290-300 duration cam in 390

268 is the most I have personally run. 300 would allow it to really breath a loooong time. Not sure what the lobe centers would have to be to get that much to even work. How much lift you looking at with that much duration? Interesting to see how it would perform. Good luck
 
jsstump#70 said:
268 is the most I have personally run. 300 would allow it to really breath a loooong time. Not sure what the lobe centers would have to be to get that much to even work. How much lift you looking at with that much duration? Interesting to see how it would perform. Good luck
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well I have been doin this for a long time but have never seen a cam with a good duration but have seen and tried different lift's....I have a 390 that I think I am going to try a 295 degree duratin. the centers should be in the neighborhood of 108?
 
What cam has the best power curve? Im trying to get my notes prepared of what I want to build to make sure I wont have any problems. How big can I bore this? Should I stroke it? Deck the block? Im sending the head off to be reworked. And planning on buyi g a built carb. I know its alot of questions but I haven't built an ohv engine yet. What about deck plate? Ive seen them but not sure about putting it on yet.
 
Before I would go to the trouble of boring a 390 (88mm) to extremes and finding a good piston and wondering if I have my liner too thin, I would just go with a 420 (90mm). Of course you can get Honda pistons in std, .010 over, .020 over and .030 over. Parsons has a pretty good piston in std and .010 over. Remember when dealing with these engines, when you see .25 over that's in millimeters. That's equal to .010 over in inches. A .50 over is equal to a .020 over and .75 is .030 over. A 390 is 64mm stroke and a 420 is 66mm stroke. Putting a 420 crank in a 390 is easy and cheap displacement increase. About a 408cc I think. If displacement is what you are really after, Vegas Carts has a 460 pretty cheap. As far as cams go, it will all depend on what other work is done to the head and what rpm you are targeting. There is no "best" cam. You can get a lot of valve lift by using Raceseng roller rockers. They have 1.2 and 1.3 ratio. You can use a small .300 lift cam and still have .390 valve lift. The Champion shaft rockers work well too and have about 1.25 ratio. Honda 390 parts (block and internals) are much better than clone stuff, in my opinion. Decking may or may not be needed to get the piston up where you want it. Be sure and check piston to valve clearance if you use a flat top or a Parsons dome, shave the head and have a big cam or ratio rockers. You can shave the head .100 without much trouble. Big valves and seats are available but to be truly utilized you will need a good ported head and a big carb. Lots of variables as with any build. Good luck and let us know what you finally do and if it worked.
 
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