Likely volume. Were they real B&S or aftermarket? It may cost more to cram lots of area in a small package. Try to find the specs, or cut an old one open. Look for bypass valves and ADBV. Then see if something small and cheap, such as a PF 47, will fit. Many of the Japanese cars use very small filters, but they tend to use the larger 20 mm thread. Likely the B$S uses the same 3/4'' one as many American engines. Come back with the thread, area, bypass setting if any, and maybe somebody here can point you to an automotive filter that will work. You can buy a huge ST 3950 for $2.