Buying Guide Porsche 924 Turbo

A sharp rise in the value of turbocharged retro Porsches has seen the 924 Turbo evolve fromone of the marque's most overlooked sports cars to a much appreciated modern classic...

Words Pete Saysell, Dan Furr, Richard Gooding

Photography Dan Sherwood

Buying Guide: Porsche 924 Turbo — what you need to know when on the hunt

BUYING 924 TURBO

Despite the 924’s ability to show most sports cars a clean pair of heels along a twisty road, demand for more power was evident from the moment of model launch in 1976. Having already found huge success with the 911 Turbo (930), Porsche decided adding a Kühnle, Kopp & Kausch (KKK) turbocharger to the 924 would give their baby sports car the boost showroom visitors were craving.

The resulting 931 (Porsche’s internal codename for the 924 Turbo) produced 170bhp (up from the normally aspirated 924’s 125bhp), making it the most powerful two-litre production car available at the time. Bridging the performance gap between the standard 924 and the 911 SC, the 924 Turbo was launched for the 1979 model year. It was as fast as the 911 SC, but more practical and far more fuel efficient. It was, however, just as expensive as the 911, but sales of 12,427 924 Turbos highlights the fact many buyers thought the new car well worth the money. Only available to purchase until 1982 (except as a ‘tax break special’ in Italy for 1983), the 924 Turbo was discontinued chiefly because it was faster than the incoming 944.

The transaxle family of Porsche products has delivered stonkingly successful entrées in Porsche’s heritage menu, proving beyond doubt our favourite manufacturer produced the right products at the right time. In November 1975, the 924 kicked off proceedings, adopting the water-cooled, front-engined, rear-transaxle configuration from the still-secret 928. Initially developed as a Volkswagen product, Porsche stepped in and took control of the 924 project (codenamed EA425) when VW's management got cold feet during the global oil crisis of 1973.

A sharp decline in sales three years after model launch meant Porsche was only too aware of the 924’s shortcomings. Reflecting the success of technologies deployed by the company's motorsport department at the track, turbocharging was thought to be the perfect answer to the 924’s commerce crisis. The 924 Turbo was soon developed, complete with a KKK K26 turbocharger, a new alloy cylinder head, reduced compression ratio (7.5:1), boost pressure of up to 10.15psi and, it must be said, striking twin-tone bodywork. Based on the same VW-derived EA831 inline-four used to power the normally aspirated 924, the Turbo’s two-litre powerplant boasted increased oil flow and new forged pistons (lubricated from below) to help cooling.

The platinum-tipped spark plugs were moved closer to the inlet valves, themselves three millimetres larger than those on the cooking 924. Other additions included a secondary fuel pump to increase delivery pressure, a recalibrated Bosch K-Jetronic fuel injection system and a blow-off valve. Whether it’s a two-tone Series 1 or a more sober Series 2, the 924 Turbo is a gem in the Porsche back catalogue. Buy one before it's too late.

IDENTITY CHECKS AND HISTORY

Telling the Series 1 and Series 2 924 Turbos apart from one another can be achieved with ease, but the fact parts between models are interchangeable often leads to confusion. In short, the Series 1 Turbo has its chassis number mounted on the offside suspension turret, whereas the Series 2 has its identity mounted to the offside bulkhead. Series 1 chassis numbers start 93***, while Series 2 numbers start WP0ZZZ***. This is the easiest way to identify which model you’re looking at. The VIN number can be decoded to glean information on model type and year. For example, on a Series 1 car with the VIN number 93A0141068, ‘93’ represents the 924 Turbo, ‘A’ references the model year 1980, and ‘014’ plus the last four digits are the car’s unique serial number. The engine number can be seen on the left-hand side of the crank case, next to the clutch.

924 Turbos have risen in value in recent years. Consequently, getting hold of a ‘matching numbers’ example, complete with its original engine, should be a buyer's chief concern. Most UK cars will have been through the hands of 924 Owners Club members. A quick check on the club’s online forum (porsche924.co.uk) should reveal pretty much all you need to know about your potential purchase. Don’t be shy — this is an excellent independent owners club and its members are happy to offer guidance and assistance when asked.

Spend a couple of quid at mycarcheck.com, where you can download a history report outlining any insurance claims, change of registration number, recorded mileage and whether there’s any outstanding finance on the car. You should also enter the vehicle’s details into the DVLA’s free-to-use MOT history database, which can be found at bit.ly/dvlamot. The service will return details of all test passes, failures and advisories registered as far back as electronic records are stored, which is helpful in identifying any ongoing mechanical or safety issues. If you have the V5 document number at your disposal, you can even see which test centre carried out each inspection.

It's important to remember the entry-level status carried by the 924 in Porsche model hierarchy. For this reason, as well as high production volume equating to a lack of exclusivity, even the 924 Turbo found itself regarded as an unloved sports car a few years back. The tide has turned, but be aware of the fact many surviving Turbos are likely to have been in the custody of owners who weren't prepared to pay for appropriate servicing and maintenance in accordance with manufacturer instruction. Check the car's paperwork thoroughly.

Full service history, ideally accompanied by invoices for any work undertaken, is desirable when buying any 924. This might be difficult to achieve with cheaper cars — the conventional, front-mounted, four-cylinder engine powering the 924 Turbo is a home-mechanic-friendly bit of kit, meaning it may have been serviced by previous owners. This isn't necessarily a bad thing, providing documentation is available to prove a sensibly observed maintenance schedule and evidence of quality parts used when the work was carried out.

MODEL OVERVIEW

Thanks to 180lb-ft at 3,500rpm, the original 924 Turbo scampered to 62mph in just 7.8 seconds, running out of puff at 140mph. This made it faster than all but the Aston Martin V8 (145mph) in a Motor magazine test featuring the 924 Turbo, the 928, 911 SC, BMW 635Csi, Lotus Eclat 523 and the Aston Martin. In terms of acceleration, the 924 Turbo was only out-gunned by the 911 SC. Impressive stuff.

As was the case with so many US-bound Porsches, anti-smog and emissions legislation zapped power, leaving the model with only 143bhp when it landed Stateside. On the road, European examples upped the standard car’s critically acclaimed handling ante with the addition of uprated dampers and an improved 49/51 weight distribution. A larger nine-inch brake servo added to the Turbo’s specification, along with 911 hubs and 282mm (front) and 289mm (rear) brake discs slotted into 928 floating calipers. Interestingly, turbocharged 924s delivered to dealerships in North America were offered with the stiffer suspension and beefier brakes as a cost option (billed as the M471 Sport Group package).

A 225mm clutch and Porsche’s own G31 five-speed gearbox — installed ahead of the differential, as opposed to the standard 924’s Audi-derived gearbox positioned behind it — were added to an impressive technical bonanza. Amazingly, even with this extra equipment on board, the 1,130kg Turbo was just fifty kilograms heavier than the normally aspirated 924.

With a UK retail price of £13,629 in 1979, the 924 Turbo’s initial reception was as hot as the car itself. Motor Sport described the special Porsche as “a new breed of supercar”, noting the smoother engine note and refinement as hard to fault. Even so, the sudden push of power from 3,000rpm gave many buyers the unexpected need to learn how to tame the beast, with contemporary commentators unable to resist comparing lively handling under load as reminiscent of what they’d experienced behind the wheel of early 911 Turbos. Warranty issues concerning blown turbochargers (failed seals and short component life due to the questionable lack of intercooler) didn’t help Porsche’s promotion of the turbocharged transaxle, but keen to promote the 924 Turbo as supremely reliable, Porsche championed the fact endurance racers, Rudi Lens and Gerhard Plattner, took a 924 Turbo from New York to Vienna in thirty-one days. The pair also put a 924 Turbo through its paces at the Nardo proving ground in Italy, pounding the track for twenty-four hours at an average speed of 130mph. Reliability issues? What reliability issues?! Both outings proved hugely successful.

To distinguish the Turbo from all other 924s, Porsche added a NACA duct to the model’s bonnet and air intakes in the front badge panel. Forged 928-style wheels were a cost option. Incidentally, 924 Turbos arrived in the USA in late 1979, but in addition to being down on power due to stringent emissions controls, these cars were also heavier than European models due to federally mandated larger bumpers. The 924 Turbo is currently the cheapest route into owning a Porsche packing forced induction, but don’t wait another forty-odd years to dive in and enjoy a slice of the turbocharged transaxle pie — prices continue to rise.

924 TURBO SERIES 2

Second-generation (often referred to as Series 2) 924 Turbos arrived in time for the 1981 model year. A rise in compression ratio to 8.5:1 accompanied a smaller KKK turbocharger running at higher boost pressure, resulting in a welcome hike in horsepower and torque. The 924 Turbo now delivered 177bhp and 184.5lb-ft. It was also faster, managing the dash to 62mph from rest in 7.5 seconds, topping out at 143mph.

In a welcome change to specification, Siemens-Hartig digital ignition timing control made the car a more parsimonious Porsche, promoting fuel economy akin to that of less exotic cars in the firm’s product range. At a constant speed of 56mph, the refreshed Turbo would sip an imperial gallon of fuel every forty-two miles, although we suspect few owners drive their 924 Turbo quite so carefully. Ahem.

Brushed aside when the 944 arrived in 1982, the 924 Turbo can lay claim to an impressive build quota tallying a smidge over twelve thousand units, proving the idea a hot transaxle could fly on the road, at the track and straight out of dealer showrooms. Perhaps this more spirited 924 should have been Porsche’s transaxle launch model? One thing's for sure: considering such lofty production volume, it's worth keeping in mind there are plenty of 924 Turbos out there for you to choose from. In other words, don't feel pressured into buying the first example you see for fear of 'missing out'. It's also worth reaching out to the previously mentioned 924 Owners Club — this tight-knit community of enthusiasts will likely be able to point you in the direction of available cars not yet known outside of club circles.

ENGINE

The 924 Turbo’s engine was hand-built in Stuttgart before being sent to the Neckarsulm plant for installation. The block, bearings and crank are the same as those of the standard 924, but the cylinder head was new to the Turbo. Pistons are different between the Series 1 and Series 2 Turbo (giving compression ratios of 7.5:1 and 8.5:1 respectively). The engine is a tough beast. Even in turbocharged guise, the two-litre unit's bottom end should be bulletproof, providing maintenance schedules are observed. 924 Turbos hate to be left idle. This causes waterways to fur up and head gaskets to rot. More than anything, this is what leads to 924 Turbo engines killing themselves. If you’re buying a neglected Turbo, it would be wise to budget for an engine strip and rebuild. Unlike the normally aspirated 924, the Turbo is powered by an interference engine. Its timing belt and tensioner kit is very cheap (around £20) and takes about twenty minutes to change. There really is no reason why you shouldn’t change these components every other year, even though Porsche's service manual says you can leave the work for three.

Detail changes occurred throughout the life of the 924 Turbo — its engine’s rudimentary design gained air/oil separators for both the crankcase breather and the turbocharger oil return. The biggest change, however, was for the 1981 model year, when the Series 2 model was released. The pistons, turbocharger, throttle body and boost tube were all different, but the main change came in the form of a Siemens- Hartig digital ignition timing control (DITC) system. DITC uses a crank sensor (no longer available) to measure revs, meaning timing can be automatically retarded to prevent detonation. This allows the Series 2’s higher compression pistons to operate safely and, along with the revised turbocharger, delivers an extra seven horsepower over the output of the Series 1.

The crank sensor is often thought of as the Series 2’s Achilles heel because Porsche no longer stocks the part and no suitable alternative has yet been found. Aftermarket parts producer, Mittelmotor, has the solution: a 123 ignition system packaged into the stock 924 Turbo distributor housing. For around €750, you can have a plug-and-play substitution for the aging DITC with the added bonus of OEM looks and programmable maps to suit your driving style. Visit mittelmotor.de or porsche924.co.uk for further information.

All two-litre 924s use the ubiquitous Bosch K-Jetronic mechanical fuel injection system. Spare parts are readily available. It’s a very reliable setup once any bugs (caused by previous owner neglect) have been ironed out. If a car is suffering from hot or cold start issues, then a simple pressure test will reveal the origin of the problem. Details are beyond the scope of this article, but a quick check on the 924 Owners Club forum will present you with a wealth of knowledge on the subject.

The KKK K26 turbocharger is oil-cooled. Caring for the turbocharger is essential, and equates to a cool down period of five minutes at the end of a run. This gentle treatment enables the unit's bearings to receive the flow of oil they need and prevents the calcifying of lubricant in oil channels. Modern synthetic oils are recommended owing to massive heat generated by the Turbo’s engine. Fully synthetic Mobil 1 extended life 10w60 contains the required zinc dialkyldithiophosphate (ZDDP) anti-wear additive. Strangely, Porsche continues to suggest 10w40 semi-synthetic as the correct oil for the car. While this might be ideal for the normally aspirated 924, it will result in low oil pressure at hot idle in the Turbo.

Oil and filter changes should be carried out every six thousand miles or once a year, whichever comes first. Consumables are readily available from independent parts specialists.

A PLUG-AND-PLAY SUBSTITUTION FOR THE AGING DITC WITH THE ADDED BONUS OF PROGRAMMABLE MAPS TO SUIT YOUR DRIVING STYLE

INTERIOR

924 interiors aren’t known for being hard-wearing — some of the cloths used by Porsche suffer badly from sun damage, and it’s common to find splits in seats. Also, the 924’s dashboard is notorious for cracking. In truth, the part is little more than cardboard covered in vinyl. New OEM covers are available, but the preferred the solution is a modern reproduction from Werk924 (werk924.com). The company’s new dashboards aren’t cheap (budget £1,300), but they offer the correct grain for period vinyls and can be ordered for both left- and righthand drive cars. Changing the dashboard is a time-consuming job, but it’s fairly straightforward. The task is made easier thanks to a detailed ‘how to’ guide found at — you guessed it — the 924 Owners Club forum.

Werk924 also supplies the original cloth and vinyl to repair or retrim 924 seats. Again, the parts can be expensive, but even Porsche refers to Werk924 when it comes to ordering many of its restoration fabrics. You're unlikely to be trimming interiors yourself, which is why you should speak to a specialist with a wealth of experience working with the 924. Awesome Classic & Custom, Dave the Trimmer and Southbound Trimmers should be at the top of your list. If you detect wet footwells, the usual suspects are sunroof drains. They may just need a blast with an airline, but more serious remedial work could be required if they’ve been left blocked for a lengthy period.

Much like the 924 Turbo's dashboard, the car’s door cards are made from cardboard covered in vinyl. Unsurprisingly, they don’t take kindly to being exposed to moisture. Plastic liners stuck to the inside door panels should be present, else the door cards will rapidly disintegrate.

COLOUR

The car’s paint code (and the colour's name) can be found on a decal in the engine bay behind the firewall. It can also be located on a sticker behind the spare wheel in the boot. You’ll find the paint code follows the standard VAG configuration for the year (four digit numbers starting with the letter L). If the paint code sticker isn’t present, head over to the Porsche 924 Owners Club forum. Its members will almost certainly be able to identify the car’s colour simply by viewing a photograph.

BRAKES

The standard 924 features disc brakes at the front and drums at the rear. While these parts provide good stopping power, they’re not up to the task of halting the Turbo, a task taken care of by a full complement of vented discs and calipers shared with the 928. This braking system lasted through later 924 S and 944 production, right up until the 944 Turbo was released with 911 Turbo-derived four-piston Brembos.

Interestingly, the rear calipers on a 924 Turbo are similar to the front calipers on the standard 924, meaning pads are interchangeable. Don’t think a regular 924 front caliper will fit at the rear of a 924 Turbo, though — the part doesn’t extend wide enough to fit over the Turbo’s large vented rear discs. If your new 924 Turbo’s rear calipers need rebuilding, make sure you retain the nylon sliders – frustratingly, most rebuild kits don’t include them. Brake fluid should be changed every two years. Master cylinders can leak. This complaint usually manifests in a brown stain on the front of the servo. Additionally, it's worth being aware of the fact the 924 Turbo’s handbrake works with shoes inside the bell of the rear disc. They are known to seize due to inactivity.

TRANSMISSION

All versions of the 924 Turbo sold in the UK featured the G31 five-speed manual gearbox. This unit is renowned for poor first and second synchros. If a test drive indicates crunching when selecting these gears, you’re looking at a potentially large bill to remediate. Tread carefully.

The synchros are intolerant of transmission oil changes occurring beyond recommended service intervals. If the Turbo you're buying at has a good gearbox, ensure you change its oil every other year with 80w90 GL4 fluid. The 924 Owners Club can point you n the direction of sources for dog teeth and synchros (these parts are no longer available to buy direct from Porsche). Although the G31’s internals are similar to those of the Type 915 gearbox found in the 911, there are few shared components.

924 Turbos were offered with the option of a limited-slip differential (LSD). If the car you’re considering shelling out for has this rare factory part fitted, it will have /12 listed at the end of the gearbox serial number. This identifier can be found on the lowest central spline on the bottom of the transmission casing. Another way to check if the car makes use of an LSD (the Type 915 gearbox differential fits and may have been retro-fitted) is to raise the car's rear end and spin one of the back wheels. An LSD will spin the other wheel in the same direction, a standard differential will spin it in the opposite direction.

Bearing wear manifests as a high-pitched whine. As long as the noise isn’t too intrusive, it shouldn’t be seen as a big problem — most well-used 924s, 944s and 968s emit a whine from the rear.

The gear linkage is fairly long. The locator on the rear has a rubber cup holding it onto the torque tube. A rose-joint replacement makes for a better part than factory rubber prone to wear.

A 924 Turbo’s gear lever includes two nylon bushes known to wear over time, resulting in a loose feel when shifting. These bushes are available to buy new and make a huge difference to the driving experience.

The G31’s dog-leg pattern is something many drivers struggle to get to grips with, but once you’re comfortable, it’s a delight on twisty B-roads, allowing you to slot up and down between second and third, keeping boost on song.

OUR STAR CAR

Thanks to Stevenage-based independent marque specialist, Renn Works, for loan of the gorgeous 924 Turbo featured in our pictures. Some of you will recall Renn Works from the company profile published in last month's issue of 911 & Porsche World. Find out more about the business by visiting rennworks.co.uk.

SUSPENSION

Aside from its thicker anti-roll bars and firmer dampers, the 924 Turbo has the same MacPherson front struts and rear torsion bar suspension as the standard 924. The front setup is very similar to that of the Mk1 Volkswagen Golf, while the rear can be seen as a close relative of equipment found on the Super Beetle. These parts make for a car capable of bettering many moderns when it comes to handling on twisty roads, and that’s with skinny 185-profile tyres.

Front wishbones are prone to rust on cars experiencing infrequent use. Most Turbos feature wishbones with a mounting lug for the anti-roll bar. These parts are more than £170 each when ordered direct from Porsche. 1981 cars use the Mk1 Golf’s wishbones (and a different mounting for the anti-roll bar). These retail at a more sensible twenty quid from most motor factors. Converting from early to late wishbones is possible, but non-trivial. The job involves fabricating mounts for the later anti-roll bar setup. An easier way to achieve the same is to remove the lugs from the old wishbones and weld them onto the Golf parts.

If a Turbo (or any 924 for that matter) isn’t handling like a dream, a suspension refresh is in order. Four-wheel laser alignment is an essential first step, followed by a thorough examination of all suspension rubbers. Thankfully, Porsche is committed to stocking the vast majority of suspension components for its legacy models.