Supercharging has long been a part of the British car scene. From factory-built Blower Bentleys and supercharged MGs of the 1920s and 1930s to aftermarket offerings from Judson, Marshall, Shorrock, Wade and others in the 1950s and ’60s, many British cars have relied on force-fed power. It only makes sense that Moss Motors is reviving the tradition of supercharged British cars.
A few years back, Moss came out with an aftermarket supercharger kit for the MG T-series. Similar in appearance to the Marshall units available in the past, the Moss kit featured a modern Eaton supercharger for higher efficiency and better drivability. That kit has evolved into a line of bolt-on supercharger kits for many of the newer favorite models, including the MGA, MGB, TR6, TR250 and 1275cc-powered Sprites and Midgets.
Before we get into the details, let’s discuss the basics of supercharging. Using an old analogy, an engine is basically a pump. It takes in a mixture of air and fuel, pushes out exhaust gasses, and makes power in between. If the engine can inhale more air/fuel or exhale the exhaust gases more efficiently, then it’s going to make more power.
Traditional ways of increasing the pumping capacity of an engine include cylinder head porting, camshaft changes and exhaust improvements. Each of these methods gives the air/fuel mixture and exhaust an easier path to follow—sort of like leading a horse to water.
With supercharging, you can actually make that horse drink. The supercharger is a high-volume, low-pressure air compressor that simply forces a larger air/fuel charge into the engine. Once that charge is burned, it’s got no choice but to force itself out through the exhaust.
This all sounds too good to be true. It is. Supercharging has some inherent side effects that need to be addressed. Number one is heat. Compressing the air/fuel mixture and forcing it into the engine causes much more induction heat than you’d get in a normally aspirated engine. This heat can cause all sorts of problems, but the worst is a higher incidence of detonation (pre-ignition, also known as knock). Another problem is the parasitic power loss needed to drive the compressor. It takes a fair amount of power to spin the belt-driven compressor, so a supercharger’s efficiency is paramount to its performance.
Historically, supercharging has enjoyed periods of dignity and disgrace. The years of high interest in the 1920s and ’30s were followed by some lulls. Supercharging saw a resurgence in the 1950s and ’60s, followed again by another long, empty period until the mid-1990s. Armed with computer-controlled, fuel-injection systems and precision manufacturing techniques, superchargers have again been embraced by automakers and the aftermarket alike.
On to the Details
Obviously, British classics don’t employ modern fuel-injection systems, but these machines can take advantage of the well-built, long-lasting superchargers installed on other types of engines. Eaton superchargers are used in many original-equipment applications including those from Jaguar, Mercedes-Benz, Ford and GM. They’ve also become a staple in aftermarket kits for Miatas, Hondas, Toyotas and others.
Moss has taken Eaton’s smaller models and integrated them into comprehensive kits that include every nut, bolt, hose clamp, and component necessary for installation. These kits contain the supercharger itself as well as a specially cast intake manifold, air filter, multi-ribbed serpentine drive belt system and brand-new carburetor—an SU unit in most cases.
Depending on the application, the kits also include new accelerator and choke cables, a water pump, a fuel pump, an alternator and cooler spark plugs. An installation manual is a critical kit component. All that’s needed to finish the job is an afternoon in the garage and basic hand tools.
To show how easy is it to install a Moss supercharger kit, the following example demonstrates the process on a 1978 MGB. Remember, start with a car in good running order; the supercharger won’t magically fix a worn-out engine.
The installation process starts by removing the stock carburetor (and exhaust manifold if the car still has the single Zenith Stromberg setup), plus the radiator, water pump, alternator and lower crank pulley/harmonic balancer.
Then the new parts are installed: Replace the balancer with the lower pulley that has grooves for the multi-ribbed belt, then put in the new water pump and pulley. The next step depends on the car: For chrome-bumper machines, install a new alternator and pulley; for rubber-bumper cars, fit only a new alternator pulley. Next, install the supercharger along with a new exhaust manifold or header if necessary.
This brings up a step that needs a little extra attention, as there are different flange thicknesses for various exhaust manifolds and headers. These flanges meet up with the intake manifold flanges at the mounting points, so alignment is critical to avoid leaks. To match the thicknesses of these parts, Moss includes shims in the kit.
Once the supercharger is mounted, install the belt and its tensioner. Then reinstall the radiator and follow Moss’ instructions to cut and modify the lower hose, rerouting it with the pieces included in the kit.
After installing new accelerator and choke cables, hook up the lines for the fuel, vacuum, PCV and anti-run-on systems before bolting on the air filter assembly. Once everything is installed, you might need a timing and idle-mixture adjustment. Then take it out for your first drive.
Stock, single-carburetor, rubber-bumper MGBs usually peak at a little more than 50 horsepower at the rear wheels. The Moss supercharger kit can immediately bump that figure up to 90 horsepower—along with a nice increase in torque in the meat of the powerband.
What about real-world acceleration? That’s where the big gains are apparent on our MGB, as its zero-to-60 times dropped from 14 seconds to 10. On the highway, the car can now easily run with traffic and pass cars with overdrive still engaged.
Driving manners are the same as before: The car still starts, idles and behaves like a normal MGB, all without overheating or crankiness.
In short, the Moss Motors superchargers have allowed some of our favorite classics to thrive in today’s world—all without any downside.
Moss Motors Supercharger Lineup
1275cc Austin-Healey Sprite
1275cc MG Midget
Adapted from a Classic Motorsports story written by Carl Heideman