Show cars pn 2290ps for stock size[1.94] intake,2290pe for the stock size 1.67 exhaust valves.The next size up.2.09 intake pn 2293pl,exhaust size 1.725,2293pe.Then there's the 2.19 stock size for the hp 409's at pn2292pis.When you enlarge the seats for bigger valves,be sure to enlarge the bowls just under the valves to about 85 percent of the new seat size,and blend them into the ports.This alone will give you about 35-40 more horse power.