odonnell #77 on very cold days odonnell #99 the rest of the time. you can try a McCoy #59 but I'm not a fan of the way they are built. odonnells are better plugs. if you want you can just order a card of novarossi's or RB plugs (both the same thing) from www.amainhobbies.com
they are good folks. if your in a rush you can call them up and ask them to ship priority and to ensure what you need is in stock. the place is run by a guy named Kenndal Bennett. hes a racer and knows how to take care of people www.advantageracingproducts.com is another good place, run by Tony Newland. the guy knows what he's doing modding a motor too. advantage is a great place to get filter foams for 1/8th scales. like 10 sets for $15 iirc.