MGB Supercharging

Moss Motors’ new MGB force-feeder increases flywheel horsepower by up to 50%

By Leonard Emanuelson

Resto-mod is a pretty cool concept. It allows you to keep everything you love about your classic British sportscar and change everything you don’t. You may love the way it looks, but hate the lack of power. Love the way it rides, but hate the way it handles. Love the way it sounds, but hate the way it stops. Some say that these shortcomings are part of the charm of owning and driving a vintage car—a return to simpler times. While that may be true, a growing number of vintage sportscar enthusiasts want to make their cars more fun to drive, safer, and more compatible with other modern vehicles on the road. For example, the first time a Honda that’s capable of stopping from 60mph in 115 feet slams on the brakes in front of your freshly painted, newly chromed restoration, you’ll appreciate your modern, upgraded brakes.

Typical resto-mods include upgraded suspension, brakes, powertrain, exhaust, wheels, and tires. A proper resto-modification is non-invasive—the vehicle can be returned to stock without a trace of evidence showing past higher performance indiscretions. In fact, most enthusiasts carefully store and catalog the original parts so they can be easily reinstalled later if necessary.

One of the first things MGB owners want to improve is engine performance. In stock form, the little 1798cc four-banger barely cranks out 50 hp to the rear wheels. Keeping up with traffic and passing on two-lane roads can be a struggle. Prior to supercharging, there wasn’t any good way to significantly increase horsepower without sacrificing drivability. Adding more compression, a hotter cam, and bigger carburetion adds limited power to the top end while taking it away from the bottom.

It’s hard to argue with the wow factor when you open the hood and reveal the Moss supercharger system. Nice details such as the MG logo cast into the manifold and the new SU carb make the supercharger system appear period-correct.

Superchargers are excellent at producing broad, useable torque curves. Their effect can be felt from off-idle to redline. Superchargers give the effect of doubling an engine’s displacement without actually increasing the physical dimensions of the engine. Moss Motors recently introduced a new supercharger system for MGBs that is fairly simple to bolt on and nearly doubles rear-wheel horsepower (40%-50% at the flywheel) without any internal engine modifications. With this increased horsepower and torque, you downshift less and don’t think twice about pulling out to pass. One of the best arguments for superchargers is that they provide power “on demand”; when you don’t need it, the supercharger is just along for the ride. A thrifty four-cylinder is just that—until you roll into the throttle and boost kicks in. Hang on, because the feeling is akin to someone adding another four cylinders of power without the weight.

R&D Background

So what does Moss Motors know about superchargers? More than you might suspect. One of its ventures is Jackson Racing, which has built its reputation on high-tech supercharger systems for the Ford Focus, Miata, Hondas, and Acuras. Typical power gains on these performance engines that come highly tuned from the factory are 40% and higher. Jackson Racing’s supercharger systems are highly sophisticated with OBD II-compliant engine management and extremely compact packaging requirements. Jackson Racing has been building supercharger systems for more than eight years, and many of its customers’ cars have more than 100,000 miles of reliable everyday service.

A couple of years ago, Moss decided to apply some of its supercharging technology to vintage British cars. Their first system (150-008) was for MG TC/TD series cars. When bolted on a 1250cc engine, it produces 6-8 psi of boost and around 40% more power.

Tons of development time went into the designing the intake manifold to provide proper distribution with the MGB’s siamesed center intake ports. The spring assembly is part of the pop-off valve that protects the supercharger in case of a backfire in the intake system.

Now Moss has turned its attention to the MGB, one of the most popular and populous British sportscars of all time. The new MGB supercharger system uses the same Eaton positive-displacement, Roots-type supercharger found on contemporary OE applications such as Mercedes-Benz and Jaguar. It’s also the cornerstone of Jackson Racing’s aftermarket systems, so Moss engineers have lots of experience with this supercharger. In spite of its modern origin, Moss was careful to design the system to look period correct. They accomplished this by using an SU carb and pressure die-cast supercharger. The Moss system almost looks and functions like it was a factory-installed option.

This is an early prototype mockup of the supercharger drive system. It’s rugged and uses a four-rib serpentine belt. Moss includes a new alternator and a cast-iron water pump to ensure trouble-free operation.

Designing supercharger systems isn’t an easy task. First you must understand the idiosyncrasies of the engine you are supercharging. An MGB challenge is its siamese center intake ports in the cylinder head. (The center two cylinders are fed by the same passage in the cylinder head.) Second, understanding the airflow discharge characteristics of the supercharger is a must. Armed with this information, Moss engineers designed an intake manifold that provides equal airflow, pressure, and fuel mixture to each cylinder. By optimizing the distribution in the manifold for each cylinder, you can run more boost pressure without the chance of harmful detonation. The Moss supercharger system comes with a 2.75-inch blower drive pulley that produces 7.5-8.25 psi of boost at sea level. Moss also sells a smaller 2.60-inch pulley that spins the blower faster, upping boost to 9.75-10 psi—ideal for modified engines with ported heads and hotter cams. For higher-compression engines needing less boost, a 2.85-inch diameter pulley will also be available.

Almost as critical as manifold design is the fuel delivery system. Instead of using a modern carburetor, Moss chose to retain the vintage flavor of the MGB and opted for an SU HIF 44 side-draft model that’s been highly tuned to work with the supercharger. A supercharger needs a large shot of fuel each time the throttle is opened to prevent a lean backfire. Since the SU carb doesn’t have an accelerator pump, its slide, needle jet, and spring have been highly modified and work quite well.

As you can see here, most of the action is on the driver’s side of the engine. Normal engine maintenance is no more difficult with the supercharger installed.

Comprehensive Kit

The remainder of the Moss supercharger kit is very complete. Accessories include a four-rib serpentine belt-drive system to ensure pulley alignment, a new alternator to ensure fresh bearings, and even a new cast-iron water pump to replace the aluminum pump on your model. A set of colder N7Y sparkplugs and a high-flow K&N air filter are also included. The instructions are extremely detailed and well illustrated. In fact, supercharger system instructions were verified during a pre-sale installation test by Moss salespeople. And if they can install it…well, you know the rest.

Here’s a prototype kit laid out so you can see all that’s included, right down to new colder spark plugs and a K&N high-flow air filter.

MGBs were manufactured from 1963 to 1980. While all of their engines displace 1798ccs, the compression ratios and engine accessories varied from year to year. Moss will roll out these MGB supercharging systems in three groups: The first wave will be for 1966-74 (150-068), the second production run covers 1975-80 (rubber bumpers), and finally for the earlier 1962-67 models. At publication time, the 1968-74 ½ system had been tested on several cars with various compression ratios and engines conditions ranging from newly rebuilt to high-mileage but well-maintained.

How impressive? Check out the dyno chart from the test car. A 70% increase in torque and a 95% increase in horsepower at the wheels certainly qualify as impressive. Where stock horsepower peaked at 4,250 rpm, supercharged horsepower now climaxes at 4,750 rpm, extending the useable power band by 500 rpm. Where the stock engine was running out of airflow, the supercharger takes over, pulling strongly through 5,500 rpm.

Dyno numbers are impressive, but how do they relate to the real-world driving experience? We test-drove the supercharger system on a Moss customer’s car. We ran it down our favorite little test road for a seat-of-the-pants evaluation. The torque increase is impressive. In traffic, we found ourselves just pushing down on the throttle instead of downshifting. The engine pulled smoothly and strongly with no bucking or hesitation. Out on the open road, the engine quickly revved to 5,500 rpm in every gear. In fact, you’ll wish you had another gear or an overdrive transmission. You can also detect a slight hint of supercharger whine at full throttle (it’s a pleasing sound for us motorheads), but otherwise you have none of the usual negative symptoms of modified engines.

The verdict? Best money you can spend on your B. The fun-to-drive factor increases 100%. Best of all, Miata owners can no longer kick sand in your face!

The Moss Motors MGB Supercharger System is compact, and installation doesn’t require cutting or permanent modifications to the car. Your engine should be in sound operating condition before you add the supercharger.