The plane was going to run on the OEM muffler for its maiden, as I didnt have the correct plugs, but things got out of hand and the pipe got bolted instead...I must agree the its a high compression engine so a head shim will be in order. It was for fun...for the hard run times and the amount of dirt she has chewed up its a wounder it runs so well..14500 rpm on the ground...I have a vid of both runs, will post when its loaded.