Porsche 964RS Motec & Supercharged Porsche 993RS

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Porsche 964RS Motec & Supercharged Porsche 993RS

GT Porsche, Jan 2003

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Porsche 964RS MOTEC & SUPERCHARGED Porsche 993RS

Porsche 964RS MOTEC


Porsche 964RS MOTEC & SUPERCHARGED Porsche 993RS. A new chip and a sporty exhaust are well known and pretty well accepted starters, but the rewards they bring can generally be meas

The Porsche 993 and Porsche 964 RS are both revered as two of the greatest 911s ever, but do they benefit from something a little extra?

In the Porsche world power is king. Yes, looks, refinement and quality are all key factors, but without power they don't amount to a hill of beans in a car carrying the legendary Stuttgart shield. A Porsche is about excitement, and the route to it is propelled by outright grunt.

The problem is the advance of time means what was fast five years ago is rarely at the cutting edge of speed today. All too quickly what was once described as a ‘whopping 260bhp' becomes a ‘meagre 260bhp' as we get used to the performance it offers. It doesn't help that ‘fast' is a relative measure and today's breed of Japanese rally-bred saloons and Europe's hot hatches can match the grunt and performance of yesterday's Porsches.

So what to do? Four-door saloons and hot hatches are out (would you swap a Porsche 911 for either?), and while buying a Porsche 911 Turbo solves most performance worries, the funds are a lifetime away for many of us. It boils down to a simple solution, albeit one that has been tainted over the last decade by the antics of those who think a Vauxhall Nova is a good car.

Modifying. It's not the first thing that springs to mind when you think Porsche, and generally, it will be received about as well by pure Porschists as Bernard Manning would be at a multi-racial gay and lesbian rights meeting. In some ways it's an understandable view to take; even the specials built by the likes of Ruf, TechArt, Gemballa, Cargraphic et al only appeal to a select band with an inside line to the appeal of these extreme Porsches. These machines are also the pinnacle of Porsche tuning, and for those in the market for a little more mid-range grunt and top-end shove, a little on the wild side. The answer then is a lot simpler, and a darn site cheaper. A new chip and a sporty exhaust are well known and pretty well accepted starters, but the rewards they bring can generally be measured in single figures. What many are looking for is a noticeable hike, for a reasonable price with solid reliability. Impossible? Not quite. The pair of Porsche RS' here have both been fettled by Colin Belton and his team at 9M. The Porsche 964RS belongs to Russell Martin, and is equipped with a MoTeC ECU replacing the standard Bosch unit: the Porsche 993RS has come from Martin Pearce's MCP Motorsport stable and features a supercharger fitted to the Porsche 993's flat-six engine.

Peering under the Porsche 964's engine cover and, aside from the outsized K&N filter, it's next to impossible to tell visually that anything is amiss. Fire the Porsche 964 up, and the sound of a de-cat exhaust is unmistakable but hardly out of the ordinary, and once warmed through it settles into a steady thrum. Those who have Porsche 964RS' will appreciate the significance of this; instead of the usual stalling and hunting, the revs remain constant, a bonus of the new ECU. So far so good, and it gets even better once on the move. Inevitably stuck in traffic for the first part of journey into Cambridgeshire, the engine is much more tractable. The revs settle to around 2000rpm when flowing with the traffic, with a dab of the throttle accompanied by an instantaneous jolt of speed, a response missing in the Bosch-governed, standard car. There's a noticeable increase in torque around the bottom end too – hardly a characteristic of the standard Porsche 964RS.

The best, though, is yet to come. Heading off the beaten track and onto quieter, and near deserted roads, and where before the engine's response to throttle inputs had been distinctly sharper, there is now a real shove, and a considerable gain made over the already impressive standard car. It's all too easy to change up too early and miss out on the engine's new found top-end shove.

The changes have pushed the Porsche 964RS into a new performance field (not that it could be described as slouch in the first place, and what is particularly pleasing is how nothing has been taken away from the rewarding Porsche 964RS experience, which on the right road at the right time this Porsche 911 delivers the purest adrenalin fix. The added edge to its outright performance and driveability is a welcome bonus. This really does feel like an all-win modification. The car's owner backs this up too. He bought the Porsche RS with modifications and track use in mind, and in both driving arenas Russell's been delighted with the advancements the MoTeC unit has made. “It's quicker than a Porsche GT3, yet the latter is twice as expensive to buy secondhand.

“I decided to get the MoTeC as I liked the idea that it was a simple and safe system – there were no turbochargers or fuelling issues – you simply plug in the new ECU. 9M said it would give more power and better fuel economy and I'm happy that it does what it was claimed to do.” As Martin Pearce sold him the car, what did he think of the MoTeC conversion? “I have a 310bhp TechArt Porsche 964RS on Cartronic which is the quickest one I've driven up to now, but this seems quicker.”

This notion is backed up by the fact that it quickly becomes apparent to all that the difference in performance between the two Porsche RS' is marginal. That's not to say the supercharged Porsche 993 is lacking, rather it's a totally different power delivery. You can, should the mood take you, select a higher than normal gear with the revs hanging around the 1000rpm mark, and still pull cleanly away from following traffic. Push it up higher through the revs and it becomes a never-ending, violent shove. But nothing can replace high-end revs for ultimate forward motion. With an extra 52bhp to add to the Porsche 993RS's already considerable 300bhp at 6200rpm, there are very few machines that could keep track of the Porsche RS's rump, particularly when implanted into a car with the poise of the last Porsche 911RS. There's no need to reach deep into the motoring stratosphere to notch up miles in moments; with the supercharger wound up, you can cross counties at ridiculous speeds in an almost civilised fashion.

Overall, it's an impressive combination of power and control. The mix of a peaky, revvy engine and the linear delivery of a supercharger is ideal; the torque from the blower pulling you to the point where the cam profiles comes into their own and the inherent power of the in-line six takes over. But you can't help wondering if you should be able to get away with being this lazy in a Porsche 993RS. If you're serious about buying one, you'll know you'll have to work to get the best out of one, and much of the joy to be had is from keeping the Porsche RS on the boil. It's the ultimate road/race car, so you want to feel like a race driver when you're behind the wheel. In this way, the supercharger does detract from Porsche 993RS's personality, and it is a different experience to drive than a standard example. It's still a beltingly good car, but it's almost a different car after the change, a fact that Colin Belton recognises.

However, it's down to personal taste. “I don't know what I was expecting from it. I was told performance would dramatically improve, and I would say that it has done. It's certainly as quick as a Porsche 993 Turbo,” explains Martin. “Part of the reason I did it was because I knew I could sell it with the supercharger, or have it removed with ease.”

After a stint in the Porsche 993RS I can appreciate his position, and Russell's, who has no intentions of parting with the Porsche 964. Undoubtedly, the Porsche 964RS has benefited considerably from the MoTeC conversion, and it is hard to point out any disadvantages – it's even easily removed should you feel the need. Supercharging the Porsche 993RS again gives impressive results, but perhaps it would (as Martin suggested) be better suited to a standard Carrera where the extra driveability through low-end torque would be more in keeping with the car's personality. It's debatable, too, that the supercharger would add much to the track day experience whereas the MoTeC most certainly does and is just as at home on the road. Both systems work a treat, but for our £5000, the MoTeC makes more sense and should add, not detract, from your Porsche's worth, and ultimately, the driving experience.


Colin Belton and his team at 9M Racing (the tuning division of Ninemeister) have been developing the Porsche 964 MoTeC conversion for the past three years. “Traditionally, the first stage of upgrading the power of a Porsche 964RS has been a drilled air box, K&N filter, a larger throttle body, a catalytic converter bypass, Cup pipe and matching ECU chip. This usually gives around 285bhp. The package costs around £1000 fitted. The next step is to fit a mass flow conversion which adds £1500 to the previous price, and sees power climb to 298bhp. After a little investigation we came to the conclusion that the fuel system was incapable of supplying enough fuel for more than 300bhp (without changing the fuel pressure).

“All car manufacturers want their cars to drive well over the widest range of conditions, and to help with this they fit the smallest injector possible to give good resolution (ie: fineness of adjustment). When controlled by the sequential Bosch Motronic engine management system, Porsche maintains optimum emission control with the very fine adjustment available around idle and part throttle. Unfortunately, the injector requirement for peak power is contrary to the choice of small injectors, and this forces the standard ECU to open them continuously at full throttle (batch fire) just to get enough fuel in.

“However, we're interested in power – if the engine will deliver it, we want to find it. For maximum power the ideal injector opens, squirts and closes again while the air is drawn into the cylinder on each intake stroke. This is full sequential injection, and is where the MoTeC system wins by allowing us to find the available power at all times.

“With the MoTeC conversion we fit much bigger injectors which can (in theory) supply enough fuel for 100bhp per injector. As a result of this over-capacity, when the throttle is flat at peak torque (maximum fuel demand) they are open just 50% of the available time, so delivering a dense charge of fuel into the slug of air going into the cylinder on each cycle. The result is a 64bhp and 55lb ft torque improvement over the standard Porsche 964RS.

“But there is more to the MoTeC system than just fuel flow. At part throttle the Bosch ECU looks at the volume and temperature of air going into the engine and calculates the correct amount of fuel to put in, whereas at full throttle the AFM (air flow meter) is wide open and then relies on a preset fuel map within the ECU. MoTeC ignores airflow and looks at throttle position and rpm only (the racing term is Alpha-N [Alpha = throttle angle, N = rpm]). The Alpha-N gives excellent throttle response and noticeable improvements in driveability. To ensure ideal settings throughout the operating range, MoTeC also has engine temperature; air temperature and manifold pressure corrections added to the basic fuel map, as well as other factors like acceleration and cold start enrichment.

“From the start we wanted to ensure we had reverse compatibility with the conversion in case a customer wanted to revert back to the original system, so we have designed an adaptor which connects the MoTeC M48 ECU to the Porsche wiring harness – it simply plugs in. “For the engine itself, we add a throttle potentiometer and air temperature sensor and replace the air box assembly with a free-flow K&N filter system. The airflow meter ends up in the parts bin, but all the other sensors are standard Porsche.

“To do the conversion, we need the car for about five days – one for installation, the rest to map it correctly. There are over 300 internal maps for MoTeC which can each have up to 1600 variables, which in total mean that we have over 4000 numbers that have to be correct.

The full package of MoTeC, with all the bits and mapped is £4000+VAT. Depending on engine condition, we usually see 320bhp and 294lb ft, although the best to date is 324bhp and 296lb ft.”


The supercharger package is also the brainchild of 9M. Colin Belton explains.

“It comes as a kit designed by Mike Levitas at TPC in the USA and is a low pressure system running at around 5.0psi of boost. The theory is interesting because there is a common misunderstanding about low pressure boosting engines and most people think that any boost is going to be a problem. What they miss is that a well designed induction system creates positive pressure in the cylinder, resulting from tuning effects of the cam, intake and exhaust systems (equivalent to around 3psi), so all we are really doing with this installation is giving the engine perfect cylinder filling throughout the entire rev range.

“The outright power gains are not enormous but the increase in torque is amazing. The standard 3.6-litre Porsche 993 has around 272bhp and 240lb ft of peak torque, and with the supercharger we're getting 340bhp and 300lb ft peaks, but where a standard engine is off tune at around 2000rpm, the supercharger still makes 280lb ft (a 40% improvement).

The main components of the Porsche 964/Porsche 993 blower kit are a replacement inlet manifold, the Eaton positive displacement blower, intake and outlet castings, crankshaft pulley, alternator pulley, belt and tensioner assembly. It uses the standard airflow meter and DME, but we fit a seventh injector to supplement fuelling when under boost.

“The ignition and fuel control is carried out by a custom-designed digital controller (the Digi-box) and is where our design for reverse compatibility comes into play again. If we used a chip to remap the ignition, we would need one for each and every possible ECU variation – which is simply unviable on a worldwide commercial basis. So we came up with the solution of the Digi-box, which works by breaking into the speed sensor wiring. By digitally slowing down the speed signal pulse to the ECU it allows us to retard the speed signal and fool the ECU into retarding the ignition spark as required. There is also a manifold pressure sensor built in, so when positive pressure is seen, the Digi-box fires the seventh injector to add the correct amount of supplementary fuel. This way we have complete computer control of the engine under load, and at all other times it relies on the standard factory mapping.

“Martin's is the first Porsche 993 3.8RS we've converted and, in fact, the first 3.8 anywhere in the world that has been fitted with the kit. The standard 3.8-litre Porsche 993RS runs at a quoted 300bhp and 260lb ft although most fall short on power. We have tried many ways to improve the standard engine including MoTeC but the best we have achieved to date is 324bhp and 289lb ft. We have deduced that the problem is with the design of the intake system and the heads, so it was no great surprise that with the supercharger fitted to Martin's we achieved 352bhp at 6200rpm and 337lb ft torque at 4500rpm and a whopping 300lb ft at 2000rpm. Put simply, for the price, the supercharger is better than anything else we can do on the 3.8-litre RS.

“The kit costs £4495+VAT and installation, which on a Varioram car like Martin's costs £1000+VAT, including a replacement throttle body. We need the car for a week to complete the conversion and to fine-tune the Digi-box mapping. The supercharger kits work on any 3.6-litre engine or above, and it will also fit the 3.2 Carrera but it is not an easy or cheap conversion to do. TPC also has a 2.5-litre Boxster system that works well, and is currently developing a chargecooled package for the 996 that has been impressive under test.”

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