Guide: Bantam Bomber - a Historical & Technical Appraisal of the AC Ace Bristol & Aceca Bristol
BACKGROUND
Launched in prototype form at the London Motor Show in October 1953, the open two-seat Ace and its fixed head sister, the Aceca, were conceived to replace AC’s ageing 2-litre Saloon and catapult the firm into an exciting new era.
Production of the gorgeous aluminium-bodied Ace began in May 1954 and the Grand Touring Aceca, which was equipped to a slightly more luxurious specification, made its debut at the London Motor Show the following October.
Together, both models combined to deliver impressive race and rally performances, but there was little doubt the Ace / Aceca platform were capable of handling a more powerful engine than AC’s own 2-litre straight six.
On April 2nd 1956, engineer and semi-professional racing driver, Ken Rudd, debuted his Bristol-engined Ace in the 13 lap Production Sports Car race at Goodwood’s annual Easter meeting. Against a field of 20 cars that included HRGs, Frazer Nashes, Austin-Healeys and even a Mercedes-Benz 300 SL Gullwing, Rudd won by nearly a minute.
Ken Rudd was well-known at AC’s Thames-Ditton factory having acquired his Ace back in 1954 which he went on to race successfully over the next couple of seasons while simultaneously running his Worthing-based sports car engineering firm.
Having realised AC’s engine had reached the limit of its tuning potential, for his 1954 campaign Rudd sourced a Bristol engine similar to the type that had successfully powered Cooper single seat racing cars as well as Frazer Nashes and Bristol’s own line of high quality sporting models.
Like the AC engine already fitted to the Ace and Aceca, the Bristol engine was a two-litre straight six and could similarly trace its origins back quite some time.
It had started life as BMW’s high performance M328 power unit as fitted to the fabled 328 of 1936 through 1940 and was a sophisticated design constructed from the highest grade materials. With the support of Britain’s War Reparations Board, Bristol had acquired licensing rights to produce the engine from BMW shortly after World War 2 and it was subsequently assembled in typically meticulous fashion.
Following Rudd’s impressive run at Goodwood, and with Bristol more than happy to supply engines and gearboxes for the Ace and Aceca as AC’s offerings did not compete directly with its own product line, the BMW-derived motor was introduced as an official option during mid 1956 by which time the first few cars had already been completed.
ENGINE / TRANSMISSION
The Bristol engine featured an iron block, an aluminium alloy cross-flow cylinder head with hemispherical combustion chambers, a nitrided crankshaft with four main bearings and forged steel connecting rods.
It notably featured an unusual valvetrain design with the camshaft located in the engine block but with the exhaust valves actuated by a transverse pushrod from the intake valves which resulted in a layout not dissimilar to a dual overhead camshaft configuration.
Another uncommon feature was the small bore and long stroke: 66mm and 96mm respectively, for an overall displacement of 1971cc.
Three downdraught Solex 32 PB 16 carburettors were fitted regardless of which engine type was installed.
In 1956, four alternative iterations of the Bristol engine were used: the 100B2, 100C, 100D and 100D2.
The rarely seen B2 motor had less radical valve timing and an 8.5:1 compression ratio for a peak output of 105bhp at 4750rpm.
Some early cars got the 100C engine which also had an 8.5:1 compression, but with uprated valve timing developed 125bhp at 5500rpm.
The B and C type engines came with a Girling crankshaft while the D type engines featured a Holbert item.
The 100D motor retained an 8.5:1 compression ratio for an unchanged 125bhp at 5500rpm, but for the D2 version this was hiked to 9.0:1 which yielded 128bhp at 5750rpm.
Transmission was through a four-speed Bristol gearbox which ran closer ratios than on AC-engined cars along with a smaller diameter clutch (once again supplied by Borg & Beck).
CHASSIS
Aside from different engine mounts, nothing was changed in the transition to Bristol trim.
The Ace’s John Tojeiro-designed ladder-type steel chassis was based around two large diameter tubes with front and rear subframes to which the suspension was attached. A skeletal frame of smaller diameter steel tubes was used to support the aluminium body. The wheelbase measured 2286mm (90-inches).
In line with its more refined, better equipped nature, the Aceca featured bulkheads and footwells moulded from fibreglass for improved sound insulation. The rear bulkhead was a new ‘half bulkhead’ that separated the front and rear cockpit compartments. Meshed aluminium stoneguards were fitted inside the fenders.
A 12 UK gallon fuel tank (14.4 US gallons or 54.5-litres) was mounted under the trunk floor.
Suspension was via coil sprung dampers running off a transverse leaf spring at either end.
The braking system comprised a Girling hydraulic circuit with 11-inch diameter Wellworthy Alfin drums at either end.
Centre-laced 16-inch diameter wire wheels (painted silver, cream or red) were originally shod with 5.50 R 16 Michelin X tyres.
BODYWORK
In terms of bodywork, a special AC badge with additional Bristol wording was added, but otherwise nothing was changed from the original Ace and Aceca.
Both cars were conventional for the period but elegantly proportioned and very pretty.
The Ace featured a large primary nose intake, outboard of which were exposed headlights and gently rounded fenders that swept back towards the cockpit.
Weather protection for the cabin comprised a full-width detachable windscreen, similarly detachable two-piece sidescreens and a basic canvas roof with framework that had to be manually erected and dis-assembled. A full cockpit tonneau cover was supplied too.
For the Ace, access to the cabin was by way of small doors without any exterior handles. Behind the doors, the Ace also had pronounced kick-up rear fenders that flowed back towards the closely cropped tail. Located on the left-hand rear fender was an exposed quick fuel filler cap.
Vertical overriders were fitted at either end, one type of which was able to accommodate the optional full width bumpers.
The Ace’s aluminium body panels were fashioned on a wheeling machine and then welded together before final shaping took place on wooden bucks. Once a satisfactory profile was achieved, the panels were pop riveted in place.
Although at first glance the front half of the Aceca Coupe appeared almost identical to an Ace, the upper surfaces were flatter and two banks of four louvres were carved out from the hood up near the bulkhead.
AC added a Fastback-style roof canopy that elegantly swept down towards the tail. A lift-up tailgate with perspex rear window opened to expose a good-sized luggage compartment. Wooden frames were used for the tailgate structure along with the more substantial doors which now featured proper push-button opening handles, wind-down windows and opening quarterlights. The rear side windows were hinged at their leading edge to allow for additional cockpit ventilation.
The Aceca’s sloping rear fenders were given a unique finned treatment and new lights. Housed on the tail fascia was a recessed number plate shroud with perspex cover.
INTERIOR
The only differences inside the cockpits of Bristol-engined Aces and Acecas compared to their AC-engined counterparts were the dash-mounted manual ignition advance and retard switch and choke control (AC engined cars had an electric choke).
The Ace was equipped with a fully trimmed cockpit that included everything needed for road use.
Standard issue was a Bluemels bakelite steering wheel which featured three groups of four banjo spokes that connected the rim to the boss.
The aluminium dash was covered in leather colour matched to the rest of the upholstery. Positioned on either side of the height-adjustable steering column was large speedometer (complete with with inset clock) and a matching rev counter. Four smaller read outs (water temperature, oil pressure and fuel along with an ammeter located underneath) were housed towards the centre of the dash.
Single-piece leather bucket seats were trimmed with pleated faces and carpeted backs. They could be adjusted fore / aft only. The doors, sidewalls and rear bulkhead were upholstered in a mixture of leather and carpet.
Leather door opening straps were fitted as opposed to conventional release catches.
Lovely AC-branded cast aluminium pedals were fitted to each car.
As for the Aceca, these Coupe versions came with a completely redesigned dash trimmed in colour matched leather complete with new burr walnut inserts for the primary instrument binnacle, centre console panel and glovebox.
Housed in the binnacle directly behind the steering wheel was a large rev counter and speedometer (again with an integral clock. In between was a smaller read out for oil pressure. More small dials (a water temperature gauge, fuel indicator and ammeter) were located in the centre console. Above the centre console was a chromed pull-out ashtray and below it were the heater controls.
If specified, the optional radio was positioned below the glovebox.
Another unique Aceca feature was properly trimmed leather-covered door panels with window winders, opening handles, small elasticated storage pockets and burr walnut caps. Dark emerald semi-transparent sun visors were also fitted along with a cloth headliner.
Out back, the rear storage carpet was carpeted as was the ‘half bulkhead’ except for its leather top roll.
OPTIONS
AC offered a comprehensive list of optional extras (some of which were Ace or Aceca specific) to include chrome-plated wheels or wheels painted a colour other than silver, cream or red, a fibreglass hardtop, racing-style aero screens, full width front and rear bumpers, windscreen washers, a Laycock de Normanville overdrive (which operated on second, third and fourth gears), external boot hinges, a wood-rimmed steering wheel, a heater, a windscreen demister, a radio, a glovebox door and an oil temperature gauge.
Other upgrades comprised a choice of alternative rear axle ratios, a second ignition coil, a secondary petrol pump, an oil cooler, an aluminium instead of steel fuel tank, a supplementary fuel tank, a fuel tank shield, a second spare wheel, a battery shield and a racing cowl for the radiator.
WEIGHT / PRODUCTION
The Brsitol-engined Ace weighed in at 812kg compared to 780kg for the AC-engined variant. With the most popular engine (the 100D2 variant) top speed went from 103mph to 116mph and the 0-62mph time dropped from a little under ten seconds to nine seconds flat.
The Bristol-engined Aceca tipped the scales at 927kg (up from 895kg for the AC-engined variant). With the 100D2 engine in place it shared an identical 116mph with the Ace while 0-62mph took 9.3 seconds.
ACE BRISTOL CHAPRON
The second Bristol-engined Ace (chassis BE 117) was dispatched to Paris on April 14th 1956 where it received coachwork by Chapron.
PRODUCTION CHANGES
In 1957, AC shortened the Ace’s trunk lid which enabled the trailing edge of the roof to be mounted further back. Double laced wheels were added to the options list along with 11-inch front disc brakes (the first disc brake-equipped example having been chassis BEX 289 in August 1957).
The 100B2 engine was discontinued and just D and D2 engines were used, the latter of which could be specified with a higher 9.5:1 compression ratio for increased performance).
In 1958, AC supplied the Ace and Aceca with 100C2, 100D, 100D2 motors and the new 100D2S engine as well. That year also saw smaller 15-inch diameter wheels become an optional extra along with a more aerodynamic, less steeply raked curved instead of flat windscreen for the Ace that provided less buffeting. Around this time, the Aceca windscreen was given curved instead of right angled lower corners to better resist water ingress.
During 1960, disc brakes and windscreen washers were made standard.
From 1961 only the 100D2 engine was used.
END OF PRODUCTION
Bristol-engined Ace and Aceca production ran from 1956 to 1964.
In total, 463 Bristol-engined Aces were completed along with 169 Acecas.
COMPETITION HISTORY
Having debuted his Bristol-engined Ace at Goodwood in April 1956, Ken Rudd went on to win that year’s Production Sports Car Championship.
Bristol-engined Aces also won the SCCA Class E championship in 1957, ‘58 and ‘59, the Class D championship in 1960 and the Class C title in 1961.
Works cars (one of which was a custom-bodied special) finished seventh and eighth overall at the Le Mans 24 Hours in 1958 (second and third in class) before Ken Rudd’s team went one better in 1959 with a seventh place finish overall to win the two-litre Sports category.
Text copyright: Supercar Nostalgia
Photo copyright: AC Cars - https://ac.cars/ & Thiesen Automobile - https://www.thiesen-automobile.com/en/
