The Imp Site

Formula Four (F4)

Winged & ground effects, single seat, open wheel, formula roadracing cars. The rules are quite liberal regarding chassis alterations and modifications, but the motor must be be production based.

Originally F4 was intended for 250cc and 650cc motorcycle-engined cars. The formula really only started to gain acceptance when the 875cc Hillman Imp engine was made elligible. Then the one-litre Imp engine was brought into the the F4 fold and more folk started to take notice.

Then the FIA decided to chop the 1-litre Formula 3 in favour of a 1600cc formula. A great number of 1-litre engines and Formula 3 chassis of varying ages were free to compete elsewhere. These were then made elligible for F4, which meant an immediate increase in drivers and competitive machinery. A degree of parity between the power outputs was achieved by regulating throttle flange sizes. Various engine types involved:

So in 1973 the formula started to show a bit of real life.

1975 regulations

   A wide range of cars and quids are catered for:
   over £3000 Delta IRF4 or new F3 type
   £2500 - £3000 current F3 type with 1-litre MAE
eg. March 733/734; GRD 373/4; Ensign LNF4
   £2000 - £2500 earlier versions of the above
March 723 or updated 713; GRD 273; Brabham BT38 or similar
   £1600 - £1900 March 713; Brabham BT35; Lotus 69; etc.
   £1400 - £1600 Brabham BT28; Chevron B17; Lotus 59/69; etc.
   £1000 - £1400 Brabham BT21; Chevron B9; Techno TF69/70; Lotus 59; etc.
   £800 - £1000 Brabham BT18; Lotus 41; etc., plus better Imp-engined cars
   £600 - £800 Brabham BT15; Lotus 22/31; Cooper T72/T76; plus other Imp-engined cars

In theory these regulations should standardise the power output at around 120bhp from each engine type, but the Ford engines - particularly the downdraught - are the more successful.

Few Imp-based Formula Four cars were used from 1975 on.

The F4 Championship of 1974 was over 16 rounds and sponsored by Low Cost Racing Ltd, the company which specialises in selling racing cars of this type. Lorina Boughton finsihed second.


In a magazine article sidecar racer Peter Williams, of Birmingham says "Keith Blainey was a genius with engines, and had a lot to do with Formula-Four car racing, which was all Imp engines at that time." and he must have been talking about the period before October 1972.
Car of the year ! / by Pete Sutton; photography John Noble. - Classic Racer, winter 1986. - pp.38-42.

The Imp Site
   Competitive Impers
      Imp Racers
         Formula Four (this file)
   Imp Specials
      Evad 4, Formula 4 Racing Car
         Evad 4, Formula 4 Racing Car - the folder
         Evad 4, Formula 4 Racing Car - press release
         Evad, RAC Regulations F4
© Franka
File version: 5 July 2013