-market model only ar present - the 185 size will comply with German regulations.

This size called for a 5 1/2-in. rim and it was decided to fit the latest safety-ledge rims which give greater security against loss in pressure when drastic cornering distorts the walls. New wheel trims with a new claw fixing are used.

The change in tyre sizes introduced clearance problems for all-weather covers at the rear and this has been overcome by using wheels with a different offset to reduce the track by 3/8 in. on each side. Obviously, use of these wheels at the front would reduce the track there too and curtail steering lock. The front hubs have, accordingly, been modified to restore the position.

Of the body, there is little to say here because it is identical with that of the 2000 and, in any case, its features are the subject of comment in the road test. The only differences in equipment are the use of improved pedal rubbers and the fitting of a 140 mph speedometer. Yet mechanically, the apparently simple job of installing an alternative engine into an otherwise highly satisfactory car has involved the surprising number of changes detailed in this report. Just how the mixture works in practive will be found in our road test - in which, too, the detailed specification of the car will be found.

Motor / UK April 1968