CREATE TABLE table_1522 ("Engine" TEXT, "Exhaust Ports" TEXT, "Bypass Ports" FLOAT, "Bypass Boosters" TEXT, "SPI" TEXT, "Tapered Grind" TEXT, "Number on cyl." TEXT)

How many bypass boosters are there on the engine with slit exhaust ports and SPI is yes?
SELECT "Bypass Boosters" FROM table_1522 WHERE "SPI" = 'Yes' AND "Exhaust Ports" = 'Slit'
SELECT "Bypass Boosters" FROM "table_1522" WHERE "Exhaust Ports" = 'Slit' AND "SPI" = 'Yes'