[pat in Santa Cruz]

Its not the muffler that is high performance, it is a muffler built for use on an engine that is high performance. Unless your engine is putting out higher volumes of exhaust due to greater intake volumes ( e.g, dual carbs, overhead valves, big cam), higher exhaust volumes ( e.g. the above and headers), and higher RPMs than a stock A engine, it would be a waste of money to put such a muffler on. The holes in the baffles are larger to reduce back pressure and accommodate the higher flow rates of a high performance engine . Any A engine under 85 hp should be fine on a stock muffler.