Radium Surge Tanks Explained: MPFST vs MPFST-R vs FCST-X for High-Power Builds Fuel starvation is the one failure mode that ends a good build day early. You come out of a long sweeper with the tank a third full, the pump picks up air, the rail pressure drops, and the engine leans out exactly when you are asking it for everything. A Radium surge tank is the fix. It keeps a small reservoir of fuel around the pump at all times, so cornering, braking and hard launches can never uncover the pickup. Radium Engineering sells three families of them, and they are not interchangeable - MPFST, MPFST-R and FCST-X each solve a different problem. This is the no-nonsense breakdown of which one your build actually needs, and which pumps fit inside. Browse the Radium surge tanks we stock in the UK: https://radiumshop.co.uk/collections/universal-fuel-surge-tanks ## What a radium surge tank actually fixes Be clear about the job before you buy. A surge tank (also called a swirl pot or surge tank canister) is a secondary reservoir plumbed between your lift pump and your high-pressure pump. The lift pump fills the tank faster than the engine can drain it, so the surge tank always sits full. The high-pressure pump then feeds the rail from that constant head of fuel, never from a sloshing OEM tank. The result: no lean spikes, no fuel pressure drop in long corners, and a rail pressure you can actually tune against. On a street-driven Subaru WRX, Mitsubishi EVO or Toyota Supra making serious power, it is the difference between a car that survives track days and a car that eats pistons. ## MPFST - the swirl-pot surge tank for Japanese platforms The Radium MPFST fuel surge tank is the workhorse of the range. It is a machined aluminium canister that accepts up to three high-flow pumps inside, and it keeps them supplied through aggressive driving where a stock tank cannot. Critically, it simplifies a high-power fuel system upgrade without opening the factory tank - you bolt the swirl pot in, plumb it, and leave the OEM tank alone. This is the tank for a built EVO or WRX that still gets driven on the road and wants a tidy, serviceable fuel system rather than a full race cell setup. See the MPFST here: https://radiumshop.co.uk/collections/universal-fuel-surge-tanks/products/radium-mpfst-walbro-f90000267-274-285-pumps-not-included ## MPFST-R - the same surge tank with a built-in regulator The Radium MPFST-R fuel surge tank takes the MPFST concept and integrates the pressure regulator into the canister. The built-in regulator returns low-pressure fuel directly into the surge tank instead of plumbing it back to the main tank, which shortens the fuel system, reduces heat and takes a component out of the engine bay. This is the version most street-and-track builds choose, and it is the one to look at if you are running a single high-flow pump. It fits the pumps UK builders actually run: Walbro GSS342, AEM 50-1200 and DeatschWerks DW440. If your shopping list already says GSS342 or DW440, the MPFST-R is the direct-fit answer. See the MPFST-R here: https://radiumshop.co.uk/collections/universal-fuel-surge-tanks/products/radium-mpfst-r-fuel-surge-tank-fits-walbro-gss342-aem-50-1200-dw-dw440 ## FCST-X - the fuel cell surge tank for dedicated race builds The Radium FCST-X fuel cell surge tank is the serious end of the lineup. Instead of dropping a swirl pot into a stock tank setup, the FCST-X is a surge tank built to serve a competition fuel cell. It holds up to three surge tank pumps plus one lift pump, and it is compatible with the Walbro F90000267 / 274 / 285 pumps that dominate high-horsepower builds. This is the choice for a track-only car, a drag build or anything running an FIA-style cell where fuel delivery has to be bulletproof. Pair it with the matching Radium fuel level sender so your dash still reads correctly. See the FCST-X here: https://radiumshop.co.uk/collections/universal-fuel-cells/products/radium-fcst-x-pumps-not-included-walbro-f90000267-274-285 ## MPFST vs MPFST-R vs FCST-X - which one for which build The selection logic is simpler than the part numbers make it look. - Street-driven WRX, EVO, Fiesta ST or Supra with a stock or lightly modified tank: MPFST-R. The integrated regulator keeps the install clean, and Walbro GSS342 / DW440 fitment covers most builds. - Three-pump or multi-pump setup inside a factory tank: MPFST. You need the pump capacity and you are keeping the OEM tank. - Track-only car or competition fuel cell: FCST-X. It is designed around the cell and the big Walbro pumps, with room for a lift pump plus three surge pumps. - Round out the fuel system: add a Radium fuel pressure regulator or a fuel pulse damper so the return side and rail pressure stay stable alongside the new surge tank. ## Fitment notes before you order Surge tanks are a system change, not a bolt-on. Budget for -10AN feed and return plumbing, an appropriate lift pump, a filter ahead of the high-pressure pump, and mounts that isolate the canister from chassis vibration. Decide your pump set first: the tank accepts the pumps, but the fittings you need follow from pump outlet size and flow rate. If you are unsure which combination matches your platform, the part numbers above are the ones we stock and ship to UK addresses, and every item is genuine Radium Engineering hardware - not a copy. ## The bottom line If your build is seeing lean spikes in corners or you are stepping up to a fuel system that can feed serious power without drama, a radium surge tank belongs on the list. MPFST-R is the right call for almost every street-driven Japanese build, MPFST when you need multi-pump capacity in a factory tank, and FCST-X when the car has a fuel cell and lives on track. Pick the tank around your pumps, plumb it properly, and the fuel starvation problem is gone for good. Shop Radium surge tanks and fuel cells at Radium Shop UK with fast UK delivery: https://radiumshop.co.uk/collections/universal-fuel-surge-tanks