The supercharger's biggest benefit, torque, is the ideal upgrade to the A-Series motor. While horsepower is typically achieved by increasing RPM, torque has been the sole property of increased displacement. A V8 has much more torque than a 4 cylinder, but the application of modern superchargers has greatly diminished this distinction. Since all A-Series motors have 3 main bearing cranks, they are best suited to lower RPM (less horsepower) and can take advantage of the major benefit of superchargers - torque!
Twin Screw Compressor Design:
The twin screw supercharger is actually a positive displacement "compressor", not just a blower. This unique design allows the Mini Mania Supercharger to force a greater volume of air, at lower temperatures, into the manifold than "Rootes" design blowers.
Volumetric Efficiency (VE) measures how well a supercharger breathes and how much leakage occurs. For example, if a supercharger has a displacement of 10 liters and only 8.8 liters exit, the unit is 88% VE. Naturally a less efficient supercharger with a lower VE will have to work that much harder to produce sufficient air. The Mini Mania supercharger has an 88% VE, while most "Rootes" type blowers will produce 60% VE.
Adiabatic Efficiency (AE), measures how well a supercharger uses the energy delivered to the drive shaft and how well it controls temperature from intake to exit. The low exit temperature of the Mini Mania Supercharger, as referenced to intake temperature, precludes the need for internal engine modifications or compression changes. The Mini Mania Supercharger requires less power to turn its rotors, and condenses the air to produce cooler air than normal blowers.
Care and Maintenance:
All Mini Mania Superchargers are self-contained and require normal oil level checks and regular lubricant changes. All gears and seals are lubricated by design during operation cycles. Unlike the virtually all turbochargers, no external lubrication system is needed.
As with all engine work, extreme care should be taken to insure a very clean environment while installing, as the fine tolerances present in this device will not tolerate dirt, grit or grime. In addition, the intake air filter should be serviced at normal intervals.
The Dyno: The Numbers & What They Mean
The facing chart shows the horsepower increases of the Mini Mania Supercharger compared to their respective un-supercharged counterparts.
The stock 1275cc engine had 8.5:1 compression with a 266 camshaft and LCB header; stock cylinder head, stock pistons, single 1 3/4" SU carb, stock everything else.
The 1275cc Race unit had 12:1 compression, Longman GT17 head, High lift rockers, 296 scatter pattern camshaft, Omega piston, twin 1 3/4" Su carbs, etc., etc.
The 1380 blown motor has a mechanical compression of 8.5:1, a stock cylinder head, "AE" big bore pistons, "731" style camshaft and an optional 5-speed transmission. Boost is 4 to 6 PSI. The only change for the race 1380 was a boost increase to 10 to 14 PSI.
The horsepower numbers are tremendous but the feel of power, the torque, the "grunt", is even more spectacular.
A Supercharged Comparison
The following shows the comparison of using a Mini Mania supercharger kit on two different versions of the same engine.
The engine was run on the same chassis dynamometer (“rolling road”) before the supercharger was added and after each major engine update. The first and third versions were run at approximately 70 degrees F and the second at approximately 50 degrees F.
All dyno figures are “at the wheels,” real world figures, not the made up ones you see for flywheel horsepower in the Mini related magazine “shoot outs.”
The dyno figures were taken as the car was tuned before arriving. There was no tuning done at the dyno to maximize figures. More work at the time the runs were made certainly would have improved figures some. The base engine, for instance, wasn’t getting its best by using the Aldon Yellow distributor. It is highly unlikely that the curve matched the standard specification of the rest of the engine.
It is unfortunate that all three tests were not run with the same 1500 rpm start point as you can see when you look at the figures.
Test run from 2500 to 6000 rpm
SUPERCHARGE ENGINE, VERSION ONE
Test run from 2000 rpm to 6000 rpm
Comparison with Base Engine
SUPERCHARGED ENGINE, VERSION TWO
The engine was extensively rebuilt.
Test run from 1500 rpm to 6000 rpm
Comparison with Base Engine
Comparison with Supercharged Engine, Version One
1. The day Version Two was run there were several other cars that ran on the dyno. A 1360 with a mildly improved head and cam and about 9.75:1 compression had the next highest torque figure at 69. Version two had that figure at 1900 rpm! A well tuned 1293 with a good street head, Isky “torquer” cam, and other mods managed 67 hp as the second highest car tested. Version Two hit 67 hp at 4000 rpm.
2. Even with all the mods and the high torque and horsepower figures, Version Two is a smooth, easily driven street engine. That much power out of an A-series by conventional means would give you a fast race engine all but impossible to drive on the street.