Installing a 27mm valve

[booya1golf]

Do you have to install a new seat or can the stock seat be enlarged to accommodate it?

 

[astrowrench]

Stock seat throat should be enlarged or you a Gaining Nothing.......... a Big Hat on a small Hole

 

[Bob Drye]

A 28.5 mm is about the limit on a stock seat.

 

[astrowrench]

Only on a Hemi intake valve

 

[gamecock]

Do you have to install a new seat or can the stock seat be enlarged to accommodate it?

It depends on the head casting FIRST. Some heads I have seen 27mm is the max and others I have done 28mm. The seat gets very thin with some heads.