Parr 997 GT3 3.9-litre The Mezger flat-six was one of Porsche’s most versatile engines and now Parr has put together a package that increases power, torque and capacity. Now feel this. To some the 997 GT3 is pure automotive perfection, but for a few this remarkable 911 has much more to offer. As this 3.9-litre Parr Motorsport example demonstrates. Story: Adam Towler. Photography: David Smith.
Parr 997 GT3 3.9
Nothing lasts forever, as the saying goes, and it seems obvious now that the golden era of the 911 GT3 will be remembered as 1999 to 2012. We’ve had 13 wonderful years of arguably the greatest lineage of race-influenced sports cars ever made and how fortunate were we to live through it first hand! Whether that was through owning them, driving them, or simply admiring from afar as Porsche enthusiasts. And if there’s one thread that unites all of them, it’s the wonderful Hans Mezger-derived flat-six. From 360hp and 3.6-litres to 500hp and 4.0-litres, every one of those engines has scintillated and seduced from the very first turn of the key. Of course, that doesn’t mean the 991 GT3 isn’t a brilliant car. It is, on paper, against the stopwatch and in the minds of some, even better than what came before. But it is also something different, a new breed of GT3, a car that’s found new customers, but that also, in the minds of some, has lost a certain appeal.
Let’s not get into an is-it-or-isn’t-it better argument now, as there’ve surely been enough debates raging around this car, and PDK, to last a lifetime. Some will think the 991 GT3 is a major step forward, and there are others that would rather drive the older car. This feature is for those in the latter camp.
Steer clear of trying the Parr 3.9 if you don’t have the funds for it, because once sampled you can’t get enough.
The trouble with eras ending is what happens next. In this case, seeing as Porsche is never going to build any more old GT3s, the solution is less than clear. It’s a conundrum that Parr Motorsport has been hearing regularly from its GT3 customers in recent months: do they spend a significant sum on a new 991 GT3 with the rather awkward knowledge that their Mezger car is currently accruing value at a significant rate – exaggerated perhaps by the 991’s rather fiery introduction into the market? It’s not a particularly inviting deal even if the more modern drive appeals in the first place. Or do they reinvest in their 997 GT3? Then again, even the 997 generation of GT3s are advancing in years these days. Take the original 997 GT3: it arrived in the UK in the summer of 2006, and even a car as tough as the GT3 wears with use and miles over eight years.
All of which brings us neatly to the car in question here. A lovely, comfort-spec Gen 1 GT3 in fine condition despite having covered a substantial 70,000 miles. The owner fell into the latter camp and provided the simplest of briefs: inject some fresh life into the car.
Mezger engines, if used correctly and well maintained, can go on for far longer before a rebuild than the mileage of this example, but this engine wasn’t rebuilt because it was worn out, it was rebuilt to produce a more contemporary level of performance.
Parr’s suggestion to the owner was its 3.9-litre engine conversion. Understandably, the firm is reluctant to divulge everything about an engine build that it’s spent considerable time and money developing, helped by its experience of running and racing GT3 and Cup cars.
The heart of the conversion is a new piston and liner set that increases the stroke by 4mm to 104mm. The bore is unchanged from the standard 3.6-litre engine at 76.4mm, but the compression ratio rises from 12 to 13:1. Naturally, there’s more to it than that, including plenty of bolts of various descriptions and a lot more besides on the parts list, not to mention the skill and tools required to build the engine up and the software to map it. The pistons and liners have a low-friction coating on them and use specific rings: they’re made using Parr’s own design of tooling, and its design allows for the use of wilder camshafts should it be desired (although the latter hasn’t been used in this particular conversion).
We’ve had 13 years of the greatest lineage of race-influenced sports cars ever made
This build also retains the standard titanium con rods, but even lighter rods can be specified. In going down this route it’s possible to enlarge the size of the engine still further, to 4.1-litres or beyond, but this becomes considerably more expensive as it requires machining of the block to fit everything in. As it is, the Parr 3.9 conversion can be completely reversed at a later date as it only involves the use of different parts in the build; given the investment potential of these cars, that’s comforting to know.
The build sheet also contains a host of other items, including the replacement of the timing chains (not essential, but as you’ll be in there anyway, why not?), the ECU remap, and high-flow catalytic converters. The engine can even be run-in on Parr’s dyno in a controlled fashion. The raw numbers are as follows. A standard 3.6-litre GT3 has 415hp at 7600rpm and 299lb ft of torque at 5500rpm: the Parr 3.9 has 450hp and a formidable-looking 314lb ft of torque.
That ultimate power figure is still a little way off that of the fabled GT3 RS 4.0, but then this is all achieved at just a fraction of the outlay required to purchase a 4.0 in the current marketplace. The day of our test is cloudy but the rain seems to be holding off. The Agate grey GT3 looks fabulous parked up. There’s a GT3 RS extractor vent installed in the nose, and a 997 Cup front splitter added below it. Furthermore, the GT3 alloy wheels have been painted black, with the instantly recognisable yellow callipers that signal carbon ceramic brakes peering out from behind the spokes.
Jumping inside and the immediacy of the 997-era cockpit comes flooding back; the way it’s possible to stretch out from the driver’s seat and touch the top of the passenger door trim, how near the windscreen is and the shallowness of the dash top compared with a 991. There are standard leather sports seats in this example too, not buckets, along with a leather steering wheel, which has worn shiny and turned a deeper black with years of palms grabbing hold of it.
Suddenly I am feeling quite old – was it really 2006 this car was launched?
Any prevailing melancholy is banished with a turn of the ignition key. It may sound like predictable journalistic waffling but there really is something special about this engine: I adore the way it rumbles and rattles away at idle, it’s the sort of engine you’ll instantly recognise even if you’d been led to the car with a blindfold on. But there’s clearly something more at work here: the tonality is the same, but the depth is deeper – so rich, the bass is almost visible in the air somehow. Cue a massive grin, followed by a selection of first gear with another instantly recognisable facet of the GT3; the stiff but deliciously mechanical action of the gear lever.
It may sound like predictable journalistic waffling but there really is something special about this engine
The brief for this car wasn’t to create a raw racer, perhaps temperamental when asked to do anything other than go flat-out. So I’m not surprised it behaves like any other 997 GT3 as we shunt through the Crawley mid-morning traffic. Nevertheless, with the gauges showing good temperature in the engine even a small throttle opening at middling revs has the GT3 lunging forward: this car feels hugely potent.
The Mezger engine has always provided a constantly shifting soundscape depending on revs and load. This one is no different. The deep rumble at idle soon fades into a more athletic tone, but there’s a segment above that, around 3000rpm where a wah-wah resonance washes through the car. It’s just at the point where you’ll be using the engine if you’re stroking along making efficient progress, and listening to it becomes addictive. Push the throttle harder and the note hardens into a roar, and it’s at this point that the extra capacity is really noticeable. The standard 3.6-litre engine has always needed plenty of revs to really give its best, but that was only made patently obvious by the arrival of the factory 3.8-litre cars within the Gen 2 series of 997 GT3s. Once you’ve driven one of those, climbing back into a 3.6 feels as though a plug lead has fallen off in the mid-range.
However, this 3.9-litre is something else again. The crucial difference is that you can now drive it really quickly and never rev it over 6000rpm. That’s not to say you might not want to, and on a circuit you surely would use all the revs available, but for fast road driving the engine now has more than enough pull to operate in a 3000-6000rpm rev band all day long. It also makes for relaxing driving when you’re just cruising around.
Another aspect to having this change in character is that you find yourself using a higher gear for corners that would otherwise have had the engine primed at higher revs in a gear below. What were second gear corners can now be taken in third, with the driver relying on the greater torque at the curve’s exit.
It’s actually quite a shock to discover that the 3.9 revs as angrily at the top end – if anything, more so – than the 3.6-litre engine. Perhaps the sensation of an engine coming on-cam is diminished in the bigger lump because it’s already been pulling hard for a while, but there isn’t that sudden step up in keenness. Even so, it pulls right round to the limiter in a burst of acceleration that stuns with its ferocity. And what a noise too, a yelp that rips both sonically and physically through the car. Bliss.
The other key modification to this car is to be found with its suspension. This is completely unrelated to the engine conversion obviously, in that Parr doesn’t insist you modify anything else if you do decide to upgrade the motor. The setup installed to this car is the choice of the owner, and is usually something that Parr fit to either dedicated track day cars or out-and-out racers. It’s Bilstein’s high-end MDS (Modular Damping System) setup, and it’s not cheap at £5000 (plus the tax man’s 20 per cent), although it does offer a multitude of setup options. In fact, talking of options, Parr would normally suggest either PSS10 or Clubsport dampers from Bilstein, or there’s even the possibility of getting the original two stage dampers rebuilt.
What a noise; a yelp that rips both sonically and physically through the car. Bliss.
As an aside, Parr reckons many GT3 owners think the standard car is too soft in the regular setting and poor on track in Sport mode. My recollection is of Sport being very firm, but I did always like the regular setting on the road, enjoying the compliance it had. If anything, I’d look for an even more absorbent setting to maximise this car’s potential on B roads. This MDS setup has some initial compliance, but soon firms up: it seems to work within a fairly small window of travel, which is fine when the road is smooth, but when there are a series of bumps it can really upset the balance of the car. If these occur in a straight line then the worst of it is a pronounced nodding sensation which is little more than uncomfortable, but it’s more of a problem when the car strikes them mid-corner because it can feel like it’s actually altering the GT3’s trajectory. At speed, in the wet, that might not be so enjoyable.
Suspension tuning is a very personal thing, and what doesn’t work for one person might be perfect in the eyes of another. Nevertheless, and with every respect to the owner, I’d be happier with the standard setup over this particular modification because for me, it leaves this car hamstrung exactly where it should be able to reap the biggest rewards from the new engine. It would be interesting to try a setup that Parr recommends expressly for the road, and indeed, to compare an example with eight-year-old dampers versus one with the OE examples newly rebuilt.
With the different damper setup on this car comes a new setting of suspension geometry, and that also has a pronounced effect on the feel of the car. The turn-in is now very positive, with a greater sense of the GT3 digging in at the front, which in turns seems to pivot the car into a more neutral state very quickly. It’s obvious right from the start of the journey, given that there is a sequence of roundabouts to get through, that the car turns-in really well, but the neutrality takes just a few miles to get used to before it feels second nature.
The burning question at this point is probably the cost. The 3.9-litre conversion is listed at £12,500 + VAT. However, this is an approximation because Parr won’t be aware of the exact condition of the candidate engine until it has been opened up in the engine builder’s workshop, but the above price reflects an engine that’s in good overall condition.
If your point of reference is running an early 944 then that surely looks like a very large sum of money, but at this end of the marketplace, and with GT3 values rising, it looks far more sensible. The additional power really gives the 3.9-litre Parr GT3 a shot in the arm, but just as with the 4.0 RS, it’s the torque and, even more specifically, where the torque is delivered that makes the biggest difference. The result is a fundamental shift in how a driver approaches the car, as well as a GT3 that’s significantly quicker point-to-point. Based on this experience, it would be worth steering clear of trying the Parr 3.9 if you don’t have the funds to go ahead with it, because it’s the sort of engine that once sampled you just can’t get enough of.
Just as with the Parr Cargraphic 997 Turbo Gen 1 we tested recently, there’s something very tempting about these modern-classic era 997s with added firepower, especially when the new alternative has become a slightly different sort of car. The 997 GT3 is a car patently worthy of worship, but with 3.9-litres in the tail, it’s something even more special.
Thank you to the to the owner for allowing us to test his car and to Parr Motorsport for its assistance: www.parr-uk.co.uk 01293 537911