TUNING TEST

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Capri 2.8i turbo by AVJ

AVJ DEVELOPMENTS on Pershore’s flourishing industrial estate, which is bordered by rolling Worcestershire agricultural land, are a company best known for their appointment as Aston Martin Service Dealers some three years ago. Proprietor Tony Jones came to the notice of Newport Pagnell through his racing preparation work on David Preece’s rely fleet DB4, but Jones has a competition and turbocharging expertise that goes back to the days of Broadspeed in Birmingham.

Today AVJ have two units and a separate test house cell (Heenan and Frauds equipped) and have three primary spheres of business: Aston Martin, competition preparation, and routine servicing work — a safety net that has been much appreciated through the recession.

However, engine preparation has always been the Jones speciality, particularly the Ford Cosworth BOA and Pinto / RS2000 / Cortina 2-litre engines, of which AVJ have “literally hundreds running all over the World”, according to the straightforward Jones who adds, “but we certainly don’t get the orders for new engines that we did three and four years ago, so I decided to have a look at some other aspects of engine building, particularly an attempt to build a responsive turbocharger installation for the road, without the need to dismantle engines — which I thought would appeal to manufacturers.”

Jones certainly had the right credentials. Developing the Broadspeed Bullit and Granada turbocharged conversions had left a number of potential customers looking around for similar modified Ford excitement in the eighties. One such candidate was Northerner Daniel Horrocks, owner of a substantial building concern who needed something to entertain while awaiting delivery of a Bentley Mulsanne.

Jones set to work and provided the neat and effective conversion that is capable of launching the Capri from rest to 60 m.p.h. in six seconds or less, raising horsepower over the production output by up to 55 b.h.p. Fuel consumption in normal use is reckoned to be in the same 21-24 m.p.g. range that is recorded by the normal 2.8i. This production Ford is a quick car in its own right, with honest 130 m.p.h. capability and 0-60 m.p.h. times of eight seconds or slightly under.

All the work was aimed at providing an external bolt-on conversion. Integral to this and Tony’s just obsession with obtaining the fastest possible response to acceleration demands was the retention of the standard 9.2:1 cr. In turn, this meant AVJ must build at least an intercooler into the system and some electronic safeguards to prevent any detonation damage that could result from the higher effective compression when full boost of 6, psi. is employed.

Finished in February and tested over 6,000 miles, the conversion features a Garret AiResearch turbocharger unit with rod-linked wastegate control mounted high on the near-side of the engine bay. Beautifully fabricated stainless steel piping is employed to link the pressure side of the turbo to the intercooler (like the oil cooler, situated behind the standard slatted grille in front of the usual Capri radiator) and from there to the production Bosch K-Jetronic fuel injection: the fuel) air mixture is drawn from the metering unit and fed to the turbocharger by another such 2, inch bore stainless steel pipe. The Ford Duraspark electronic ignition system is augmented with a spark retard pack and an electronic sensor within the injection air box. The latter signals the fuel injection “brain” to supply supplementary mixture enrichment — up to 30 per cent — as boost rises. Since boost is available from a mere 1,500 r.p.m. in fourth gear, with full boost supplied, extremely rapidly, by the time 2,750 r.p.m. is reached under full throttle, this enrichment facility can he employed frequently. This provides the 200 horsepower performance feel of a good BMW 3½-litre but such use will naturally pull the m.p.g. down into the teens.

The exhaust system after the turbocharger is totally different, the pipes from both banks interconnected under the car. That is an obvious low point to watch, so a small protective shield protects the vulnerable crossover. The main system then runs only down the nearside of the Capri underbody, emerging in one sturdy exit pipe. Ancillary details include taking off the sump to fit the turbo oil drain and arranging the oil cooler in-line to feed the engine with cooler oil. An electronic fuel shut off sensor acts as a second failsafe to the wastegate in case of severe over-boost.

At present the conversion, fitted only at AVJ, costs £2,500 exc. VAT. That can only be an approximation as the stainless steel could go in favour of alloy castings and the fact that a car manufacturer is interested in the system. This does not mean you will seeing it on a Capri — though MOTOR SPORT readers are doubtless aware that a 2.8-litre carburated Capri turbo is produced in very limited number by Zakspeed for sale in Germany through the Ford RS network — but it might mean that costs were lowered to the customer if larger scale manufacture goes ahead.

As the conversion was intended to provide extra power with supreme flexibility rather than “sudden acceleration as if a house had fallen on you,” as in Tony’s laconic description, the Capri Injection was unaltered in respect of brakes, suspension and general chassis. It Is already a good car in Tony’s estimation although, “for budding Laudas we would do four piston calipers and stiffen the suspension a touch.”

The engine sounds much the same and started with no preliminary throttle depression or clutch-dipping tricks first thing in the morning. There is some initial surge while the mixture is enriched for that first start and there is a softness in the clutch that betrays a variety of drivers checking out the claimed 5.8s to 60 m.p.h. from rest. This means that the engine feels as though it will die against the rising clutch unless r.p.m. are kept to 2,000 r.p.m. or more, but once the clutch is home you can feel that Mr. Jones really did achieve his flexibility power aims.

The acceleration under full boost from a slow second gear corner will literally smoke the tyres into oversteer slides, and subsequent brisk progress through third and fourth gears brings 120 mph indicated (110 m.p.h. true) with exhilarating speed: knocking the velocity off again is possible with the standard system, but better brakes would top any sane driver’s priority list.

Driven as Tony intended, as a pleasant touring system, the results are even more impressive. As soon as you tickle the throttle the boost gauge twitches, quickly reaching for the 0.5 bar redline, but reducing to 0.3 rapidly if the accelerator pressure is maintained. The charm comes in fourth gear overtaking between between 50 and 70 m.p.h., when you slowly depress the throttle and leave it in the slightly open position. The boost builds with a rush that is all over by 60 m.p.h., the turbine singing the most encouraging light refrain upon a whistling theme that I have heard in a turbocharged vehicle. In fact the sounds are straight out of a novel featuring supercharged Bentleys and matching clichés.

So mid-range power is magnificent and the way in which it would idle through traffic with an imperceptible rise in water temperature augurs well for AVJ’s intentions too. As the previous owner (for 5,000 miles) of a standard 2.8i Capri I was surprised that the upper r.p.m. range of the turbo conversion was comparatively lazy: it would reach 6,000 r.p.m. in top (126 m.p.h.) and it would pull through 5,250 r.p.m. to 6,000 r.p.m. in the gears, but it didn’t feel as eager as the production car because of the awesome initial thrust you get from that sensibly arranged 1,500to0 4,500 r.p.m. boost pattern.

Overall this conversion has achieved exactly what AVJ intended. The engine proved so attractive that I drove the car another 60 miles or so rather than give it back at the pre-arranged time, and I found the overtaking performance was sorely missed when I weny back to more mundane motoring.

Reservations? It would be nice to see a manufacturer assess this high compression / intercooler layout over 20,000 miles to study not only the obvious durability aspects of running such a high effective compression under normal road circumstances, but also the marvellous response advantages such a system supplies. In less than 300 miles I was not able to come to a definite conclusion on the fuel consumption front compared with the standard Capri 2.8i, but my guess is that a high compression turbo could overcome two of the primary problems that have blocked turbocharging progress on the road: fuel consumption and the much discussed “lag”.

In its freedom from pinking and immensely attractive power delivery, this AVJ turbocharger installation was actually better mannered than much of the work offered by some prestige car makers during the eighties. — J.W.