The original SU electric fuel pump fitted to classic MGs during production is a remarkable piece of engineering, reliable in standard service, simple in operation, and easy to renew when the time comes. For owners running modified or tuned engines, the standard pump's flow rate can become a limitation, with the engine drawing more petrol than the pump can supply during sustained high-load running, producing hesitation, a flat spot under hard acceleration, or a momentary loss of power at the top of the rev range. Performance fuel pumps address this with higher flow rates, more consistent pressure delivery, and in some cases more modern internal construction that improves long-term reliability, and they also serve as a reliability upgrade on standard cars where the original pump has become tired or intermittent, a common issue on pumps with worn contact points.
SU-Pattern & Modern Solid-State Pumps
SU-pattern performance pumps retain the visual appearance and the mounting arrangement of the original pump while increasing the flow rate and improving the internal construction, the body, diaphragm, and electrical contacts all built to higher specifications, so the pump fits in the original location, looks identical from the outside, but supplies enough petrol for a tuned engine running hard, making it the better choice where original appearance matters. Modern solid-state pumps are increasingly popular alternatives, the Hardi range using metal-bodied pumps with printed-circuit-board electronics in place of the conventional brush-and-points arrangement, eliminating the principal long-term wear item of the original design, with all Hardi pumps being dual-polarity and operating correctly on both positive and negative earth systems without modification, a real ordering convenience since many cars left the factory positive-earth but have been converted. The Facet Posi-Flow pump features self-priming solid-state technology with a one-way check valve that retains fuel in the line when the pump is not running for immediate delivery on start-up, and delivers 1 to 4.5 psi, suiting SU and Stromberg float chambers without a separate regulator, the appropriate choice for a like-for-like modern replacement of a tired original pump.
When an Uprated Pump Is Needed
On a standard car running its original SU pump in sound condition, an uprated pump is not necessary, as the original pump is matched to the factory carburettor specification. The case for a direct-replacement solid-state pump arises when the original has reached the end of its service life and the owner prefers a modern unit rather than a points-pattern rebuild, while the case for a higher-flow performance pump arises only on engines built significantly beyond standard, a tuned cylinder head, performance camshaft, higher compression, larger carburettors, or full competition specification, where the standard pump's flow rate would be the limiting factor under sustained high load. A complete performance pump kit is supplied with the pump, mounting blocks, unions, and an inline filter, and the physical mounting should be confirmed against the chosen pump's form factor, as modern pumps differ in shape from the original SU body.
Pressure Regulation & Safety
Both pump families, with the exception of the Facet Posi-Flow, deliver petrol at higher pressure than SU and Stromberg carburettors are designed to accept directly, as those carburettors expect petrol at around 1.5 to 3 psi at the float chamber while higher-flow pumps typically deliver 4 to 7 psi, too high for the floats to handle correctly. A fuel pressure regulator fitted between the pump and the carburettor reduces the delivered pressure to the design specification, and is essential for any high-flow pump feeding a standard SU or Stromberg setup, as running one without a regulator overcomes the float needle valve and causes flooding, rich running, and a fire risk. An in-line fuse holder with a suitable fuse must always be fitted in the pump's electrical supply, as a pump that continues to run after an accident or electrical fault is a serious fire risk, and the regulator options are covered in the dedicated Fuel Regulators section.