803cc BMC A Series engine power curves

Issued by Aquaplane.

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Reproduced here is a chart that came with an old Aquaplane tuning catalogue in the 1950s, and it might prove useful for anyone who is trying to eke out a little more power from this tiny engine, not noted for its tune-ability, the preferred option often was to upgrade to the 948cc or 1098cc variants of the A series engine. The definition of the chart elements, found on the reverse of the leaflet, reads as follows:

Power Curves for the BMC 803cc OHV engine fitted with Aquaplane Speed Equipment.

"In issuing these dynamometer test results it may be noted that our tests on the standard engine may not coincide with the manufacturer's figures. While we do not dispute the latter we do advise designers to base their calculations on the curves overleaf and to use our standard curve for all performance comparisons.
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While the improvements afforded by the use of Aquaplane Speed Equipment on the BMC 803cc engine are undoubtably very impressive, the design our our equipment has been tempered with the realization that, even in an engine of excellent basic specification there are, naturally, mechanical limitations. We consider that, in designing equipment for the attainment of higher power, the necessity of retaining the inherent reliability of the unit as a whole must not be overlooked. More power than we show in the curves can be obtained from these engines but we consider that it cannot be done without impairing reasonable reliability. If, however, in some particular application this factor is not important, we are prepared to advise."

Curve No.1 - Engine in standard form as received from the manufacturers.

Curve No.2 - Fitted with Aquaplane Twin SU Inlet Manifold (Part no. MM/900/2SUK).

Curve No.3 - Fitted with Aquaplane Twin SU Inlet Manifold as in No.2, plus Sports Inner Valve Springs which were used to eliminate valve bounce at the higher rpm (Part no. MM/828/S).

Curve No.4 - Fitted as No.3, plus Aquaplane Exhaust Manifold (Part no. MM/1400). Part No. MM/EX/STD Manifold Adapter was used together with standard exhaust pipe and silencer.

Curve No.5 - Fitted Aquaplane Inlet and Exhaust as above, plus Racing Valve Springs (Part no. MM/825/R) instead of Sports Inner Springs. Manifold Adapter MM/EX/A was used together with large bore High Efficiency Exhaust System and Straight-Through Silencer (Part no. MM/1410/PK).

Curve No.6 - As No.5, plus Aquaplane Cylinder Head Service which includes increase in compression ratio and necessary attention to ports.

Power bands for the 803 A series engine

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