All Groups - BMC "A" Series (or Triumph 1500 type) engine blocks & cylinder heads must be retained.
5 port cylinder heads only
Groups A,B & C: Maximum engine capacity 1500cc. Marina/Ital blocks permitted.
Groups B & C: Must retain standard length stroke.
5.(7).1 PERMITTED MODIFICATIONS:
(a) All Groups - Cylinder heads may be gas flowed and have ports/chambers re-shaped and polished.
Groups A & B - Valve size free.
Group C - Must retain standard size valves (Rimflow type valves are permitted)
i.e.' A' Series:- Inlet 1,31” Dia., Exhaust 1.15” Dia..
Triumph 1500:- Inlet 1.38” Dia., Exhaust 1.17” Dia.,
(b) Group C - On ‘A’ Series engines dished pistons (Min. 6cc Dish) must be used.
Triumph 1500 type engines must use standard specification pistons only
(c) All Groups - Reboring of cylinders permitted within proscribed limits.
(d) Groups A & B - Camshaft free. Camshaft drive free
Group C - All engine types - Camshaft free. Camshaft to be chain driven from crankshaft.
(e) Groups A & B - Lightening of engine components permitted.
Group C - Balancing of reciprocating parts is allowed. Engines must retain component weights to within 5% tolerance of homologated figures.e.g. ‘A’ Series
Crankshaft: 22.25 lb. (10.1 Kg)
Con-Rod: 1.47 lb. (0.67 Kg)
Flywheel/Clutch : 23.02 lb. (10.4 Kg)
(f) All Groups - 948/1098/1275/1500 engines may be fitted to alternate chassis.
(g) Group C - On ‘A’ Series engines vernier timing gear may be used, with chain - not belt.
5(7).2 PROHIBITED MODIFICATIONS:
Supercharging, turbocharging, fuel injection, use of 8 port heads.
Electronic ignition systems triggered by Flywheel/Crankshaft or systems which process intelligent information from engine and/or ambient conditions.
Group C - No off- set rockers/bushes/roller rockers or ratio changes.
’A’ series Maximum engine capacity must not exceed 0,060" overbore.
5(7).3 LOCATION: Group A only - Engine mountings may be moved.
5(7).4 OIL/WATER COOLING: Original type system to be retained. Group C will use OE radiator in original position. Oil cooler may be fitted. Thermostat, by-pass hose & Heater may be removed.
5(7).5 INDUCTION SYSTEMS: .See Yearbook J5.4.2. Applies to all classes.
Groups A & B Carburettor & Manifolds free.
Groups C - Retain original carburettors & size of throttle bore/plate.
5(7).6 EXHAUST SYSTEMS: Free, but Groups B & C not run through interior of body shell.
See - Ref. J5.17. Noise Limits
5.(7).7 IGNITION SYSTEM: Electronic ignition permitted subject to 5.(7).2
5(7).8 FUEL DELIVERY SYSTEM: Free
Page No 14 of 18- Issue No 3 – 9.12.10
Published by Midget Competition Group – MG MIDGET CHALLENGE-2011