Competition in the European Touring Car Championship was traditionally intense, and being the premier European series in which Porsche competed, it was especially important to do well. In the early 1970s, Porsche was experiencing increased competition in Group 2 from the likes of Alfa Romeo, Ford Capri, and BMW, which eroded its domination and presented Porsche with a challenge.
This wasn't the first time Porsche had come up against stiff opposition on the race circuits of Europe as a result of its "light but nimble" philosophy. Ferry Porsche's vision for Porsche cars from the outset had been built on producing the fastest race car based on lightness and reliability, and this approach dated back to the time of the company's inception. But Porsche's strength also lay in the flexibility and versatility of its boxer engine, an ingenious design that allowed for development and capacity increases in the future.
The 1970s was a time of great engineering innovation and experimentation, and the engineers were particularly hard at work in the Porsche workshops in Stuttgart. Rules governing European GT racing in 1971 limited the capacity to which Porsche could increase its existing 2.2L engine, as they were allowed to increase the bore but not the stroke. The 2.2L 911 engine at this time was fitted with Biral cylinder liners, and this restricted the bore to just 87.5 mm as wall thickness was crucial if cylinder strength was to be maintained. With the 66mm stroke, a capacity ceiling of 2,380 cc was possible, well short of the 2,500cc class limit.
In 1972, Porsche introduced its largest 911 engine to date, the 2.4L unit, producing 190 bhp in "S" trim. Through lessons learned in racing with the 917, the engineers used Nikasil liners and pistons supplied by Mahle in the 2.4L engine. Keeping the stroke standard as required by regulation, this treatment allowed the bores to be increased to 86.7 mm, giving an enlarged capacity of 2,492 cc and raising power to a hefty 270 bhp at 8,000 rpm.
Described as a motorsports-orientated version, the 911 S with M491 option and 2.5L engine (Type 911/70) has become known as the 911 ST. Strictly speaking, it is referred to by the factory as a 911 S 2.5, but the "ST" model reference was a carry-over from the 2.3 ST, which was a racing model, and as the 2.5 S was intended for racing, this ST naming stuck.
The only trouble with the 911 2.5 ST is that there weren't very many made. Records show that just 21 examples were produced by the factory in 1972, along with two works 2.5 ST rally cars. There is some room for argument here as to the total numbers produced because the body shells were taken directly from the 911 production line, and therefore no separate register of ST cars exists. Some authoritative books put the total at 23 cars, while Porsche Classic claims it was 24 cars, but it very much depends on who you talk to as to what answer you get.
When a body shell selected for 2.5 S treatment arrived in the race department, the roof and interior panels were fitted with black felt and two bucket seats were installed for the driver and passenger. The front and rear fenders were widened by 50 mm on either side in accordance with the rules, to accommodate wider racing wheels, and the front bumper was a fiberglass unit with air dam. The 2.5L engine would have arrived directly from the test department as each engine intended for racing would have been individually prepared and tested.
With such low production numbers, the value of original cars today, assuming you could find one, are sky high. This leaves enthusiasts who are hankering after owning a particular piece of Porsche history with just one option, to make one to original spec. So, when restoration specialists Historika happened upon a 1972 911 2.4 S, the "barn find" lent itself to an ST build rather than a Carrera RS conversion. The car had lost its original engine and gearbox along the way, and so it offered pretty much a blank canvas for any aspiring owner. The reasons behind creating a 2.5 ST were historically sound as the car was equipped with an external oil filler in the right rear fender, a feature found only on the 1972 E-series cars. This 911 quirk was reversed on the 1973 F-series Carrera RS when the oil tank was moved back to behind the right rear wheel, as some owners had complained that fuel had inadvertently been put into the oil tank on occasion.
Having spent some years outside, unprotected and somewhat unloved, the 911's body had to be professionally cleaned and prepped before restoration could begin. On behalf of the car's then owner, Historika sent the body off to Cleaning Consultants in West Sussex, where it was gently blasted with a plastic medium. This low-pressure process using angular particles ensures the old paint and corrosion are removed by the irregularly shaped plastic medium rather than being hammered by a spherical bead. The body was then sprayed with a clear phosphate spray, which allowed the body restorer to see the quality of the surface to be worked on. This process also promoted paint adhesion and neutralized any microscopic traces of rust left behind. The result was a truly clean body, free of rust and best of all, free of chemicals that could affect the painting process.
Just as on the original ST, the front fenders, front spoiler, luggage compartment lid, as well as the engine cover are all fabricated from fiberglass. The horns, located behind a pair of chrome grilles next to the front indicators, have been removed, leaving just the grilles. Because the original ST had widened fenders, these had to be fabricated from scratch for the project car. While the front fenders were molded in fiberglass, the steel rear fenders required some rather special attention. The bodywork was handled by Kevin Moffatt at Historika, and fortunately he had one genuine ST rear fender from which a pair of wooden bucks were made. The rear fenders were then fashioned in steel on these bucks for the car. Body shell strengthening was carried out in accordance with factory recommendations in period for cars to be used in racing.
The aim was to build this car as closely to the original STs in period as possible, and accordingly, the interior is a faithful re-creation in the spirit of the '72 car. All sound deadening material was removed and there is no carpeting, just floor mats. The seats are lightweight racing seats with Schroth harnesses. The door cards are basic lightweight board, while the glovebox lid has been excluded and the dashboard clock blanked off, leaving just four dials facing the driver.
When asked why he bought this ST re-creation, current owner of the car, Rob Gooding, said, "I already have a Carrera RS and I wanted an ST. The aesthetics of the body, if you look down the length of it, it definitely has more of a Coke bottle shape to it, with bigger hips. It is just a beautiful-looking car." It is not hard to understand why Rob likes the ST, finished in that same Hellgelb (Light Yellow) as on the well-known Toad Hall Racing 911 ST that crossed the line 13th overall in the 1972 Le Mans 24-Hours. A lot of time and money has been spent on this car, and so there just had to be an aspect of the ST that was his favorite. "It is the engine, really; it is the fact that it is so aural, so visceral. It is more of a brute than the RS."
So with this in mind, what exactly lurks under the engine cover? A "2.4" badge on the rear grille gives a hint, but is in fact misleading. Sure enough, the 2.4L engine was the starting point for the ST engine as explained earlier, but Rob inherited an engine that already had much work done on it. Prior to his acquiring it, the cases had been time-serted due to the inherent aging characteristics of magnesium. They were then shuffle-pinned to prevent the crankcase halves from distorting and "nipping" the crankshaft. The crankshaft webs were also boat-tailed to reduce windage and stress. Close attention was paid to the barrel deck heights to ensure that the heads were perfectly flat and the barrels the same depth. An imbalance would twist the cam carrier, resulting in a friction problem in the camshaft, which would be constantly trying to bend to compensate for the misalignment.
When Rob Gooding took delivery of his ST, the only non-ST component on the car was the fuel pump. The engine had been fitted with a 2.4 S fuel pump, which did not work correctly because the higher-revving 2.5 engine needed the fuel pump from a 2.0L S engine. Gooding explains, "It is a high-revving engine. It is not torquey like the 2.7, but needs to be revved to get the best out of it. So it is more like an angry wasp."
It was while searching for the right fuel pump that Rob was referred to Neil Bainbridge of BS Motorsport. Neil picks up the story, "The bottom line is that it would never look like an ST unless you put an ST pump on it. We had to basically match the pump to the engine, so we took the engine out and gave it a good looking over. While the engine was out, we gave it a leak test because it was a bit lazy, and we eventually pulled the top end off the engine." This revealed that the engine had had clearance problems, and in an earlier life the pistons had been machined and one even had a crack in it where there had been valve-to-piston contact. A new set of barrels and pistons was sourced, then the heads were stripped and Neil did some work on the ports. When the engine was rebuilt, it had the correct 10.3:1 compression ratio.
A fuel pump was eventually sourced in Germany and fitted to the engine, together with the high butterfly system. During early testing, the foot on one of the exhaust rocker arms broke, which slowed their progress somewhat. "We put the pump on, ran it on the dyno, took the pump off and modified it, put it back on and tested it, took it off again and modified it a bit more, until Rob ended up with what he has now," Neil explains. After the pump was set and running properly, the engine showed 256 brake horsepower at 7,500 rpm with 185 lb-ft of torque. The cold-start solenoid was removed and replaced with a manual system consisting of a cockpit-mounted toggle switch. This system just squirts fuel directly into the combustion chambers to fire it up from cold.
Chris Franklin at Center Gravity sorted out the car's suspension and ride. "Rob came to me and said, 'The car is trying to kill me.'" When a customer approaches Chris to set up their car properly, he first has to establish what the 80 percent use for the car will be. Although the 20 percent use might be some form of track day use, it just isn't practical to set up the car for that minority use. Chris explains, "Some people are disappointed because when they have bought their £250,000 worth of iconic sports car, they want an event! But the maxim is that the car should be a pleasure to drive."
After an initial investigation, the ST was found to have right steering bias. At slow speeds, the steering was very stiff; it was vague at 45 mph; and above 60 mph, it was unstable and the tramlining was severe. The car was sitting 90 mm lower than the factory settings at the front and 67 mm lower at the back, and there was absolutely no travel in the front suspension before the bumpstop; it had to be lifted up to a proper height. Both rear wheel bearings had significant play, which Chris retorqued and re-pinned, as they just hadn't been tightened properly. This allowed the direction of the rear wheels to be constrained, so in other words, the rear wheels were no longer steering the car.
Another surprise awaited Chris and his team, as he explains, "Rob had 7mm wheel spacers on the front and rear axles, so I took them off and threw them in the bin. The problem with wheel spacers on these cars, especially on the front axle, is they increase the scrub radius, and this was contributing to its severe tendency to tramline. My job is to optimize the tire contact patch and to be wary of the compromises, because you shouldn't have to make compromises for the fact that it is a Porsche. It should drive like a car first, before we ask it to do Porsche things."
With the car's ride height sorted, the corner weighting was adjusted, which allowed Chris to turn his attention to the suspension geometry. "The car was wearing toe out on the front axle with more than half a degree of camber difference on the front axle, which meant the car was listing to starboard by 5 mm," Chris outlines. In an effort to balance the settings, Chris' team ended up trimming the cambers all the way around in order to maximize the size of the contact patch, and therefore ensure stability and equilibrium on the front and rear axles. "What I opted for in the end was light rear toe so that the front of the car was able to grip in turning. So, we are now running quite conservative cambers because of how Rob intends to enjoy the car, which is primarily what I term 'road sport' as opposed to 'track sport.' When you accelerate now, the car is razor-sharp straight," Chris adds.
"The handling of the ST is different from the RS; it is less inclined to slide and it sticks a lot more. The RS has progressive slip with narrower tires, so you cannot press on as quickly. The ST will slide and bite because it has a wider track with wider tires, so it is stickier, whereas the RS will just slide. The ST is a harder car to drive quickly because it will let go with less warning, but then bite, so it is a handful, a proper event. You drive the ST hanging on a bit, whereas the RS you drive with your fingertips," Rob explains.
Having sought out the 2.5 ST, what is the owner's purpose in having such a car? "Well, track days are a bit difficult because the car is too loud. But because I live in Wales, where the roads are so great, a group of us take our cars for a spirited run through the hills. I will also show it at various meetings and I have lent it to garages to put on display. But really I bought this to drive more than the RS because the value of the RSs has crept up," Rob says.
One thing that one is immediately conscious of when climbing aboard, is just how small the car is inside compared to more modern 911s, but this just helps the driver to focus on what he is doing. The car fired up without hesitation, and we pulled away, smoothly, progressively, and with a sense that there was a lot happening behind our heads. The work that Chris had done on the suspension, and that Neil had done on the engine, all combined wonderfully to create the most spine-tingling orchestra of sound and movement. The ST steered a straight and true course, and as we took the curves in quick succession through those Welsh hills, the car hunkered down as the tires bit into the tarmac against the camber of the road.
Every penny that had been spent on the car, every hour of work, was well worth it as the ST conjured up thoughts of what a well-sorted ST must have been like in its day doing battle around Sebring, the Targa Florio, the Nurburgring, or Le Mans. If you cannot find a genuine ST today, re-creating one to give you that white-knuckle ride is a convincing argument.