Would 6 litres be enough to beat the Repco V8?

[Riain]

For 1966 Australian Group A sports cars were given a 5 litre capacity cap, which was all well and good, a series of 4 Elfins were built with the alloy Olds, SB Chev and 289 Ford engines. But in mid 1967 the Repco V8 of Brabham F1 lineage became available for customers which was 4.4 litres in Sport Car trim in 67 growing to 4.9l in 1969 and in quad cam 760 form made something like 640bhp. Unsurprisingly cars this engine won everything of note from mid 67 to the end of the 1972 season.

What capacity limit would be sufficient to handle the Repco V8? Would 6 litres be enough, or should CAMS just go unlimited? Obviously the SB Chev is available in that size, but what about Fords, IIUC the Honker used an alloy head 351 with 550hp in 1967?

 

[marathag]

Getting the 351W to 372 cubes isn't hard, since 408 Strokers are common now for that block with rod change and offset grind cranks.

 

[Riain]

The issue I would like to address is that when Frank Matich went to the US to race in 1967 of the 7 events the initially 1 then 2 Matich SR3s started Matich got an 8th in a USRRC race at Laguna Seca a DNF at another USRRC race and DNFs at 4 Can Am events with customer car driven by Tony Settember getting another 2 Can Am DNFs. Apparently the reason for this lack of reliability was the light construction of the Australian cars, deriving from the small engines they were forced to use and the fact that Australian sports car races were generally about 80 miles in length compared to the 150-200 mile USSRC and Can Am races.

Of the 2 reasons the latter is easiest to change, make the Australian Tourist Trophy (the premier Sports Car event in Australia up to 1968) and the 3 round Australian Sports Car Championship from 1969 onwards 120 or more mile races. All the other races throughout the year can be ~80 miles, but those premier events should set a minimum standard closer to what is required in the US.

The other reason is a bit tougher to swing. The 5 litre cap was decided in 1965 to apply to the 66 season. At the time this didn't look to be a problem, the engines being fitted to the 4 groundbreaking (for Australia) Elfin 400s built in 1966 were Traco-Olds 4.4 litres, a Ford 289 with Australia designed 4 valve heads (replaced by a regular 289) Bob Jane with the very first customer Repco V8 and a SB Chev. Frank Matich then built 3 SR3s which were basically Elfin 400 copies with totally different bodywork-aerodynamics, these started out with Traco-Olds but by mid 1967 Matich switched to Repco power and that was it for Australia Sports Car racing.

The Repco didn't exist in 1965 when CAMS made the 5 litre decision and the Sports Car version only became available in late 1966 to mid 1967, so there doesn't appear any reason for CAMS to choose a higher limit in 1965 although it's possible to see that they might do so in 1967 as the Repcos start dominating. I think that if CAMS had said 6 litres back in 1965 the Elfin 400s would not have been fitted with the lightweight Traco-Olds but bigger SB Chev and Fords until the 3rd car got the Repco. Perhaps making tougher cars would have gotten Frank Matich up in the points and the money in the Can Am in late 1967 instead of all those DNFs.

 

[Riain]

Getting the 351W to 372 cubes isn't hard, since 408 Strokers are common now for that block with rod change and offset grind cranks.

In 1966 I think you could bore and stroke a 289 out to something like 320 cubes, which cold then go into the 2nd Elfin 400. A 351 with alloy heads could be fitted in 1967 or 68.