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Want to race an MGB? - Competition Car Profile: MGB

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At the top historic level, this is what goes into it, and this is what it will take.

Strong and reliable, the MGB makes a great long-distance racer at less money than you’d imagine, with a new turn-key car available from specialists starting at around £30,000. Here’s what goes into a racer complying with FIA appendix K rules.

Bodyshell
Needs to be standard, with seam welding not allowed – although apparently some folk do. ‘I reckon by the time we get a bodyshell back, painted, it’s £7000,’ says Doug Smith, whose MG Motorsport company has built 30 B FIA race cars. You can’t cut holes in the front valance, and he reckons there’s no point going to the expense of ally wings and door skins. The roll cage can be weld-in, with an allowed maximum of six mounting points, but no extra horizontal bars are permitted except for the seat belt mounts; door bars must be unboltable. All racers use works-type hardtops to improve the aerodynamics. Minimum homologated weight for a B is 830kg, with 850 realistically achievable. Technically, Heritage bodyshells are allowed: ‘But you still need a donor car for the identity, and because only the early-type narrow (three-synchro) transmission tunnels are allowed.’

Suspension and brakes
Standard pick-up points, says the rule book, and most racers get some negative camber on the front suspension with offset top bushes. Dampers must remain the original lever-arm type all round, with adjustables allowed at the back. Spring rates are free, with ‘multi-leaf’ specified at the rear, as original spec – which means parabolics (twin-leaf springs) are in. ‘You don’t want them too stiff as you want to keep the wheels on the ground,’ says Doug Smith. FIA ride height is 100mm clearance, including the exhaust.

Bolt-on wheels are faster to change, and alloys are stronger and lighter than wires; maximum homologated size is 5½x14, though it’s worth noting that some Minilite-type wheels make the track wider than allowed. MG Motorsport sells its own wheels with 10mm extra inset, which keeps the track standard. Tires for FIA racing are 5.50 Dunlop CR65 L-section racers: ‘And the car’s in a four-wheel drift in every corner,’ notes Smith.

Brakes need to be standard discs front and drums rear, and friction material is free but race organisers do check pad sizes. Driver-adjustable bias and pressure-reducing valves in the rear brake line are not allowed, but racers can achieve a certain amount of front/rear bias preference by juggling rear wheel cylinder sizes.

Engine
Five-bearing engines rather than the B’s weaker original type three-bearing unit are allowed, because they appeared in 1965, and FIA rules allow a 1.2mm overbore, meaning 1853cc for the B-series ‘four’. Camshafts are free and cylinder heads can be modified, but valve sizes are supposed to remain standard. Lightening the flywheel is allowed but exotic cranks and rods aren’t, and neither are roller rockers. A standard oil pump is adequate because all the motor needs is 60psi of hot oil pressure. Because of the FIA’s ruling on choke numbers and sizes needing to stay the same as original, carburetion is a single Weber 45 (or a 48 if the team thinks it can get away with it), or twin SU HS4s, as standard: ‘Which I’ve never seen on a race car,’ says Doug Smith. He also adds that though some cars ran 2in SUs, a rule change last year has made these illegal. This spec means around 165bhp @ 6300rpm.

A complete built engine from a specialist varies between £7000-12,000 depending on who you shop with, but they’re not expensive to look after. As Doug Smith explains: ‘The beauty of the B is that they’re so reliable because the low revs mean they’re not highly stressed; and after two years of endurance racing we just take them apart, hone them and change the rings and bearings, so a freshen-up is less than two grand.’

Gearbox and diff 
A three-synchro box is specified, and all racers use straight-cut close-ratio gearsets. A rebuilt box with new gears comes out at about £2000. Overdrives aren’t generally used because they add weight and aren’t strong enough. LSDs can be used as they were available as an option, but only the plate type, with a good selection of crown wheels and pinions for a wide range of final drive ratios from 3.9 to 4.875:1; a new diff and CWP is about £1500.

Rally cars
Cost about the same as a racer; although more parts, trim and equipment go into them, the engines tend to be much more standard and therefore cheaper to build.

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