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Insane!

Turbocharged or supercharged? - "Oh, we'll have both....."

By Neil Perkins, pics by Tony North

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Mohammed Ben Sulayem just cannot stop building exotic cars. Not content with a US$1.5 million dollar Mercedes CLK GTR, the Dubai-based multiple rally champion is now driving a new addition to the range - a 500hp Mercedes C-Class based on a AMG C32 Kompressor.

International television companies have regularly featured Mohammed Ben Sulayem and his range of super cars. He is frequently seen along the vast open highways of Dubai in a Ferrari F50, an F40, a Bentley, a high-powered Toyota Landcruiser, a Porsche 959, a 911 GT1 or his mega Mercedes. But his latest project revolves around the modifications his team at Ben Sulayem Performance have made to a Mercedes C32 AMG, originally acquired in standard specification from Germany for 134,000 DM and now his regular mode of transport in the UAE.

"The great thing about the C-Class is the base package," admits Ben Sulayem, currently defending his FIA Middle East rally championship title for the 14th time. "The car has a great chassis, good suspension, handling and brakes. The chassis is easy to work with and all the safety aspects are already there."

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Mohammed duly acquired the standard car and it arrived at his workshops ready for some serious tweaking. "The standard car is 350hp and supercharged, but this wasn't quick enough for me," jokes Ben Sulayem. "I couldn't feel it...! I knew it needed much more power. We decided to fit twin Garrett turbochargers to bring it up to the performance that I need."

Although it looks similar to a near standard Mercedes C32 AMG from the outside, Mohammed's latest creation now delivers around 480-500hp through a five-speed automatic transmission and boasts in the region of a massive 660Nm of torque.

"Believe me, it feels great to drive now. It's comfortable and very quick. There's so much power. You need to use the ESP (electronic stability control), because the rear wheels are still spinning when you reach 120 km/h...!"

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Much of the development work and underbonnet improvements were carried out by Australian automotive engineer Steve Bijok, who is the workshop manager at BSP, near the airport in Dubai. An admitted petrol head, 29-year-old Steve spent eight years working in the performance tuning business in Australia and left his home in Sydney after spending time working for Subaru tuner MRT Performance.

Steve talked us through some of the modifications: "We had the policy that if it ain't broke, don't fix it, so there was no point making changes to the chassis, suspension and brakes. The car was acquired with numerous AMG enhancements and Mohammed stressed a few extra options. He asked for a ported and polished cylinder head, a free flow exhaust system and no catalytic converter (they are not required by law in the UAE)."

The car was fitted with a screw-type supercharger, which was effective from as low as 1000 rpm, but ran out of steam above 4500 rpm.

"I discussed this with Mohammed and he suggested that we opt for twin turbochargers, which could take over at higher revs to boost the overall power and efficiency of the engine. This could then be taken a step further by sequencing the turbo system so that once the turbocharger was making enough boost, the factory supercharger was switched off and this further increased the horsepower otherwise lost driving the supercharger."

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Bijok admits that the basic core engine remained relatively unchanged, although the intake and exhaust manifolds were match ported. The oil sump was modified to improve oil scavenging, in addition to a slight increase in oil capacity to offset the effects of the turbo system. Improvements were made to the transmission oil cooling system, although Bijok was confident that the adaptive learning programme, built into the transmission, would retune itself to handle the extra power and torque being generated. Modifications were also made to the Mercedes ASR system to improve general driveability, although Bijok states that the car's interior remains standard, save for a boost gauge and a colour-coded dashboard gauge pod holder.

"The major work revolved around the turbochargers," says Steve. "Initially we looked at a pair of watercooled Garett 250hp ball bearing turbos. But there were no concerns about turbo lag and the engine's powerband because of the supercharger, so we opted for a pair of Hybrid 400hp Garetts instead."

The major challenge they faced was fitting the units into limited space in the engine bay. Sections of the firewall were removed, remoulded and rewelded into place. The factory exhaust manifolds were modified, with Bijok saying that the driver's side turbo proved to be the biggest headache. "The steering shaft to the rack goes right through the place where the turbo should fit and we were forced to install the turbo low down in relation to the oil sump. Because of this we had to install an electric oil pump, a turbo timer and a small oil cooler to lower the temperature of the oil supply to the turbochargers."

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Bijok reckons that he and fabricator Virgilio Noel spent over 80 hours working on the system...

Intercoolers were fitted to either side of the front bumper bar and the original factory fog lamps were removed to cater for air intake grilles for the intercoolers. The final major jobs were the actual mechanics of the bypass system built into the throttle body to allow the transition between the supercharger and turbochargers.

"Put simply, the heart of the system is an additional throttle body installed between the factory throttle body and the supercharger operated by a turbo wastegate actuator. This is connected to turbo pressure via an electronic wastegate controller programmed to open the throttle body at a preset boost pressure."

An electronically-controlled unloader valve is fitted to control an overboost situation, which occurs on the transition between the two forms of forced induction, and the system was completed with the addition of a relay to control the supercharger drive. This switches off the blower for the last 2000 rpm of engine operation.

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Other additions to the specification were a 600hp fuel pump to supplement the factory-fit unit and a 70hp fuel injector fitted to the two intake manifold plenum chambers. "A programmable voltage clamp was fitted to the factory MAP sensor to allow the overall boost pressure to be raised from 0.9 bar to 1.2 bar," adds Steve. "We had a few little problems along the way," he adds. "Little things like exhaust leaks, oil scavenging and the general clearance of components, but the last challenge was to fool the factory computer into thinking that the engine was standard and was not carrying two extra turbos..."

"It's a fantastic car," endorses Steve. "It makes a Porsche GT2 look positively anaemic. I suppose it's best described as having the feeling of an 8.0-litre big block V8...."

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What about Mohammed's next project?

"I have three motoring aims this year," he confesses. "One is to retain my Middle East rally crown with Ford, the second is to run a successful UAE Desert Challenge race in November and the third is to build a new Mercedes based on the AMG SL55. My base car should be delivered towards the end of the year. That is fitted with a 5.5 supercharged V8 and should be superb. I think we will be looking at around 600hp with that one..."

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