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Valve size for bore size??
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watercooledguy
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PostPosted: Thu Sep 16, 2021 5:32 pm    Post subject: Valve size for bore size?? Reply with quote

I'm in the process of building a 1967cc 92x74.ive been looking at cb and the 501 heads both available with 44 or 42 valves.is there pros and cons of each.would 44 be a over kill for a 92 bore?
Running a w120 and 44s
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txoval
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PostPosted: Thu Sep 16, 2021 7:25 pm    Post subject: Re: Valve size for bore size?? Reply with quote

Yes, run the Panchitos (40x35.5), CNC chambers
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Glenn Premium Member
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PostPosted: Thu Sep 16, 2021 7:32 pm    Post subject: Re: Valve size for bore size?? Reply with quote

txoval wrote:
Yes, run the Panchitos (40x35.5), CNC chambers

Agreed.

Last year I built a 2017 (90.5x78.4) with those heads and it runs great and pulls to redline.
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Maxpower
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PostPosted: Thu Sep 16, 2021 8:28 pm    Post subject: Re: Valve size for bore size?? Reply with quote

I totally agree with you guys but usually you ask what hes using it for. And the main question was pros and cons which is obviously powerband related (kinda)is it a Baja or track only. There is guys running small motors with big valves would
be nice to hear more than run this head and the reason why I know a lot cuz I respect your opinion but I read too much.
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Paul.H
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PostPosted: Thu Sep 16, 2021 11:19 pm    Post subject: Re: Valve size for bore size?? Reply with quote

Smaller valves will seat better for longer and pick up less heat especially on the exhaust , they are lighter requiring less spring and they are stronger so if you want a high mile engine then stick with a 40mm intake. If you are a "horsepower hero" then put the biggest valve available
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txoval
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PostPosted: Fri Sep 17, 2021 4:07 am    Post subject: Re: Valve size for bore size?? Reply with quote

A 42 or 44 valve would be lazy down low with that engine combo and I doubt the increase above 4500 rpms would be much. That cam is also done at 6000 unless you run ratio rockers.

If you haven’t bought the cam, switch to the W125
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bugguy1967
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PostPosted: Fri Sep 17, 2021 12:28 pm    Post subject: Re: Valve size for bore size?? Reply with quote

Depends on how much power you want. A 42mm valve can support over 200hp. A 40 can supply around 180hp with good ports.
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PostPosted: Fri Sep 17, 2021 12:42 pm    Post subject: Re: Valve size for bore size?? Reply with quote

watercooledguy wrote:
I'm in the process of building a 1967cc 92x74.ive been looking at cb and the 501 heads both available with 44 or 42 valves.is there pros and cons of each.would 44 be a over kill for a 92 bore?
Running a w120 and 44s


With your cam and carb choice, 40mm x 35.5mm valves(in a head with the proper ports) will give you the best HP/Torque numbers. Anything bigger and you will actually lose HP and/or torque
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