1.78 I belive. Benifits from a larger valve? Yes and no. What all do you have done to your engine? 25thmustang has unported E7's with GT40 Valves with much success. I ran Thumper's ported E7's with a lot of sucess. Thumper has his veiws on valve size. Check them out on his site. www.thumperoforangepark.com Check under "Valve Size"
Valve size WAS the way to increase flow and more power.. and still is to a point!! BUT, stuffing large valves cause a number of small issues. Like the larger valve wont fit the stock valve notch in the stock Ford Forged pistons, oops.. bent that one!! Or stuffing a large valve in a small chamber and you will actually LOSE flow do to shrouding in the chambers...or even the cylinder!! Try this.. the GT40s make good power with their 1.85 and 1.55 valve size... then comes the GT40P's.. the flow more and make MORE than the 40's... right?? Oh hell yeah!! but the P's have a smaller exhaust valve than the 40s... they went BACK to the 1.46 exhaust size!! SOOOooo... it isnt "exactly" the size that matters!! ( seems I have heard that some where...hmmmmmm.. LOL)
IF done correct and NOT too large in a certain chamber.. the power will be there... more than the smaller valve... but stuffing in a set of 1.9/1.55 valve arent the whole story!! cool?? at least on the 40s and the E7s..
Ya, valve sizes aren't the key... Just look at Edelbrocks performer/RPM heads. The only difference is the 1.9 to 2.02 valve. The 2.02 flowed around 5cfm more at certain lift intervals but the 1.9s made more power on the typical HCI car.