NC31 head porting

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Bike owned: NC31
Location: Russia, Moscow
NC31 head porting

Post by pugnator » Mon Oct 30, 2017 6:31 am

Does anyone has information about CB(R)400 head porting results?
Exhaust ports are seem to be restricted in order to increase VE on low and mid revs.
If I need only max output on custom cams - what about to port them? I have this head from a junkyard and wanna try to check if there any "meat" to bore the outlets...

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Re: NC31 head porting

Post by theEK1 » Fri Jan 12, 2018 10:53 pm

I haven't done any precise measurements therefore calculations of the ports, but in My opinion, not much power gained there(well maybe in definite race bike - 10000 rpm up). But what could gain some power is the exhaust system(that one I did measure), I think it's too big. The header pipes are the same size as 600cc superbikes, which have 1.5 times the displacement and 2x the power.

Check this calculator -
Also cams could gain some lift probably.
But that's just My opinion.

And what cams do you have in mind? Regrind?

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