i have a 1990 honda civic with a SOHC ZC engine inside. lately it has been feeling slower than when i first got it. nothing has been done to the car in regards to performance as i'm currently fixing other problems but i fear that this lack of speed is really another problem in the making. the head gasket blew a few months ago on me and it was replaced, timing and everything was done and set back properly. is there anything i can do to increase performance? can i turn my little sohc zc to a dohc? if so whats the procedure? will iridium spark plugs help to give me the kick my car once had?