An AC ME 3000 and Reliant Scimitar Coupé turbocharged by Robin Rew.
After Robin Rew founded the Reliant Sabre and Scimita Owners’ Club in 1973, this well-known motor racing photographer and one-time Silverstone Press Officer was so inundated with requests for technical information and assistance that he was forced to exchange Pentax for spanner. New Rew runs a thriving little business specialising in the tuning and repair of Sabres and Scimitars from his home at Overbeck House, Bengal Lane, Greens Norton, just a couple of miles from Silverstone.
Rew, and engineer with AEI before his then hobby of photography overwhelmed his life, gained his enthusiasm for the Tamworth marque from his own ex-works competition Sabre. This stalwart car, with wishbone rear suspension, has been a familiar sight in sprints, hill-climbs, the Pomeroy Trophy and occasional races for more than a decade, Rew showing notable competence behind the wheel. For the 1979 season, however, the straight-six Sabre was given a well-earned rest, while its owner transferred allegiance to a 3-litre V6 Scimitar Coupé. This dull grey, ten-year-old car has surprised more than a few people, for under its bonnet lurks a very effective turbocharged system.
It was the turbocharger development upon Ford’s 3-litre V6 Essex engine which took me back to Overbeck House, which I first visited in 1969 to sell Rew a 2” SU carburettor and manifold off the Group 1 engine of my ex-works BMC 1800, by then modified to Stage 5. At that time Rew’s only interest was to add a bit more steam to his own road car, now he does the same for other enthusiasts’ cars. And it was a customer’s vehicle which lent the major interest to this visit, for Reg Phillips, at 64 perhaps the doyen of British hill-climbing, had commissioned Rew to turbocharge a brand-new AC ME3000, ready for the 1980 season. This order resulted from a friendly duel on the hills throughout 1979 between Phillips’ TVR Turbo and Rew’s turbocharged Scimitar Coupé. “At Shelsley Reg used to pip me by about ¼ sec. and at Prescott I pipped him by about ¼ sec.”, Rew relates. “We were this close throughout the reasons and had a marvellous arrangement where the winner bought the beer for the opposing team!” Now that Phillips has played into the hands of the opposition, who will be the big-spender at the bar in the 1980 season?
While the principles of turbocharging the mid-engined AC’s Essex engine are exactly the same as for the Scimitar’s similar Ford cast-iron transverse engine layout have necessitated a separate development approach. The basics are the same: an Air Research turbocharger blowing, rather than sucking, through a 1½” choke Reece-Fish carburettor. Rew prefers this particular Air Research turbocharger for semi-competition applications in a light car because the characteristics of the tubro-housing let boost pressure rise more quickly. He uses Rotomaster turbochargers in what he terms production road car applications and Rotomaster waste-gates (blow-off valves) exclusively.
The AC’s transverse layout makes for a particularly neat turbocharger installation, neater perforce than in Rew’s Reliant. The turbocharger nestles to the offside of the engine, above the clutch housing, its compressor outlet linked by a straight pipe to the Reece-Fish carburettor, which is mated to the standard inlet manifold by an alloy adaptor plate. Air id drawn into the compressor via convoluted trunking from big Volvo air-cleaned tucked down in the nearside rear wing. Mike Broad, of Auto-Power Services, Daventry, with whom Rew liaised on turbocharger development, designed the very tidy exhaust manifolds, essentially large pipes linked to each port flange by a smaller stub, the horizontal manifold from each bank being linked into a Y-piece collector upon which the turbocharger sits. A big-bore pipe takes the waste exhaust gases from the turbine into a big, transverse Thrush silencer with but one exhaust tail pipe instead of the AC’s usual two. This is a temporary exhaust system; Rew is having a stainless steel arrangement manufactured. A reflective stainless steel heat shield contains the white-hot glow of the turbine housing. The Rotomaster waste gate is hidden beneath the turbocharger, on the Y-piece, and a fuel pressure regulating valve lives on the nearside panel of the engine bay. A Bosch electric pump provides the high pressure fuel flow. Low compression cylinder heads reduce the compression ratio from 8.9:1 to 8:1, equating to a real ratio of about 10:1 with the turbocharger set at 7 p.s.i. boost. When engines are rebuilt during the turbocharger conversion, Rew fits low compression pistons rather than change the heads, but eh AC’s brand-new “short” engine was not disturbed.
An unexpected installation problem arose in finding a suitable throttle cable for this mid-engined sports car. There aren’t many alternatives available with the required 10 foot length! The production cable was just a few inches too short. As a solution, Rew used an outboard motor control cable.
Rew’s first attempts at turbocharging, on Scimitars, used the suck-through system with the carburettor attached to the inlet ‘side of the compressor, through which the fuel/air mixture is drawn and fed to the engine via a long pipe. Now he favours the blow-through system, with the carburettor attached directly to the inlet manifold, fed by air from the turbocharger compressor. The shorter inlet tract encourages better throttle response and also prevents the freezing to which a Reece-Fish carburettor is prone with a suck-through system, without necessitating some form of carburettor heating. One assumes that it must be of benefit also to low-speed running in the normally aspirated mode before boost pressure builds up. Another advantage to the blow-through system is its relative compactness, an essential consideration in the AC’s restricted underbonnet space. No bodywork modifications are required: the stumpy Reece-Fish fits atop the engine without requiring an unsightly bulge in the bonnet.
Rew holds the Reece-Fish carburettor in high regard for its good fuel atomisation, mixture distribution, fuel economy and ease of tuning. “My theory is that it isn’t possible to supply a properly developed turbocharger system using fixed-jet or SU carburettors without years of development to get the correct jetting and spring/needle combination,” he say. “With the Reece-Fish it can be found in an hour.” One drawback with this carburettor is its lack of cold start facility. This did not prevent the cold engines of the AC and Reliant starting promptly in my presence. Plans are afoot to blow through Ford’s standard Weber carburettor on road cars in order to incorporate a choke, but the Reece-Fish will still be used on competition cars.
Both cars were made available to me for testing round the miserably wet and muddy Northamptonshire lanes. The dull-grey SE4 Reliant was first on the turbo menu. This wolf in sheep’s clothing has had an active season of sprints, hill-climbs and the odd club race, yet has only disgraced itself once, when Rew overfilled its sump in the 750 MC’s Six-Hour Relay Race at Donington Park; the Scimitar finished its appointed sessions with broken ring-lands on two pistons. Rew claims that turbocharging has made it 25 m.p.h. faster than before, with overall performance like a Morgan Plus 8, yet it returns 24 m.p.g. on the road for everyday motoring and 30+ m.p.g. on motorways. It achieved a best of 38.5 at Shelsley Walsh and 55.3 sec. at Prescott.
The system fitted to the Reliant is similar to that on the AC except that the exhaust manifolding is much less complicated and easier to fit; only one manifold has to be changed, linked to the other by cross-over pipe running beneath the engine. Low compression pistons are fitted and a Holley high-pressure fuel pump is used. Maximum boost pressure is set at 9 p.s.i., to which the AC will be upgraded when its engine is fully run-in.
This 1969 car surprised from the start with its excellent chassis behaviour, quite belying the age off its design. Rew has removed the positive camber from the font wheels, fitted stiffer front springs Koni shock-absorbers and installed a Powr-Lok limited slip unit in the Salisbury differential. These minor changes have resulted in a very taut, well-balanced and pleasantly handling car with precise and responsive steering; it felt very vice-free and easy to drive in spite of its gross performance increase and the slippery roads. No wonder then that on Rew’s first competitive outing with it at last yer’s VSCC Pomeroy Trophy meeting, the combination came first overall in the high-speed steering test against some very thoroughbred opposition. On the same day it was timed at 15.7 sec. over the standing quarter-mile, and that with its turbocharged engine not fully sorted out. I might add that the brakes are considerably better than might have been gauged from the Scimitar’s zero performance in the braking test, which prompted a cryptic comment from Peter Hull in his report for Motor Sport; “Robin Rew gained no marks and perhaps should have been build some reverse thrust into his turbocharging”!
On this brief acquaintance Rew’s Reliant showed up all that is good about turbocharging with none of the frequently encountered drawbacks. At low revolutions, off boost, the engine feels to have lost none of its standard performance and has no holes at all it its carburation. It is smoother and more flexible too and only transmission snatch foils attempts to pull less than 1,000 r.p.m. in the very high overdrive top gear, with the standard 3.58:1 final drive ratio. With plenty of throttle applied in that same gear, boost starts to rise rapidly from as low as 2,000 r.p.m. In the lower gears, with less load, maximum boost is reached at about 3,200 r.p.m. For practical, fast and economic motoring, the engine is best kept “on the boil” between 3,000 and 3,500 r.p.m., pretty quick on the Scimitar’s gearing. There is no jolting step as the turbocharger comes in, so this is an easy car to drive smoothly at modest speeds around the engine revolutions where boost comes in, without giving rise to the on-off feeling of some turbocharger installations. Driven in anger, the old Reliant whooshes horizon-wards like the proverbial, so fast that on the slippery roads of the test the use of its maximum 6,000 r.p.m. was out of the question. Rew has proved its ultimate performance pretty conclusively during the course of the season.
A subtle change to the gearbox ratios has helped both the performance and the driveability. Like me, those readers familiar with the Scimitar’s Zodiac-type overdrive gearbox will have cursed the massive gap between second and third. Rew has overcome this by fitting a Granada layshaft cluster and second gear into the existing casing. It’s a service he can offer to customers and well worthwhile.
Excessive heat build-up under the bonnet is a problem which afflicts standard Scimitars, let alone turbocharged ones. I remember vividly being left out on a limb, while overtaking a long line of nose-to-tail cars on a two-lane road, when vaporisation in the fuel pump cut dead the engine of the road test GTE I was driving to the 1971 British Grand Prix. A change from a glass bowl to an all metal pump on later models cured this characteristic fault but the underbonnet heat build up remains to this day. With the added heat of the turbocharger installation this could lead to fuel vaporisation in stop-start traffic or after the car is parked. To overcome this Rew raises slightly the rear edge of the bonnet and fits a Kenlowe fan which runs on for a few minutes after the engine has been switched off. if vapour lock persists, Rew has developed a tiny heat exchanger which fits into the float chamber of the Reece-Fish. Fitting it is only a 20-minute job.
The AC ME3000 was less lively than the Reliant, for reasons which will be removed before Phillips takes to the hills. The new engine and transmission were tight, boost pressure was set to a more modest 7 p.s.i. (Rew boosted one Scimitar at 11 p.s.i. at the customer’s request and no problems have been encountered) and the gearing was too high to enable the best use of the engine characteristics. Phillips is fitting new sprockets (yes, sprockets!) to lower the final drive.
Again, the engine had no throttle lag, though that lengthy cable made the throttle action somewhat dead. Apart from the less vivid performance, the AC’s Ford V6 behaved just as satisfactorily as that in the Scimitar, if rather more noisily and with a pronounced bellow as the turbocharger stalled when the throttle was released.
Underbonnet heat is less of a problem on the AC so no special precautions have had to be taken.
I don’t propose to discuss the AC’s general behaviour here, as we hope a standard road test car will materialise early in the New Year. Brief impressions of a prototype appeared in MOTOR SPORT, August 1975. Certainly Rew’s modifications showed Phillips’ car to have a lot of potential.
Similar turbocharger conversions on the AC will cost around £1,800. The less complex installation in the Scimitar (all V6 models) is about £1,250.
The Reliants are Rew’s main interest and for these he offers a compressive practical and parts service, including reconditioned and uprated engines and reconditioned axles and gearboxes. His stainless steel, tubular exhaust manifolds have shown an extra 8 b.h.p. at 3,000 r.p.m. on the rolling road. These cost £90 plus VAT or £80 if bought with his £148 plus VAT stainless steel exhaust systems. Other items available include uprated, chrome vanadium road springs, Koni dampers, heavy gauge replacement fuel tanks for the SE5 and SE5a GTEs and bib spoilers.
Rew, or his assistant, Geoff Burrows, can be contacted on Towcester 50753.
The Reliant Sabre and Scimitar Owners Club, which Rew instigated, now has some 1,600 or 1,700 members. Among the benefits of membership is one of the brightest, and most useful in terms of technical tips, magazines I have seen from a small one-marque club. Membership details are available from Roger Tipler, The Old Bakery, 1, Silver Street, Brixworth, Northants. NN6 9BY. – C. R.
An AC ME 3000 and Reliant Scimitar Coupé turbocharged by Robin Rew.