MANIFOLDS - Breathing Easy

A desire to solve induction installation problems and assist in the choice of induction types for many ‘A’ series applications, led to the production of a new range of Manifolds from Mini Spares, London, to mount on the ubiquitous SU carb of various types and sizes.

Despite numerous manifolds being available from many different sources, there seem to be three times as many problems when trying to install an induction system equipped with one of these manifolds. You can’t fit an air filter without judicial modification to the bulkhead, the speedo cable is forced to run at severely awkward angles causing regular failure, and certain manifolds will only fit 1300 type engines even with bulkhead modifications. While it is plain that some of these manifolds have been designed with maximum performance in mind, for most applications it would be rare for an engine to produce sufficient performance to utilise the total potential of these manifolds.

Mini Spares started their R & D programme with two unchangeable criteria. The cylinder head mounting face and carburettor mounting face when fitted on a small bore engine. Using these two points meant that any air filter from standard upwards could be fitted with no alterations necessary and that this would apply to ALL A series engines fitted into a Mini. A fair amount of time was spent producing the best shape conducive to good airflow, and the Mini Spares manifold was born.

The ports as standard will supply practically all small bore engines with all the fuel/air mix they need, and will also cope with 1275s up to fast road specification. The casting was made purposely thick to allow port enlargement for engines tuned to a higher specification. The “As Cast” finish provides excellent fuel/air mixing and it is not advisable to polish the ports. If enlargement is undertaken, it is advised to work towards an even stone-ground or rough-taped finish, to retain good fuel air mixing. Polished ports create fuel “puddling’ which is detrimental to both power and economy.

For engines employing more extensively modified cylinder heads with port sizes of 1.35” and over, Mini Spares have produced a manifold with 1.4” port runners designed along exactly the same criteria as its smaller brother, so fitment is not a problem. Using this manifold and an HIF6 carb, power outputs comparable to a twin choke side draught have been achieved. Only a marginal difference at the top end, but better fuel economy, and a fair bit cheaper! Correct calibration is, of course, essential.

Both manifolds have the facility for water heating using the conventional ½” pipe, unlike some manifolds equipped with a 5/8” pipe – another aspect that makes fitment a chore. Using this facility usually produces smoother low to mid range running and better economy. Maximum power requires as cool an inlet change as possible, so leave un-connected if this is your aim.