No need for nitrous. You will need at least a 2.81 bore, preferably a stroker crank and rod, forged piston, custom welded chamber head with some really good port work and at least 32/27 valves, a good .930 or bigger pipe, air filter adapter, tillotson or a very good gx390 carb, good cam with .400+ lift, roller rockers, block bracing/girdle, flywheel, all of that at the very least....and be prepared to spend over $1000. Flow is going to be a key to achieving 25+hp, so a well built head is going to be very important along with a carb capable of matching the head. I dont know many people who realistically are getting 25+hp out of these engines, most that think they are doing it are most likely being fed false or exaggerated dyno sheets from their builders/friends. Seems like alot of people think you can just throw some big valves, a little port work, big ol carb and a big ol piston in one of these engines and achieve those numbers when realistically it takes a well thought out and well built combo to even get close. I have seen several builds listed on here and advertised as 25-30+ that just made me laugh a little because people actually believed they were making those numbers, if it was that easy everyone would be doing it. Having one make that kind of power, and at the same time be somewhat reliable is a rare thing.
Havoc Racing has recently came out with some very nice domed pistons for the Honda/clone/predator engines that will make a nice piece for any serious builder, and would make achieving those kind of numbers a little easier on the wallet with the prices of those pistons being around half the price of similar pistons out there. I cant wait to get one myself for the open animal i have
