BIG VALVEs

[foggy]

what's the seat angle of those big valves
available on ebay?
Will they easily enough fir into s2 rope seal motor cyl hd???

Any improvement? I read in the Dave Bean Cataloguw, that they are only
marginally larger than the original valves...

Thanks
Steve

[Elan45]

BIG Valves: Only the intake is larger, by .031". In my mind, you must enlarge the port just under the valve to realise any value from the larger valve. If you don't, I would think fitting "big valves" to a standard head w/ no other modifications would reduce performance, because the larger valve would tend to block the flow. The valve must be matched to the size of the port and valve seat. You do not necessarily have to fit new seats, but the seat/port ID should be enlarged by approximately .028" to match the new larger valve size. This based on rule of thumb for port to be 90% size of valve.
Roger


available on ebay?
Will they easily enough fir into s2 rope seal motor cyl hd???

Any improvement? I read in the Dave Bean Cataloguw, that they are only
marginally larger than the original valves...

Thanks
Steve

["e s"]

most of the horsepower increase in the big valve engine comes from the compression increase.



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[steveww]

And the different cam. It is understood that the bigger valves gave a 1
bhp increase. (see Miles Wilkins book)

e s wrote:

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Regards,

Steve Waterworth
***@***.***

Einstein: "The faster you drive, the slower you age..."

[twincamracing]

Roger, I believe Superflow recommends 85% of the net valve area, that
is with the OD of the valve measured from the inside edge of the
sealing surface of the seat and subracting the area of the valve stem.

FWIW I routinely use a 70 degree cutter on the seat to bring the
sealing surface further out the face of the valve. I just finished a
set of 2.5 V6 Alfa heads and gained 2mm in effective valve size on both
the intake and exhaust without having the seal at the edge of the
valve.
Cheers,
Scott

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