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Jim Clark’s Lotus 35 Ford Cosworth SCA 1 litre F2 car at rest in the Pau paddock on the 25 April weekend in 1965…

You forget what delicate little flowers these cars were. When I glanced at Ian Gordon’s wonderful shot I initially thought it was a ‘screamer’, a 1 litre F3 of the same era. Not so.

Remember the pantheon of single-seater formulae at the time was 1.5 litre F1 engines giving 205-215’ish bhp, 1 litre pushrod F3’s breathing through a single carburettor choke giving about 100bhp and 1 litre OHC race engine F2’s giving 115 initially towards 150 bhp plus by the formula change to 1.6 litres in 1967.

Jim won at Pau from Dick Attwood’s Lola T60 SCA and Jochen Rindt, also SCA powered in a Brabham BT16.

The engine in Clark’s winning Lotus is Keith Duckworth’s conception based on the production Ford 116E block. The SCA (single cam series A) was the dominant F2 engine of 1965. It won all of the ‘Internationals’- there was no European F2 Championship until 1967, with the exception of the ‘Autocar Trophy’ at Snetterton in May. Graham Hill took that win, BRM P80 powered, aboard a John Coombs Brabham BT16.

Ian Gordon became a well known and respected Australian race mechanic, later working for Alec Mildren Racing and Max Stewart amongst others. He was on a racing holiday in 1965 and snapped these fantastic photos of the ‘F2 Engines of 1965’ during the Pau Grand Prix weekend. The engines are the SCA, BRM P80 and Honda S800.

For Jim it was the first of five F2 wins in ’65- that amazing season of Clark domination (F1 World Title, Tasman Championship and Indy 500 win), the others were at Crystal Palace, Rouen, Brands Hatch and the Albi GP late in the season.

The real threat to Cosworth SCA dominance into 1966, not that it was necessarily apparent at the time, were the 1 litre DOHC, injected Honda 4 cylinder engines fitted to various of Jack’s works Brabhams during 1965. The peaky nature of the engines power delivery was the primary issue which was addressed in spades over the winter. Click here for my article on Brabham Honda dominance in 1966.

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Duckworth’s First Cylinder Head Design…

By the beginning of 1963 new F3 and F2 categories were announced, the former to replace Formula Junior to take effect from 1 January 1964.

Duckworth, armed with 17,500 pounds of support from Ford set to work on the new ‘SCA’ engine which would use the Ford 116E block known so well to them.

Sitting atop it would be an aluminium cylinder head with a line of vertical valves, two per cylinder ‘It was really an overhead cam version of the last Formula Junior engine’ Duckworth quipped in Graham Robson’s wonderful ‘Cosworth’ book.

The engine was notable for its bowl in piston combustion chamber or ‘Heron Head’ design. ‘My simple argument was that at the compression ratios we could use, and the valve sizes needed to ensure good breathing, that a bathtub type of chamber ended up masking the valves. It was an awfully long way around their periphery. I argued with myself, that if I put the combustion chamber in the piston, then for most of the time the valves would be out of the way, and that they wouldn’t impede the flow’ Duckworth said.

The steeply aligned inlet port of the SCA owed much to the Mk XVII pushrod 1963 engine engine which was heavily modified by having tubular downdraught inlet ports brazed into the casting. It wasn’t easy to do or cheap to make but improved gasflow. The SCA in some ways mirrored that approach.

KD ‘The SCA was the first cylinder head that I ever designed, and now I think their was quite a lot wrong with it. We had all sorts of trouble with the combustion- we couldn’t make it burn- but it was still good enough to win a lot of F2 races. In the end there was so much spark advance, that it wasn’t reasonable. We ended up with 49 degrees. The SCA chamber suffered from a lack of circumferential swirl’.

 

Duckworth- ‘It might not have been right, but we had to make it work. It won the F2 Championships of 1964 and 1965…and…until the Honda engine of 1966 with four valves and twin overhead camshafts, tungsten carbide rockers and torsion bar valve springs appeared in Jack Brabham’s cars. We’d run out of breathing at 11,000 rpm so we obviously needed more valve area. That’s what started me thinking about 4-valve heads’.

‘Mike Costin  and I exercised great ingenuity- we had ports that curved around, we had the piston of the week with every kind of shape, dint and odd hole- but the combustion was not good, the mixture never burned properly’.

All the same, the dominant F2 engine of 1964 and 1965 did so producing between 115 bhp @ 8700 rpm in its original Weber 40 IDF carburettor form and ultimate ’66 spec Lucas injected form 143 bhp.

Ford 5 bearing 116E block. Single, (train of seven gears) gear driven overhead camshaft, two valves per cylinder , Cosworth rods and pistons, Laystall steel crank. 997cc- 81mm x 48.35mm bore-stroke.

SCB variant 1498cc 175 bhp – 3 engines only built including the Brabham BT21B raced by ex-Brabham mechanic Bob Ilich in Western Australia

SCC variant 1098cc 135 bhp for North American sportscar racing

Bibliography…

‘Cosworth: The Search for Power’ Graham Robson, tentenths.com, F2 Index

Photo Credits…

Ian Gordon, Peter Windsor, John Marsden

Tailpiece: Jim Clark’s Lotus 35 Cosworth SCA on the way to victory in the 80 lap, 221Km Pau GP on 25 April 1965. Its only when you look hard you realise that it is not an F1 Lotus 33!…

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