Turbo v worker

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Donington Park’s annual SMMT testday gave us the opportunity to drive a convincing testimonial to the capability and durability of the Sprintex supercharger, and to compare it with its Turbo Technics counterpart in a similar Ford.

Dennis Priddle Racing (he of drag racing fame) has taken over production of the effective Sprintex belt-driven unit that originated in Clydebank. At Yeovil in Somerset, DPR now makes “about 25” Sprintex units a month, and expects to double that figure by the close of July. It offers Sprintex forced-induction for the Range Rover, and had just completed a BMW 325i prior to the Donington test day.

Our choice for a brief test was a 53,000 mile-old Sierra 4×4. I had just stepped from Turbo Technics’ latest 2.9-litre Sierra 4×4, and wanted to see what the 1989 difference is between turbo and supercharging. There could not have been a greater contrast in presentation, for the Turbo Technics machine was an immaculate 5000miler which carried the latest (and much improved) Ford MT75 manual five-speed for Granadas, Scorpios and Sierras. But despite the high mileage and tough Glaswegian life lived by the ex-Power Engineering Sprintex Sierra (“It’s abused daily” said Priddle drily), it drove with an absence of temperament that marginally outperformed the TT Garrett T2 twin-turbo 2.9-litre.

Boosting at 8 psi on a standard 9.2:1 cr, the Sprintex installation would take any combination of gear and throttle without a hint of the pinking that haunts so many conversions today. From 1000 to 5000. rpm it provided a steady stream of power without noticeable steps. The normal claim is for 250 bhp and 140 mph from this conversion, but it did not feel quite as rapid between 2000 and 5000 rpm as the 225 bhp-rated Turbo Technics installation.

The twin-turbo Sierra was a far more comprehensively developed package, with its supplementary injectors paired to operate under separate electronic management. A CNC computer-controlled milling machine nibbles out cylinder-head chambers to allow an 8.6:1 compression ratio in association with minimal 0.42-bar boost. TT proprietor Geoff Kershaw contends that “lag is only an academic question with a well-designed turbo installation”. This conversion — and a 305 bhp twin-turbo jaguar 3.6 I have also driven — prove the point.

Flawless progression and boost are apparent from 1500 rpm; at that point the TT twin-turbo Ford develops more torque than the standard 2.9i V6, progressing to reach a handsome 2731k ft. All this TT performance is delivered with exhilarating response, a soft moan from the turbochargers, and upon lead-free fuels. No Pinking is evident at full throttle in high gears and low rpm. Yet the demon exists around 5200 rpm under stern acceleration. Only a journalist or an engineer would persist in the use of more than 5000 rpm on the current Ford V6 anyway, and the twin-turbo is brilliantly conceived to allow the unit to give the plump best of its convincing mid-range.

That it had just the same bottom-end performance as the supercharged unit demonstrates how far electronics and small-capacity twin-turbo installations have come. Costs for the supercharged and turbocharged Ford V6s are similar. Turbo Technics charges £2950 + VAT for its unit, and lists many options (such as improved brakes and suspension) at further costs. This is backed by the knowledge that TT have completed over 1200 Ford V6 turbo sales since it started exploring the market with the Capri and the Sierra XR4i; currently, it is “slightly embarrassed” by demand, and plans to make 25-30 such turbo Sierras and Granadas monthly.

DPR charges “about £3500” for the supercharged 2.8-litre V6, and a 2.9-litre version is under way at Power Engineering in Uxbridge. We were pleasantly surprised by the Sprintex Ford and, as ever, Turbo Technics presented itself with professional pride and delivered the promised goods. More of the same attitude could yet see Britain’s aftermarket power providers equalling the TUV homologation standards set by Alpina, AMG and Brabus on West German products. JW