BSI RACING Custom Spec Miata Weight Box BSI Racing, Inc. » Product Catalog » BSI RACING Custom Products » BSI RACING Custom Spec Miata Weight Box BSI RACING - Custom Fabricated Weight box. Bolts into your existing floorboard, with studs to anchor down plenty of lead weight for your needs. Box itself weighs 37.5 lbs. This makes weight installation very easy, very clean, and safe. Price: $225.00