The Central Railroad of New Jersey based their pacific design on the Reading's G1s, but with more weight, larger cylinders, and slightly smaller drivers. This resemblance to Reading engines was to decrease as time went on. All of CNJ's pacifics can point to the Reading G1s as an increasingly distant ancestor. The G3s and G4s were based on the G1s, but with additional equipment, such as stokers, mechanical lubricators, feedwater heaters, and a narrower firebox.

These first two classes were hand fired until the 1940s, when stokers were applied. Retirements began in 1948, and the last were retired in 1954.

Class G3s, had Elesco feedwater heaters, stokers, and mechanical lubricators. The firebox was smaller on these engines; 8 feet wide, versus 9 feet wide for the G1s and G2s classes. CNJ was burning more and more soft coal, and these engines reflected that fact. Engines 831-833 were painted in Blue Comet Colors from 1929 to the mid 1930s. Engine 834 was painted a dark green briefly for service on the Bullet. Engine 835 remained black her whole life. Class G3s had what were essentially copies of USRA 10,000 gallon tenders for coal and water; these tenders were a bit larger than the 9,000 gallon tenders that came with the earlier Pacifics. The G3s class was built in 1928, and the last were retired in 1955.

CNJ's last five Pacifics were the G4s class. These engines had smaller drivers for service in the hills and tunnels of eastern Pennsylvania. The G4s class had 13,000 gallon welded tenders. These engines were otherwise similar to the G3s class. The last G4s was retired in 1955.

CNJ changed their locomotive class system several times during the life of these engines. The first change was in 1944, when the small letter s (for superheating) was dropped from locomotive classifications. In 1945, CNJ came up with a new class system. P was for Pacifics, and the two digits were for the tractive effort in thousands of pounds. The G1s and G2s class became P43. The G3s class became class P47, and the G4s class became P52.