MG Deep Breathers

Air filters that improve performance and looks

By Matt Hardesty; photography by Shane Reichardt

It’s the age-old parable: an engine is nothing more than a big, noisy air pump. It needs fuel and fire to push atmosphere down on pistons to spin a crank, the transmission, and eventually the tires. Getting that air in and out is paramount to power; more of each begets more power. However, an open intake and exhaust is not the best solution. Beside the fact that an open exhaust is TOO LOUD, ingesting dust and debris into the engine obviously isn’t good. A decent muffler will keep things quiet and flowing freely; however, the air intake is a little different.

To achieve good airflow and more power, the air filter and intake can’t be too restrictive. Factory air cleaners and paper filters are designed to be replaced often because the paper media gets dirty and clogs quickly. As dirt accumulates, less air gets through and performance goes down as the engine begins to run richer. Paper filters vary slightly from one manufacturer to another, but they all tend to perform about the same.

The biggest advance manufacturers made in air filters was going from oil baths to paper back in the ’50s, but little has been done by them since. Aftermarket companies such as K&N pioneered the high-performance air filter in the late ’60s. K&N realized that paper filters couldn’t handle the two jobs of providing good filtering with excellent airflow over extended periods. K&N filters use several layers of surgical cotton gauze that’s sandwiched between a wire mesh. The gauze is treated with oil and pleated to increase filter area while reducing the overall size of the filter. This combination provides excellent airflow, filtration, and longevity. Since the filter can be cleaned, it’s cheaper in the long run and more environmentally friendly.

We investigated performance air filter options for a ’72 MGB. (Intended to be our “hot” daily driver, the little B has had some engine work, and we’ve installed a set of SU carbs for better performance.) Moss Motors offers three different K&N setups for this MGB: stock replacement elements (372-395), complete filter assemblies (222-950), and a filter-plate set with cast-aluminum cover (222-910).

Replacement Element


  1. Here’s the new K&N filter (top) and the stock, paper-element filter. The K&N has fewer pleats, but filters and flows much better than paper. Plus, it can be cleaned and reused.


  1. We cleaned, sandblasted, and repainted the stock filter housings for a nice, restored look.


  1. We placed the OE base on the K&N filter, then slid it inside the housing. The K&N unit is an exact replacement for the original filter and fits perfectly.


  1. We installed a new gasket on each carburetor prior to installing the base assembly. The gasket ensures that all air going into the engine is clean and filtered.


  1. Wrangling the two housings together via the center crossover tube takes a little elbow grease.


  1. With both housings in place, you can now tighten the bolts that hold the air cleaner to the carburetor. Don’t over-tighten—you can deform the air filter or dent the housing.


  1. The finished product looks fresh as new but has improved performance lurking underneath. The nice thing about the factory housings is that the inlet tube siphons air away from the exhaust manifold area.

Cast-Aluminum Assembly

cast al 1

  1. We assembled the Moss custom-plate filter kit next. The cast-aluminum cover is finned for a slick look and ties the two filters together. The original base plates are still needed. Also be sure to install new gaskets as seen here.

cast al 2

  1. Fitting both carbs at the same time can be tricky as you try to line up the bolts and then tighten the nuts down. Be sure that the gaskets remain in position while getting everything lined up.

cast al 3

  1. You’ll need two wrenches to get on the bolt and the nut. Again, do not over-tighten, as this can damage the filter, the top, or the base.

cast al 4

  1. The finished product: a custom look with great airflow for more performance.

Chrome Assemblies

chrome 1

  1. We installed the individual chrome air filter assemblies next by attaching the base and new gasket.

chrome 2

  1. Here are the two bases bolted to the carbs and awaiting the filters and tops. The bases use studs so that chrome acorn nuts can be used to hold the lid on. This makes for a clean look when complete.

chrome 3

  1. The filter and lid fit on the base as shown. Be sure that the filter fits flush into the base to ensure a good seal.

chrome 4

  1. Don’t over-tighten the acorn nuts, as mentioned earlier. Also, be careful not to scratch the lid’s chrome finish with the tools.

chrome 5

  1. The finished product looks great. It’s racy and modern with a bright finish that looks good against the carbs.

K&N Oil Filter

kn filter

While we were at it, we installed a new K&N Performance Gold oil filter in place of the stocker. The Performance Gold features a unique design that outperforms OE-style paper oil filters for added protection.

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'MG Deep Breathers' has 1 comment

  1. March 3, 2017 @ 10:30 am Derek

    Does updating air filters mean changing carb settings ?


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