Based on the USRA Heavy Pacifics, which the Erie was the only one to receive, it received ten more locomotives in 1923. These were similar in size to the USRA engines, but had a larger superheater and were slightly heavier. The original 10,000 gallon water and 16 short tons of coal tenders were soon replaced with larger 16,500 gallon, 24 short tons tenders. In 1926, a single K-5b was ordered to test uniflow cylinders. Since these did not lead to the desired results, they were replaced with conventional cylinders. 