DIY Supercharger Conversion with Intercooler for 948, 1098, 1275 A-series MG Midget, Austin Healey Sprite, and Morris Minor.
The venerable A-series engine is the beating heart of some of Britain's most beloved automobiles, but achieving a meaningful increase in horsepower requires dismantling the engine and spending serious money. Also, using conventional means to modify a naturally-aspirated A-series to achieve 100 h.p. or more negatively impacts the engine’s street manners and fuel economy.
A viable alternative is forced induction, via a turbocharger or supercharger.
Turbochargers have been successfully fitted to the A-series engine, but no kits, fabrication templates, or detailed instructions are available. Also, turbochargers require custom exhaust work and exhibit a lag in generating boost.
However, if you prefer a turbo, you no longer need to find a costly MG Metro intake manifold and clumsy cast snorkel adapter, which requires hacking a hole in your Spridget's bonnet for clearance.
Creative Spridgets now offers a CNC-machined snorkel adapter and performance air cleaner mount for the SU HIF44 carburetor, available here and pictured below. The profile of the ram pipe is optimized to accelerate the intake charge as it enters the carburetor, and works well with naturally aspirated cars as a direct or remote mount for a performance air filter.
The SU HIF44 mounts directly to a Minispares C-AHT770 cast aluminum manifold shown below, which costs just $67 including shipping from the United Kingdom.
You can convert a standard HIF44 for pressurized operation as described here.
You can add an intercooler in the nose of your Spridget for denser mixture and more power as described here.
According to Eaton’s website, “[u]nlike turbocharging, Eaton superchargers provide instant throttle response and torque across the engine's entire powerband.” Superchargers also do not require custom exhaust work, which is unavoidable when turbocharging the A-series engine.
But until now, only two systems would fit under the Spridget's sloping bonnet: the Moss Motors 'roots style' kit, which costs $4,400, and the High Performance Products twin-screw offering, which begins at $6,000. Mama mia!
Moreover, in addition to their excessive cost, neither the Moss nor the High Performance system can be fitted with an intercooler. As a result, the amount of boost these ‘draw-through’ systems can handle without harmful detonation and back-firing is quite limited, unless you disassemble the engine and install low-compression pistons or retard the ignition.
But now, there's another option: the Creative Spridgets DIY intercooled supercharger conversion for the 948, 1098 and 1275 A-series MG Midget, Austin Healey Sprite, and Morris Minor!
True to our aim of providing the least expensive route to desirable performance upgrades, adding a supercharger and intercooler to your A-series powered vehicle can be done for under $3,000—a savings of $1,400 to $3,000!
If you already run a single SU HIF44 and locate a serviceable used supercharger from a ‘you pull it’ auto recycler, your cost may be closer to $2,000—but that’s for an intercooled system featuring a vacuum-operated, Mini Cooper S bypass valve for greater economy and reduced wear on the supercharger.
benefits and OVERVIEW
Installing a supercharger and intercooler on an otherwise stock 1275cc A-series engine can increase horsepower by 50% to 100 h.p., without harmful detonation or impacting your Spridget’s smooth idle and street manners.
Adding high-lift rocker arms, a long-center-branch header, free-flowing 1.75" exhaust system and smaller supercharger pulley will net even more power.
Standing-start acceleration is dramatically improved, as are passing and hill-climbing in top gear.
Our intercooled supercharger conversion is compatible with an SU HIF44 carburetor or electronic fuel injection. Keep your eyes peeled for our GM/Hitachi or Megasquirt DIY EFI conversion—currently in research & development—or source a throttle body and ECU of your choice.
*Note: we have designed a bespoke GM temperature sensor mount to enable EFI for A-series engines, pictured below and available by clicking here.
However, the mount is also necessary to supercharge Spridgets and Morris Minors with early, down-flow radiators or fitted with a VW Rabbit dual-pass crossflow radiator, as described here.
Our intercooled supercharger conversion utilizes Eaton's M45 (45 C.I.D.) blower, model no. 207018, which is OEM equipment on the 1999 to 2003 Mercedes Benz SLK230 Kompressor coupe and some 1999-2000 Mercedes Benz C230 models—but in either case without an electronic clutch.
This supercharger has the same displacement as the unit fitted to the modern Mini Cooper S. However, it has a simpler design, is more compact at 11" long, 6.5" wide and 5" high, and weighs only 16 lbs. (7.26 kg):
This model features inlet and outlet ports on the same side of the housing:
This configuration allowed us to engineer a one-piece inlet/outlet manifold that uses the stock Mercedes gasket:
A single inlet/outlet manifold not only dramatically reduces production cost, a savings we pass on to you; it enables an intercooled conversion that fits beneath the Spridget's sloping bonnet.
While fitting an intercooler is optional, doing so provides a cooler, denser mixture and eliminates the need to retard the timing or dismantle the engine to install low-compression pistons. A pre-heated intake charge and potentially damaging back-firing, significant concerns with existing conversions that bolt the supercharger directly to the head via a shallow plenum manifold, are eliminated.
Our conversion uses an inexpensive, widely available intercooler from a 1999 Audi A4 1.8L Turbo, which fits neatly behind the Spridget's original grille. The horns, and the heater control vane in some models, are relocated as described here:
The system is designed to generate approximately 5.5 psi. (.379 Bars) of boost on a stock 1275cc A-series engine, running a 3.1" supercharger pulley at 6,000 ft. elevation (1,829 meters).
We recommend using the modular supercharger pulley kit offered by Smoothflow Pulleys pictured below, as it allows you to easily swap pulleys to dial-in the level of boost you desire:
The same pulley combination may produce greater boost at lower elevations, and of course internal engine modifications and the condition of your engine will yield varying results. Please use our contact form and we will post the figures you achieve in a table available in the online instructions webpage.
To get started, review the FAQs and step-by-step online instructions, and then visit our purchasing page to download free plans to fabricate the mild steel supercharger mounts, and to order an M45 supercharger manifold, SU HIF44 snorkel adapter, the thermostat housing adapter (if running a vertical flow or VW Rabbit radiator), and the 5-rib crankshaft and water pump pulleys required for the serpentine belt conversion.
You can then run your car naturally aspirated while completing the balance of the conversion in stages to suit your budget and time constraints.