Hi all -
I am preparing to replace valve guides in my 1972 manufacture Combat cylinder head.
I noticed that the intake porting is very smooth but the exhaust ports are in a raw state - tool marks and facets from die grinder still visible . Is there any advantage to cleaning up the ports ( surface texture ) while the guides are out ? I understand that the rough nature of the exhaust ports in their current state actually gives them more surface area and therefore may aid in cooling but beyond that I am uncertain which may be best . I would welcome any input on this - Thanks Gents ( and ladies if Anna chimes in ! )
Greater surface area in the exhaust port will result in increased heat flow INTO the head, not cooling of it
Thanks for the reply - I think we agree without realizing it . If the flow of heat is increased into the head where it is conducted into the surrounding air mass through the finning , then the localized area of the exhaust ports themselves must stay cooler then they would if the flow were not as great .
Returning to to the original point - will smoothing up the area in the exhaust ports improve the engine performance to any degree ?
For some reason Norton chose not to do so originally - perhaps economic .
According to Paul Dunstall in his tome on Norton tuning, the carbon adhering to the exhaust port in effect insulates it from the exhaust flow and aids in cooling and is not therefore a cause for concern.
Given the low (relatively) state of tune of the production Nortons, I do not think that it will make any difference if you cleaned up the ports.
Thanks to all for their input- I think I will leave them as is .
Cheers - Richard