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.

Hewland ratio change in Jacks BT16 in the Pau paddock- there were lots of them as Brabham tried to match ratios to the peaky 1965 variant of Honda’s S800 engine. Brabham raced much of the ’65 F2 season in SCA powered cars as Honda development continued (Gordon)

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.


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’.

Colin Chapman sub-contracted the running of his F2 team to Ron Harris, the two wheels of the car alongside Clark’s Lotus 35 in the opening photo are those of his teammate Brian Hart- Brians 35 is BRM P80 powered and is shown above. The story of BRM’s 4 cylinder P80 F2 engine is one for another time but its vital statistics are an all aluminium, DOHC, 2 valve, Lucas injected 998cc (71.88X61.6mm bore/stroke) dry sumped motor giving circa 125 bhp @ 9750 rpm. (Gordon)


BRM P80 1 litre F2 engine cutaway (J Marsden)

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


‘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!…



  1. Jim Culp says:

    Such a tidy car. I’ve got a photo of Carolyn Dimmer vintage racing a Lotus 35 in 1965 Tasman trim (Coventry Climax power) posted on Flickr. This car is currently on display at America’s Car Museum in Tacoma, Washington, USA. https://www.flickr.com/photos/jimculp/718141576/in/photolist-eab32G-26sEtj-ea5nov-bWe1Ht-26ou3i-9ci4j9

    • markbisset says:

      Thanks Jim,
      Great looking car- I didn’t realise a 2.5FPF had been fitted to a Lotus 35.
      John Dimmer brought a Tyrrell out to run in the Tasman Historic Meeting at Eastern Creek, Sydney, a decade or so ago- mighty fine car. Got a photo somewhere!

  2. Martin says:

    Hi Mark,

    As this is my first time commenting. Thanks for your blog, always very interesting reading.

    John Dimmer also brought the Lotus 35 “Tasman” to Australia, for the Adelaide Historic meeting in 1999 or 2000. (maybe both). I think I still have some video recorded off the TV from these meetings. The Lotus 35 was also at a Eastern Creek Historic meeting, but can’t recall the year.

    The Lotus 35 seems to be the only Lotus Tasman car that didn’t compete in the Tasman series. My recollection of the Works cars are, Lotus 32B 2.5FPF. Lotus 39 2.5FPF, Lotus 33 2.0FWMV, Lotus 48 1.6FVA (Graham Hill) and Lotus 49 2.5DFW. Have I somehow missed it?

    I have wondered why the Lotus 35 Tasman was built, was it meant to be a Team Lotus entry?
    Maybe your investigative skills, could unearth its history.


    • markbisset says:

      Great to hear from you Martin,
      Your list of the works Tasman Lotuses is spot on- you could add the 18’s and 21’s from the pre-Tasman phase I guess for a complete list.
      As to the Dimmer car see the link attached to a Ten Tenths blog thread where JD gives a quick history of his car- in short the car started life as a works F2 machine and was converted by Lotus to Tasman spec- tho not raced in period in Australasia.
      Keep in touch,

  3. Martin says:

    Thanks Mark,
    That answers the question.


  4. Emery says:

    A note about the Pau paddock pictures. What first drew my eye to them was the very stretched tires mounted to the rear rims… certainly not a normal configuration, which makes me wonder if Clark was trying to fight severe understeer on Pau’s tight corners?

    Second curious item is that they’re Goodyears rather than Dunlops. Kevin Whittle’s “Lotus 35 a History” confirms that Clark ran the Goodyears in practice, but switched to Dunlop R5s for the race while the rest of the field were on R6s. There is no more mention of Goodyears for the 1965 season.

    Man, I sure learned more than I ever thought I wanted to know about 1 liter F2s from Kevin’s book!

    • markbisset says:

      Thanks for the insights Emery,
      I’m not familiar with that book, but will seek it out on good ole ebay. I’m a big F2 fan, should do a few more articles. Love the 1.6 litre formula and earlier 2 litre days. Such a shame there is no longer an equivalent with the variety that went with it!

  5. Luc says:

    very interesting article. I just wonder about the Honda engine used in 1965, it was the S800 rebored at 1000 cc and you say it’s RA302E type. But the RA302E is the F1 engine used in 1968, a V8 3 l.
    I may be wrong or you can explain me what I don’t understand. Thanks

    • markbisset says:

      Spot on, big mistake on my part! Thanks for picking it up, it’s quite a popular article and you are the first to spot the error. Blowed if I can find the correct designation for the engine, F2Index which is my reference source for F2 results, simply call it ‘S800’ so I have changed two articles to use that designation.
      Thanks for getting in touch.

  6. Chris Helliwell says:

    Hi Mark,

    Love the article and your blog. Wondered if you had ever heard of the BMC 1000cc F2 engine that was developed in 1964/5 but never actually raced? It was tested several times but struggled with reliability issues and was eventually abandoned, due to the coming reg change from 1967 to 1600cc, and that BMC believed the SCA was producing much more power. If you have any paddock photos from Silverstone March 1965, you may just spot it – as it was apparently there! But otherwise few pictures exist – i do have some though, along with a Cooper T75 chassis that the engine was fitted to, and a running engine plus spares! So the stillborn project does lie on, and has completed a few races in recent years! Let me know if you’d like to know more – i’m always on the hunt for more period pictures and info!

    Best Wishes,


    • markbisset says:

      Sounds like an interesting car and engine- one I am not familiar with at all. By all means send me some material- my turn-around is pretty slow at present, I ‘owe’ so many folks articles already! But keen to learn more.
      Thanks for getting in touch.

  7. […] Click here for an article about the Lotus 35- and the Cosworth SCA and a little on the P80 BRM unit- the excerpt above is from this piece; https://primotipo.com/2017/11/06/jim-clark-lotus-35-and-the-cosworth-sca-f2-engine/ […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s