Having mentioned that my 2.2S engine is being built partially along the lines of a 2.3 ST unit – I thought it might be worthwhile describing what the 2.3 ST is.
As the Porsche factory started to become more interested in establishing the marque through racing success they began to focus on providing their very successful privateer customers with the right cars to win races. Consequently – more focus was placed on modifying 911 road cars to compete successfully across a number of race disciplines.
The 2.3 ST was aimed firmly towords Group 4 track racing but there were other developments such as the 2.2 S/Rallye and Safari models aimed towards rallying success.
The 2.3 and 2.4 ST/GT cars were based upon the 2.2 short stroke engine as used in the road 911s of 1970 and 1971 model years.
In 1970/71 the FIA Group 4 rules on engine modifications allowed the capacity to be increased from standard road cars but this could only be achieved through an expansion of cylinder bore by 1mm to 85 mm giving an increased capacity for the 2.2ST of 2247cc. Stroke had to remain unchanged at 66mm.
Additional improvement to the 1970 2.3 ST engine included twin plug cylinder heads, uprated camshafts derived from the Porsche Carrera 6 race car, modified Mahle pistons, increased compression (10.3:1), polished conrods and high butterly throttle bodies and trumpets used in conjunction with Bosch Mechanical Fuel Injection. All of these modifications delivered around 270bhp at 7800rpm.
To handle the increased power, the track of the car was widened by 2 inches and wider wheels and tyres were fitted front and rear (7″ and 9″ respectively).
Remaining race preparation consisted of some extreme weight saving (lightweight steel shell, alloy doors, no soundproofing or underseal, thin fibre glass bonnet/engine lid/bumpers/wheelarches, perspex rear and side windows and thinner Glaverbel glass front screen, stripped out interior losing glovebox lid, ashtray, rear seats etc. All of this resulted a car which weighed just 840kg which meant the car had a fantastic power to weight ratio.