JZM History: Manthey Racing 3.9-litre Porsche 996 conversion

Here’s a copy of a feature by Chris Knapman of GT Porsche magazine from ten years ago – December 2007 – detailing a Manthey Racing conversion carried out on our friend Didier’s LHD 996 GT3 to bring it to 3.9-litres with 455bhp on tap. This was a very special car at the time and we have built many more since! Email steve@jzmporsche.com to discuss modifying and tuning your 911 for fast road or track use using the many high quality components supplied by JZM.

What’s in your garage? Manthey-tuned Porsche 996 GT3

It takes something special to stand out at a track day where there are 964, 996 and 997 generations of Cup car, a Carrera GT, and any number of modified RSs. But stand out is precisely what Didier Denat’s black 996 GT3 does, both in the paddock and out on the track which, as you’ve no doubt spotted in this case, is the Nürburgring Nordschleife.

At first glance you might mistake this modified Mk2 GT3 for a repainted RS. After all, it has a genuine RS front bumper, a carbon rear wing and italicised script running down the base of the doors. Look a little closer, though and that script doesn’t read GT3 RS, but rather ‘GT3 CS’, recalling the Carrera Club Sport of the late Eighties.

“The brief was to create a car that I could drive to the ‘Ring and still be relaxed when I arrive, and then that I will also be one of the quicker cars out on the track,” says Didier of his 996. Interpreting that brief, Manthey Motors and its UK distributor JZM Porsche created this GT3 M440 Club Sport.

“I did a bit of research and really wanted to go to the best guys in the business, and I wanted somebody that knows the ‘Ring inside out to do the setup. This was about two-and-a-half years ago. The first thing I did was the suspension with Manthey’s three-way adjustable coilovers built by KW Suspension, and then the brakes, for which I used JZM Porsche’s setup.”

The brakes in question are ceramic floating discs, which JZM says are 1.5kg lighter each than the standard GT3 steel discs. Measuring 360mm (original Mk2 discs are 350mm), the discs are built to JZM’s specifications and offer improved braking power and longevity over the standard items (note: we have now upgraded these items further with our custom carbon brakes from Surface Transforms). JZM Porsche also fitted the KW Suspension to Didier’s car, along with a Manthey K410 engine upgrade.

The K410 consists of a full Manthey sports exhaust that is 6.7kg lighter than the original, and a reprogramming of the GT3’s Motronic to yield more power from the flat-six engine. However, as is so often the case when it comes to modifying cars, Didier wasn’t quite finished: “Nine months after the first modifications I did a second batch with Manthey Motors. They exchanged the gearing, fitting 20 per cent shorter ratios, as well as a race clutch, single mass flywheel, race diff and uniball strut tops to improve turn-in, and set it up very nicely for the ‘Ring.

“Then at the beginning of this year I was thinking ‘what should I do next – keep that car or get a 997 GT3 RS?’, but because the RS was going to require a lot of extra money, I decided instead to put this towards improving my car further. Speaking to Steve McHale at JZM Porsche and Manthey’s engineers, I decided to go for Manthey’s 3.9-litre engine conversion: the ultimate step it offers for the GT3.

“Manthey was amazing because the first time after they did the engine conversion they put it on the dyno and it was doing 451bhp. Before, with the K410, it was pulling about 424bhp. So I said to Manthey that spending all that money on the 3.9-litre conversion for an extra 27bhp seemed like a lot. There was a lot more torque – about 332 lb ft – but, because I was hoping for more power, Manthey took the engine out of the car again and checked everything, but when they put it back in and back on the dyno it was the same. The guys then said they would do something a bit special so that my car would be beyond the normal 3.9-litre conversion figures.”

It is for this reason that a Cup filter resides under the engine cover of Didier’s car, combined with a carbon ram air intake system, which results in a naturally aspirated engine with 455 bhp and 347 lb ft of torque. “What is particularly impressive is the power from 180km/h,” explains Didier. “It now accelerates like it used to in third gear. You can get very easily to 280-290kmh, and I’ve hit the limiter at 8200 revs with 309km/h on the clock.”

Of course the GT3 philosophy isn’t only about maximising power. “I wanted to really lighten the car as well, so we put on BBS magnesium wheels, the carbon doors, carbon bonnet and took all the air bags out, as well as removing the regular seat belts and fitting plastic windows in place of the rear screen and rear side windows. Just this Cup steering wheel, believe it or not, is five kilos difference and the doors are 11 kilos lighter each. Then we fitted the rear wing, a proper RS front bumper with the air intake, and JZM canted the radiator back to improve the airflow.”

Given the car’s obvious focus toward track work, one wonders how usable it is on the road. “It’s amazing as a road car,” enthuses Didier. “I took the insulation between the engine and the cabin out but it’s actually no noisier than it was before, although it does pull slightly more revs because of the shorter gearing. And while it’s lighter, I have kept the radio and the air-con because removing these doesn’t make sense.”

And what about on the track? “Oh, it’s amazing. In a straight line it pulls away from Cup cars. I remember when I first bought this car I wasn’t that comfortable with it. It was a bit understeery and a bit jittery, but now it is superb – you just turn and it goes. Under heavy braking, the ceramic brakes are absolutely amazing and the car stays completely flat. With the original car I couldn’t trail brake into the corners because the back end would move around, but now it is really stable.”

So, the perfect GT3? “I certainly don’t think that there’s much left to do!” says Didier laughing. “I don’t think I’ll ever sell this car. It’s so special – you take a project and spend so much time thinking what you’ll do and all the research that by the end you don’t want to part with it. The next thing I want to do would be to buy a Cup car and race that. I would love to do this but I think I need to get a bit better first, so I’ve started racing at Caterham and after a couple of seasons I might be ready to move on. For track days it’s difficult to justify buying a Cup car though, because I think that my car at the moment is faster, plus you can get a lot of fun from driving it on the road.”

It won’t surprise you to hear that this isn’t the first Porsche Didier has owned, his relationship with the marque starting off with a 996 Carrera 4, which he swapped for a 996 Turbo. “I had the Turbo tuned to 540 horsepower by PSI Motorsport and kept it for two years, but on the track it wasn’t that great and I wanted to get to the next level, so that’s why I got a GT3.”

A couple of quick passenger laps on a deserted Nordschleife demonstrate that the next level is precisely what Didier has ended up with. With an abundance of torque and a surefootedness GT3 owners might well crave at the ‘Ring, it feels a phenomenal machine. We may not have found this Manthey GT3 M440 Club Sport at Didier’s garage, but it’s fair to say that the ‘Ring is its rightful second home.

Download the full feature on our Manthey JZM Porsche 996 GT3 3.9-litre conversion.

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