NC31 head porting

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pugnator
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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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theEK1
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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 - http://precisionmoto.com/1803-2/
Also cams could gain some lift probably.
But that's just My opinion.

And what cams do you have in mind? Regrind?

pugnator
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Re: NC31 head porting

Post by pugnator » Wed Jan 24, 2018 10:45 pm

theEK1 wrote:
Fri Jan 12, 2018 10:53 pm
Also cams could gain some lift probably.
But that's just My opinion.

And what cams do you have in mind? Regrind?
Thanks. Locally I can resurface-regrind cams with any specs, it will cost about 300-350$ plus original cams. Not too costy I think. I didn't measure stock cams yet, but looking at piston's shape I'm afraid of the fact that valves are too close to piston at TDC for additional valve lift. At least intake ones. Any info about plausible variants? I tried to google it, but no info about it.
I saw some japanese owners with custom cams but they don't know/dont wanna tell the specs.

I've installed online tunable EFI and looking for ways where I can gain some additional HPs.
This bike is mostly for engineering fun.

amorti
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Re: NC31 head porting

Post by amorti » Fri Feb 02, 2018 11:42 pm

Humbly I suggest this is the wrong bike to start building a high-revs motor for. If you want that, then you need to start with a motor from the CBR400 which already has an aggressive cam plus the gear driven cams so it can handle higher rpm. The block is the same, so it should fit into your frame, albeit the intake tract is different. Better still, get the CBR400 and ride that. A naked bike really doesn't suit a high revs race engine, it just doesn't make sense.

amorti
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Re: NC31 head porting

Post by amorti » Fri Feb 02, 2018 11:46 pm

I did try an nc23 cam in my CB-1 for a time. It has more duration and overlap, although the lift is the same I believe (not certain on that). But that was a much easier job than it would be on your bike, since both bikes have gear driven cams already. I gave up on it as too much hassle since I couldn't get it to run nice without excessive dyno time. No one else in the online world had done the swap, so there was no base jetting to start from, and I was not up for blazing a trail just for a handful of high end bhp.


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