To vague a question. More details would help. Nothing wrong with a good HEI unit. We bought a cheap one for our endurance car. Worked great until we hit the track and the gear stripped ran like canned ass over 3500rpm. Dropped the stock 160k unit back in and it ran great. If you bought some junk then it is to be expected. If you hoked it up wrong again, expected. Look at what you did and re-do it all over again. A simple bad ground can cause major issues,