Liege-Rome Rally 1998
Bentley Continental Rally Preparation
When the Continental was relatively new, many were used by enthusiastic owners in any number of competitive events. These included, timed runs, sprints, flying miles and kilometres, hill climbs and rallies. Over time, these types of events largely disappeared from the sporting calendar. It was not until the advent of retrospective historic rallies in the 1980s that a venue existed where the Continental could again be used competitively.
The purpose of this development was to prepare the Bentley Continental
for competitive use in retrospective rallies. For the car to be both competitive
and safe, the efficiency and strength of the mechanical systems needed
to be enhanced within the parameters of their robust original design.
It was important that this was achieved without significantly altering
the character of the Continental. The development work was greatly aided
by the availability of the original Crewe Technical Drawings and the Crewe
Experimental Department engine and chassis reports. Many of the modifications
were based upon work carried out by the Hythe Road Service Department
for individual customers and by the Experimental Department for the 1955/56
model (R-Type) Continental, which was never put into production. The first
Continental to be rally prepared was BC-65-C, in 1996.
226 BHP Continental Engine
Engine
Specifications
Displacement 4.9 litre (4.886 cc)
Bore 3 3/4'' (95mm)
Stroke 4 1/2'' (114mm)
Compression Ratio 8.8-1
BHP 226 @ 4550 RPM
Torque 334 @ 2950 RPM
The engine is an in-line 6
cylinder with a cast iron mono-block, aluminium cylinder head, 6 overhead
inlet valves, 6 side exhaust valves, single gear driven camshaft, forged
aluminium pistons, forged steel connecting rods, forged nitrided steel
crankshaft, and a wet sump lubrication system.
The development of this engine resulted in a significant increase in useable
power, without sacrificing any of the long-term reliability or driving
flexibility of the original design. This was achieved by: greatly reducing
the weight of all the rotating and reciprocating components as well as
improving the volumetric efficiency of the design.
Reducing the weight of every moving part has improved inertial acceleration,
lowered component stress and allowed the red line to be raised from 4,250
to 5,000 RPM. By way of example piston, weight was nearly halved and 18
pounds were removed from the flywheel. The revised original designs must
have driven component manufacturers mad with demands that they produce
items with more strength and longevity than the original parts at half
the weight. Fortunately, the march of technology was on our side and most
of these requests were today, well within the realms of possibility, if
not sanity.
Improving the volumetric efficiency and raising the compression ratio
without changing the camshaft profile has significantly increased power
within the useable RPM range. This was achieved using a Bentley prototype,
big valve, high compression cylinder head, three-carburettor induction
system and a free flow exhaust. The engine now produces 226 BHP compared
to the 158 BHP produced by the standard Continental engine. It has also
been designed to run on Super Unleaded Petrol.
Continental BC-65-C climing the Stelvio Pass
on the 2000 Liege-Rome Rally
Cylinder
Head
The 6 port, big
valve cylinder head was one of a number originally supplied by the Hythe
Road as a kit, (OPWAS), for up rating power on R-Type Continentals from
1955. The cylinder head has since had extensive gas flow testing to improve
the shape and efficiency of the three plenums, inlet ports, valves and
combustion chambers. The compression ratio has been raised to 8.8-1 by
machining .050 from the bottom of the head. The inlet and exhaust valves
are lightweight competition stainless steel with reduced stem diameter
and hardened faces. The valve seats are hardened. The inner and outer
valve springs are balanced and the installed poundage has been up rated
by 25%. All valve springs have lightweight titanium retainers. The rocker
arms have been lightened and polished. The lightened pushrods are hollow
4130 chrome-molly steel with hardened ends.
Induction System
The induction system is a specially fabricated three plenum
aluminium inlet manifold. The design was based upon a manifold made by
the Experimental Department and supplied through the Hythe Road. The new
manifold has been fitted with three 2-inch S.U. HD-8 carburettors. The
carburettors carry 3-inch ram pipes designed by TWM in California. As
originally fitted to the prototype Continental 9B-VI/BC-26-A, a cold air
box ducts outside air from the offside wing, through 4 inch flexible trunking.
A K&N air filter has been fitted at the end of the trunking. The fuel
metering needles are the result of extensive testing on the rolling road
at PTS. They were specially made by David Morris, a retired senior development
engineer at S.U.
Twin 2 1/8-inch exhaust system
Exhaust
System
The exhaust system
has a tuned six-branch manifold consisting of 32-inch primary pipes joining
separate12-inch tapered collectors. Each collector joins a separate 21/8-inch
pipe in the twin exhaust system that exits at the rear of the car on the
near side. There is one 22-inch straight through silencer for each exhaust
pipe consisting of an expansion chamber and glass wool packing. The silencers
were computer designed in California and fabricated by Padgett Motor Engineers.
Ignition System
The ignition system has an optical trigger in the distributor.
This runs an MSD capacitive system that fires the spark plugs twice during
each ignition cycle. The coil is a special high output type. The ignition
wires have solid copper cores. The spark plugs are Champion N9YC gapped
to .040.
Electrical System
The electrical system has been uprated with a 48 amp Lucas
competition C-48 dynamo and regulator. The original Lucas PF 770 headlamps
and Lucas 'Flame Thrower' driving lamps have been fitted with 55 Watt
BPF base halogen bulbs.
Engine
Block Assembly
The original engine block has been fitted with full length
high-chrome steel liners and bored to 3 ¾ inches. Hardened exhaust
valve seats have been installed for the exhaust valves. The exhaust ports
have been extensively modified and the restrictive boss around the valve
guide has been completely removed. The pistons are made by JE to our design.
They are three ring, short skirt, forged aluminium and weight 520 grams.
They have been further lightened by hand and balanced to 1/10th of a gram.
The Connecting rods are made by Carrillo to our design. They are forged
steel with 3/8th SPS bolts and have been rifle drilled to provide internal
lubrication to the gudgeon pins. Carrillo balanced both ends to 1/10th
of a gram. The original crankshaft is forged steel with nitrided standard
journals and required no modification other than balancing. The clutch
assembly is an 11'' Borg and Beck competition unit with uprated springs
and facings. The Flywheel has been trued and lightened by 18lbs. Both
items were balanced separately using the crankshaft as a mandrel. The
friction damper has been replaced by an 8'', competition, Fluidamper.
This is mounted on a specially designed hub at the front of the crankshaft.
It runs out of sight within the existing aluminium gear housing. The Fluidamper
has made such an enormous improvement that the engine, which is now mounted
solidly to the chassis, is smoother throughout the RPM range than a standard
engine. Oil pressure has been raised 15% by adjusting the high-pressure
relief spring in the bypass valve.
Cooling System
The water-cooling system has been uprated by fitting a competition
aluminium radiator built to the original design. A 16'' electric cooling
fan has replaced the belt driven mechanical fan, freeing an additional
3 BHP. The oil cooling system has had a 19 row thermostatically controlled
Serck oil cooler, similar to that originally fitted to the prototype,
mounted in the air stream at the front of the off-side front wing.
Gearbox and Back Axle
The manual gearbox has the close ratio Continental gear-set
with the factory modifications increasing the thickness and strength of
the thrust washers. It is mounted solidly to the chassis and has a strengthened
thrust rod with aluminium washers. The back axle has the Continental crown
wheel and pinion. Uprated drive keys have been fitted between the pinion
and the input flange. The centre support bearing also has uprated drive
keys. The propeller shaft assembly has been balanced.
Steering and Suspension
The steering has had a modification limiting the float
of the opposed springs in the draglink. This provides greater feel, increased
feedback and more precise steering. Castor angles have been set to 3/4
positive to provide greater self-centring action. The R-R adjustable dampers
have been set up on the damper test rig at P & A Wood and have heavier
duty oil and uprated valve settings. Large diameter front and rear anti-roll
bars have been developed by Rhoddy Harvey-Bailey. The front ride height
was lowered by 1/2 inch. Rear spring poundage has been raised by 10%.
Brakes
The brake drums are Alfin type, machined from solid aluminium
billets, with shrunk-in and bolted cast iron friction surfaces. The backing
plates have been fitted with cooling ducts and exhaust vents. The hydraulic
master cylinder and wheel cylinders have been lined with stainless steel
sleeves. The flex lines are Aeroquip braided steel. The brake shoes have
been lined by the Mintex competition department with uprated Mintex 242
or are Carbotech Metallic.
Wheels
and Tyres
The wheels are cast aluminium Dunlop Racing type measuring
6.00 X 16. Circumferential holes extract air and aid brake cooling. A
painted aluminium disc covers the wheel nuts and is fastened by the Bentley
centre hub nut. The wheels widen the track by 1-inch to 571/2-inches front
and 581/2-inches rear. This adds greatly to straight-line stability and
cornering speeds. Dunlop 650-16 Racing Tyres were Type Approved by Dunlop
in 1994 for the R-Type Continental. They are similar to those originally
fitted to the prototype Continental and are used for all Rally and Roadwork.
Tyre pressure is set hot to 30 psi. Front and 32 psi. Rear.
Speedometer showing 128mph!
Testing
and Use
In 1998 BC-65-C was tested on the Autobahn in Germany to
a speed of 132 MPH. Top speed is higher, but traffic conditions obstructed
further testing. In 1999, with a less powerful 201 BHP version of the
current engine, this Continental was tested over ¼ of a mile at
Santa Pod. The results were a consistent 16.1-second 1/4 mile. The car
has successfully competed on: The Claret and Classics Rally in 1995, 1996
and 1997 and The Leige-Rome Rally in 1998,1999, 2000, 2001 and 2002
Other Continentals
Three other Continentals have since been 'rally prepared'
by Padgett Motor Engineers to identical specification. BC-19-C was completed
in 1999 and BC-27-C was completed in 2000. Work has commenced to similarly
overhaul and rally prepare BC-3-B, which will be completed in 2002. BC-19-C
and BC-27-C competed along with BC-65-C in the 2000, 2001, and 2002 Liege-Rome
Rally.
Two other Continentals have also been extensively modified for retrospective
rallies along similar lines. Ricky Cann prepared BC-22-C in 2000 and P&A
Wood prepared BC-35-D in 1998.
