Rover 3500 V8

The 3.5-litre Rover V8 is an exceptional car. Its small and lightweight V8 engine has rare ability in relation to its modest cubic capacity, particularly in that it revs eagerly.

In South African production, this automatic-transmission car was introduced a year or so ago, with the lower "export" compression ratio of 8.5 to 1.

The Borg Warner three-speed transmission has a three-element hydrokinetic torque converter coupling, capable of an infinitely variable rate between 2.1 to 1 and direct drive. It is controlled by a smooth console-mounted selector which enables the driver to hold individual ratios - but preferably only if he has a rev-counter fitted and red-lined at 5200 rpm.

Higher C.R.

At the time of our original Road Test of this car, with 8.5 to 1 compression ratio engine, in February 1970, we guessed that in its high-compression form (10.5 to 1, as marketed in Britain) it would be a contender for top honours among the Republicīs performance models.

The higher compression ratio is achieved merely by fitting a set of high-compression pistons, which can be obtained in kit form at a cost of about R170, and would involve something like R100 in fitting costs.

This boosts engine output by just under 14 per cent, and torque by 7.5 per cent, according to factory specifications, at the same time increasing engine range from 5000 to 5200 rpm.

Special Test

Quite by chance, the opportunity arose recently to re-test the same car, now fitted with the high-compression pistons.

And with high-octane (probably 98) fuel just round the corner, we were able to push this test into the realm of pure research by testing the high-compression engine twice: with 100-octane racing fuel, and - subject to a 6-degree ignition retard - on the standard 93-octane "premium" we have become accustomed to.

The results are something of a mixed bag, and do not necessarily give a decisive answer to owners who may be considering uprating their carsī engines with high-compression pistons when our new octane rating arrives.

Performance is up - but not by a shattering amount - and fuel economy seems to be virtually unaffected. With the proposed high-octane fuel bound to be up considerably in price, this is an important consideration.

Performance - 93

With timing set on TDC and the tank filled with 93-octane, we did a full set of performance runs, using manual control to go to 5000 rpm through the indirect ratios. There was a distinct gain in torque, affecting gradient ability and acceleration.

Taking the acceleration to cruising speeds as the most indicative, the improvement in acceleration times averaged 5.4 per cent, while maximum speed potential goes up slightly. Top-gear pulling power was considerably improved, particularly at higher speeds.

Performance - 100

Next stage was to drain the tank, fill up with 100-octane racing fuel, advance timing at 6 degree before TDC (factory specification) and re-test.

Another surprise: small improvements in acceleration and gradient ability, and slightly more in maximum speed potential, with fuel economy again remaining fairly constant - though showing signs of improving towards the high-speed range.

This time, the improvement in acceleration times over our original test was 8.2 per cent - only 2.8 per cent of it accounted for by the super-octane petrol!

Maximum speed potential in this form went up to 185.3 km/h (114.9 mph) - making this South Africaīs top automatic-transmission car in terms of straight-line speed. Not even some of those hairy big V8 models are likely to match this, except in manual-transmission form.

Octane tolerance

This test certainly showed that the Rover V8 engine, with its advanced design, is extremely octane-tolerant. With 10.5 cr it performed perfectly happily on 93-octane fuel with TDC timing - indicating that owners on the Reef would probably be able to operate with the raised cr on 93-octane at full 6-degree advance.

The other question is: is it worthwhile doing the conversion on cars already built, with the low-compression engines?

Our reaction would be: probably not. Should Leykor at a later stage introduce a 10.5-cr model to take advantage of better fuel, that is a different matter: we imagine buyers would accept this very happily.

But the advantage of modifying an older car is not marked enough to be worth it, in ordinary circumstances. The cost is fairly high, and the gain small. Our choice would be to leave those low-compression pistons where they are!

  93-octane 100-octane
0-80 km/h 7.5 sec 7.3 sec.
0-100 km/h 11.2 sec. 11.0 sec.
0-120 km/h 16.0 sec. 15.7 sec.
top speed 180.2 km/h 185.3 km/h

CAR / South Africa 1/1971