How to supercharge an A-series engine

When we started this project, we knew we wanted to supercharge our Bugeye Sprite. A car this cool should be truly quick, right?

After buying a vintage supercharger, we took stock of the project: We’d still had to source or fabricate the manifold, mounting brackets and the like with period-correct parts. It just wasn’t worth the time and money to get maybe 20 more horsepower.

So, we sold the supercharger at the Carlisle import swap meet and invested in Moss’s supercharger kit.

This kit, which lists for $5199, comes with everything needed to supercharge an A-series engine. While the kit fits any Sprite/Midget and presumably other A-series powered cars like a Turner, it does not fit a front-drive Mini due to packaging restraints.

The kits are based around an Eaton positive-displacement, roots-type supercharger (as found on many modern cars). At about 6 psi of boost, it offers a roughly 40% power increase.

While we have not dynoed our car yet, we feel it will be in the 120-horsepower range. This calculation is based on the rest of the modifications we have made to our engine: increased compression, better cam, porting the head, balancing and blueprinting, plus a header and straight-through exhaust.

The common wisdom when building a practical, streetable A-series engine is to raise compression to about 10.5:1. This would be disastrous on a supercharged engine, so we kept compression closer to 9.5:1.

Our original intent was to install the engine with its original twin SU carbs and break in the engine and then later add our Moss supercharger kit.

Since the kit came with everything, including radiator hoses, a new SU carburetor and every other detail you could think of, we went ahead and installed the kit as soon as we put the engine in.

Some of the included items, like the idler pulley, crank pulley, and some mounting brackets, are easier to put on the engine when it is still out of the car, so we took advantage of that reality as well.

The installation book was quite helpful. Follow it.

Moss felt the job would take about 9-10 hours, but that is assuming you have to first remove everything from a running engine. In our situation, with everything new and still in the process of engine installation, adding the supercharger kit added only a few hours, if that.

The biggest part of the job was mounting the generator/alternator bracket, along with the idler pulley, as the kit moves from the original V-belt to a modern serpentine belt. The kits even include a spare belt, since it would be hard to find one out on the road unless you knew the original donor.

At the same time, we also picked up a Moss Motors alternator conversion kit

Then, essentially, you just bolt the supercharger onto the supplied intake manifold.

Once we got the kit installed, we were blown away with how cool and vintage the installation looks–and even more impressed with how quickly we got the car up and running and tuned correctly.

We did weld in an oxygen sensor port and used an Innovate Motorsports LM-2 air/fuel ratio meter to get the car running correctly.

While we have just started test driving the car and are still breaking in the engine, we can tell you that this is one quick Sprite. We expect zero-to-60 times to be in the 6-to-7-second range.

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TerryV New Reader
4/11/24 2:12 p.m.

Good luck not breaking a rear axle. I broke 2 with 43 horse power and I wasn't dropping the clutch when they broke.

RoadRunnerKen New Reader
4/12/24 9:52 a.m.

That is Beautiful ! ! !      I love it ! ! ! 

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