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alot of debate on 4valve vs 2 valve heads..the advantage of the 4valve falls off on the higher rpms, basically comes down to swirl in the chamber,

lets look at 2 heads that flow the same cfm, 1 being 4 valve the other being 2 valve, they difference will be port velocity between the 2 heads

4 valve has smaller ports and in theory should reach velocity quicker where as the 2 valve needs more rpm to get velocity up,

problem on the 4valve is that the ports begin to tumble into the chamber where as a 2valve can swirl, steps are being taken with off setting valve sizes in the 4 valve head to help promote swirl though

also m8s (imo) have too much cylinder head, they flow way more than they need to for even the larger m8s, so they pick up well with higher lift cams

however i will say ( and again imo) because the heads are so big, cam companies are putting smaller duration cams in and really screwing with exhaust durations to help draw out upper rpm power, and the fact that alot of exhauat companies are making smaller than even stock headers to try to offset the large head on the m8 and help give it more torque, all this is bad for the quy who wants real power

best thing you can do with an m8, make it into a 140ci or bigger, have a pipe made with a header of 2inch and have a cam made with more reasonable durations, like 250 on both intake and exhaust along with .550 lift or so

once you get all the m8 parts working together and sized correctly, you will have a monster on your hands
 

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rpm and what is concidered high rpm is debatable, as rpm is not a good way to look at what is high in the rev range but rather engine stroke and piston speed, just by the numbers a 2.25 inch stroke at 12,000 rpm will have the same piston speed as a 4.5 inch stroke at 6000 rpms, and piston speed is the limiting factor along with acceleration rates, which gets into long vs short rod to stroke ratios...and ultimately piston speed is what draws on the ports
 

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what kind of power are these m8 oem flywheels handling? I put a 131 s.e. kit in a friends bike we did swap to the woods 77x cam and have the 2inch thunder header on it....hasnt been to the dyno yet but with the wide band auto tuner from dhynojet..she already rips.
 
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