Ok I belive i have read that the gt40 and the gt40p valves are the same except fot the exh valve gt40 1.54 or 1.55 and gt40p is 1.45 or 1.46. Do you thank it be worth $$ cuting the gt40p exh valves out to the gt40 exh valve size? 1.85/1.46 valves (compared to 1.85/1.54 for the standard GT-40). The exhaust port was redesigned and is more efficient, thus the ability to use the smaller exhaust valve. This actually works well since to get equal flow numbers the velocity must be higher.....exactly what we want. There's a little bit of room for larger valves but start going larger on the intake side and you're going to have to grind on that plug boss to clear it. And....don't forget.....a bigger valve isn't necessarily better. The whole reason these heads work so well is the decent flow they provide while still having smaller port dimensions. If you're not careful and hog out the bowls for big valves you could easily hurt flow. Just remember this when planning your mods.
I wouldn't spend the dough. If I did, I would put 1.60s in there and be done with it. Remember that our cars have shock towers that cause header designs that are far from perfect. So even if these heads are super effecient in a larger engine bay with room for softer turns in the exhaust tubes, they are hampered somewhat in our cars. Dave
