Regrettably, the 924’s engine let loose with a fair amount of noise, and R&T repeated that this racket and the car’s buzziness and Milquetoast performance were simply unacceptable for a $10,000 automobile -- especially a Porsche. This was underscored in a later comparison test with the even more formidable Datsun 280ZX, Mazda RX-7, and Chevrolet Corvette. Here, the 924 finished third (ahead of the ’Vette), despite winning six “firsts” (braking, handling, visibility, exterior finish, and interior and exterior styling). “When it’s good, it’s very good, but when it’s bad, watch out,” the magazine warned.
The Porsche 924 Turbo delivered performance worthy of the Porsche crest.
“Very well,” the Zuffenhausen folks likely said. “We will fix those problems -- and we will give you a turbocharged 924 for good measure.” So it was that a turbo 924 was introduced to Europe in 1979 and to America as a 1980 model.
This time, Porsche built both car and engine. The latter retained the basic 2.0-liter block (shipped from Neckarsulm) but hardly anything else. There was a new Porsche-designed cylinder head, still cast alumimum but boasting larger valves, modified hemispherical combustion chambers, and new water seals consisting of copper gasket and silicon rings. Spark plugs now had platinum tips and sat on the intake (left) side. So did the starter, displaced by the turbocharger mounted low on the right.
The blower itself, supplied by Germany’s KKK (Kuhnle, Kopp & Kausch), fed a huge cast pipe that sent boost pressures of up to 10.15 psi (7 psi on U.S. models) up and over the head to the intake manifold, then down to the ports. Compression was suitably lowered, as was then necessary with turbocharging, set at 7.5:1 for all versions. The K-Jetronic injection was recalibrated to match, and there were two fuel pumps to assure full system pressure at all times. A standard oil cooler helped deal with the extra heat of pressurized power. As on the 930, a wastegate prevented boost from exceeding the specified maximum. Porsche also fitted a blow-off valve as “fail-safe” backup.
The result of all this in European tune was 125 horsepower (DIN) at 5,500 rpm and an abundant 181 pounds/feet of torque at 3,500 rpm. American-model figures were 143 horsepower (SAE net) at 5,500 and 147 pounds/feet of torque at 3,000 rpm, the latter figure still a worthy improvement. At 2,780 pounds, the Turbo was considerably heavier than the normally aspirated 924 (and even most 911s), but its performance advantage was enormous: four seconds quicker in the 0-60 run -- about 7-8 seconds -- and almost 20 mph faster all-out. Similar gains were seen in Europe, where Autocar’s test car hit 60 from rest in 6.9 seconds and topped out at 144 mph.
To handle the Turbo’s extra surge, Porsche took typical pains with the 924 chassis. The driveshaft was enlarged to 25 mm to reduce chances of whipping, rear halfshafts were strengthened, and rolling stock was upgraded to 15 ´ 6-inch rims with 185/70 rubber. Gear ratios, spring/shock rates, and anti-roll bars were all revised, too, and a larger servo boosted the brakes, which were now ventilated four-wheel discs for Europe; American Turbos retained the previous disc/drum combo. The standard and only gearbox was the Getrag five-speed, complete with the awkward racing-style shift pattern that once plagued 911s.
Most early “turbo-era” cars were prone to poor low-rpm or “off-boost” performance, as well as turbo lag, the delay in response to throttle changes caused by turbocharger inertia. Both were apparent in the 924 Turbo but not irksome. Boost on the U.S. version began at a low 1,600 rpm and peaked at just 2,800 rpm. The larger, slower-revving European turbocharger began boosting at 1800 rpm.
Car and Driver observed, “As the turbo comes in, you can feel the zooming whee! of the crossover point and, with it, the character change in propulsion. . . . The boost is right there, coming aboard quickly with a firm punch that rushes you forward, picking off normal traffic and predictably defining the correct arc through every corner.”
Internal gearbox ratios were altered to match this power and torque delivery, and were the same for all Turbos except fifth gear, which was somewhat taller for the United States -- 0.60:1 against Europe’s 0.71:1 -- though that was offset by a shorter 4.71:1 final drive (versus 3.17:1). Road & Track’s John Dinkel observed, “Even though 5th is an over-overdrive (60 mph is only 2,280 rpm), you can let the revs drop to below 2,000 rpm in top gear, tromp the go-pedal and the engine pulls smoothly, albeit slowly. Try that with a stock 924 and you’ll be greeted with a chorus of shakes, shudders, buzzes and groans of protest that won’t stop until you downshift at least two gears.”
So the 924 engine had been pleasingly transformed. Much of the old noise and harshness were gone, because the turbo helped quiet things somewhat -- though its high-pitched whistle might make occupants think John Law was in hot pursuit. Porsche also added sound-deadening at strategic places in both 924s. That also helped, if not enough to satisfy C/D: “[It] does little to hide the thrumming, hissing, gurgling and sucking that come through the firewall like the sounds of plumbing in a cheap apartment. . . .” Still, those editors felt that “once you begin to associate the aural effects with the performance they accompany, you warm quickly to your little sound-effects symphony under the hood.”
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The Porsche 924 Turbo went on sale in the U.S. in 1980 to critical acclaim.
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