I will try to get the OD 97T plug. For now I will have to deal with the plugs I have. The local AE guys here in Brazil are running the OS P3 plug. All I have left are RT3, RT4 and some OS P4 plugs. I noticed that the 97T is also reasonably priced as well. Is there any difference in top speed with these plugs? What changes to compression ratio are needed. The local expert is suggesting that changing the head gasket may be good. I am running the head gasket that came with the engine.