Im pretty familiar with GM engines and it does not look like anything GM produced. I wondered if it was the mazda. how expensive are they to rebuild or should I look for a used engine. the one I have runs fairly well. but seems a little weak. I did a compression check on it today despite not wanting to see the results. I was rewarded with dismal results as I had suspected. to be honest Im surprised it runs as well as it does based on the numbers the compression check gave me. any suggestions? it has 14811 hours on it and the maintenance on it was very poor at best prior to me getting it.