A MC59 is a hot plug so I guess I should've had an 8 in there. These Novas supposedly come shimmed for 25% but they say you are ok to run 30% with the stock shimming. I even went beyond that and added another copper shim. I spoke to another guy today who seems to think I wasn't getting a good seal in the head shims. He said it would only take a pin hole leak to do this and said he has seen it before...