I contacted Holley, asking about what replaced the old 300-36. They weren't aware of a direct replacement, but suggested that the 8501 may be close. I then asked what the differences are between the 8150 and the 8501. The tech rep told me that the 8150 has an exhaust port cross over (increasing heat), which helps fuel atomize better for improved street drivability, 8150 and the 8501 has an air gap to reduce heat. 8501 Other than that, he said they are identical.